ISO/ASTM 51608:2015

Practice for dosimetry in an X-ray (bremsstrahlung) facility for radiation processing at energies between 50 keV and 7.5 MeV

ISO/ASTM 51608:2015 outlines the dosimetric procedures to be followed during installation qualification, operational qualification, performance qualification and routine processing at an X-ray (bremsstrahlung) irradiator. Other procedures related to operational qualification, performance qualification and routine processing that may influence absorbed dose in the product are also discussed. ISO/ASTM 51608:2015 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 Practice 52628, "Practice for Dosimetry in Radiation Processing". In contrast to monoenergetic gamma radiation, the X-ray energy spectrum extends from low values (about 35 keV) up to the maximum energy of the electrons incident on the X-ray target.

Practique de la dosimétrie dans une installation de traitement par des rayons X (bremsstrahlung) entre 50 KeV et 7,5 MeV

General Information

• Status: Published
• Publication Date: 16-Mar-2015
• ICS: 17.240 - Radiation measurements
• Technical Committee: ISO/TC 85 - Nuclear energy, nuclear technologies, and radiological protection
• Drafting Committee: ISO/TC 85 - Nuclear energy, nuclear technologies, and radiological protection
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 04-Jun-2020

Relations

• Revises: ISO/ASTM 51608:2005 - Practice for dosimetry in an X-ray (bremsstrahlung) facility for radiation processing
• Effective Date: 07-Jun-2014

Standards Content (Sample)

INTERNATIONAL ISO/ASTM
STANDARD 51608
Third edition
2015-03-15
Practice for dosimetry in an X-ray
(bremsstrahlung) facility for radiation
processing at energies between 50 KeV
and 7.5 MeV
Pratique de la dosimétrie dans une installation de traitement par
des rayons X (bremsstrahlung) entre 50 KeV et 7,5 MeV
Reference number
ISO/ASTM 51608:2015(E)
© ISO/ASTM International 2015

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ISO/ASTM 51608:2015(E)
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ii © ISO/ASTM International 2015 – All rights reserved

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ISO/ASTM 51608:2015(E)
Contents Page
1 Scope. 1
2 Referenced documents. 1
3 Terminology. 2
4 Significance and use. 3
5 Radiation source characteristics. 4
6 Types of facilities. 4
7 Selection and calibration of dosimetry system. 4
8 Process parameters. 4
9 Installation qualification. 5
10 Operational qualification. 5
11 Performance qualification. 7
12 Routine product processing. 8
13 Certification . 9
14 Measurement dose uncertainty and process variability . 10
15 Keywords. 10
Annex. 10
Figure A1.1 Beam current density distributions along the scan direction (wide curves) and
perpendiculartothescandirection(narrowcurves)ofNo.1acceleratorofJAERITakasaki(Fig.
2.1 from Ref (61)). 11
Figure A1.2 X-ray intensity per 2 MeV electron incident perpendicularly on a tantalum target
with thickness of one CSDA electron range as a function of emitting angle calculated by the
ETRAN code (Fig. 3.3 from Ref (61)). 11
Figure A1.3 X-ray intensity per 5 MeV electron incident perpendicularly on a tantalum target
withthicknessofoneCSDAelectronrangeasafunctionofemittinganglecalculatedbyETRAN
code (Fig 3.4 from Ref (61)). 11
Figure A1.4 X-ray emission rates from high-Z targets (Fig. E 1 from Ref (76)). 12
Figure A1.5 Spectrum of transmitted photons (Fig 2a from Ref (21)). 12
Figure A1.6 Spectrum of reflected photons (Fig. 2b from Ref (21)). 12
Figure A1.7 Depth dose distributions (Fig. 1 from Ref (9)). 12
Figure A1.8 Dose contour map, moving exposure (Fig. 3 from Ref (62)). 13
FigureA1.9 Measured attenuation curves for 5 MeV X-Rays in absorbers of various densities,
with moving conveyor and scanning beam (Fig. 5 from Ref (3)). 13
Figure A1.10 Measurement of a high-resolution attenuation curve for 5 MeV X-rays in the
heaviest absorber (chipboard) with moving conveyor and scanning (Fig. 6 from Ref (3)). 13
© ISO/ASTM International 2015 – All rights reserved iii

