ASTM ISO/ASTM51261-13(2020)

Standard Practice for Calibration of Routine Dosimetry Systems for Radiation Processing

SIGNIFICANCE AND USE
4.1 Ionizing radiation is used to produce various desired effects in products. Examples of applications include the sterilization of medical products, microbial reduction, modification of polymers and electronic devices, and curing of inks, coatings, and adhesives (4).  
4.2 Absorbed-dose measurements, with statistical controls and documentation, are necessary to ensure that products receive the desired absorbed dose. These controls include a program that addresses requirements for calibration of routine dosimetry system.  
4.3 A routine dosimetry system calibration procedure as described in this document provides the user with a dosimetry system whose dose measurements are traceable to national or international standards for the conditions of use (see Annex A4). The dosimetry system calibration is part of the user’s measurement management system.
SCOPE
1.1 This practice specifies the requirements for calibrating routine dosimetry systems for use in radiation processing, including establishing measurement traceability and estimating uncertainty in the measured dose using the calibrated dosimetry system.
Note 1: Regulations or other directives exist in many countries that govern certain radiation processing applications such as sterilization of healthcare products and radiation processing of food requiring that absorbed-dose measurements be traceable to national or international standards (ISO 11137-1, Refs (1-3)2).  
1.2 The absorbed-dose range covered is up to 1 MGy.  
1.3 The radiation types covered are photons and electrons with energies from 80 keV to 25 MeV.  
1.4 This document is one of a set of standards that provides recommendations for properly implementing dosimetry in radiation processing, and describes a means of achieving compliance with the requirements of ASTM E2628 “Practice for Dosimetry in Radiation Processing” for the calibration of routine dosimetry systems. It is intended to be read in conjunction with ASTM E2628 and the relevant ASTM or ISO/ASTM standard practice for the dosimetry system being calibrated referenced in Section 2.  
1.5 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 environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2020
• ICS: 17.240 - Radiation measurements
• Technical Committee: E61 - Radiation Processing
• Drafting Committee: E61.01 - Dosimetry

Relations

• Refers: ASTM E170-17 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2017
• Refers: ASTM E170-16a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Oct-2016
• Refers: ASTM E178-16 - Standard Practice for Dealing With Outlying Observations
• Effective Date: 01-Jun-2016
• Refers: ASTM E170-16 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Feb-2016
• Refers: ASTM E170-15a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2015
• Refers: ASTM E170-15 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Mar-2015
• Refers: ASTM E170-14a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Oct-2014
• Refers: ASTM E170-14 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2014
• Refers: ASTM E170-10 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2010
• Refers: ASTM E170-09a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Aug-2009
• Refers: ASTM E2628-09 - Standard Practice for Dosimetry for Radiation Processing
• Effective Date: 15-Aug-2009
• Refers: ASTM E170-09 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Jun-2009
• Refers: ASTM E170-08d - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Nov-2008
• Refers: ASTM E178-08 - Standard Practice for Dealing With Outlying Observations
• Effective Date: 01-Oct-2008
• Refers: ASTM E170-08c - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2008

Overview

ASTM ISO/ASTM51261-13(2020), titled Standard Practice for Calibration of Routine Dosimetry Systems for Radiation Processing, provides internationally recognized guidelines for calibrating dosimetry systems used in radiation processing. Developed by ASTM, this standard ensures that dose measurements performed during processes like sterilization, polymer modification, and medical product validation are accurate, traceable, and meet regulatory requirements. Traceability to national or international standards is a central feature, helping facilities comply with both quality management and legal directives.

Key Topics

• Calibration of Dosimetry Systems

  • Guidance on selecting and calibrating dosimeters for routine use.
  • Procedures for establishing measurement traceability to international or national standards.
  • Requirements for estimating measurement uncertainty and developing uncertainty budgets.

• Types of Radiation and Dosimetry Systems

  • Applicable to photons and electrons with energies from 80 keV to 25 MeV, up to 1 MGy dose range.
  • Addresses both Type I and Type II dosimeters and the required methods for calibration verification.

• Calibration Methods

  • Use of approved laboratories (accredited to ISO/IEC 17025) for calibration irradiation.
  • In-situ or in-plant calibration procedures for alignment with facility-specific processing conditions.
  • Development and verification of calibration curves that reflect true absorbed-dose measurements.

• Measurement Traceability and Quality Assurance

  • Emphasizes calibration as part of a comprehensive measurement management system.
  • Requirements for documentation, statistical controls, and direct linkage of dose measurements to primary and reference standards.

• Uncertainty Estimation

  • Establishes protocols for calculating and documenting uncertainties arising from calibration, instrument performance, and environmental factors within the dosimetry process.

Applications

The standard is critical in settings where precise absorbed-dose delivery is essential. Practical applications include:

• Sterilization of Healthcare Products: Ensures compliance with regulations requiring accurate, traceable dose measurements in the sterilization of medical devices and pharmaceuticals.
• Radiation Processing of Food: Supports food safety and regulatory standards by mandating traceability and uncertainty estimation in dose delivery.
• Polymer and Electronics Modification: Provides confidence in dose-dependent manufacturing processes for polymers and electronic components, ensuring product quality and consistency.
• Curing of Inks, Coatings, and Adhesives: Guarantees that irradiation-based curing processes deliver the intended physical and chemical changes.
• Process Validation and Monitoring: Facilitates ongoing process quality assurance by establishing protocols for recalibration, stability verification, and corrective actions if deviations are observed.

