ASTM ISO/ASTM51608-15(2022)

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 51608:2015 (Reapproved 2022)(E)
Standard Practice for
Dosimetry in an X-Ray (Bremsstrahlung) Facility for
Radiation Processing at Energies between 50 keV and 7.5
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
bility of regulatory limitations prior to use.
processing applications.
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.
2.1 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 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
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 Dec. 1, 2022. Published December 2022. Originally
published asASTM E 1608–94. Last previousASTM edition E 1608–00.ASTM E
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 www.astm.org, or contact ASTM Customer Service at service@astm.org. For
51608:2015(2022)(E) is a reapproval of the last previous edition ISO/ASTM Annual Book of ASTM Standards volume information, refer to the standard’s
51608:2015(E), which replaced ISO/ASTM 51608:2005(E). Document Summary page on the ASTM website.
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(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.
3.1.3.1 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-
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)
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
width and to the electron beam axis. In case of product that is 3.1.10.1 Discussion—Unit is usually electron volt (eV),
kiloelectron volt (keV), or megaelectron volt (MeV). 1 eV is
stationary during irradiation, ‘beam length’ and ‘beam width’
may be interchangeable. the kinetic energy acquired by a single electron accelerated
throughapotentialdifferenceof1V.1eVisequaltoenergyof
-19
1.602 × 10 joules.
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.
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
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 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(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.
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(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
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),
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 the X-ray
establish the values of all process parameters for the radiation
converterandtheproduct(11),orbytheuseofamagnetbefore
process under consideration.
the X-ray converter to control the divergence of the beam.
8.6 During routine product processing, operating param-
eters are continuously controlled and monitored for process
TheboldfacenumbersinparenthesesrefertotheBibliographyattheendofthis
standard. control.
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(E)
9. Installation qualification 9.4.1 All equipment associated with operating the irradiator
shall be tested to verify that the irradiator is operating in
9.1 Objective—The purpose of an installation qualification
accordance with design and performance specifications. All
program is to obtain and document evidence that the irradiator
test results shall be recorded.
with its associated processing equipment and measurement
9.4.2 Theperformanceofmeasurementinstrumentsshallbe
instruments has been delivered and installed in accordance
verifiedorcalibrated(ifrequired)toensurethattheinstruments
with their specifications. Installation qualification includes
are operating in accordance with design and performance
documentation of the irradiator and the associated processing
specifications. All test results shall be recorded.
equipment and measurement instruments, establishment of the
9.4.3 If any modification or change is made to the process-
testing, operation and calibration procedures for their use, and
ing equipment or measurement instruments during installation
verification that they operate according to specifications.
qualification, they shall be re-tested.
9.2 Equipment Documentation—Document descriptions of
9.4.4 The characteristics of the electron beam (such as
the irradiator and the associated processing equipment and
average beam current, energy) and X-ray field (such as
measurement instruments installed at the irradiator.This docu-
dimension and uniformity) shall be determined and recorded.
mentation shall be retained for the life of the irradiator. At a
They typically include the following:
minimum, it shall include:
9.4.4.1 Electron beam energy estimation with direct mea-
9.2.1 Description of the location of the irradiator (accelera-
surement (also see ISO/ASTM 51649)—When the electron
tor) within the operator’s premises in relation to the areas
beam is accessible, the depth-dose distribution is measured by
assigned and the means established for ensuring the segrega-
irradiating dosimeters in a stack of plates of homogeneous
tion of un-irradiated products from irradiated products,
material or by placing dosimeters or a dosimeter strip at an
9.2.2 Accelerator specifications and characteristics,
angle through a homogeneous absorber. Electron beam energy
9.2.3 Operating procedure of the irradiator,
can be determined from depth-dose distribution parameters
9.2.4 Description of the construction and operation of the
based on established relationships.
product handling equipment,
9.4.4.2 Electron beam energy estimation with indirect
9.2.5 Description of the materials and construction of any
measurement—When the electron beam is not readily
containers used to hold products during irradiation,
accessible,forexamplewhentheX-rayconverterisattachedto
9.2.6 Description of the process control system,
the end of the scanner and the electron beam is not transmitted
9.2.7 Description of any modifications made during and
intotheairbeforestrikingtheX-raytarget,thentheattenuation
after the irradiator installation, and
ofX-radiationinasuitablereferencematerialmightbeusedto
9.2.8 Description of X-ray converter characteristics indirectly estimate the electron beam energy.
(dimension, materials and nature of construction).