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ISO/ASTM 51608:2015(E)
Foreword
ISO(theInternationalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for
voting. Publication as an International Standard requires approval by at least 75% of the member bodies
casting a vote.
ASTM International is one of the world’s largest voluntary standards development organizations with global
participation from affected stakeholders. ASTM technical committees follow rigorous due process balloting
procedures.
A project between ISO and ASTM International has been formed to develop and maintain a group of
ISO/ASTM radiation processing dosimetry standards. Under this project, ASTM Committee E61, Radiation
Processing, is responsible for the development and maintenance of these dosimetry standards with
unrestricted participation and input from appropriate ISO member bodies.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. Neither ISO nor ASTM International shall be held responsible for identifying any or all such patent
rights.
International Standard ISO/ASTM 51608 was developed by ASTM Committee E61, Radiation Processing,
through Subcommittee E61.03, Dosimetry Application, and by Technical Committee ISO/TC 85, Nuclear
energy, nuclear technologies and radiological protection.
This third edition cancels and replaces the second edition (ISO/ASTM 51608:2005), which has been
technically revised.
iv © ISO/ASTM International 2015 – All rights reserved

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ISO/ASTM 51608:2015(E)
An American National Standard
Standard Practice for
Dosimetry in an X-Ray (Bremsstrahlung) Facility for
Radiation Processing at Energies between 50 keV and 7.5
1
MeV
This standard is issued under the fixed designation ISO/ASTM 51608; 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 keV) up to the maximum energy of the electrons incident on
the X-ray target (see Section 5 and Annex A1).
1.1 This practice outlines the dosimetric procedures to be
followed during installation qualification, operational
1.6 Informationabouteffectiveorregulatorydoselimitsand
qualification, performance qualification and routine processing
energy limits for X-ray applications is not within the scope of
at an X-ray (bremsstrahlung) irradiator. Other procedures
this practice.
related to operational qualification, performance qualification
1.7 This standard does not purport to address all of the
androutineprocessingthatmayinfluenceabsorbeddoseinthe
safety concerns, if any, associated with its use. It is the
product are also discussed.
responsibility of the user of this standard to establish appro-
NOTE 1—Dosimetry is only one component of a total quality assurance
priate safety and health practices and determine the applica-
program for adherence to good manufacturing practices used in radiation
processing applications. bility of regulatory limitations prior to use.
NOTE 2—ISO/ASTM Practices 51649, 51818 and 51702 describe
dosimetric procedures for electron beam and gamma facilities for radia-
2. Referenced documents
tion processing.
2
2.1 ASTM Standards:
1.2 For radiation sterilization of health care products, see
E170Terminology Relating to Radiation Measurements and
ISO 11137-1, Sterilization of health care products – Radiation
Dosimetry
– Part 1: Requirements for development, validation and
E2232Guide for Selection and Use of Mathematical Meth-
routine control of a sterilization process for medical devices.In
ods for CalculatingAbsorbed Dose in Radiation Process-
those areas covered by ISO 11137-1, that standard takes
ing Applications
precedence.
E2303Guide for Absorbed-Dose Mapping in Radiation
1.3 Forirradiationoffood,seeISO14470, Food irradiation
Processing Facilities
– Requirements for development, validation and routine con-
2
2.2 ISO/ASTM Standards:
trol of the process of irradiation using ionizing radiation for
51261Practice for Calibration of Routine Dosimetry Sys-
the treatment of food. In those areas covered by ISO 14470,
tems for Radiation Processing
that standard takes precedence.
51539Guide for Use of Radiation-Sensitive Indicators
1.4 This document is one of a set of standards that provides
51649Practice for Dosimetry in an Electron Beam Facility
recommendations for properly implementing and utilizing
for Radiation Processing at Energies Between 300 keV
dosimetry in radiation processing. It is intended to be read in
and 25 MeV
conjunction with ISO/ASTM Practice 52628, “Practice for
51702Practice for Dosimetry in a Gamma Facility for