Related Standards

• ASTM E2628: Practice for Dosimetry in Radiation Processing - Provides comprehensive requirements for dosimetry applied to routine processing.
• ISO 11137-1: Sterilization of healthcare products-Radiation - Details validation and control procedures for radiation sterilization.
• ISO/IEC 17025: General Requirements for the Competence of Testing and Calibration Laboratories - Specifies laboratory accreditation requirements to ensure valid calibration results.
• ISO/ASTM 51607: Practice for Use of an Alanine-EPR Dosimetry System - Reference for a specific type of dosimetry system.
• ISO/ASTM 51707: Guide for Estimating Uncertainties in Dosimetry for Radiation Processing - Provides guidance on uncertainty analysis.
• ASTM E2701: Guide for Performance Characterization of Dosimeters and Dosimetry Systems for Use in Radiation Processing - For system performance evaluation.

Practical Value

Implementing ASTM ISO/ASTM51261-13(2020) enhances the reliability and traceability of absorbed-dose measurements in radiation processing environments. Facilities benefit by:

• Conforming to international best practices
• Mitigating risk through robust quality control and documentation
• Ensuring process repeatability and compliance with ISO, ASTM, and regulatory directives
• Maintaining customer and regulatory confidence through validated, traceable procedures

Keywords: calibration of dosimetry systems, radiation processing, absorbed dose measurement, measurement uncertainty, traceability, photons and electrons, quality assurance, ISO/ASTM 51261, ASTM E2628, ISO 11137-1, ISO/IEC 17025, medical product sterilization, dosimeter calibration.