NOTE 5—A procedure suitable for typical industrial irradiation
processes, which is based on common practice in the field of therapeutic
9.3 Testing, Operation and Calibration Procedures—
X-ray treatment, has been published (14).Additionally, measurements of
Standard operating procedures for the testing, operation and
induced radioactivity in certain elements with threshold values below 8
calibration (if necessary) of the installed irradiator and its
MeV might be used for energy determination (15, 16).
associatedprocessingequipmentandmeasurementinstruments
9.4.4.3 X-ray field characterization (width, length and
shall be established.
depth)—The target cooling system and target geometry have a
9.3.1 Testing Procedures—These procedures describe the
significant effect on X-ray field, and therefore the X-ray field
testing methods used to ensure that the installed irradiator and
shall be characterized before OQ is started (See Figs. A1.1-
its associated processing equipment and measurement instru-
A1.3). The electron beam width and length are measured by
ments operate according to specification.
placing dosimeter strips or discrete dosimeters at selected
9.3.2 Operation Procedures—These procedures describe
intervalsoverthefullbeamwidthandlengthrangewithoutthe
how to operate the irradiator and its associated processing
converter in place, or if not possible, directly on the converter.
equipmentandmeasurementinstrumentsduringroutineopera-
Wheneverpossible,dosimetersshallalsobeplacedbeyondthe
tion.
expectedbeamdimensiontoidentifythelimitsofthefullbeam
9.3.3 Calibration Procedures—These procedures describe
dimensions. X-ray field may be characterized by placing
periodic calibration and verification methods that ensure that
dosimeterstripsordiscretedosimeteratselectedintervalsover
the installed processing equipment and measurement instru-
thefullX-raybeamwidthandlengthrangeatvaryingintervals
ments continue to operate within specifications.The frequency
and distances from the X-ray target.
of calibration for some equipment and instruments might be
specified by a regulatory authority. Calibration of some equip- 10. Operational qualification
ment and instruments is required to be traceable to a national
10.1 Objective—The objective of the operational qualifica-
or international standard.
tion (OQ) of an X-ray irradiator is to obtain and document
9.4 Testing of Processing Equipment and Measurement evidence that installed equipment and instrumentation operate
Instruments—It must be verified that the installed processing within predetermined limits when used in accordance with
equipment and measurement instruments operate within their operational procedures. The purpose of dosimetry during
designspecificationsbyfollowingthetestingproceduresnoted operational qualification is to establish baseline operational
in 9.3.1. The equipment and instruments shall be calibrated limitsandperformanceexpectationsforroutineprocessingand
according to the calibration procedures. in turn evaluate the following characteristics:
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(E)
10.1.1 Ability to predict the delivered dose for the range of dosimeters mixed randomly with and carried by product
conditions of operation for the key operating parameters that throughtheirradiationzone.Astatisticalmodelshouldbeused
affect absorbed dose in the product. to estimate the number of dosimeters required. Calculations of
minimumandmaximumabsorbeddosesmaybeanappropriate
10.1.2 Ability of the irradiator to deliver reproducible dose
alternative.
for the range of conditions of operation for the key operating
parameters that affect absorbed dose in the product (17).
NOTE 8—Theoretical calculations may be performed using the Monte
10.1.3 Absorbed-dose distribution in process loads.
Carlo methods (18), and applied to industrial radiation processing (19).
The use of the point-kernel method can be considered for X-ray facilities
NOTE 6—The absorbed dose received by any portion of product in a
(20). Both of these methods require that accurate radiation interaction
process load depends on the conveyor design, the converter design, the
cross-sections for all materials between and surrounding the source point
X-ray field geometry and characteristics, the process load characteristic
and dose point are known. General-purpose software packages are
and configuration, the treatment geometry.
available for these types of calculations (see ASTM Guide E2232).
Modelsbuiltusingthesecodesshouldbevalidatedagainstdosimetrydata
10.1.4 Dosimetry tests carried out during IQ (see 9.4.4)
for their predictions to be meaningful. Empirically derived models built
should be repeated as part of irradiator OQ.
directlyfromdosimetrydatamaybesatisfactorybutshouldbeconfinedto
the boundaries of experiments at a specific irradiator.
10.2 Absorbed-dose Mapping—Absorbed-dose mapping is
NOTE 9—For an X-ray irradiator, the depth-dose distribution in a
performedtocharacterizetheirradiatorwithrespecttothedose
homogeneous material of low atomic number is approximately
distribution and reproducibility of absorbed-dose delivery.
exponential,andpenetrationfor5MeVX-radiationisslightlygreaterthan
Mapping the absorbed-dose distribution is carried out by
that for cobalt-60 gamma radiation (see Fig. A1.7).
placing sets of dosimeters in a three-dimensional array within
10.3 Absorbed Dose and Operating Parameters:
a process load containing reference material. For guidance on
10.3.1 Objective—The absorbed dose in the product de-
performing absorbed-dose mapping see ASTM Guide E2303.
pends on several operating parameters. Over the expected
10.2.1 The amount of reference material in each irradiation
range of these parameters, establish the absorbed-dose charac-
container should be the amount expected during typical pro-
teristics in a reference material using an appropriate calibrated
duction runs or should be the maximum design volume for the
dosimetry system.
irradiation container.
