ASTM ISO/ASTM51649-22

Standard Practice for Electron Beam Radiation Processing at Energies Between 300 keV and 25 MeV

SIGNIFICANCE AND USE
4.1 Various products and materials are routinely irradiated at pre-determined doses at electron beam facilities to preserve or modify their characteristics. Dosimetry requirements may vary depending on the radiation process and end use of the product. A partial list of processes where dosimetry may be used is given below.  
4.1.1 Polymerization of monomers and grafting of monomers onto polymers,  
4.1.2 Cross-linking or degradation of polymers,  
4.1.3 Curing of composite materials,  
4.1.4 Sterilization of health care products,  
4.1.5 Disinfection of consumer products,  
4.1.6 Food irradiation (parasite and pathogen control, insect disinfestation, and shelf-life extension),  
4.1.7 Control of pathogens and toxins in drinking water,  
4.1.8 Control of pathogens and toxins in liquid or solid waste,  
4.1.9 Modification of characteristics of semiconductor devices,  
4.1.10 Color enhancement of gemstones and other materials, and  
4.1.11 Research on radiation effects on materials.  
4.2 Dosimetry is used as a means of monitoring the irradiation process.
Note 2: Dosimetry with measurement traceability and known uncertainty is required for regulated radiation processes such as sterilization of health care products (see ISO 11137-1 and Refs (1-36)) and preservation of food (see ISO 14470 and Ref (4)). It may be less important for other processes, such as polymer modification, which may be evaluated by changes in the physical and chemical properties of the irradiated materials. Nevertheless, routine dosimetry may be used to monitor the reproducibility of the treatment process.
Note 3: Measured dose is often characterized as absorbed dose in water. Materials commonly found in single-use disposable medical devices and food are approximately equivalent to water in the absorption of ionizing radiation. Absorbed dose in materials other than water may be determined by applying conversion factors (5, 6).  
4.3 An irradiation process usually requires a minimum ab...
SCOPE
1.1 This practice outlines dosimetric procedures to be followed in installation qualification (IQ), operational qualification (OQ) and performance qualifications (PQ), and routine processing at electron beam facilities.  
1.2 The electron beam energy range covered in this practice is between 300 keV and 25 MeV, although there are some discussions for other energies.  
1.3 Dosimetry is only one component of a total quality assurance program for adherence to good manufacturing practices used in radiation processing applications. Other measures besides dosimetry may be required for specific applications such as health care product sterilization and food preservation.  
1.4 Specific standards exist for the radiation sterilization of health care products and the irradiation of food. For the radiation sterilization of health care products, see ISO 11137-1 (Requirements) and ISO 11137-3 (Guidance on dosimetric aspects). For irradiation of food, see ISO 14470. In those areas covered by these standards, they take precedence. Information about effective or regulatory dose limits for food products is not within the scope of this practice (see ASTM Guides F1355, F1356, F1736, and F1885).  
1.5 This document is one of a set of standards that provides recommendations for properly implementing and utilizing dosimetry in radiation processing. It is intended to be read in conjunction with ISO/ASTM 52628, “Practice for Dosimetry in Radiation Processing”.
Note 1: For guidance in the calibration of routine dosimetry systems, see ISO/ASTM Practice 51261. For further guidance in the use of specific dosimetry systems, see relevant ISO/ASTM Practices. For discussion of radiation dosimetry for pulsed radiation, see ICRU Report 34.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and env...

General Information

• Status: Published
• Publication Date: 30-Nov-2022
• ICS: 17.240 - Radiation measurements
• Technical Committee: E61 - Radiation Processing
• Drafting Committee: E61.03 - Dosimetry Application

Relations

• Replaces: ASTM ISO/ASTM51649-15 - Standard Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 300 keV and 25 MeV
• Effective Date: 01-Dec-2022

Overview

ASTM ISO/ASTM51649-22 is an international standard that establishes best practices for electron beam radiation processing at energies between 300 keV and 25 MeV. Developed by ASTM in conjunction with ISO, this standard is a crucial document for organizations involved in radiation processing of materials and products. Electron beam facilities use controlled doses to achieve specific changes in materials or to preserve products, and implementing this standard ensures consistent results, regulatory compliance, and quality assurance. Proper dosimetric procedures during installation qualification (IQ), operational qualification (OQ), performance qualification (PQ), and routine processing are detailed, supporting a wide range of industrial and research applications.

Key Topics

• Dosimetric Procedures: Outlines steps for qualifying and validating electron beam irradiation equipment and processes. Emphasis is placed on accurate dosimetry for monitoring and mapping radiation doses.
• Quality Assurance: Dosimetry is presented as one part of a comprehensive quality program, mandating traceability to national or international measurement standards and known uncertainty levels for critical applications.
• Process Validation: Explains requirements for equipment installation (IQ), operation (OQ), and production performance (PQ). Each phase demands documentation and verification for regulatory and customer assurance.
• Routine Monitoring: Details the necessity for ongoing, documented dosimetry during regular processing to ensure reliable results and consistent, reproducible dose delivery.
• Safety and Compliance: Encourages adherence to safety and environmental best practices in line with recognized international guidelines.

Applications

ASTM ISO/ASTM51649-22 applies to a diverse set of industries and research fields that utilize electron beam irradiation. Key applications include:

• Polymer Processing: Used for polymerization, grafting, cross-linking, or controlled degradation to enhance material properties.
• Composite Curing: Radiation curing of composite materials for improved strength and durability.
• Medical Product Sterilization: Ensures effective sterilization of health care products, requiring rigorous dosimetry in accordance with regulatory standards.
• Consumer Product Disinfection: Applied to disinfect various consumables, curtailing pathogen load.
• Food Irradiation: Used for shelf-life extension, pathogen control, and insect disinfestation for food products. Dosimetry is central to regulatory compliance in these applications.
• Water and Waste Treatment: Facilitates pathogen and toxin control in drinking water and waste streams.
• Electronics and Gemstones: Employed for modifying semiconductor characteristics and enhancing gemstone coloration.
• Radiation Effects Research: Critical for controlled studies on the effects of radiation on various materials.

Related Standards

Comprehensive implementation of electron beam radiation processing benefits from integration with related national and international standards, such as:

• ISO 11137-1 & ISO 11137-3: Standards for sterilization of health care products, defining specific dosimetric and process validation requirements.
• ISO 14470: Requirements for food irradiation processes.
• ISO/ASTM 52628: Practice for dosimetry in radiation processing, intended to be used in conjunction with ASTM ISO/ASTM51649-22.
• ISO/ASTM 51261: Specifics for calibration of routine dosimetry systems.
• ASTM Guides F1355, F1356, F1736, F1885: Guidance for irradiation of fresh produce, meat, aquatic food products, and dried spices.
• ISO/IEC 17025: General requirements for the competence of calibration and testing laboratories, ensuring dosimetry traceability.
• ICRU Reports 34, 35, 37, 80, 85a: Fundamental guidance on radiation units, stopping powers, and dosimetry best practices.

Practical Value

Adhering to ASTM ISO/ASTM51649-22 maximizes the effectiveness of electron beam radiation processing by:

• Enhancing Process Reliability: Ensuring precise and repeatable dose delivery for consistent product quality.
• Facilitating Regulatory Compliance: Meeting international guidelines for health care, food safety, and environmental protection.
• Supporting Innovation: Providing a robust framework for research and development in new material applications and process improvements.
• Mitigating Risk: Identifying and controlling variables, and maintaining traceable documentation for audits and product recalls if necessary.