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.
ISO/ASTM 51261:2013 (Reapproved 2020)(E)
Standard Practice for
Calibration of Routine Dosimetry Systems for Radiation
Processing
This standard is issued under the fixed designation ISO/ASTM 51261; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision.
1. Scope 2. Referenced documents
1.1 This practice specifies the requirements for calibrating 2.1 ASTM Standards:
routine dosimetry systems for use in radiation processing, E170Terminology Relating to Radiation Measurements and
includingestablishingmeasurementtraceabilityandestimating Dosimetry
uncertainty in the measured dose using the calibrated dosim- E178Practice for Dealing With Outlying Observations
etry system. E2628Practice for Dosimetry in Radiation Processing
NOTE 1—Regulations or other directives exist in many countries that
E2701Guide for Performance Characterization of Dosim-
govern certain radiation processing applications such as sterilization of
eters and Dosimetry Systems for Use in Radiation Pro-
healthcare products and radiation processing of food requiring that
cessing
absorbed-dose measurements be traceable to national or international
2.2 ISO/ASTM Standards:
standards (ISO 11137-1, Refs (1-3) ).
51607Practice for Use of an Alanine-EPR Dosimetry Sys-
1.2 The absorbed-dose range covered is up to 1 MGy.
tem
1.3 The radiation types covered are photons and electrons
51707Guide for Estimating Uncertainties in Dosimetry for
with energies from 80 keV to 25 MeV.
Radiation Processing
1.4 This document is one of a set of standards that provides
2.3 International Commission on Radiation Units and Mea-
recommendations for properly implementing dosimetry in
surements Reports:
radiation processing, and describes a means of achieving
ICRU Report 85aFundamental Quantities and Units for
compliance with the requirements of ASTM E2628 “Practice
Ionizing Radiation
for Dosimetry in Radiation Processing” for the calibration of 5
2.4 ISO Standards:
routinedosimetrysystems.Itisintendedtobereadinconjunc-
ISO 11137-1 Sterilization of health care products—
tion withASTM E2628 and the relevantASTM or ISO/ASTM
Radiation—Requirements for the development, validation
standard practice for the dosimetry system being calibrated
and routine control of a sterilization process for medical
referenced in Section 2.
devices
1.5 This standard does not purport to address all of the 5
2.5 ISO/IEC Standards:
safety concerns, if any, associated with its use. It is the
17025General Requirements for the Competence ofTesting
responsibility of the user of this standard to establish appro-
and Calibration Laboratories
priate safety, health, and environmental practices and deter-
2.6 Joint Committee for Guides in Metrology (JCGM)
mine the applicability of regulatory limitations prior to use.
Reports:
1.6 This international standard was developed in accor-
JCGM 100:2008, GUM 1995, with minor corrections,
dance with internationally recognized principles on standard-
Evaluation of measurement data – Guide to the Expres-
ization established in the Decision on Principles for the
sion of Uncertainty in Measurement
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM and ISO/ASTM standards, visit the ASTM website,
www.astm.org, or contact ASTM Customer Service at [e-mail]. For
This practice is under the jurisdiction of ASTM Committee E61 on Radiation Annual Book of ASTM Standards volume information, refer to the standard’s
Processing and is the direct responsibility of Subcommittee E61.01 on Dosimetry, Document Summary page on the ASTM website.
and is also under the jurisdiction of ISO/TC 85/WG 3. Available from International Commission on Radiation Units and
Current edition approved Oct. 1, 2020. Published November 2020. Originally Measurements, 7910 Woodmont Avenue, Suite 800, Bethesda, MD 20814, USA.
published asASTM E1261–88. Last previousASTM edition E1261–00.ASTM Available from International Organization for Standardization (ISO), 1, ch. de
ε1
E 1261–94 was adopted by ISO in 1998 with the intermediate designation ISO la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
15556:1998(E). The present International Standard ISO/ASTM 51261:2013(20)(E) www.iso.ch.
replacesandisareapprovalofthelastpreviouseditionISO/ASTM51261:2013(E). DocumentproducedbyWorkingGroup1oftheJointCommitteeforGuidesin
The boldface numbers given in parentheses refer to the bibliography at the end Metrology (JCGM/WG 1). Available free of charge at the BIPM website (http://
of this guide. www.bipm.org).
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
3. Terminology 3.1.12 measurement management system—set of inter-
related or interacting elements necessary to achieve metrologi-
3.1 Definitions:
cal confirmation and continual control of measurement pro-
3.1.1 approved laboratory—laboratory that is a recognized
cesses.
nationalmetrologyinstitute;orhasbeenformallyaccreditedto
3.1.13 primary standard dosimetry system—dosimetry sys-
ISO/IEC 17025; or has a quality system consistent with the
tem that is designated or widely acknowledged as having the
requirements of ISO/IEC 17025.
highest metrological qualities and whose value is accepted
3.1.1.1 Discussion—A recognized national metrology insti-
without reference to other standards of the same quantity.
tute or other calibration laboratory accredited to ISO/IEC
3.1.14 reference standard dosimetry system—dosimetry
17025 should be used in order to ensure traceability to a
system, generally having the highest metrological quality
national or international standard. A calibration certificate
available at a given location or in a given organization, from
provided by a laboratory not having formal recognition or
which measurements made there are derived.
accreditation will not necessarily be proof of traceability to a
national or international standard.
3.1.15 routine dosimetry system—dosimetry system cali-
brated against a reference standard dosimetry system and used
3.1.2 calibration—set of operations that establish, under
for routine absorbed dose measurements, including dose map-
specified conditions, the relationship between values of quan-
ping and process monitoring.
tities indicated by a measuring instrument or measuring
3.1.16 traceability—propertyoftheresultofameasurement
system, or values represented by a material measure or a
or the value of a standard whereby it can be related to stated
reference material, and the corresponding values realized by
references, usually national or international standards, through
standards.
an unbroken chain of comparisons all having stated uncertain-
3.1.3 calibration curve—expression of the relation between
ties.
indication and the corresponding measured quantity value.
3.1.16.1 Discussion—Measurementtraceabilityisarequire-
3.1.4 charged-particle equilibrium (referred to as electron
ment of any measurement management system (see Annex
equilibriumin the case of electrons set in motion by photon A4).
beam irradiation of a material)—condition in which the kinetic
3.1.17 transfer standard dosimetry system—dosimetry sys-
energy of charged particles (or electrons), excluding rest mass,
tem used as an intermediary to calibrate other dosimetry
entering an infinitesimal volume of the irradiated material
systems.
equals the kinetic energy of charged particles (or electrons)