10.3.1.1 The dose distribution within a process load de-
10.2.2 Dosimeter placement patterns should be selected to
pends on photon energy spectrum, photon field geometry, the
identify the locations of the absorbed-dose maxima and
distance to the X-ray target and the reference material charac-
minima. It may be necessary to place more dosimeter sets in
teristics.
these locations and fewer dosimeter sets in locations likely to
NOTE 10—For X-ray irradiators, photon energy spectrum and angular
receive intermediate absorbed doses to adequately identify the
distribution depend on the design and composition of the X-ray converter
absorbed-dose maxima and minima. Dosimetry data from
and on the electron beam energy spectrum. Higher energy electrons will
previously qualified irradiators of the same design or calcula-
increase forward concentration of the photon distribution and therefore
tions using mathematical models (see ASTM Guide E2232)
improve penetration in the product (9, 21, 22).
may provide useful information for determining the number
10.3.2 The relationships between the minimum and maxi-
and location of dosimeters for this qualification process.
mum doses for an irradiation container filled with a reference
material of known density, and product speed (or irradiation
NOTE 7—Dosimeter strips or sheets may be used to increase spatial
resolutionoftheabsorbed-dosemap,iftheuseofindividualdosimetersis
time), beam characteristics and parameters controlling the
inadequate.
photon field over the expected range of these parameters
should be established. These relationships should be estab-
10.2.3 Asufficientnumberofprocessloads(minimum3)of
lishedforeachdensity(10.2.5)andirradiatorpathway(10.2.6).
homogenous density should be dose mapped to estimate the
variability of the magnitude and distribution of the absorbed 10.3.2.1 Establish the range of absorbed dose that can be
delivered, the range of densities that can be processed and the
dose within the process load. Dosimetry data from previously
qualified irradiators of the same design may provide useful number of irradiator pathways that can be used during routine
processing. This will set the operational limits for the irradia-
information for determining the number of process loads for
this qualification. tor.
10.2.4 The number of process loads preceding and follow-
NOTE 11—The conveyor speed and the beam current may be linked
ing the dose-mapped process load shall be sufficient to effec-
during routine product processing so that a variation in one causes a
corresponding change in the other to maintain a constant delivery of the
tively simulate an irradiator filled with the product.
dose.
10.2.5 Absorbed-dose mapping shall be carried out at and
between the density range for products expected to be irradi- 10.4 Dose Variability:
ated routinely. 10.4.1 The magnitude of the dose variations in a reference
10.2.6 Absorbed-dosemappingshallbecarriedoutforeach material should be estimated by, for example, passing dosim-
eters in the reference geometry through the irradiation zone on
different irradiator pathway to be used for routine product
processing. the product conveyor at time intervals appropriate to the
frequency of the parameter fluctuations.
10.2.7 The procedures for absorbed-dose mapping outlined
in this section may not be feasible for some types of bulk-flow
NOTE 12—It is often difficult to separate the effect of operating
irradiators. In such cases, minimum and maximum absorbed
parameter variability and dosimetry system uncertainty; thus, the mea-
doses should be estimated by using an appropriate number of sured variability will often be a combination of the two.
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(E)
10.4.2 Routine Monitoring Positions—If the locations of 10.9.2 Changes to the irradiation container,
absorbed dose extremes identified during the dose mapping
10.9.3 Repair or replacement of scanning magnet,
procedure are not readily accessible during production runs,
10.9.4 Repair or replacement of beam bending magnet,
alternative locations (external or internal to the process load)
10.9.5 Changes in the element of the irradiator creating
may be used for routine product processing dosimetry. These
scattering effects, and
positionscouldbelocatedontheirradiationcontaineroronthe
10.9.6 Changes to the X-ray Target (including cooling
process load. Dose variability in routine monitoring position
system).
shall be evaluated.