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Keywords: electron beam irradiation, ASTM 51649-22, dosimetry, radiation processing, quality assurance, process validation, electron beam energy, food irradiation standard, medical device sterilization, dosimetric calibration, ISO standards, regulatory compliance.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: 51649 − 22
Standard Practice for
Electron Beam Radiation Processing at Energies Between
300 keV and 25 MeV
This standard is issued under the fixed designation 51649; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This practice outlines dosimetric procedures to be fol-
1.7 This international standard was developed in accor-
lowed in installation qualification (IQ), operational qualifica-
dance with internationally recognized principles on standard-
tion (OQ) and performance qualifications (PQ), and routine
ization established in the Decision on Principles for the
processing at electron beam facilities.
Development of International Standards, Guides and Recom-
1.2 The electron beam energy range covered in this practice
mendations issued by the World Trade Organization Technical
is between 300 keV and 25 MeV, although there are some
Barriers to Trade (TBT) Committee.
discussions for other energies.
2. Referenced documents
1.3 Dosimetry is only one component of a total quality
assurance program for adherence to good manufacturing prac-
2.1 ASTM Standards:
tices used in radiation processing applications. Other measures
E2232 Guide for Selection and Use of Mathematical Meth-
besides dosimetry may be required for specific applications
ods for Calculating Absorbed Dose in Radiation Process-
such as health care product sterilization and food preservation.
ing Applications
E2303 Guide for Absorbed-Dose Mapping in Radiation
1.4 Specific standards exist for the radiation sterilization of
Processing Facilities
health care products and the irradiation of food. For the
E3083 Terminology Relating to Radiation Processing: Do-
radiation sterilization of health care products, see ISO 11137-1
simetry and Applications
(Requirements) and ISO 11137-3 (Guidance on dosimetric
F1355 Guide for Irradiation of Fresh Agricultural Produce as
aspects). For irradiation of food, see ISO 14470. In those areas
a Phytosanitary Treatment
covered by these standards, they take precedence. Information
F1356 Guide for Irradiation of Fresh, Frozen or Processed
about effective or regulatory dose limits for food products is
Meat and Poultry to Control Pathogens and Other Micro-
not within the scope of this practice (see ASTM Guides F1355,
organisms
F1356, F1736, and F1885).
F1736 Guide for Irradiation of Finfish and Aquatic Inverte-
1.5 This document is one of a set of standards that provides
brates Used as Food to Control Pathogens and Spoilage
recommendations for properly implementing and utilizing
Microorganisms
dosimetry in radiation processing. It is intended to be read in
F1885 Guide for Irradiation of Dried Spices, Herbs, and
conjunction with ISO/ASTM 52628, “Practice for Dosimetry
Vegetable Seasonings to Control Pathogens and Other
in Radiation Processing”.
Microorganisms
NOTE 1—For guidance in the calibration of routine dosimetry systems,
see ISO/ASTM Practice 51261. For further guidance in the use of specific
2.2 ISO/ASTM Standards:
dosimetry systems, see relevant ISO/ASTM Practices. For discussion of
51261 Practice for Calibration of Routine Dosimetry Sys-
radiation dosimetry for pulsed radiation, see ICRU Report 34.
tems for Radiation Processing
1.6 This standard does not purport to address all of the
51275 Practice for Use of a Radiochromic Film Dosimetry
safety concerns, if any, associated with its use. It is the
System
responsibility of the user of this standard to establish appro-
51539 Guide for the Use of Radiation-Sensitive Indicators
51608 Practice for Dosimetry in an X-Ray (Bremsstrahlung)
Facility for Radiation Processing
This practice is under the jurisdiction of ASTM Committee E61 on Radiation
Processing and is the direct responsibility of Subcommittee E61.03 on Dosimetry
Application. Originally developed as a joint ASTM/ISO standard in conjunction
with ISO/TC 85/WG 3. For referenced ASTM and ISO/ASTM standards, visit the ASTM website,
Current edition approved Dec. 1, 2022. Published May 2024. Originally www.astm.org, or contact ASTM Customer Service at [e-mail]. For
approved in 1994. Last previous edition approved in 2015 as ISO/ASTM Annual Book of ASTM Standards volume information, refer to the standard’s
51649:2015(E). DOI: 10.1520/51649-22. Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
51649 − 22
51702 Practice for Dosimetry in a Gamma Facility for joule per kilogram in the specified material (1 Gy = 1 J/kg).
Radiation Processing The mathematical relationship is the quotient of dε¯ by dm,
51707 Guide for Estimating Uncertainties in Dosimetry for
where dε¯ is the mean incremental energy imparted by ionizing
Radiation Processing radiation to matter of incremental mass dm. (See ICRU Report
51818 Practice for Dosimetry in an Electron Beam Facility
85a.)
for Radiation Processing at Energies Between 80 and 300
D 5 dεH/dm
keV
3.1.1.2 Discussion—(2) Absorbed dose is sometimes re-
52628 Practice for Dosimetry in Radiation Processing
ferred to simply as dose.
52701 Guide for Performance Characterization of Dosim-
3.1.2 approved laboratory—laboratory that is a recognized
eters and Dosimetry Systems for Use in Radiation Pro-
cessing national metrology institute; or has been formally accredited to
ISO/IEC 17025, or has a quality system consistent with the
2.3 ISO Standards:
requirements of ISO/IEC 17025.
ISO 11137-1 Sterilization of Health Care Products–Radia-
tion – Part 1: Requirements for development, validation,
3.1.2.1 Discussion—A recognized national metrology insti-
and routine control of a sterilization process for medical
tute or other calibration laboratory accredited to ISO/IEC
devices
17025 or its equivalent should be used for issue of reference
ISO 11137-3 Sterilization of Health Care Products–Radia-
standard dosimeters or irradiation of dosimeters in order to
tion – Part 3: Guidance on dosimetric aspects
ensure traceability to a national or international standard. A
ISO/TS 11137-4 Sterilization of Health Care Products–Ra-
calibration certificate provided by a laboratory not having
diation – Part 4: Guidance on process control
formal recognition or accreditation will not necessarily be
ISO 14470 Food Irradiation – Requirements for the
proof of traceability to a national or international standard.
development, validation and routine control of the process
3.1.3 average beam current—time-averaged electron beam
of irradiation using ionizing radiation for the treatment of
current; for a pulsed accelerator, the averaging shall be done
food
over a large number of pulses (see Fig. 1).
ISO 10012 Measurement Management Systems – Require-
ments for Measurement Processes and Measuring Equip-
3.1.4 beam length—dimension of the irradiation zone along
ment
the direction of product movement at a specified distance from
ISO/IEC 17025 General Requirements for the Competence
the accelerator window (see Fig. 2).
of Calibration and Testing Laboratories
3.1.4.1 Discussion—Beam length is therefore perpendicular
2.4 International Commission on Radiation Units and Mea-
to beam width and to the electron beam axis. In case of product
surements (ICRU) Reports:
that is stationary during irradiation, ‘beam length’ and ‘beam
ICRU Report 34 The Dosimetry of Pulsed Radiation
width’ may be interchangeable.
ICRU Report 35 Radiation Dosimetry: Electron Beams with
3.1.5 beam width (W )—dimension of the irradiation zone
b
Energies Between 1 and 50 MeV
perpendicular to the direction of product movement at a
ICRU Report 37 Stopping Powers for Electrons and Posi-
specified distance from the accelerator window (see Fig. 2).
trons
3.1.5.1 Discussion—For a radiation processing facility with
ICRU Report 80 Dosimetry for Use in Radiation Processing
a conveyor system, the beam width is usually perpendicular to
ICRU Report 85a Fundamental Quantities and Units for
the direction of motion of the conveyor (see Fig. 2). Beam
Ionizing Radiation
width is the distance between two points along the dose profile,
2.5 Joint Committee for Guides in Metrology (JCGM)
which are at a defined level from the maximum dose region in
Reports:
the profile (see Fig. 3). Various techniques may be employed to
JCGM 100:2008, GUM 1995 with minor corrections, Evalu-
produce an electron beam width adequate to cover the process-
ation of measurement data – Guide to the expression of
ing zone, for example, use of electromagnetic scanning of a
uncertainty in measurement
pencil beam (in which case beam width is also referred to as
3. Terminology scan width), defocussing elements, and scattering foils.
3.1 Definitions: 3.1.6 compensating dummy—see simulated product.
3.1.1 absorbed dose (D)—quantity of ionizing radiation
3.1.7 depth-dose distribution—variation of absorbed dose
energy imparted per unit mass of a specified material.
with depth from the incident surface of a material exposed to
3.1.1.1 Discussion—(1) The SI unit of absorbed dose is the
a given radiation.
gray (Gy), where 1 gray is equivalent to the absorption of 1
3.1.7.1 Discussion—Typical distributions along the beam
axis in homogeneous materials produced by a normally inci-
Available from International Organization for Standardization, 1 Rue de
dent monoenergetic electron beam are shown in Annex A2.
Varembé, Case Postale 56, CH-1211 Geneva 20, Switzerland.
3.1.8 dose uniformity ratio (DUR)—ratio of the maximum
Available from the International Commission on Radiation Units and
Measurements, 7910 Woodmont Ave., Suite 800, Bethesda MD 20814, U.S.A.
to the minimum absorbed dose within the irradiated product.
Document produced by Working Group 1 of the Joint Committee for Guides in
3.1.8.1 Discussion—The concept is also referred to as the
Metrology (JCGM/WG 1). Available free of charge at the BIPM website (http://
www.bipm.org). max/min dose ratio.
51649 − 22
FIG. 1 Example showing pulse beam current (I ), average beam current (I ), (pulse width (W) and repetition rate (f) for a pulsed
pulse avg
accelerator
3.1.10.1 Discussion—Electron volt (eV) is often used as the
-19
unit for electron beam energy where 1 eV = 1.602·10 J. In
radiation processing, where beams with a broad electron
energy spectrum are frequently used, the terms most probable
energy (E ) and average energy (E ) are common. They are
p a
linked to the practical electron range R and half-value
p
depth R by empirical equations (see Fig. 4 and Annex A4).
3.1.11 electron beam facility—establishment that uses ener-
getic electrons produced by particle accelerators to irradiate
product.
3.1.12 electron energy spectrum—particle fluence distribu-
tion of electrons as a function of energy.
3.1.13 installation qualification (IQ)—process of obtaining
and documenting evidence that equipment has been provided
and installed in accordance with its specification.
3.1.14 operational qualification (OQ)—process of obtaining
and documenting evidence that installed equipment operates
FIG. 2 Diagram showing beam length and beam width for a
within predetermined limits when used in accordance with its
scanned beam using a conveyor system
operational procedures.
3.1.15 performance qualification (PQ)—process of obtain-
3.1.9 dosimetry system—system used for measuring ab-
ing and documenting evidence that the equipment, as installed
sorbed dose, consisting of dosimeters, measurement instru-
and operated in accordance with operational procedures, con-
ments and their associated reference standards, and procedures
sistently performs in accordance with predetermined criteria
for the system’s use.
and thereby yields product meeting its specification.
3.1.10 electron beam energy—kinetic energy of the acceler- 3.1.16 process load—volume of material with a specified
ated electrons in the beam. Unit: J product loading configuration irradiated as a single entity.
51649 − 22
FIG. 3 Example of electron-beam dose distribution along the scan direction, where the beam width is specified at a defined fractional
level f of the average maximum dose D
max
characteristics of the irradiation process, such as scan
uniformity, depth-dose distribution, and reproducibility of dose
delivery.
3.1.19 reference plane—selected plane in the radiation zone
that is perpendicular to the electron beam axis.