3.1.18 type I dosimeter—dosimeter of high metrological
emerging from it.
quality, the response of which is affected by individual influ-
3.1.5 dosimeter batch—quantity of dosimeters made from a
ence quantities in a well-defined way that can be expressed in
specific mass of material with uniform composition, fabricated
terms of independent correction factors.
in a single production run under controlled, consistent
3.1.19 type II dosimeter—dosimeter, the response of which
conditions, and having a unique identification code.
isaffectedbyinfluencequantitiesinacomplexwaythatcannot
3.1.6 dosimeter stock—partofadosimeterbatchheldbythe
practically be expressed in terms of independent correction
user.
factors.
3.1.7 dosimetry system—system used for measuring ab- 3.1.20 uncertainty (of measurement)—parameter associated
sorbed dose, consisting of dosimeters, measurement instru- with the result of a measurement that characterizes the disper-
sion of the values that could reasonably be attributed to the
ments and their associated reference standards, and procedures
measurand or derived quantity.
for the system’s use.
3.1.21 uncertainty budget—quantitative analysis of the
3.1.8 electron equilibrium—chargedparticleequilibriumfor
component terms contributing to the uncertainty of a
electrons. (See charged-particle equilibrium.)
measurement, including their statistical distribution, math-
3.1.9 influence quantity—quantity that is not the measurand
ematical manipulation and summation.
but that affects the result of the measurement.
3.2 validation (of a process)—establishment of documented
3.1.10 in-situ/in-plant calibration—calibration where the
evidence, which provides a high degree of assurance that a
dosimeter irradiation is performed in the place of use of the
specified process will consistently produce a product meeting
routine dosimeters.
its predetermined specifications and quality attributes.
3.1.10.1 Discussion—In-situ/in-plant calibration of dosim-
3.3 verification—confirmation by examination of objective
etry systems refers to irradiation of dosimeters along with
evidence that specified requirements have been met.
reference or transfer standard dosimeters, under operating
3.3.1 Discussion—In the case of measuring equipment, the
conditions that are representative of the routine processing
result of verification leads to a decision either to restore to
environment, for the purpose of developing a calibration curve
service or to perform adjustments, repair, downgrade, or
for the routine dosimetry systems.
declare obsolete. In all cases it is required that a written trace
3.1.11 measurand—specific quantity subject to measure- of the verification performed be kept on the instrument’s
ment. individual record.
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
bration curve generated under conditions that are representative of the
3.4 Definitions of other terms used in this standard that
routineprocessingenvironment.Anin-situ/in-plantcalibrationmaynotbe
pertain to radiation measurement and dosimetry may be found
valid or may require calibration verification if the calibration conditions
in ASTM Terminology E170. Definitions in ASTM Terminol-
can not be maintained during routine use. For example, the calibration
ogy E170 are compatible with ICRU Report 85a; that
irradiations are carried out as a single exposure, but the dosimeter is used
document, therefore, may be used as an alternative reference.
for dose measurement of fractionated irradiations.
5.3 Uncertainties:
4. Significance and use
5.3.1 Allmeasurementsofabsorbeddoseneedtobeaccom-
4.1 Ionizing radiation is used to produce various desired panied by an estimate of uncertainty (see ISO/ASTM 51707,
effects in products. Examples of applications include the
Refs (5,6) and GUM).
sterilization of medical products, microbial reduction, modifi-
5.3.2 All components of uncertainty should be included in
cation of polymers and electronic devices, and curing of inks,
the estimate, including those arising from calibration, dosim-
coatings, and adhesives (4).
eter reproducibility, instrument stability and the effect of
influencequantities.Afullquantitativeanalysisofcomponents
4.2 Absorbed-dose measurements, with statistical controls
of uncertainty is referred to as an uncertainty budget and is
and documentation, are necessary to ensure that products
often presented in the form of a table. Typically, the uncer-
receive the desired absorbed dose. These controls include a
tainty budget will identify all significant components of uncer-
program that addresses requirements for calibration of routine
tainty together with their methods of estimation, statistical
dosimetry system.
distributions and magnitudes.
4.3 A routine dosimetry system calibration procedure as
5.3.3 Examples of components of uncertainty in the dosim-
described in this document provides the user with a dosimetry
etry system calibration include inherent variation in dosimeter
system whose dose measurements are traceable to national or
response, uncertainty in the calibration irradiation dose, uncer-
international standards for the conditions of use (see Annex
tainty in the calibration curve fit and uncertainty in dosimeter
A4). The dosimetry system calibration is part of the user’s
response correction parameters such as dosimeter thickness,
measurement management system.
dosimetermass,unirradiatedresponseandirradiationtempera-
ture.
5. Dosimeter system calibration overview
5.3.4 Additional components of uncertainty might be pres-
5.1 Calibrationofaroutinedosimetrysystemconsistsofthe
entwhentheconditionsofusearedifferentthantheconditions
following:
of calibration. In these instances, a calibration verification is
5.1.1 Selection of the calibration dosimeters from the user
conducted to quantify a component of uncertainty to account
stock (see Section 8).
for these differences (see 9.1.8 and 9.2.9).
5.1.2 Irradiation of the calibration dosimeters (see 9.1 and
9.2).
6. Requirements for a routine dosimetry system
5.1.3 Calibration and/or performance verification of mea-
calibration
surement instruments (see Section 7).
6.1 Dosimetry system calibration shall be conducted for
5.1.4 Measurement of the calibration dosimeters response
each new dosimeter batch.
(see 9.1.6 and 9.2.5.1).
NOTE 4—The response of different dosimeter stocks purchased at
5.1.5 Analysis of the calibration dosimeter response data
different times from a given dosimeter batch should be verified to ensure
(see 9.1.7 and 9.2.6).
equivalent response.Astatistical test should be used to determine if there
5.1.6 Verification of the calibration curve for conditions of
is any significant difference between the stocks. This should be repeated
at several doses over the calibration dose range.
use, if appropriate (see 9.1.8 and Note 2).
5.1.7 Estimation of the combined uncertainty for the condi-
6.2 Routinedosimetrysystemsshallbecalibratedusingone
tions of use (see 9.1.10 and 9.2.7).
of the methods described in 9.1 and 9.2.
5.1.8 Verification of the calibration curve at a time other
6.3 Therationaleforselectingamethodforcalibrationshall
than calibration for assessment of continuing validity of the
be documented (see 9.1.4 and 9.2.3).
calibration curve (see 9.1.11, 9.2.9, and Note 2).