Dosimetry in Radiation Processing”.
Radiation Processing
51707Guide for Estimating Uncertainties in Dosimetry for
1.5 In contrast to monoenergetic gamma radiation, the
Radiation Processing
X-ray energy spectrum extends from low values (about 35
51818Practice for Dosimetry in an Electron Beam Facility
for Radiation Processing at Energies Between 80and 300
keV
1
This practice is under the jurisdiction of ASTM Committee E61 on Radiation
52628Practice for Dosimetry in Radiation Processing
Processing and is the direct responsibility of Subcommittee E61.03 on Dosimetry
Application, and is also under the jurisdiction of ISO/TC 85/WG 3.
Current edition approved Sept. 8, 2014. Published February 2015. Originally
published asASTM E 1608–94. Last previousASTM edition E 1608–00.ASTM E
2
1608–94 was adopted by ISO in 1998 with the intermediate designation ISO For referenced ASTM or ISO/ASTM standards, visit the ASTM website,
15567:1998(E). The present International Standard ISO/ASTM 51608:2015(E) is a www.astm.org, or contact ASTM Customer Service at [e-mail]. For
major revision of the last previous edition ISO/ASTM 51608:2005(E), which Annual Book of ASTM Standards volume information, refer to the standard’s
replaced ISO/ASTM 51608:2002(E). Document Summary page on the ASTM website.
© ISO/ASTM International 2015 – All rights reserved
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ISO/ASTM 51608:2015(E)
52701Guide for Performance Characterization of Dosim- 3.1.3 beam width—dimension of the irradiation zone per-
etersandDosimetrySystemsforuseinRadiationProcess- pendiculartothedirectionofproductmovement,ataspecified
ing distance from the accelerator window.
3
3.1.3.1 Discussion—For graphic illustration, see ISO/
2.3 ISO Standards:
ASTM Practice 51649. This term usually applies to electron
ISO 11137-1Sterilization of health care products – Radia-
irradiation.
tion – Part 1: Requirements for development, validation
and routine control of a sterilization process for medical
3.1.4 bremsstrahlung—broad-spectrum electromagnetic ra-
devices
diation emitted when an energetic charged particle is influ-
ISO 14470 Food irradiation – Requirements for the
enced by a strong electric or magnetic field, such as that in the
development,validationandroutinecontroloftheprocess
vicinity of an atomic nucleus.
of irradiation using ionizing radiation for the treatment of
3.1.4.1 Discussion—In radiation processing, bremsstrahl-
food
ung photons with sufficient energy to cause ionization are
2.4 International Commission on Radiation Units and Mea- generated by the deceleration or deflection of energetic elec-
4
surements (ICRU) Reports: trons in a target material. When an electron passes close to an
ICRU Report 14Radiation Dosimetry: X Rays and Gamma atomicnucleus,thestrongcoulombfieldcausestheelectronto
RayswithMaximumPhotonEnergiesBetween0.6and50 deviate from its original motion. This interaction results in a
MeV loss of kinetic energy by the emission of electromagnetic
ICRU Report 34Dosimetry of Pulsed Radiation radiation.Suchencountersareuncontrolledandtheyproducea
ICRU Report 35Radiation Dosimetry: Electron Beams with
continuous photon energy distribution that extends up to the
Energies Between 1 and 50 MeV maximum kinetic energy of the incident electron. The
ICRU Report 37Stopping Powers for Electrons and Posi-
bremsstrahlung energy spectrum depends on the electron
trons energy, the composition and thickness of the X-ray target, and
ICRU Report 80Dosimetry Systems for Use in Radiation
theemissiondirectionofphotonangleofemissionwithrespect
Processing to the incident electron.
ICRU Report 85aFundamental Quantities and Units for
3.1.5 charged-particle equilibrium (referred to as electron
Ionizing Radiation
equilibrium in the case of electrons set in motion by photon-
2.5 Joint Committee for Guides in Metrology (JCGM)
beam irradiation of a material)—condition in which the kinetic
Report:
energy of charged particles (or electrons), excluding rest mass,
JCGM 100:2008, GUM 1995, with minor corrections,
entering an infinitesimal volume of the irradiated material
Evaluation of measurement data–Guide to the expression
equals the kinetic energy of charge particles (or electrons)
5
of uncertainty in measurement
emerging from it.
3.1.6 dose uniformity ratio—ratio of the maximum to the
3. Terminology
minimum absorbed dose within the irradiated product.
3.1 Definitions:
3.1.6.1 Discussion—The concept is also referred to as the
3.1.1 absorbed dose (D)—quantity of ionizing radiation