3.1.20 routine monitoring position—position where ab-
sorbed dose is monitored during routine processing to ensure
that the product is receiving the absorbed dose specified for the
process.
3.1.20.1 Discussion—This position may be a location of
minimum or maximum dose in the process load or it may be an
alternate convenient location in, on or near the process load
where the relationship of the dose at this position with the
minimum and maximum dose has been established.
3.1.21 simulated product—material with radiation absorp-
D : Dose at entrance surface
tion and scattering properties similar to those of the product,
e
R : Depth at which dose at descending part of curve equals D
opt e
material or substance to be irradiated.
R : Depth at which dose has decreased to 50 % of its maximum
value 3.1.21.1 Discussion—Simulated product is used during irra-
R : Depth at which dose has decreased to 50 % of D
50e e
diator characterization as a substitute for the actual product,
R : Depth where extrapolated straight line of descending curve
p
material or substance to be irradiated. When used in routine
meets depth axis
production runs in order to compensate for the absence of
FIG. 4 A typical depth-dose distribution for an electron beam in
product, simulated product is sometimes referred to as com-
a homogeneous material
pensating dummy. When used for absorbed-dose mapping,
simulated product is sometimes referred to as phantom mate-
rial.
3.1.17 production run—series of process loads consisting of 3.1.22 standardized depth (z)—thickness of the absorbing
materials or products having similar radiation-absorption
material expressed as the mass per unit area, which is equal to
characteristics, that are irradiated sequentially to a specified the product of depth in the material t and density ρ.
range of absorbed dose.
3.1.22.1 Discussion—If m is the mass of the material
3.1.18 reference material—homogeneous material of known beneath area A of the material through which the beam passes,
radiation absorption and scattering properties used to establish then:
51649 − 22
z 5 m/A 5 tρ 3.2.11 pulse beam current, for a pulsed accelerator—beam
The SI unit of z is in kg/m , however, it is common practice
current averaged over the top ripples (aberrations) of the pulse
to express t in centimetres and ρ in grams per cm , then z is
current waveform.
in grams per square centimetre. Standardized depth may also
be referred to as surface density, area density, mass-depth or
3.2.11.1 Discussion—Its value may be calculated as I /wf,
avg
mass-thickness.
where I is the average beam current, w is the pulse width,
avg
and f is the pulse rate (see Fig. 5).
3.2 Definitions of Terms Specific to This Standard:
3.2.12 pulse rate (for a pulsed accelerator) (f)—pulse rep-
3.2.1 beam power—product of the average electron beam
etition frequency in hertz, or pulses per second.
energy and the average beam current.
3.2.2 beam spot—shape of the unscanned electron beam
3.2.12.1 Discussion—This is also referred to as the repeti-
incident on the reference plane.
tion (rep) rate.
3.2.13 pulse width (for a pulsed accelerator) (w)—time
3.2.3 continuous-slowing-down-approximation (CSDA)
range (r )—average pathlength traveled by a charged particle interval between two points on the leading and trailing edges of
as it slows down to rest, calculated in the continuous-slowing- the pulse current waveform where the current is 50 % of its
peak value (see Fig. 5).
down-approximation method.
3.2.3.1 Discussion—In this approximation, the rate of en-
3.2.14 scanned beam—electron beam that is swept back and
ergy loss at every point along the track is assumed to be equal
forth with a varying magnetic field.
to the total stopping power. Energy-loss fluctuations are
3.2.14.1 Discussion—This is most commonly done along
neglected. The CSDA range is obtained by integrating the
one dimension (beam width), although two-dimensional scan-
reciprocal of the total stopping power with respect to energy.
ning (beam width and length) may be used with high-current
Values of r for a wide range of electron energies and for many
0 electron beams to avoid overheating the beam exit window of
materials can be obtained from ICRU Report 37.
the accelerator or product under the scan horn.
3.2.4 duty cycle (for a pulsed accelerator)—fraction of time
3.2.15 scan frequency—number of complete scanning
the beam is effectively on.
cycles per second.
3.2.4.1 Discussion—Duty cycle is the product of the pulse
3.2.16 scan uniformity—degree of uniformity of the dose
width (w) in seconds and the pulse rate (f) in pulses per second.
measured along the scan direction.
3.2.5 electron beam range—penetration distance in a
3.3 Definitions—Definitions of other terms used in this
specific, totally absorbing material along the beam axis of the
standard that pertain to radiation measurement and dosimetry
electrons incident on the material.
may be found in ASTM Terminology E3083. Definitions in
3.2.6 extrapolated electron range (R )—depth in homoge-
ex E3083 are compatible with ICRU 85a; that document,
neous material to the point where the tangent at the steepest
therefore, may be used as an alternative reference.
point (the inflection point) on the almost straight descending
portion of the depth-dose distribution meets the depth axis (see
4. Significance and use
Fig. A2.6 in Annex A2).
4.1 Various products and materials are routinely irradiated
3.2.7 half-entrance depth (R )—depth in homogeneous
50e
at pre-determined doses at electron beam facilities to preserve
material at which the absorbed dose has decreased to 50 % of
or modify their characteristics. Dosimetry requirements may
its value at the entrance surface of the material (see Fig. 4).
vary depending on the radiation process and end use of the
3.2.8 half value depth (R )—depth in homogeneous mate-
product. A partial list of processes where dosimetry may be
rial at which the absorbed dose has decreased to 50 % of its
used is given below.
maximum value (see Fig. 4).
4.1.1 Polymerization of monomers and grafting of mono-
mers onto polymers,
3.2.9 optimum thickness (R )—depth in homogeneous ma-
opt
4.1.2 Cross-linking or degradation of polymers,
terial at which the absorbed dose equals its value at the
4.1.3 Curing of composite materials,
entrance surface of the material (see Fig. 4).
4.1.4 Sterilization of health care products,
3.2.10 practical electron range (R )—depth in homoge-
p
4.1.5 Disinfection of consumer products,
neous material to the point where the tangent at the steepest
4.1.6 Food irradiation (parasite and pathogen control, insect
point (the inflection point) on the almost straight descending
disinfestation, and shelf-life extension),
portion of the depth-dose distribution curve meets the extrapo-
4.1.7 Control of pathogens and toxins in drinking water,
lated X-ray background (see Fig. 4 and Fig. A2.6 in Annex
4.1.8 Control of pathogens and toxins in liquid or solid
A2).
waste,
3.2.10.1 Discussion—Penetration can be measured from
4.1.9 Modification of characteristics of semiconductor
experimental depth-dose distributions in a given material.
devices,
Other forms of electron range are found in the dosimetry
4.1.10 Color enhancement of gemstones and other
literature, for example, extrapolated range derived from depth-
materials, and
dose data and the continuous-slowing-down-approximation
4.1.11 Research on radiation effects on materials.
range. Electron range is usually expressed in terms of mass per
-2
unit area (kg·m ), but sometimes in terms of thickness (m) for 4.2 Dosimetry is used as a means of monitoring the irradia-
a specified material. tion process.
51649 − 22
Horizontal axis: Time, μs
Vertical axis: Pulse beam current, mA
FIG. 5 Typical pulse current waveform from an S-Band linear accelerator
NOTE 2—Dosimetry with measurement traceability and known uncer-
4.6 Before a radiation facility is used, it must be character-
tainty is required for regulated radiation processes such as sterilization of
ized to determine its effectiveness in reproducibly delivering
health care products (see ISO 11137-1 and Refs (1-3 )) and preservation
known, controllable doses. This involves testing and calibrat-
of food (see ISO 14470 and Ref (4)). It may be less important for other
ing the process equipment, and dosimetry system.
processes, such as polymer modification, which may be evaluated by
changes in the physical and chemical properties of the irradiated materials.
4.7 Before a radiation process is commenced it must be
Nevertheless, routine dosimetry may be used to monitor the reproducibil-
validated. This involves execution of Installation Qualification
ity of the treatment process.
(IQ), Operational Qualification (OQ), and Performance Quali-
NOTE 3—Measured dose is often characterized as absorbed dose in
water. Materials commonly found in single-use disposable medical fication (PQ), based on which process parameters are estab-
devices and food are approximately equivalent to water in the absorption
lished that will ensure that product is irradiated within specified
of ionizing radiation. Absorbed dose in materials other than water may be
limits.
determined by applying conversion factors (5, 6).
4.8 To ensure consistent and reproducible dose delivery in a
4.3 An irradiation process usually requires a minimum
validated process, routine process control requires that docu-
absorbed dose to achieve the desired effect. There may also be
mented procedures are established for activities to be carried
a maximum dose limit that the product can tolerate while still
out before, during and after irradiation, such as for ensuring
meeting its functional or regulatory specifications. Dosimetry
consistent product loading configuration and for monitoring of
is essential, since it is used to determine both of these limits
critical operating parameters and routine dosimetry.
during the research and development phase, and also to
confirm that the product is routinely irradiated within these
5. Radiation source characteristics
limits.
5.1 Electron sources considered in this practice are either
4.4 The dose distribution within the product depends on
direct-action (potential-drop) or indirect-action (Radio Fre-
process load characteristics, irradiation conditions, and operat-
quency (RF) or microwave-powered accelerators. These are
ing parameters.
discussed in Annex A1.
4.5 Dosimetry systems must be calibrated with traceability
6. Documentation
to national or international standards and the measurement
6.1 Documentation for the irradiation facility must be re-
uncertainty must be known.
tained in accordance with the requirements of a quality
management system. Typically, all facility related documenta-
tion is retained for the life of the facility, and product related
The boldface numbers in parentheses refer to the Bibliography at the end of this
standard. documentation is related for the life of the product.
51649 − 22
NOTE 5—Calibration under the approximate conditions of use can only
7. Dosimetry system selection and calibration
be accomplished after installation qualification and after establishment of
7.1 Selection of dosimetry systems:
process operating settings and appropriate process control procedures.
7.1.1 ISO/ASTM 52628 identifies requirements for selec-
9. Operational qualification
tion of dosimetry systems. Consideration shall specifically be
given to the limited range of electrons which might give rise to
9.1 Operational qualification (OQ) is carried out to charac-
dose gradients through the thickness of the dosimeter. By
terize the performance of the irradiation equipment with
choosing thin film dosimeters this problem can be minimized.
respect to reproducibility of dose to product.
7.1.2 When selecting a dosimetry system, consideration
NOTE 6—Dose measurements for OQ may have to be carried out using
a dosimetry system calibration curve obtained by irradiation at another
shall be given to effects of influence quantities on the response
facility. This calibration curve should be verified as soon as possible, and
of the dosimeter (see ISO/ASTM 52701).
corrections applied to the OQ dose measurements as needed.
7.1.3 Different dosimetry systems may be selected for
NOTE 7—Multiple beam systems can be characterized individually or as
different dose measurement tasks due to different requirements
the combined facility.
on, for example, dosimetry systems for dose mapping and
9.2 The relevant OQ dose measurements are described in