6.4 Recalibration of an existing batch or stock shall be
NOTE 2—Calibration verification is conducted as part of the calibration
conducted at a frequency specified by the user based on the
when the calibration irradiation conditions are different from the condi-
known characteristics of the dosimetry system.
tions of use (5.1.6). Calibration verification is also conducted between
calibrations to ensure continued suitability of the calibration curve for the
6.4.1 Additional calibration or calibration verification may
conditions of use (5.1.8).
be required to determine if changes have occurred that affect
5.2 Calibration Irradiation Methods—There are two meth- thecalibration.Examplesarechangesinthevaluesofinfluence
ods for irradiating dosimeters for calibration:
quantities, such as temperature or humidity, changes in the use
5.2.1 Calibration irradiations performed at an approved of the dosimetry system and change in response due to
laboratory followed by a calibration verification exercise.
dosimeter aging. Changes in influence quantities can result
5.2.2 In-situ/in-plant calibration irradiations of routine do- from seasonal changes in ambient conditions or changes in
simeters along with transfer standard dosimeters issued and source activity or distribution.
analyzed by an approved laboratory.
6.5 Calibration curves are specific to the measurement
NOTE 3—Valid in-situ/in-plant calibration irradiations result in a cali- instrument used to generate them. They shall not be used with
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
otherinstrumentsunlessithasbeendemonstratedthatthedose 9.1.1 Overview—The routine dosimeter may be a Type I or
measurements agree within user defined limits. Type II dosimeter. The calibration irradiation at an approved
laboratory has the advantage that the dosimeters are irradiated
6.6 All software associated with dosimetry system and
to known doses under well-controlled and documented condi-
calibration data analysis shall be validated for its intended use.
tions. However, when conditions of use (in-situ/in-plant) differ
7. Requirements for measurement instruments
from calibration conditions, significant uncertainties may be
calibration and performance verification
introducedinthecombineduncertaintyoftheroutineabsorbed
dosemeasurement.Transportofthedosimeterstoandfromthe
7.1 All measurement instrumentation associated with the
approvedlaboratorymayalsointroduceuncertaintiesfrompre-
dosimetry system shall either be calibrated, or have its perfor-
and post-irradiation influence quantities that are difficult to
mance verified, before use. Performance checks and/or recali-
characterize.
brationshallbecarriedoutatuser-specifiedintervals,basedon
9.1.2 Post Irradiation Response—Post-irradiation response
the known characteristics of the instrument.
characteristics of the routine dosimeter shall be determined
7.1.1 Where recognized standards exist, the calibration of
prior to calibration irradiation and incorporated into the cali-
the instrument shall be traceable to national or international
bration procedure.
standards.
9.1.3 Transport of Calibration Samples—The effect of in-
7.1.2 Where recognized standards do not exist, the perfor-
tended transportation on dosimeter response shall be evaluated
mance of the instrument shall be verified in accordance with
toestablishcriteriaforacceptablepackagingandtransportation
industry or manufacturer recommended practices and proce-
of calibration dosimeters. The evaluation should be based on
dures.
characterization data of the routine dosimetry system (see
NOTE 5—For example, the Alanine-EPR dosimetry system employs
ASTM E2701).
electron paramagnetic resonance (EPR) spectroscopy for analysis. The
9.1.4 Irradiation Conditions—Arationale shall be prepared
properoperationoftheEPRspectrometerisverifiedwithappropriateEPR
for the calibration target dose levels, their spacing and irradia-
spin reference such as irradiated alanine dosimeters, pitch sample, or
Mn(II) in CaO (see ISO/ASTM Practice 51607).
tionconditions,forexample,doserateandirradiationtempera-
ture specified to the approved laboratory. Document the allow-
7.1.3 When maintenance or modification of the measure-
able variation from these conditions.
ment instrumentation has occurred that may affect its
9.1.4.1 Forexample,fordoserangesoflessthanonedecade
performance, instrument performance shall be verified and, if
(factor of ten), dose levels should be distributed arithmetically
necessary, the instrument shall be re-calibrated.
uniformly (for example, 10, 20, 30, 40, 50 kGy). For dose
8. Requirements for the sampling of calibration
ranges of more than one decade, dose levels should be
dosimeters
distributedgeometricallyuniformly(forexample,1.0,1.5,2.3,
8.1 Dosimeters selected for the calibration shall constitute a 3.4, 5.1, 7.6, 11.4, 17.1, 25.6, 38.4, 57.7, 86.5 kGy).
representativesampleofthedosimeterstockheldbytheuserto 9.1.5 Dosimeter Irradiation—The dosimeters shall be irra-
be used in routine processing.These dosimeters are referred to diated at an approved laboratory to the specified absorbed
doses. The absorbed dose is usually specified in terms of
as ‘calibration dosimeters’.
absorbed dose to water.
8.2 Calibration dosimeters shall be labelled to ensure seg-
9.1.5.1 The approved laboratory shall report deviations
regation and identification throughout the calibration exercise.
from the conditions specified by the user (see 9.1.4).
8.3 The number of dose levels required for developing the
9.1.6 Dosimeter Response Measurement—The performance
calibration curve depends on the range of utilization. At least
of measurement instrumentation shall be verified (see 7.1).
five dose levels shall be used for each factor of ten span of
9.1.6.1 Measure the calibration dosimeter response upon
absorbed dose (for example, choose five dose levels fora5to
return from the approved laboratory in accordance with the
50 kGy range).
users calibration and measurement procedures.
8.3.1 The minimum number of dose levels to be used in the
9.1.7 Analysis of Dosimetry Data:
calibration can be determined as follows: divide the maximum
9.1.7.1 If required, each dosimeter response shall be ad-
dose (D ) of the dose range by the minimum dose (D )of
max min
justed for dosimeter parameters such as dosimeter thickness,
the dose range; calculate log (base 10) of this ratio: Q =
mass or unirradiated dosimeter response following established
log(D /D ). If Q is equal to or greater than 1, calculate 5 ×
max min
measurement practice.
Q, and round this up to the nearest integer value. This value
9.1.7.2 The individual dosimeter response, the sample stan-
representstheminimumnumberofdoselevelstobeused.If Q
dard deviation and the coefficient of variation of the replicate
is less than 1 use five dose levels.
measurements at each dose level shall be determined and
8.4 Aminimum of four dosimeters for each dose level shall documented.
be used. However, using a larger number of dosimeters per
NOTE 6—In general, if the coefficient of variation at any dose level is
dose level may reduce the uncertainty associated with the
greater than a user-defined limit, a re-determination of the data should be
calibration. considered (for example, perform a visual inspection to identify potential