max/min dose ratio.
energy imparted per unit mass of a specified material. The SI
3.1.7 dosimeter—device that, when irradiated, exhibits a
unit of absorbed dose is the gray (Gy), where 1 gray is
quantifiable change that can be related to absorbed dose in a
equivalent to the absorption of 1 joule per kilogram of the
given material using appropriate measurement instrument(s)
specified material (1 Gy = 1 J/kg). The mathematical relation-
and procedures.
ship is the quotient of dε by dm, where dε is the mean
3.1.8 dosimeter response—reproducible, quantifiable effect
incremental energy imparted by ionizing radiation to matter of
produced in the dosimeter by ionizing radiation.
incremental mass dm (see ICRU Report 85a).
3.1.9 dosimetry system—system used for measuring ab-
D 5dε/dm (1)
sorbed dose, consisting of dosimeters, measurement instru-
3.1.2 beam length—dimension of the irradiation zone along
ments and their associated reference standards, and procedures
thedirectionofproductmovement,ataspecifieddistancefrom
for the system’s use.
the accelerator window.
3.1.10 electron energy—kinetic energy of an electron.
3.1.2.1 Discussion—Beam length is perpendicular to beam
3.1.10.1 Discussion—Unit is usually electron volt (eV),
width and to the electron beam axis. In case of product that is
stationary during irradiation, ‘beam length’ and ‘beam width’ kiloelectron volt (keV), or megaelectron volt (MeV). 1 eV is
the kinetic energy acquired by a single electron accelerated
may be interchangeable.
throughapotentialdifferenceof1V.1eVisequaltoenergyof
-19
1.602 × 10 joules.
3
Available from the International Organization for Standardization, 1 Rue de
3.1.11 electron energy spectrum—particle fluence distribu-
Varembé, Case Postale 56, CH–1211, Geneva 20, Switzerland.
4
tion of electrons as a function of energy.
Available from the International Commission on Radiation Units and
Measurements, 7910 Woodmont Ave., Suite 800, Bethesda, MD 20814, U.S.A.
3.1.12 installation qualification (IQ)—process of obtaining
5
DocumentproducedbyWorkingGroup1oftheJointCommitteeforGuidesin
and documenting evidence that equipment has been provided
Metrology (JCGM/WG 1). Available free of charge at the BIPM website (http://
www.bipm.org). and installed in accordance with its specifications.
© ISO/ASTM International 2015 – All rights reserved
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ISO/ASTM 51608:2015(E)
3.1.13 irradiation container—holder in which product is metal with a high atomic number (such as tantalum), high
placed during the irradiation process.
melting temperature, and high thermal conductivity.
3.1.13.1 Discussion—“Irradiation container” is often re-
3.3 Definitions of other terms used in this standard that
ferred to simply as “container” and can be a carrier, cart, tray,
pertain to radiation measurement and dosimetry may be found
product carton, pallet, product package or other holder.
inASTM Terminology E170. Definitions in E170 are compat-
3.1.14 measurement management system—set of interre-
ible with ICRU Report 85a, which may be used as an
latedorinteractingelementsnecessarytoachievemetrological
alternative reference.
confirmation and continual control of measurement processes.
3.1.15 operational qualification (OQ)—processofobtaining 4. Significance and use
and documenting evidence that installed equipment operates
4.1 A variety of products and materials are irradiated with
within predetermined limits when used in accordance with its
X-radiation to modify their characteristics and improve the
operational procedures.
economic value or to reduce their microbial population for
3.1.16 performance qualification (PQ)—process of obtain-
health-related purposes. Dosimetry requirements might vary
ing and documenting evidence that the equipment, as installed
depending on the type and end use of the product. Some
and operated in accordance with operational procedures, con-
examples of irradiation applications where dosimetry may be
sistently performs in accordance with predetermined criteria
used are:
and thereby yields product meeting its specification.
4.1.1 Sterilization of health care products;
3.1.17 process load—volume of material with a specified
4.1.2 Treatment of food for the purpose of parasite and
loading configuration irradiated as a single entity.
pathogencontrol,insectdisinfestation,andshelflifeextension;
3.1.18 processing category—group of different product that
4.1.3 Disinfection of consumer products;