dosimetry systems for routine monitoring.
more detail in Annex A2 – Annex A9. They typically include
7.2 Dosimetry system calibration:
the following:
7.2.1 The dosimetry system shall be calibrated in accor-
9.2.1 Depth-dose distribution and electron beam energy
dance with ISO/ASTM 51261, and the user’s procedures,
estimation—The depth-dose distribution is measured by irra-
which should specify details of the calibration process and
diating dosimeters in a stack of plates of homogeneous material
quality assurance requirements.
or by placing dosimeters or a dosimeter strip at an angle
7.2.2 The dosimetry system calibration is part of a measure-
through a homogeneous absorber. See Annex A2 and Annex
ment management system.
A3. Electron beam energy can be determined using established
relationships between beam energy and depth-dose distribution
8. Installation qualification
parameters. The method used for energy calculation must be
specified. See Annex A4.
8.1 Installation qualification (IQ) is carried out to obtain
9.2.2 Dose as function of average beam current, beam width
documented evidence that the irradiation equipment and any
and conveyor speed—Dose to the product irradiated in an
ancillary items have been supplied and installed in accordance
electron beam facility is proportional to average beam current
with their specifications.
(I), and inversely proportional to conveyor speed (V) and to
8.2 The specification of the electron beam facility shall be
beam width (W ), for a given electron beam energy. This
b
documented in the agreement between the supplier and the
relationship is valid for product that is conveyed through the
operator of the facility. This agreement shall contain details
radiation zone perpendicular to the beam width. This is
concerning the following:
expressed as:
8.2.1 Operating procedures for the irradiator and associated
Dose 5 ~K * I! ⁄ ~V * W ! (1)
b
conveyor system.
8.2.2 Test and verification procedures for process and an-
where:
cillary equipment, including associated software, to verify
D = Absorbed dose (Gy),
operation to design specifications. The test method(s) shall be
I = Average beam current (A),
-1
documented and the results shall be recorded.
V = Conveyor speed (m s ),
8.2.3 Any modifications made to the irradiator during in-
Wb = Beam width (m), and
stallation.
K = Slope of the straight line relationship in Eq 1
8.2.4 The characteristics of the electron beam (such as
(Gy * m )/(A * s).
electron energy, average beam current, beam width and beam
In order to determine the relationship, dose shall be mea-
uniformity) shall be determined and recorded.
sured at a specific location and for a specific irradiation
8.2.5 Specification for equipment for conveying product
geometry using a number of selected parameter sets of beam
through the irradiation zone.
current, conveyor speed and beam width to cover the operating
range of the facility. See Annex A5.
NOTE 4—The dose measurements carried out during IQ will often be
the same as the ones carried out during Operational Qualification (OQ).
9.2.3 Beam width—The beam width is measured by placing
Details of these dose measurements are given under OQ.
dosimeter strips or discrete dosimeters at selected intervals
8.2.6 IQ typically involves measurements of beam over the full beam width and at defined distance from the beam
penetration, beam width and beam width uniformity that can be window. See Annex A6.
used to estimate process throughput to verify the equipment 9.2.4 Beam homogeneity:
performance specifications. 9.2.4.1 For scanned beams it shall be ensured that there is
8.2.7 A dosimetry system calibration curve obtained by sufficient overlap between scans at the highest expected prod-
dosimeter irradiation at another facility with similar operating uct speeds through the irradiation zone.
characteristics might be used for these dose measurements, but 9.2.4.2 For scanned and pulsed beams it shall be ensured
in order to ensure that the dose measurements are reliable, the that there is sufficient overlap between beam pulses in the scan
calibration curve must be verified for the actual conditions of direction at the highest expected scan frequency and lowest
use. expected pulse frequency.
51649 − 22
9.2.4.3 For a pulsed and scanned beam it is necessary to effect and the maximum acceptable dose. For PQ product dose
have information about the beam diameter, because degree of mapping guidance, see ASTM Guide E2303.
overlap between scans and pulses can be calculated if the size
NOTE 10—Dose mapping exercises do not have to be carried out at the
same dose as used for product irradiations. The use of higher doses, for
and the shape of the beam spot are known. The beam spot can
example, can enable the dosimetry system to be used in a more accurate
be measured by irradiating dosimeters or sheets of dosimeter
part of its operating range, thereby improving the overall accuracy of the
film at defined distance from the beam window. See Annex A7.
dose mapping. This may be allowed provided that the linear relationship
9.2.5 Dose distribution in reference material—The distribu-
in 9.2.2 has been demonstrated.
tion of dose in a homogeneous reference material shall be
10.3 OQ dose mapping can in some cases be used as PQ
measured by placing dosimeters in a specified pattern within
dose mapping. For example, this is the case for irradiation
the material. See Annex A8.
treatment of wide webs of infinite length or in the case where
9.2.6 Process interruption—A process interruption can be
no more than a single process load at a given time is processed
caused by, for example, failure of beam current delivery or the
at the facility. In most other cases, such as medical device
conveyor stoppage. The effect of a process interruption shall be
sterilization, it is required to carry out specific PQ product dose
determined, so that decisions about possible product disposi-
mapping.
tion can be made. See Annex A9.
10.4 A loading pattern for product irradiation shall be
9.3 The measurements in 9.2 shall be repeated a sufficient
established for each product type. The specification includes:
number of times (three or more) to estimate the extent of the
10.4.1 dimensions and bulk density of the process load,
operating parameter variability based on a statistical evaluation
of the dose measurements.
10.4.2 composition of product and all levels of packaging,
10.4.3 orientation of the product within its package, and
NOTE 8—An estimate of operating parameter variability can be ob-
tained from the scatter between repeated dose measurements made at
10.4.4 orientation of the product with respect to the material
different times using identical operating parameter settings. This measured
handling system and beam direction.
dose variability has two sources: dosimetry uncertainty and operating
parameter variability, and it is generally difficult to separate these two
10.5 Dosimeters shall be placed throughout the volume of
components. Thus, the measured dose variability will often be a combi-
interest (see ASTM Guide E2303). Placement patterns that can
nation of the two.
most probably identify the locations of the dose extremes shall
9.3.1 Based on the estimated variability of the operating
be selected. Dosimeters shall be concentrated in areas expected
parameters, it can be determined if their specifications are met.
to receive maximum and minimum doses, while fewer dosim-
NOTE 9—The specifications may be adjusted as data from repeated OQ
eters might be placed in areas likely to receive intermediate
studies are accumulated.
absorbed dose. In addition, dosimeters are placed at the
9.4 Requalification—OQ measurements shall be repeated at
monitoring position(s) to be used in routine processing.
intervals specified by the user’s documented procedure, and
10.6 Dosimeters used for dose mapping shall be able to
following changes that might affect dose or dose distribution.
detect doses and dose gradients likely to occur within irradiated
The intervals shall be chosen to provide assurance that the
products. Dosimeter films in sheets or strips may be useful for
facility is consistently operating within specifications. Requali-
obtaining this information.
fication is typically carried out on an annual cycle, with
NOTE 11—Irradiation of complex product, such as many medical
specific parts of requalification at shorter time intervals within
devices, often produces dose gradients where dose may change by a factor
this cycle. If requalification measurements show that the
of 10 or more within millimetre distances, such as for dose mapping small
irradiator has changed from previous OQ measurements, then
metal components. It is necessary to use dosimeter systems that can
PQ might have to be repeated.
measure dose correctly under these conditions. This may involve use of
9.4.1 See Annex A11 for examples of changes that might thin film dosimeters that are analyzed on measurement equipment with
high spatial resolution.
lead to repeat of OQ.
10.7 Some dosimeters are provided in protective packaging.
10. Performance qualification
For dose mapping it might be needed to use dosimeters without
the protective packaging in order for the dosimeters to be
10.1 Performance Qualification (PQ) uses specific product
placed in close proximity to product surfaces.
to demonstrate that the facility consistently operates in accor-
dance with predetermined criteria to deliver specified doses, 10.7.1 Using dosimeters without protective packaging may
thereby resulting in product that meets the specified require- result in irradiation of the dosimeters under conditions that are
ments. Therefore, the objective of performance qualification is different from the conditions of calibration. For such cases, it
to establish all process parameters that will satisfy absorbed is essential to verify the validity of the calibration curve.
dose requirements. This is accomplished by establishing the
10.7.2 Verification of the calibration curve can be carried
dose distribution throughout the process load for a specific
out by irradiating such un-packaged dosimeters and reference
product loading pattern. Key process parameters include elec-
standard dosimeters together during dose mapping. It must be
tron beam energy, beam current, material handling system
ensured that the two dosimeters received the same dose
parameters (conveyor speed or irradiation time), beam width,
through the use of appropriate irradiation phantoms.
process load characteristics and irradiation conditions.
10.7.3 A correction factor to be applied to dose map results
10.2 PQ dose mapping is carried out to demonstrate that is determined from analysis of the irradiated dose map dosim-
product can be irradiated to doses required for the intended eters and reference standard dosimeters.
51649 − 22
10.8 During PQ dose mapping the locations and magnitudes irradiation, dosimeters are only placed at a routine monitoring
of minimum and maximum doses, as well as the dose at a position that is insulated from the effects of temperature of the
routine monitoring position, are determined. product.
10.14.4 Dose mapping of a product may be performed at the
10.9 The ratio between maximum and minimum doses
actual product temperature, using a dosimetry system that is
(dose uniformity ratio, DUR) should be calculated. If a routine
calibrated at the intended processing temperature.
monitoring location is used for process monitoring, then the
10.15 Unacceptable Dose Uniformity Ratio:
ratios between the maximum and minimum dose and the dose
at the monitoring position should be calculated and docu- 10.15.1 If the dose mapping reveals that the minimum or
maximum, or both, doses during processing will be
mented. This ratio is used during process control (see 11.1.3).
unacceptable, it may be possible to change the process param-
10.10 PQ dose mapping measurements shall be repeated for
eters to reduce the dose uniformity ratio to an acceptable level.
a sufficient number of process loads to allow statistical evalu-
Alternatively, it may be necessary to change the product
ation and characterization of the dose distribution data.
configuration within the process load or the shape, size, or flow
NOTE 12—“A sufficient number of process loads” is often interpreted as
pattern of the process load itself.
a minimum of three. However, a higher degree of confidence in the