dosimeter damage, repeat the calibration irradiation at the dose level or
9. Calibration of dosimetry systems
perform an outlier test).
9.1 Calibration of Dosimetry Systems using irradiations at 9.1.7.3 Derivethecalibrationcurveinmathematicalform, y
an approved laboratory: = f(x), where dosimeter response is the dependent variable (y)
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
and absorbed dose is the independent variable (x). Choose an during calibration irradiation, reducing the dose range of the
analytical form (for example, linear, polynomial, or exponen- calibration curve, developing calibration curves for specific
tial) that provides an appropriate fit to the measured data. The irradiator pathways, applying a correction factor to the routine
ease of deriving dose from measured dosimeter response (the dosimeter response in cases where a single factor is applicable
mathematical inverse of the analytical form) may also be a over the entire calibration curve, or calibrating using an
consideration in selecting the analytical form (see Annex A2 in-situ/in-plant calibration method (see 9.2).
and Annex A3). 9.1.10 Dosimetry System Measurement Uncertainty—
(1)The resulting calibration curve shall be evaluated for Prepare an estimate of the combined uncertainty in the mea-
goodness of fit within user defined limits. sured dose using the calibrated dosimetry system for the
9.1.8 Calibration Verification (as part of calibration)—Prior conditions of use (see Annex A3 and ISO/ASTM 51707).
9.1.11 Stability Verification—The suitability of the calibra-
to implementation of a calibration curve, a calibration verifi-
cation shall be performed to assess the suitability of the tioncurveshallbeverifiedoveritsperiodofuseinaccordance
with the requirements of 6.4.1.
calibration curve for the conditions of use. This is usually
achieved by in-situ/in-plant irradiation of transfer standard
9.2 In-situ/In-plant Calibration of Routine Dosimetry Sys-
dosimeters supplied by an approved laboratory alongside
tems in a Production Irradiator Using Transfer Standard
representative samples from the routine dosimeter stock under
Dosimetry System:
the conditions of use. The dosimetry system being calibrated
9.2.1 Overview—The routine dosimeter may be a Type I or
andthetransferstandarddosimetrysystemusedforcalibration
Type II dosimeter. The calibration irradiation of the routine
verification should, if possible, be based on different types of
dosimeterstogetherwiththetransferstandarddosimetersinthe
dosimeters. For example, if the dosimetry system being cali-
production irradiator has the advantage that the influence
bratedisbasedonalaninedosimeters,andthetransferstandard
quantityvaluerangeswillbeverysimilarinroutineapplication
dosimetry system is also based on alanine dosimeters, then the
and calibration, provided the calibration irradiation conditions
effect of an inappropriate correction for influence quantities,
are chosen appropriately. This method takes into account the
such as temperature, will not be apparent as both systems will
effect of the influence quantities of the conditions of use to the
respond in the same way.
extent that the transfer standard dosimeter response can be
9.1.8.1 The calibration verification shall be conducted at a
corrected for the difference between the fixed influence quan-
minimum of three dose levels targeted near the extremes and
tity values of its calibration and the production irradiation
near the center of the calibration dose range.
influence quantities profile by the approved laboratory issuing
9.1.8.2 The routine dosimeters for the calibration verifica-
and analyzing the transfer standard dosimeters. Care must be
tion shall be selected from the same dosimeter stock as the
taken to ensure that the routine dosimeters and transfer
calibration dosimeters.
standard dosimeters irradiated together receive the same ab-
9.1.8.3 Theirradiationoftheroutinedosimetersandtransfer
sorbed dose.
standard dosimeters shall consist of complete pathways
9.2.2 Post-Irradiation Response—Post-irradiation response
through the irradiator.
characteristics of the dosimeter shall be determined prior to
9.1.8.4 The routine and transfer dosimeters shall be irradi-
calibration irradiation and incorporated into the calibration
atedsothatitisensuredthattheyreceivethesamedosewithin
procedure.
predetermined limits (see Annex A1).
9.2.3 Irradiation Conditions—A rationale for target dose
levelsandirradiationconditionsforcalibrationirradiationshall
NOTE 7—The temperatures associated with the calibration verification
be prepared and documented. The irradiation conditions se-
irradiations should be similar to those expected to be encountered during
routine use of the dosimetry system. lected for calibration irradiation should be such that the
irradiation conditions are similar to those expected during the
9.1.8.5 In a few instances it may be impossible to conduct
intendeduseoftheirradiator,forexample,duringperformance
the calibration verification as described. In these instances, the
qualification and routine process monitoring.
user shall develop a verification method and rationale that is
9.2.3.1 Forexample,fordoserangesoflessthanonedecade
capable of demonstrating that the calibration curve of the
(factor of ten): dose levels should be distributed arithmetically
routine dosimetry system is suitable for the conditions of use.
uniformly (for example, 10, 20, 30, 40, 50 kGy). For dose
The rationale for the need to use this alternative method shall
ranges of more than one decade, dose levels should be
be documented.
distributedgeometricallyuniformly(forexample,1.0,1.5,2.3,
9.1.8.6 Thecalibrationverificationresultsshallbeevaluated
3.4, 5.1, 7.6, 11.4, 17.1, 25.6, 38.4, 57.7, 86.5 kGy).
to identify difference between the measured dose values of the
9.2.4 Dosimeter Irradiation—The calibration dosimeters
routineandtransferstandarddosimetrysystemsandtoprovide
shallbeirradiatedwithtransferstandarddosimetersissuedand
anestimateofoneofthecomponentsofcalibrationuncertainty
analyzed by an approved laboratory. The irradiation phantom
(see Annex A3).
used to co-locate the calibration dosimeters and the transfer
9.1.9 Corrective Action—If the calibration verification re-
standard dosimeters shall be characterized to ensure both the
sult exceeds a user defined acceptable limit, corrective action
calibration dosimeters and the transfer standard dosimeters
inaccordancewiththemeasurementmanagementsystemshall
receive the same absorbed dose (see AnnexA1).The absorbed
be implemented.
dose is usually specified in terms of absorbed dose to water.
9.1.9.1 Correctiveactionmayinclude:repeatingthecalibra-
tion using more appropriate influence quantity conditions NOTE 8—The temperatures of the routine dosimeters during calibration
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
irradiation should be similar to those expected to be encountered during
reducing the dose range of the calibration curve, developing
routine use of the dosimetry system.
calibration curves for specific irradiator pathways.
9.2.9 Stability Verification—The suitability of the calibra-
9.2.5 Dosimeter Response Measurement—Verifytheperfor-
tioncurveshallbeverifiedovertheperiodofuseinaccordance
mance of the measurement instrumentation (see 7.1 – 7.1.3).
with the requirements of 6.4.1.