can be processed together.
4.1.4 Cross-linking or degradation of polymers and elasto-
3.1.18.1 Discussion—Processing categories can be based
mers;
on, for instance, composition, density or dose requirements.
4.1.5 Curing composite material;
3.1.19 reference material—homogeneousmaterialofknown
4.1.6 Polymerization of monomers and oligomer and graft-
radiation absorption and scattering properties used to establish
ing of monomers onto polymers;
characteristics of the irradiation process, such as scan
4.1.7 Enhancement of color in gemstones and other mate-
uniformity,depth-dosedistribution,throughputrate,andrepro-
rials;
ducibility of dose delivery.
4.1.8 Modification of characteristics of semiconductor de-
3.1.20 simulated product—material with radiation attenua-
vices; and
tion and scattering properties similar to those of the product,
4.1.9 Research on materials effects of irradiation.
material or substance to be irradiated.
3.1.20.1 Discussion—Simulatedproductisusedduringirra-
NOTE 3—Dosimetry with measurement traceability and with known
diator characterization as a substitute for the actual product,
measurement uncertainty is required for regulated irradiation processes,
material or substance to be irradiated. When used in routine such as the sterilization of health care products and treatment of food.
Dosimetry may be less important for other industrial processes, such as
production runs in order to compensate for the absence of
polymer modification, which can be evaluated by changes in the physical
product, simulated product is sometimes referred to as com-
propertiesoftheirradiatedmaterials.Nevertheless,routinedosimetrymay
pensating dummy. When used for absorbed-dose mapping,
be used to monitor the reproducibility of the radiation process.
simulated product is sometimes referred to as phantom mate-
4.2 Radiation processing specifications usually include a
rial.
pair of absorbed-dose limits: a minimum value to ensure the
3.2 Definitions of Terms Specific to This Standard:
intended beneficial effect and a maximum value that the
3.2.1 X-radiation—ionizing electromagnetic radiation,
product can tolerate while still meeting its functional or
which includes both bremsstrahlung and the characteristic
regulatory specifications. For a given application, one or both
radiation emitted when atomic electrons make transitions to
of these values may be prescribed by process specifications or
more tightly bound states. See bremsstrahlung.
regulations. Knowledge of the dose distribution within irradi-
3.2.1.1 Discussion—In radiation processing applications,
ated material is essential to help meet these requirements.
the principal X-radiation is bremsstrahlung.
Dosimetry is essential to the radiation process since it is used
3.2.2 X-ray—of or relating to X-radiation.
to determine both of these limits and to confirm that the
3.2.2.1 Discussion—X-ray is used as an adjective while
product is routinely irradiated within these limits.
X-radiation is used as a noun.
4.3 Several critical parameters must be controlled to obtain
3.2.3 X-ray converter—device for generating X-radiation
reproducible dose distributions in the process load. The
(bremsstrahlung)fromanelectronbeam,consistingofatarget,
absorbed-dose distribution within the product depends on the
means for cooling the target, and a supporting structure.
overallproductdimensionsandmassandirradiationgeometry.
3.2.4 X-ray target—component of the X-ray converter that
The processing rate and dose distribution depend on the X-ray
isstruckbytheelectronbeamandwhichproducesX-radiation. intensity, photon energy spectrum, and spatial distribution of
3.2.4.1 Discussion—The X-ray target is usually made of the radiation field and conveyor speed.
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ISO/ASTM 51608:2015(E)
4.4 Before an irradiator can be used, it must be qualified 6.4 Product Handling System—The process load size for
(IQ, OQ) to determine its effectiveness in reproducibly deliv- optimum photon power utilization and dose uniformity de-
ering known, controllable absorbed doses. This involves test- pendsonthemaximumphotonenergyandproductdensity.The
ing the process equipment, calibrating the equipment and narrow width of X-Ray field favors the use of continuously
dosimetry system, and characterizing the magnitude, distribu- moving product rather than shuffle-dwell systems to improve
tion and reproducibility of the absorbed dose delivered by the dose uniformity.
irradiator for a range of product densities.