measurement result is obtained by using a greater number of measure- 10.15.2 Changing the beam characteristics, for example, by
ments.
optimizing the electron beam energy, can change the dose
extremes. Other means to change the dose extremes may be
10.11 For partially-loaded process loads, additional perfor-
employed, such as use of attenuators, scatterers and reflectors.
mance qualification shall be carried out as for fully-loaded
10.15.3 Irradiation from two sides is often used to achieve
process loads.
an acceptable dose distribution. For two-sided irradiation, the
10.11.1 Variations to the dose distribution from partial
magnitudes and locations of dose extremes are usually quite
loading may in some cases be minimized by filling the process
different from those for single-sided irradiation. Slight fluctua-
load with simulated product.
tions in density or thickness of product within the process load
NOTE 13—If simulated product is used, procedures must be in place to
separate this from product after irradiation. or fluctuations in electron beam energy may cause more
pronounced changes in absorbed dose and its distribution
10.12 For irradiators used in a bulk flow mode, absorbed-
within the product for two-sided irradiation as compared to
dose mapping as described above may not be feasible. In this
single-sided irradiation.
case, absorbed dose extremes may be estimated by using an
10.15.4 Irradiation from more than two sides may be used to
appropriate number of dosimeters mixed with and carried by
further reduce the dose uniformity ratio.
the product through the irradiation zone. Enough dosimeters
10.15.5 For some cases, a redesign of the process load may
should be used to obtain statistically significant results. Calcu-
be needed to achieve an acceptable dose uniformity ratio.
lation of the absorbed dose extremes may be an appropriate
alternative (7-9).
11. Routine process control
NOTE 14—In case the required doses are not met with the values of the
11.1 For routine product processing, process parameters
operating parameters used for the dose map study, the parameters may be
scaled in order to achieve the required doses provided that the linear shall be selected as established during performance qualifica-
relationship in 9.2.2 has been demonstrated. There may be cases where
tion. The average beam current I and the conveyor speed V may
values of operating parameters for dose mapping are intentionally chosen
be set in such a way that the quotient I/V has the same value in
to fit a specific dosimetry system.
performance qualification and routine product processing.
10.13 Repeat of PQ dose mapping is needed if product is
NOTE 16—This means that if, for example, the beam current is lowered
changed, thus affecting dose or dose distribution significantly,
by 20 % the process speed has to be decreased by the same percentage in
or if OQ measurements show that the irradiation facility is
order to deliver the same absorbed dose.
changed. The rationale for decisions taken shall be docu-
11.1.1 The operating parameters (beam energy, beam
mented.
current, beam width and conveyor speed) shall be monitored
10.14 Dose Mapping for Irradiation at High or Low Tem-
and recorded during the process. The measuring intervals shall
peratures:
be chosen to provide assurance that the facility is consistently
10.14.1 Some applications require irradiation at tempera-
operating within specifications.
tures different from the dosimeter calibration temperature, such
NOTE 17—Electron beam energy, electron beam current and beam
as irradiation of frozen food or irradiation of pharmaceutical
width are usually not routinely measured directly, but are obtained through
products at liquid nitrogen in order to reduce adverse radiation
indirect measurements.
effects on the product.
11.1.2 The dose at the routine monitoring position shall be
10.14.2 For these applications, absorbed-dose mapping may
measured at intervals specified by the operator of the facility.
be performed with simulated or real product at a temperature
The intervals shall be chosen to verify that the irradiator
where dosimetry results will not be affected.
operates within specifications, and thereby ensuring that the
NOTE 15—This requires that there be no change in any parameter (other product specifications were achieved.
than temperature) that may affect the absorbed dose during processing of
NOTE 18—It is common practice to place dosimeters – as a minimum –
the heated or cooled product.
at start and end of a production run. More frequent placement of
10.14.3 During routine processing of product where product
dosimeters during the production run may reduce the risk of discarding
is maintained at higher or lower temperatures during product should some operational failure arise.
51649 − 22
NOTE 19—Some processes, such as the modification of material
qualification, performance qualification, and routine product
properties, may not require dosimetry.
processing. Include date, time, product type, product loading
11.1.3 Acceptance limits for the variation of the monitored diagrams, and absorbed doses for all products processed.
operating parameters (11.1.2) and measured routine dose 12.1.4 Dosimetry Uncertainty—Include estimates of the
(11.1.3) shall be established. measurement uncertainty of absorbed dose (see Section 13) in
records and reports, as appropriate.
11.2 Procedures shall be in place describing actions to be
12.1.5 Facility Log—Record the date the product lot is
taken in case monitored operating parameters or measured
processed and the starting and the ending times of the
routine doses exceed specifications.
irradiation run. Record the name of the operator, as well as any
11.3 For some types of bulk-flow irradiators (for example,
special conditions of the irradiator or the facility that could
where fluids or grains continuously flow during irradiation), it
affect the absorbed dose to the product.
is not feasible to place dosimeters at the locations of minimum
12.1.6 Product Identification—Ensure that each product lot
or maximum absorbed dose or at defined routine monitoring
that is processed bears an identification that distinguishes it
position during routine processing. In these cases, several
from all other lots in the facility. This identification shall be
dosimeters shall be added to the product stream at the
used on all lot documents.
beginning, the middle, and near the end of the production run.
12.2 Review and Certification:
Each set of absorbed-dose measurements requires several
12.2.1 Prior to release of product, review routine dosimetry
dosimeters to ensure, within a specified level of confidence,
result
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: ISO/ASTM 51649 − 2015(E) 51649 − 22
Standard Practice for
Dosimetry in an Electron Beam Facility for Radiation
Processing at Energies Between 300 keV and 25 MeV
This standard is issued under the fixed designation ISO/ASTM 51649; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice outlines dosimetric procedures to be followed in installation qualification (IQ), operational qualification (OQ)
and performance qualifications (PQ), and routine processing at electron beam facilities.
1.2 The electron beam energy range covered in this practice is between 300 keV and 25 MeV, although there are some discussions
for other energies.
1.3 Dosimetry is only one component of a total quality assurance program for adherence to good manufacturing practices used
in radiation processing applications. Other measures besides dosimetry may be required for specific applications such as health care
product sterilization and food preservation.
1.4 Specific standards exist for the radiation sterilization of health care products and the irradiation of food. For the radiation
sterilization of health care products, see ISO 11137-1 (Requirements) and ISO 11137-3 (Guidance on dosimetric aspects). For
irradiation of food, see ISO 14470. In those areas covered by these standards, they take precedence. Information about effective
or regulatory dose limits for food products is not within the scope of this practice (see ASTM Guides F1355, F1356, F1736, and
F1885).
1.5 This document is one of a set of standards that provides recommendations for properly implementing and utilizing dosimetry
in radiation processing. It is intended to be read in conjunction with ISO/ASTM 52628, “Practice for Dosimetry in Radiation
Processing”.
NOTE 1—For guidance in the calibration of routine dosimetry systems, see ISO/ASTM Practice 51261. For further guidance in the use of specific
dosimetry systems, see relevant ISO/ASTM Practices. For discussion of radiation dosimetry for pulsed radiation, see ICRU Report 34.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory requirementslimitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This practice is under the jurisdiction of ASTM Committee E61 on Radiation Processing and is the direct responsibility of Subcommittee E61.03 on Dosimetry
Application, and is also under the jurisdiction of . Originally developed as a joint ASTM/ISO standard in conjunction with ISO/TC 85/WG 3.
Current edition approved Dec. 1, 2022Sept. 8, 2014. . Published May 2024February 2015. Originally published as E 1649–94. Last previous ASTM edition E 1649–00.
ε1
ASTM E 1649–94. Originally approved in 1994. Last previous edition approved was adopted by ISO in 1998 with the intermediate designation ISO 15569:1998(E). The
present International Standard ISO/ASTM 51649:2015(E) is a major revision of the last previous edition ISO/ASTM 51649:2005(E), which replaced ISO/ASTM
51649:2002(E).in 2015 as ISO/ASTM 51649:2015(E). DOI: 10.1520/51649-22.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
51649 − 22
2. Referenced documents
2.1 ASTM Standards:
E170 Terminology Relating to Radiation Measurements and Dosimetry
E2232 Guide for Selection and Use of Mathematical Methods for Calculating Absorbed Dose in Radiation Processing
Applications
E2303 Guide for Absorbed-Dose Mapping in Radiation Processing Facilities
E3083 Terminology Relating to Radiation Processing: Dosimetry and Applications
F1355 Guide for Irradiation of Fresh Agricultural Produce as a Phytosanitary Treatment
F1356 Guide for Irradiation of Fresh, Frozen or Processed Meat and Poultry to Control Pathogens and Other Microorganisms
F1736 Guide for Irradiation of Finfish and Aquatic Invertebrates Used as Food to Control Pathogens and Spoilage
Microorganisms
F1885 Guide for Irradiation of Dried Spices, Herbs, and Vegetable Seasonings to Control Pathogens and Other Microorganisms
2.2 ISO/ASTM Standards:
51261 Practice for Calibration of Routine Dosimetry Systems for Radiation Processing
51275 Practice for Use of a Radiochromic Film Dosimetry System
51539 Guide for the Use of Radiation-Sensitive Indicators
51608 Practice for Dosimetry in an X-Ray (Bremsstrahlung) Facility for Radiation Processing
51702 Practice for Dosimetry in a Gamma Facility for Radiation Processing
51707 Guide for Estimating Uncertainties in Dosimetry for Radiation Processing
51818 Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 80 and 300 keV
52628 Practice for Dosimetry in Radiation Processing
52701 Guide for Performance Characterization of Dosimeters and Dosimetry Systems for Use in Radiation Processing
2.3 ISO Standards:
ISO 11137-1 Sterilization of Health Care Products–Radiation – Part 1: Requirements for development, validation, and routine
control of a sterilization process for medical devices
ISO 11137-3 Sterilization of Health Care Products–Radiation – Part 3: Guidance on dosimetric aspects
ISO/TS 11137-4 Sterilization of Health Care Products–Radiation – Part 4: Guidance on process control
ISO 14470 Food Irradiation – Requirements for the development, validation and routine control of the process of irradiation
using ionizing radiation for the treatment of food
ISO 10012 Measurement Management Systems – Requirements for Measurement Processes and Measuring Equipment
ISO/IEC 17025 General Requirements for the Competence of Calibration and Testing Laboratories
2.4 International Commission on Radiation Units and Measurements (ICRU) Reports:
ICRU Report 34 The Dosimetry of Pulsed Radiation
ICRU Report 35 Radiation Dosimetry: Electron Beams with Energies Between 1 and 50 MeV
ICRU Report 37 Stopping Powers for Electrons and Positrons
ICRU Report 80 Dosimetry for Use in Radiation Processing
ICRU Report 85a Fundamental Quantities and Units for Ionizing Radiation
2.5 Joint Committee for Guides in Metrology (JCGM) Reports:
JCGM 100:2008, GUM 1995 , with minor corrections, Evaluation of measurement data – Guide to the expression of uncertainty
in measurement
3. Terminology
3.1 Definitions:
3.1.1 absorbed dose (D)—quantity of ionizing radiation energy imparted per unit mass of a specified material.
3.1.1.1 Discussion—
(1) The SI unit of absorbed dose is the gray (Gy), where 1 gray is equivalent to the absorption of 1 joule per kilogram in the
specified material (1 Gy = 1 J/kg). The mathematical relationship is the quotient of dε¯ by dm, where dε¯ is the mean incremental
energy imparted by ionizing radiation to matter of incremental mass dm. (See ICRU Report 85a.)
D 5 dεH/dm
For referenced ASTM and ISO/ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book
of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from International Organization for Standardization, 1 Rue de Varembé, Case Postale 56, CH-1211 Geneva 20, Switzerland.
Available from the International Commission on Radiation Units and Measurements, 7910 Woodmont Ave., Suite 800, Bethesda MD 20814, U.S.A.
Document produced by Working Group 1 of the Joint Committee for Guides in Metrology (JCGM/WG 1). Available free of charge at the BIPM website
(http://www.bipm.org).
51649 − 22
3.1.1.2 Discussion—
(2) Absorbed dose is sometimes referred to simply as dose.
3.1.2 approved laboratory—laboratory that is a recognized national metrology institute; or has been formally accredited to
ISO/IEC 17025, or has a quality system consistent with the requirements of ISO/IEC 17025.
3.1.2.1 Discussion—
A recognized national metrology institute or other calibration laboratory accredited to ISO/IEC 17025 or its equivalent should be
used for issue of reference standard dosimeters or irradiation of dosimeters in order to ensure traceability to a national or
international standard. A calibration certificate provided by a laboratory not having formal recognition or accreditation will not
necessarily be proof of traceability to a national or international standard.
3.1.3 average beam current—time-averaged electron beam current; for a pulsed accelerator, the averaging shall be done over a
large number of pulses (see Fig. 1).
3.1.4 beam length—dimension of the irradiation zone along the direction of product movement at a specified distance from the
accelerator window (see Fig. 2).
3.1.4.1 Discussion—
Beam length is therefore perpendicular to beam width and to the electron beam axis. In case of product that is stationary during
irradiation, ‘beam length’ and ‘beam width’ may be interchangeable.
3.1.5 beam width (W )—dimension of the irradiation zone perpendicular to the direction of product movement at a specified
b
distance from the accelerator window (see Fig. 2).
3.1.5.1 Discussion—
For a radiation processing facility with a conveyor system, the beam width is usually perpendicular to the direction of motion of
the conveyor (see Fig. 2). Beam width is the distance between two points along the dose profile, which are at a defined level from
the maximum dose region in the profile (see Fig. 3). Various techniques may be employed to produce an electron beam width
adequate to cover the processing zone, for example, use of electromagnetic scanning of a pencil beam (in which case beam width
is also referred to as scan width), defocussing elements, and scattering foils.
FIG. 1 Example showing pulse beam current (I ), average beam current (I ), (pulse width (W) and repetition rate (f) for a pulsed
pulse avg
accelerator
51649 − 22
FIG. 2 Diagram showing beam length and beam width for a scanned beam using a conveyor system
3.1.6 compensating dummy—see simulated product.
3.1.7 depth-dose distribution—variation of absorbed dose with depth from the incident surface of a material exposed to a given
radiation.
3.1.7.1 Discussion—
Typical distributions along the beam axis in homogeneous materials produced by a normally incident monoenergetic electron beam
are shown in Annex A2.
3.1.8 dose uniformity ratio (DUR)—ratio of the maximum to the minimum absorbed dose within the irradiated product.
3.1.8.1 Discussion—
The concept is also referred to as the max/min dose ratio.
3.1.9 dosimetry system—system used for measuring absorbed dose, consisting of dosimeters, measurement instruments and their
associated reference standards, and procedures for the system’s use.
3.1.10 electron beam energy—kinetic energy of the accelerated electrons in the beam. Unit: J
3.1.10.1 Discussion—
-19
Electron volt (eV) is often used as the unit for electron beam energy where 1 eV = 1.602·10 J. In radiation processing, where
beams with a broad electron energy spectrum are frequently used, the terms most probable energy (E ) and average energy (E )
p a
are common. They are linked to the practical electron range R and half-value depth R by empirical equations (see Fig. 4 and
p 50
Annex A4).
3.1.11 electron beam facility—establishment that uses energetic electrons produced by particle accelerators to irradiate product.
3.1.12 electron energy spectrum—particle fluence distribution of electrons as a function of energy.
3.1.13 installation qualification (IQ)—process of obtaining and documenting evidence that equipment has been provided and
installed in accordance with its specification.
3.1.14 operational qualification (OQ)—process of obtaining and documenting evidence that installed equipment operates within
predetermined limits when used in accordance with its operational procedures.
3.1.15 performance qualification (PQ)—process of obtaining and documenting evidence that the equipment, as installed and
operated in accordance with operational procedures, consistently performs in accordance with predetermined criteria and thereby
yields product meeting its specification.
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FIG. 3 Example of electron-beam dose distribution along the scan direction, where the beam width is specified at a defined fractional
level f of the average maximum dose D
max
D : Dose at entrance surface
e
R : Depth at which dose at descending part of curve equals D
opt e
R : Depth at which dose has decreased to 50 % of its maximum value
R : Depth at which dose has decreased to 50 % of D
50e e
R : Depth where extrapolated straight line of descending curve meets depth axis
p
FIG. 4 A typical depth-dose distribution for an electron beam in a homogeneous material
3.1.16 process load—volume of material with a specified product loading configuration irradiated as a single entity.
3.1.17 production run—series of process loads consisting of materials or products having similar radiation-absorption
characteristics, that are irradiated sequentially to a specified range of absorbed dose.
3.1.18 reference material—homogeneous material of known radiation absorption and scattering properties used to establish
characteristics of the irradiation process, such as scan uniformity, depth-dose distribution, and reproducibility of dose delivery.
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3.1.19 reference plane—selected plane in the radiation zone that is perpendicular to the electron beam axis.
3.1.20 routine monitoring position—position where absorbed dose is monitored during routine processing to ensure that the
product is receiving the absorbed dose specified for the process.
3.1.20.1 Discussion—
This position may be a location of minimum or maximum dose in the process load or it may be an alternate convenient location
in, on or near the process load where the relationship of the dose at this position with the minimum and maximum dose has been
established.
3.1.21 simulated product—material with radiation absorption and scattering properties similar to those of the product, material or
substance to be irradiated.
3.1.21.1 Discussion—
Simulated product is used during irradiator characterization as a substitute for the actual product, material or substance to be
irradiated. When used in routine production runs in order to compensate for the absence of product, simulated product is sometimes
referred to as compensating dummy. When used for absorbed-dose mapping, simulated product is sometimes referred to as
phantom material.
3.1.22 standardized depth (z)—thickness of the absorbing material expressed as the mass per unit area, which is equal to the
product of depth in the material t and density ρ.
3.1.22.1 Discussion—
If m is the mass of the material beneath area A of the material through which the beam passes, then:
z 5 m/A 5 tρ
2 3
The SI unit of z is in kg/m , however, it is common practice to express t in centimetres and ρ in grams per cm , then z is in
grams per square centimetre. Standardized depth may also be referred to as surface density, area density, mass-depth or mass-
thickness.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 beam power—product of the average electron beam energy and the average beam current.
3.2.2 beam spot—shape of the unscanned electron beam incident on the reference plane.
3.2.3 continuous-slowing-down-approximation (CSDA) range (r )—average pathlength traveled by a charged particle as it slows
down to rest, calculated in the continuous-slowing-down-approximation method.
3.2.3.1 Discussion—
In this approximation, the rate of energy loss at every point along the track is assumed to be equal to the total stopping power.
Energy-loss fluctuations are neglected. The CSDA range is obtained by integrating the reciprocal of the total stopping power with
respect to energy. Values of r for a wide range of electron energies and for many materials can be obtained from ICRU Report
37.
3.2.4 duty cycle (for a pulsed accelerator)—fraction of time the beam is effectively on.
3.2.4.1 Discussion—
Duty cycle is the product of the pulse width (w) in seconds and the pulse rate (f) in pulses per second.
3.2.5 electron beam range—penetration distance in a specific, totally absorbing material along the beam axis of the electrons
incident on the material.
3.2.6 extrapolated electron range (R )—depth in homogeneous material to the point where the tangent at the steepest point (the
ex
inflection point) on the almost straight descending portion of the depth-dose distribution meets the depth axis (see Fig. A2.6 in
Annex A2).
3.2.7 half-entrance depth (R )—depth in homogeneous material at which the absorbed dose has decreased to 50 % of its value
50e
at the entrance surface of the material (see Fig. 4).
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3.2.8 half value depth (R )—depth in homogeneous material at which the absorbed dose has decreased to 50 % of its maximum
value (see Fig. 4).
3.2.9 optimum thickness (R )—depth in homogeneous material at which the absorbed dose equals its value at the entrance surface
opt
of the material (see Fig. 4).
3.2.10 practical electron range (R )—depth in homogeneous material to the point where the tangent at the steepest point (the
p
inflection point) on the almost straight descending portion of the depth-dose distribution curve meets the extrapolated X-ray
background (see Fig. 4 and Fig. A2.6 in Annex A2).
3.2.10.1 Discussion—
Penetration can be measured from experimental depth-dose distributions in a given material. Other forms of electron range are
found in the dosimetry literature, for example, extrapolated range derived from depth-dose data and the continuous-slowing-
-2
down-approximation range. Electron range is usually expressed in terms of mass per unit area (kg·m ), but sometimes in terms
of thickness (m) for a specified material.
3.2.11 pulse beam current, for a pulsed accelerator—beam current averaged over the top ripples (aberrations) of the pulse current
waveform.
3.2.11.1 Discussion—
Its value may be calculated as I /wf, where I is the average beam current, w is the pulse width, and f is the pulse rate (see Fig.
avg avg
5).
3.2.12 pulse rate (for a pulsed accelerator) (f)—pulse repetition frequency in hertz, or pulses per second.
3.2.12.1 Discussion—
This is also referred to as the repetition (rep) rate.
3.2.13 pulse width (for a pulsed accelerator) (w)—time interval between two points on the leading and trailing edges of the pulse
current waveform where the current is 50 % of its peak value (see Fig. 5).
Horizontal axis: Time, μs
Vertical axis: Pulse beam current, mA
FIG. 5 Typical pulse current waveform from an S-Band linear accelerator
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3.2.14 scanned beam—electron beam that is swept back and forth with a varying magnetic field.
3.2.14.1 Discussion—