9.2.5.1 The calibration dosimeter response shall be mea-
9.2.9.1 Changes to the intended conditions of use of the
sured in accordance with the users’ calibration and measure-
routine dosimetry system may render the calibration curve
ment procedures.
unsuitable. An example of such a change is that of dose
9.2.6 Analysis of Dosimetry Data—If required, each dosim-
fractioning during the intended use when the calibration
eterresponseshallbeadjustedforresponseparameterssuchas
irradiation consists of a single exposure. In such instances, the
dosimeter thickness, mass or unirradiated dosimeter response
effect of the change shall be evaluated.
following established measurement practice.
NOTE 10—Performing a calibration verification is one method of
9.2.6.1 The individual dosimeter response, the sample stan-
evaluating the effect of changes to the conditions of intended use,
dard deviation and the coefficient of variation of the replicate
reference 9.1.8 and Note 7.
measurements at each dose level shall be determined and
10. Minimum documentation requirements
documented.
10.1 Document the dosimetry system being calibrated in-
NOTE 9—In general, if any coefficient of variation is greater than a
cluding the dosimeter manufacturer, type and batch number,
user-definedlimit,are-determinationofthedatashouldbeconsidered(for
and measurement instrumentation.
example, perform a visual inspection to identify potential dosimeter
damage, repeat the calibration irradiation at the dose level or perform an
10.2 Document the rationale for the calibration method.
outlier test).
10.3 Document the dosimetry system calibration data, irra-
9.2.6.2 Derivethecalibrationcurveinmathematicalform, y
diation parameters, irradiation date, transfer standard
= f(x), where dosimeter response is the dependent variable (y)
dosimeters, and description of the irradiation facility used.
and absorbed dose is the independent variable (x). Choose an
10.4 Document or reference a description of the radiation
analytical form (for example, linear, polynomial, or exponen-
source(s) used in calibration and processing, including the
tial) that provides an appropriate fit to the measured data. The
type, nominal activity or beam parameters, and any available
ease of deriving dose from measured dosimeter response (the
information on the energy spectrum.
mathematical inverse of the analytical form) may also be a
10.5 Document irradiation temperatures and, if necessary,
consideration in selecting the analytical form (see Annex A2
and Annex A3). the relative humidity.
9.2.6.3 Theresultingcalibrationcurveshallbeevaluatedfor
10.6 Document the combined uncertainty in the measured
goodness of fit within user defined limits.
dose using the calibrated dosimetry system.
9.2.7 Dosimetry System Measurement Uncertainty—Prepare
10.7 Referencethemeasurementmanagementsystematthe
an estimate of the combined uncertainty in the measured dose
radiation facility.
using the calibrated dosimetry system for the conditions of use
11. Keywords
(see Annex A3 and ISO/ASTM 51707).
9.2.8 Corrective Action—If the combined uncertainty ex-
11.1 absorbed dose; accredited laboratory; dosimeter; do-
ceeds a user defined acceptable limit, corrective action in
simetry system calibration; dosimetry system; electron beam;
accordancewiththemeasurementmanagementsystemshallbe
gammaradiation;ionizingradiation;measurementtraceability;
implemented.
radiation processing; reference standard dosimetry system;
9.2.8.1 Correctiveactionmayinclude:repeatingthecalibra- routine dosimeter; transfer standard dosimetry system; Type I
tion using more appropriate calibration irradiation conditions, dosimeter; Type II dosimeter; X-ray; X-radiation
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
ANNEXES
(informative)
A1. PHANTOM GEOMETRY
A1.1 Aphantomofknownhomogenousmaterialisusedfor A1.3 When thick and thin dosimeters are irradiated
the irradiation of the dosimeters in order to minimize the together,thethindosimetersshouldbesurroundedbysufficient
difference between the absorbed doses received by the routine
polymericmaterialtoensurethattheattenuationcharacteristics
and transfer standard dosimeters. The phantom design should
are similar to the thick dosimeters and that the dosimeters
hold the two types of dosimeters so that they do not signifi-
receive the same dose.
cantly influence each other and provide a geometry that is
A1.4 Dose variation within the phantom can be character-
appropriate for the radiation source employed (see Fig. A1.1
and Fig. A1.2 for examples of such phantoms employed for ized by irradiating the phantom with the same type of dosim-
gamma or X-ray irradiation; see Fig.A1.3 for an example of a eter in all the dosimeter positions within the calibration
phantom suitable for high energy electron-beam irradiation).
irradiationphantom.However,differenceingeometrybetween
the routine dosimeters and transfer standard dosimeters must
A1.2 Theuseofaphantomcanresultindifferentirradiation
be taken into account.
temperature and temperature profile than the conditions of use
oftheroutinedosimeterwithoutaphantom.Theeffectofthese
differences should be evaluated as part of the calibration
procedure.
FIG. A1.1 Example of calibration phantom allowing alanine dosimeters to be placed on either side of thin film routine dosimetry system
dosimeter
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
FIG. A1.2 Example of calibration phantom allowing reference standard dosimeter ampoules and routine dosimetry system dosimeter to
be placed adjacent to each other
FIG. A1.3 Example of 10 MeV calibration phantom allowing alanine dosimeters and thin-film routine dosimetry system dosimeters to be
irradiated at the same position on the depth-dose curve
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
A2. CURVE FITTING
n
A2.1 Curve fitting is the application of regression analysis
SSE 5 w y 2 yˆ (A2.3)
~ !
i i i
(
techniques to a set of data where by the selected mathematical
i51
where:
form(model)definesthedependentvariable(Y)intermsofthe
independentvariable(X).Regressionanalysisisusedtofitdata
y = the observed dependent variable at an independent
i
to a model and provide estimates of the fit parameters
variable value,
(coefficients) based on a minimization technique.
ŷ = the model predicted value of the dependent variable at
i
the corresponding independent variable, and
A2.2 Regressionmodelsareeitheranempiricaloramecha-
w = assigned weight which in most cases is assumed to be
i
nistic model. The empirical model describes the general shape
1 unless a weighting is applied to compensate for a
of the data set. The parameters of the empirical model do not
deviation of homoscedasticity (A2.3.1.3).
correspond to an underlying biological, chemical or physical
NOTE A2.3—When the Gaussian distribution of error assumption is
process. The mechanistic model is formulated to provide
invalid due to appreciable tails in the residuals distribution, the assump-
insight or description of the process under study.
tionthatleastsquaresprovidesthemaximumlikelihoodfitisalsoinvalid.
In these instances a robust method of minimization may be used. The
A2.3 The two basic types of regression analysis are linear
essence of robust fitting is to use a minimization technique that is less