7. Selection and calibration of dosimetry system
4.5 Toensureconsistentdosedeliveryinaqualifiedirradia-
tion process, routine process control requires procedures for
7.1 Selection of Dosimetry Systems—Dosimetry systems
routine product dosimetry and for product handling before and
suitable for the expected radiation processing applications at
after the treatment, consistent product loading configuration,
the irradiator shall be selected in accordance with the selection
control and monitoring of critical process parameters, and
criteria listed in ISO/ASTM 52628. During the selection
documentation of the required activities and functions.
process, for each dosimetry system, the performance behavior
with respect to relevant influence quantities and the dose
5. Radiation source characteristics
measurement uncertainty associated with it shall be taken into
5.1 X-radiation (bremsstrahlung) is a form of electromag-
account.
netic radiation, which is analogous to gamma radiation. Al- NOTE4—Mostdosimetrysystemssuitableforgammaradiation(suchas
60
those from Co) may also be suitable for X-radiation (3, 12, 13).
though its effects on irradiated materials are generally similar,
it differs in energy spectrum, angular distribution, and dose
7.2 The dosimetry system shall be calibrated in accordance
rate.
with ISO/ASTM 51261, and the user’s procedures, which
should specify details of the calibration process and quality
5.2 ThephysicalcharacteristicsoftheX-rayfielddependon
assurance requirements.
the design of the X-ray converter and the parameters of the
electron beam striking the target, that is, the electron energy
7.3 The dosimetry system calibration is part of a measure-
spectrum, average electron beam current, and beam current
ment management system.
distribution on the target.
5.3 These aspects of X-radiation and its suitability for 8. Process parameters
radiation processing are reviewed in more detail in AnnexA1.
8.1 Absorbeddoseinaproductisdeterminedandcontrolled
by several characteristics of the irradiator as well as of the
6. Types of facilities
product. Thus, all parameters characterizing the irradiator
6.1 The design of an irradiator affects the delivery of
components, process load and the irradiation conditions that
absorbed dose to a product. Therefore, the irradiator design
affect absorbed dose are referred to as “process parameters.”
should be considered when performing the absorbed-dose
They should, therefore, be considered when performing the
measurements described in Sections9–11.
absorbed-dose measurements required in Sections10–12.
6.2 The electron beam energy range used to produce
8.2 For X-ray facilities, process parameters include:
X-radiation covered in this practice is between 50 keVand 7.5
8.2.1 Beam characteristics (for example, electron beam
MeV. The upper limit is determined to avoid the induction of
energy, beam current, pulse frequency),
6
activity in a tantalum target and or product (1, 2).
8.2.2 Beam dispersion (for example, scan width, scan
6.3 Irradiator Components—An X-ray irradiator typically
frequency, collimator aperture, parallel magnet),
includes an electron accelerator with X-ray converter, product
8.2.3 Product handling characteristics (for example, con-
conveyor system, radiation shield with personnel safety
veyor speed),
system, products loading and storage areas, auxiliary equip-
8.2.4 Product loading characteristics (for example, size of
ment for power, cooling, ventilation, etc., equipment room,
the process load, bulk density, orientation of product), and
laboratory for dosimetry and product testing, and personnel
8.2.5 Irradiation geometry (for example, multiple passes,
offices. The irradiator design shall conform to applicable
rotation, source or product overlap.
regulations and guidelines. For information on some industrial
8.3 Theparametersin8.2.1,8.2.2and8.2.3characterizethe
facilities, see Refs (3-7).
irradiatorwithoutreferencetotheproductortheprocess.These
6.3.1 Discussion—TheconfigurationoftheX-rayconverter,
subsetsofparametersarereferredtoas“operatingparameters.”
theelectronbeamdistributionontheX-raytarget,thepenetrat-
ing characteristic of the radiation, and the size, shape, and
8.4 Procedures during operational qualification (OQ) deal
densityoftheprocessloadaffectthedoseuniformityratio(see
with operating parameters.
Refs 3, 4, 8-10). In some cases, the dose uniformity ratio may
8.5 The objective of performance qualification (PQ) is to
be improved by the use of collimators between
...