This is most commonly done along one dimension (beam width), although two-dimensional scanning (beam width and length) may
be used with high-current electron beams to avoid overheating the beam exit window of the accelerator or product under the scan
horn.
3.2.15 scan frequency—number of complete scanning cycles per second.
3.2.16 scan uniformity—degree of uniformity of the dose measured along the scan direction.
3.3 Definitions—Definitions of other terms used in this standard that pertain to radiation measurement and dosimetry may be found
in ASTM Terminology E170E3083. Definitions in E170E3083 are compatible with ICRU 85a; that document, therefore, may be
used as an alternative reference.
4. Significance and use
4.1 Various products and materials are routinely irradiated at pre-determined doses at electron beam facilities to preserve or
modify their characteristics. Dosimetry requirements may vary depending on the radiation process and end use of the product. A
partial list of processes where dosimetry may be used is given below.
4.1.1 Polymerization of monomers and grafting of monomers onto polymers,
4.1.2 Cross-linking or degradation of polymers,
4.1.3 Curing of composite materials,
4.1.4 Sterilization of health care products,
4.1.5 Disinfection of consumer products,
4.1.6 Food irradiation (parasite and pathogen control, insect disinfestation, and shelf-life extension),
4.1.7 Control of pathogens and toxins in drinking water,
4.1.8 Control of pathogens and toxins in liquid or solid waste,
4.1.9 Modification of characteristics of semiconductor devices,
4.1.10 Color enhancement of gemstones and other materials, and
4.1.11 Research on radiation effects on materials.
4.2 Dosimetry is used as a means of monitoring the irradiation process.
NOTE 2—Dosimetry with measurement traceability and known uncertainty is required for regulated radiation processes such as sterilization of health care
products (see ISO 11137-1 and Refs (1-3 )) and preservation of food (see ISO 14470 and Ref (4)). It may be less important for other processes, such
as polymer modification, which may be evaluated by changes in the physical and chemical properties of the irradiated materials. Nevertheless, routine
dosimetry may be used to monitor the reproducibility of the treatment process.
NOTE 3—Measured dose is often characterized as absorbed dose in water. Materials commonly found in single-use disposable medical devices and food
are approximately equivalent to water in the absorption of ionizing radiation. Absorbed dose in materials other than water may be determined by applying
conversion factors (5, 6).
4.3 An irradiation process usually requires a minimum absorbed dose to achieve the desired effect. There may also be a maximum
The boldface numbers in parentheses refer to the Bibliography at the end of this standard.
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dose limit that the product can tolerate while still meeting its functional or regulatory specifications. Dosimetry is essential, since
it is used to determine both of these limits during the research and development phase, and also to confirm that the product is
routinely irradiated within these limits.
4.4 The dose distribution within the product depends on process load characteristics, irradiation conditions, and operating
parameters.
4.5 Dosimetry systems must be calibrated with traceability to national or international standards and the measurement uncertainty
must be known.
4.6 Before a radiation facility is used, it must be characterized to determine its effectiveness in reproducibly delivering known,
controllable doses. This involves testing and calibrating the process equipment, and dosimetry system.
4.7 Before a radiation process is commenced it must be validated. This involves execution of Installation Qualification (IQ),
Operational Qualification (OQ), and Performance Qualification (PQ), based on which process parameters are established that will
ensure that product is irradiated within specified limits.
4.8 To ensure consistent and reproducible dose delivery in a validated process, routine process control requires that documented
procedures are established for activities to be carried out before, during and after irradiation, such as for ensuring consistent
product loading configuration and for monitoring of critical operating parameters and routine dosimetry.
5. Radiation source characteristics
5.1 Electron sources considered in this practice are either direct-action (potential-drop) or indirect-action (Radio Frequency (RF)
or microwave-powered accelerators. These are discussed in Annex A1.
6. Documentation
6.1 Documentation for the irradiation facility must be retained in accordance with the requirements of a quality management
system. Typically, all facility related documentation is retained for the life of the facility, and product related documentation is
related for the life of the product.
7. Dosimetry system selection and calibration
7.1 Selection of dosimetry systems:
7.1.1 ISO/ASTM 52628 identifies requirements for selection of dosimetry systems. Consideration shall specifically be given to the
limited range of electrons which might give rise to dose gradients through the thickness of the dosimeter. By choosing thin film
dosimeters this problem can be minimized.
7.1.2 When selecting a dosimetry system, consideration shall be given to effects of influence quantities on the response of the
dosimeter (see ISO/ASTM 52701).
7.1.3 Different dosimetry systems may be selected for different dose measurement tasks due to different requirements on, for
example, dosimetry systems for dose mapping and dosimetry systems for routine monitoring.
7.2 Dosimetry system calibration:
7.2.1 The dosimetry system shall be calibrated in accordance with ISO/ASTM 51261, and the user’s procedures, which should
specify details of the calibration process and quality assurance requirements.
7.2.2 The dosimetry system calibration is part of a measurement management system.
8. Installation qualification
8.1 Installation qualification (IQ) is carried out to obtain documented evidence that the irradiation equipment and any ancillary
items have been supplied and installed in accordance with their specifications.
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8.2 The specification of the electron beam facility shall be documented in the agreement between the supplier and the operator
of the facility. This agreement shall contain details concerning the following:
8.2.1 Operating procedures for the irradiator and associated conveyor system.
8.2.2 Test and verification procedures for process and ancillary equipment, including associated software, to verify operation to
design specifications. The test method(s) shall be documented and the results shall be recorded.
8.2.3 Any modifications made to the irradiator during installation.
8.2.4 The characteristics of the electron beam (such as electron energy, average beam current, beam width and beam uniformity)
shall be determined and recorded.
8.2.5 Specification for equipment for conveying product through the irradiation zone.
NOTE 4—The dose measurements carried out during IQ will often be the same as the ones carried out during Operational Qualification (OQ). Details of
these dose measurements are given under OQ.
8.2.6 IQ typically involves measurements of beam penetration, beam width and beam width uniformity that can be used to
estimate process throughput to verify the equipment performance specifications.
8.2.7 A dosimetry system calibration curve obtained by dosimeter irradiation at another facility with similar operating
characteristics might be used for these dose measurements, but in order to ensure that the dose measurements are reliable, the
calibration curve must be verified for the actual conditions of use.
NOTE 5—Calibration under the approximate conditions of use can only be accomplished after installation qualification and after establishment of process
operating settings and appropriate process control procedures.
9. Operational qualification
9.1 Operational qualification (OQ) is carried out to characterize the performance of the irradiation equipment with respect to
reproducibility of dose to product.
NOTE 6—Dose measurements for OQ may have to be carried out using a dosimetry system calibration curve obtained by irradiation at another facility.
This calibration curve should be verified as soon as possible, and corrections applied to the OQ dose measurements as needed.
NOTE 7—Multiple beam systems can be characterized individually or as the combined facility.
9.2 The relevant OQ dose measurements are described in more detail in Annex A2 – Annex A9. They typically include the
following:
9.2.1 Depth-dose distribution and electron beam energy estimation—The depth-dose distribution is measured by irradiating
dosimeters in a stack of plates of homogeneous material or by placing dosimeters or a dosimeter strip at an angle through a
homogeneous absorber. See Annex A2 and Annex A3. Electron beam energy can be determined using established relationships
between beam energy and depth-dose distribution parameters. The method used for energy calculation must be specified. See
Annex A4.
9.2.2 Dose as function of average beam current, beam width and conveyor speed—Dose to the product irradiated in an electron
beam facility is proportional to average beam current (I), and inversely proportional to conveyor speed (V) and to beam width (W ),
b
for a given electron beam energy. This relationship is valid for product that is conveyed through the radiation zone perpendicular
to the beam width. This is expressed as:
Dose5~K * I!⁄~V * W ! (1)
b
where:
D = Absorbed dose (Gy),
I = Average beam current (A),
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-1
V = Conveyor speed (m s ),
Wb = Beam width (m), and
K = Slope of the straight line relationship in Eq 1 (Gy * m )/(A * 2).
K = Slope of the straight line relationship in Eq 1 (Gy * m )/(A * s).
In order to determine the relationship, dose shall be measured at a specific location and for a specific irradiation geometry using
a number of selected parameter sets of beam current, conveyor speed and beam width to cover the operating range of the facility.
See Annex A5.
9.2.3 Beam width—The beam width is measured by placing dosimeter strips or discrete dosimeters at selected intervals over the
full beam width and at defined distance from the beam window. See Annex A6.
9.2.4 Beam homogeneity:
9.2.4.1 For scanned beams it shall be ensured that there is sufficient overlap between scans at the highest expected product speeds
through the irradiation zone.
9.2.4.2 For scanned and pulsed beams it shall be ensured that there is sufficient overlap between beam pulses in the scan direction
at the highest expected scan frequency and lowest expected pulse frequency.
9.2.4.3 For a pulsed and scanned beam it is necessary to have information about the beam diameter, because degree of overlap
between scans and pulses can be calculated if the size and the shape of the beam spot are known. The beam spot can be measured
by irradiating dosimeters or sheets of dosimeter film at defined distance from the beam window. See Annex A7.
9.2.5 Dose distribution in reference material—The distribution of dose in a homogeneous reference material shall be measured
by placing dosimeters in a specified pattern within the material. See Annex A8.
9.2.6 Process interruption—A process interruption can be caused by, for example, failure of beam current delivery or the conveyor
stoppage. The effect of a process interruption shall be determined, so that decisions about possible product disposition can be made.
See Annex A9.
9.3 The measurements in 9.2 shall be repeated a sufficient number of times (three or more) to estimate the extent of the operating
parameter variability based on a statistical evaluation of the dose measurements.
NOTE 8—An estimate of operating parameter variability can be obtained from the scatter between repeated dose measurements made at different times
using identical operating parameter settings. This measured dose variability has two sources: dosimetry uncertainty and operating parameter variability,
and it is generally difficult to separate these two components. Thus, the measured dose variability will often be a combination of the two.
9.3.1 Based on the estimated variability of the operating parameters, it can be determined if their specifications are met.