regression and non-linear regression. Linear regression is
influenced by potential outliers and the range of the dependent variable.
Several examples of nonlinear robust minimization are Least Absolute
wheretheunknownparameters(coefficients)appearlinearlyin
Deviation, Lorentzian, and Pearson.
the expression as in Eq A2.1. Non-linear regression is where
theunknownparameters(coefficients)appearinanon-linearor
A2.5 Goodnessoffitdescribeshowwellthemodelfitsaset
nested fashion as in Eq A2.2.
of data. Measures of goodness of fit typically summarize the
2 3
discrepancy between observed values (y) and the values
y 5 a1bx1cx 1dx (A2.1)
i
predicted by the model (ŷ).Areview of a plot of the residuals
a
y 5 (A2.2) is critical when assessing goodness of fit.The most commonly
c
x
usedstatisticsforassessinggoodnessoffitarethecoefficientof
S D
b
determination, lack of fit sum of squares (F statistic), confi-
NOTEA2.1—In the context of regression analysis, the terms linear and
dence intervals of the fit coefficients, and the F test when
non-lineardonotrefertotheshapeoftheplottedcurve,forexample,both
Eq A2.1 and Eq A2.2 represent curved plots.
comparing fits between different models. Another powerful
non-statistical evaluation method is a review of the plot of the
A2.3.1 In both types of regression analysis (linear and
residuals.
nonlinear) several assumptions are made:
A2.3.1.1 X is known precisely and all error is in Y. (It is
A2.5.1 A plot of the residuals can reveal behaviour in the
sufficient that imprecision in measuring X is very small
data that is otherwise difficult to see in the curve fit.Aplot of
compared to the variability in Y. Error refers to deviation from
the residuals should not demonstrate a form or trend. A
the average.)
residuals plot may also indicate potential or suspect outliers
A2.3.1.2 Variability of Y at any X follows a known
(see A2.6).
distribution, typically assumed to be Gaussian or near Gauss-
A2.5.2 Thecoefficientofdetermination(r )hasnounitsand
ian.
ranges in value between 0 and 1 which is computed as shown
A2.3.1.3 Thestandarddeviationoftheresidualsisthesame
in Eq A2.4. A value of 1.0 indicates the curve passes through
along the curve (homoscedasticity).
all the data points. The coefficient of determination can be
NOTE A2.2—– In some dosimetric calibration data, homoscedasticity
interpreted as the fraction of the total variance in y that is
does not exist and is corrected with the use of a weighting factor, see Eq
explained by the model. A common mistake is using the
A2.3 and Eq A2.4.
coefficient of determination solely as the gauge of goodness of
A2.3.1.4 Observations (Y) are independent (whether one
fit; this may lead to the selection of a model that may fluctuate
point is above or below the regression analysis model curve is
wildly with very large confidence intervals.
a matter of chance and does not influence whether another
n
point is above or below the regression analysis model curve).
w ~y 2 yˆ !
( i i i
SSE
i51
r 51 2 51 2 (A2.4)
n
A2.4 A minimization technique is used to determine the
SSM
w ~y 2 y¯ !
coefficientsoftheregressionmodelformthatprovidesthebest ( i i i
i51
fit. The most common technique for linear fitting is a least
where:
squares algorithm which minimizes the sum of the squares of
SSE = sum of the squares of the residuals,
the residuals (SSE) where a residual is the vertical distance
SSM = sum of the squares deviation about the mean,
between the data point and regression model curve (reference
y¯ = average response at dose level i, and
i
EqA2.3).The most common technique for non-linear fitting is
w = assigned weight which in most cases is assumed to
i
theLevenberg-Marquardtalgorithm.Mostcommerciallyavail-
be 1 unless a weighting is applied to compensate for
able regression software will provide linear and non-linear
a deviation of homoscedasticity (A2.3.1.3).
regression and multiple minimization algorithms.
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 51261:2013 (2020)(E)
A2.5.3 The F-statistic is a measure of the extent to which significance.Thismeansthat5%ofthetruepopulation(either
the given model represents the data. The F-statistic is calcu- in a single-sided or double-sided test) will be identified by the
lated as the ratio of the mean square error of the regression to statistical outlier test as significant. Unless it can be identified
the mean square error: that the suspect observation is the result of an experimental
error or the sample is in violation of criterion applied qualify-
SSM 2 SSE
S D ing it as a viable sample, it can not be conclusively proven to
MSR m 21
F 5 5 (A2.5)
come from a different population by a statistical outlier test.
MSE SSE
S D Althoughnotconclusiveinandofthemselves,severalmethods
DF
are used to identify suspect outliers:
where:
A2.6.2.1 Visual inspection of plot of the residuals (qualita-
n
SSM =
tive).
w ~y 2y¯ !
(
i i i
i5n1
SSE = A2.6.2.2 Confidence Intervals (quantitative).
w y 2y¯
~ !
( i i i
i51
A2.6.2.3 Prediction Limits (quantitative).
m = number of coefficients fitted,
A2.6.2.4 Statistical test such as a t-test (quantitative).
n = number of data points, and
DF = n·m
A2.6.3 A visual inspection of the residuals plot is a quali-
A larger F ratio indicates the model fits the data well. tative means of quickly identifying suspect outliers.
A2.5.4 The regression analysis estimates coefficients of the A2.6.4 Confidenceintervalsmakeuseoftheassumptionsof
model for the fit of the data. Most commercially available
linear and non-linear regression about the population distribu-
regression software provides an estimate of the standard error tion of the observations used to identify a measure estimate,
for each coefficient and the 95 % confidence interval about the
specifically the assumption of a Gaussian distribution of error.
coefficient estimate.The value of the standard error and the 95 The confidence interval is a range of values where at a
% confidence interval provides a means to gauge how well the
specified confidence coefficient (95 or 99 %) the ‘true’ value
regression has determined the coefficients. If the assumptions
exists. For regression analysis, this is an interval wherein the
of A2.3 are not significantly violated, the 95 % confidence
‘true’best fit curve lies for a specified level of confidence, for
interval is considered to be an interval that has a 95 % chance
example, 95 % probability for the given model.This is not the
of containing the ‘true’ value of the coefficient. If the confi-
same as inferring a 95 % confidence interval contains 95 % of
dence intervals are wide, the coefficient has not been deter-
the observations. Given this, a confidence interval is not a
mined precisely. If the confidence intervals are narrow, the
suitable measure for identifying suspect outliers.
coefficients have been determined precisely.
A2.6.5 Prediction intervals, similarly to confidence
intervals, assume a Gaussian distribution of error. The predic-
A2.6 Suspect outlying observations can typically be identi-
tion interval describes error about the curve or scatter associ-
fied from a review of the residuals plots (reference A2.5.1).
ated with the individual observations. In this case a 95 %
Generally,adosimetrysystemcalibrationconsistsofrelatively
prediction interval is expected to contain 95 % of the
...