NOTE 9—The specifications may be adjusted as data from repeated OQ studies are accumulated.
9.4 Requalification—OQ measurements shall be repeated at intervals specified by the user’s documented procedure, and following
changes that might affect dose or dose distribution. The intervals shall be chosen to provide assurance that the facility is
consistently operating within specifications. Requalification is typically carried out on an annual cycle, with specific parts of
requalification at shorter time intervals within this cycle. If requalification measurements show that the irradiator has changed from
previous OQ measurements, then PQ might have to be repeated.
9.4.1 See Annex A11 for examples of changes that might lead to repeat of OQ.
10. Performance qualification
10.1 Performance Qualification (PQ) uses specific product to demonstrate that the facility consistently operates in accordance with
predetermined criteria to deliver specified doses, thereby resulting in product that meets the specified requirements. Therefore, the
objective of performance qualification is to establish all process parameters that will satisfy absorbed dose requirements. This is
accomplished by establishing the dose distribution throughout the process load for a specific product loading pattern. Key process
parameters include electron beam energy, beam current, material handling system parameters (conveyor speed or irradiation time),
beam width, process load characteristics and irradiation conditions.
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10.2 PQ dose mapping is carried out to demonstrate that product can be irradiated to doses required for the intended effect and
the maximum acceptable dose. For PQ product dose mapping guidance, see ASTM Guide E2303.
NOTE 10—Dose mapping exercises do not have to be carried out at the same dose as used for product irradiations. The use of higher doses, for example,
can enable the dosimetry system to be used in a more accurate part of its operating range, thereby improving the overall accuracy of the dose mapping.
This may be allowed provided that the linear relationship in 9.2.2 has been demonstrated.
10.3 OQ dose mapping can in some cases be used as PQ dose mapping. For example, this is the case for irradiation treatment of
wide webs of infinite length or in the case where no more than a single process load at a given time is processed at the facility.
In most other cases, such as medical device sterilization, it is required to carry out specific PQ product dose mapping.
10.4 A loading pattern for product irradiation shall be established for each product type. The specification includes:
10.4.1 dimensions and bulk density of the process load,
10.4.2 composition of product and all levels of packaging,
10.4.3 orientation of the product within its package, and
10.4.4 orientation of the product with respect to the material handling system and beam direction.
10.5 Dosimeters shall be placed throughout the volume of interest (see ASTM Guide E2303). Placement patterns that can most
probably identify the locations of the dose extremes shall be selected. Dosimeters shall be concentrated in areas expected to receive
maximum and minimum doses, while fewer dosimeters might be placed in areas likely to receive intermediate absorbed dose. In
addition, dosimeters are placed at the monitoring position(s) to be used in routine processing.
10.6 Dosimeters used for dose mapping shall be able to detect doses and dose gradients likely to occur within irradiated products.
Dosimeter films in sheets or strips may be useful for obtaining this information.
NOTE 11—Irradiation of complex product, such as many medical devices, often produces dose gradients where dose may change by a factor of 10 or more
within millimetre distances, such as for dose mapping small metal components. It is necessary to use dosimeter systems that can measure dose correctly
under these conditions. This may involve use of thin film dosimeters that are analyzed on measurement equipment with high spatial resolution.
10.7 Some dosimeters are provided in protective packaging. For dose mapping it might be needed to use dosimeters without the
protective packaging in order for the dosimeters to be placed in close proximity to product surfaces.
10.7.1 Using dosimeters without protective packaging may result in irradiation of the dosimeters under conditions that are
different from the conditions of calibration. For such cases, it is essential to verify the validity of the calibration curve.
10.7.2 Verification of the calibration curve can be carried out by irradiating such un-packaged dosimeters and reference standard
dosimeters together during dose mapping. It must be ensured that the two dosimeters received the same dose through the use of
appropriate irradiation phantoms.
10.7.3 A correction factor to be applied to dose map results is determined from analysis of the irradiated dose map dosimeters and
reference standard dosimeters.
10.8 During PQ dose mapping the locations and magnitudes of minimum and maximum doses, as well as the dose at a routine
monitoring position, are determined.
10.9 The ratio between maximum and minimum doses (dose uniformity ratio, DUR) should be calculated. If a routine monitoring
location is used for process monitoring, then the ratios between the maximum and minimum dose and the dose at the monitoring
position should be calculated and documented. This ratio is used during process control (see 11.1.3).
10.10 PQ dose mapping measurements shall be repeated for a sufficient number of process loads to allow statistical evaluation and
characterization of the dose distribution data.
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NOTE 12—“A sufficient number of process loads” is often interpreted as a minimum of three. However, a higher degree of confidence in the measurement
result is obtained by using a greater number of measurements.
10.11 For partially-loaded process loads, additional performance qualification shall be carried out as for fully-loaded process
loads.
10.11.1 Variations to the dose distribution from partial loading may in some cases be minimized by filling the process load with
simulated product.
NOTE 13—If simulated product is used, procedures must be in place to separate this from product after irradiation.
10.12 For irradiators used in a bulk flow mode, absorbed-dose mapping as described above may not be feasible. In this case,
absorbed dose extremes may be estimated by using an appropriate number of dosimeters mixed with and carried by the product
through the irradiation zone. Enough dosimeters should be used to obtain statistically significant results. Calculation of the
absorbed dose extremes may be an appropriate alternative (77-9, 8).
NOTE 14—In case the required doses are not met with the values of the operating parameters used for the dose map study, the parameters may be scaled
in order to achieve the required doses provided that the linear relationship in 9.2.2 has been demonstrated. There may be cases where values of operating
parameters for dose mapping are intentionally chosen to fit a specific dosimetry system.
10.13 Repeat of PQ dose mapping is needed if product is changed, thus affecting dose or dose distribution significantly, or if OQ
measurements show that the irradiation facility is changed. The rationale for decisions taken shall be documented.
10.14 Dose Mapping for Irradiation at High or Low Temperatures:
10.14.1 Some applications require irradiation at temperatures different from the dosimeter calibration temperature, such as
irradiation of frozen food or irradiation of pharmaceutical products at liquid nitrogen in order to reduce adverse radiation effects
on the product.
10.14.2 For these applications, absorbed-dose mapping may be performed with simulated or real product at a temperature where
dosimetry results will not be affected.
NOTE 15—This requires that there be no change in any parameter (other than temperature) that may affect the absorbed dose during processing of the
heated or cooled product.
10.14.3 During routine processing of product where product is maintained at higher or lower temperatures during irradiation,
dosimeters are only placed at a routine monitoring position that is insulated from the effects of temperature of the product.
10.14.4 Dose mapping of a product may be performed at the actual product temperature, using a dosimetry system that is
calibrated at the intended processing temperature.
10.15 Unacceptable Dose Uniformity Ratio:
10.15.1 If the dose mapping reveals that the minimum or maximum, or both, doses during processing will be unacceptable, it may
be possible to change the process parameters to reduce the dose uniformity ratio to an acceptable level. Alternatively, it may be
necessary to change the product configuration within the process load or the shape, size, or flow pattern of the process load itself.
10.15.2 Changing the beam characteristics, for example, by optimizing the electron beam energy, can change the dose extremes.
Other means to change the dose extremes may be employed, such as use of attenuators, scatterers and reflectors.
10.15.3 Irradiation from two sides is often used to achieve an acceptable dose distribution. For two-sided irradiation, the
magnitudes and locations of dose extremes are usually quite different from those for single-sided irradiation. Slight fluctuations
in density or thickness of product within the process load or fluctuations in electron beam energy may cause more pronounced
changes in absorbed dose and its distribution within the product for two-sided irradiation as compared to single-sided irradiation.
10.15.4 Irradiation from more than two sides may be used to further reduce the dose uniformity ratio.
10.15.5 For some cases, a redesign of the process load may be needed to achieve an acceptable dose uniformity ratio.
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11. Routine process control
11.1 For routine product processing, process parameters shall be selected as established during performance qualification. The
average beam current I and the conveyor speed V may be set in such a way that the quotient I/V has the same value in performance
qualification and routine product processing.
NOTE 16—This means that if, for example, the beam current is lowered by 20 % the process speed has to be decreased by the same percentage in order
to deliver the same absorbed dose.
11.1.1 The operating parameters (beam energy, beam current, beam width and conveyor speed) shall be monitored and recorded
during the process. The measuring intervals shall be chosen to provide assurance that the facility is consistently operating within
specifications.
NOTE 17—Electron beam energy, electron beam current and beam width are usually not routinely measured directly, but are obtained through indirect
measurements.
11.1.2 The dose at the routine monitoring position shall be measured at intervals specified by the operator of the facility. The
intervals shall be chosen to verify that the irradiator operates within specifications, and thereby ensuring that the product
specifications were achieved.
NOTE 18—It is common practice to place dosimeters – as a minimum – at start and end of a production run. More frequent placement of dosimeters during
the production run may reduce the risk of discarding product should some operational failure arise.
NOTE 19—Some processes, such as the modification of material properties, may not require dosimetry.
11.1.3 Acceptance limits for the variation of the monitored operating parameters (11.1.2) and measured routine dose (11.1.3) shall
be established.
11.2 Procedures shall be in place describing actions to be taken in case monitored operating parameters or measured routine doses
exceed specifications.
11.3 For some types of bulk-flow irradiators (for example, where fluids or grains continuously flow during irradiation), it is not
feasible to place dosimeters at the locations of minimum or maximum absorbed dose or at defined routine monitoring position
during routine processing. In these cases, several dosimeters shall be added to the product stream at the beginning, the middle, and
near the end of the production run. Each set of absorbed-dose measurements requires several dosimeters to ensure, within a
specified level of confidence, that the minimum (and maxi
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