10.5 Effect of adjacent process loads with different product
11. Performance qualification
densities—For a production run with process loads of different
11.1 Objective—The objective of performance qualification
densities close to each other, dose distribution within adjacent
is to obtain and document evidence that the equipment and
process loads may be different. These effects may be due to
instrumentation, as installed and operated in accordance with
scattering of X-radiation from the process load which is front
operational procedures, can consistently process product
of the target, and they can be determined by dose mapping of
withinthespecifiedabsorbed-doselimits.Dosimetryisusedto
the process load in front of the source as well as the adjacent
obtainthisevidenceandtodeterminetheappropriatevaluesof
process loads for these geometries to verify that the maximum
allkeyprocessparameters.Minimumandmaximumabsorbed-
and minimum dose values are acceptable. Multiple combina-
dose limits are almost always associated with irradiation
tionsofdifferentdensitiesadjacenttoeachshouldbeevaluated
applications. For a given application, one or both of these
todeterminethemagnitudeoftheeffect,ifany,andtoestablish
limits may be prescribed by government regulations. Dosim-
acceptable operational limits for this effect.
etry is used in performance qualification to determine the
10.6 Partially Filled Irradiation Containers—The absorbed
appropriate process parameters, including treatment time,
dose distributions and the magnitudes of the minimum and
beam current, conveyor speed, and product loading configura-
maximum absorbed dose in partially filled irradiation contain-
tion to ensure that the absorbed-dose requirements for a
ers in a given production run may be affected by or affect
particular process can be satisfied. This is accomplished by
adjacent irradiation containers in the production run or in
absorbed-dose mapping of irradiation containers with specific
adjacent product runs. These effects will be due to any
productandproductloadingconfigurations.Thepurposeofthe
differences between the radiation scattering characteristics and
mapping is to determine the magnitudes and locations of the
emptyvoidsintheirradiationcontainerofthegivenproduction
minimumandmaximumabsorbeddosesandtheirrelationships
run and those of the products in the adjacent production runs.
to the absorbed doses at locations used for monitoring during
Absorbed dose distribution studies should be conducted with
routine product processing.
partially filled irradiation containers of different fill levels to
11.2 Product Loading Configuration—A process load con-
evaluate the magnitude of this effect, if any, and to establish
figuration shall be established for each product.The documen-
acceptable operational limits for this effect.
tationforthisloadingconfigurationshallincludespecifications
10.7 Process Interruption/Restart—In the case of a process
for parameters that influence the absorbed-dose distribution.
interruption, the implication of a restart on dose delivery (for
Examples of such parameters include product size, product
example, uniformity of dose in a reference plane) shall be
mass, material composition, product density/bulk density, and
investigated.
product orientation.
10.7.1 Thiscanbeachievedbyexposingastripofdosimeter
11.3 Processing category—If the concept of a processing
film in a reference plane through a stop/start sequence of the
category is to be used for the purpose of routine processing,
conveyor system.
product shall be assessed against documented criteria as to
10.7.2 Influence of process interruption/restart should be
whether it is to be included in a processing category. Assess-
evaluated for the extremes of the operating parameters.
ment shall include consideration of product-related variables
10.7.3 If there is any effect on dose delivery to product of a
that affect dose to product and process specification. The
process interruption, its magnitude shall be determined to
outcomeoftheassessmentshallbeevaluatedanddocumented.
establish acceptable operational limits for this effect.
11.3.1 A processing category limit shall be defined and the
10.8 Documentation and Maintenance of OQ—Operational
performance qualification shall be carried out at the extreme
qualification procedures shall be repeated at a defined time
limits of the processing category.
interval. The interval shall be justified and the rationale
documented to provide assurance that the irradiator is consis-
11.4 Absorbed-Dose Mapping (See ASTM Guide E2303)
tently operating within specifications.
11.4.1 Minimum and Maximum Dose Locations:
10.9 Irradiator Changes—If changes that could affect the 11.4.1.1 The locations of the regions of minimum and
dosedistributionaremadetotheirradiator(forexample,beam
maximum absorbed dose for the selected product loading
characteristics, X-ray converter, conveyor) or its mode of configuration shall be established. This is accomplished by
operation, the operational qualification should be repeated to
placing dosimeters throughout the volume of interest for three
the extent necessary to determine the effect on the process. ormoreprocessloads.Theplacementpatternsshallbeselected
Examples of such changes include:
to identify the locations of the absorbed-dose extremes, using
10.9.1 Changes to the conveyor, data obtained from the absorbed-dose mapping studies during
© ISO/ASTM International 2022 – All rights reserved
ISO/ASTM 51608:2015 (2022)(E)
operational qualification which can be combined from theo- that can be characterized at the intended processing tempera-
retical calculations (see ASTM Guide E2232). Dosimeters tureorwhoseresponseisnotsignificantlyaffectedbytempera-
ture.
shall be concentrated in the expected regions of minimum and
11.4.6 Bulk-Flow Irradiators—Absorbed-dose mapping
maximumabsorbeddosewithfewerdosimetersplacedinareas
likely to receive intermediate absorbed dose. maynotbefeasibleforproductsflowingthroughtheirradiation
zone in bulk. In this case, minimum and maximum absorbed
11.4.1.2 Particular attention should be given to process
doses should be estimated by using an appropriate number of
loads containing voids or non-uniform product. More dosim-
dosimeters mixed randomly with and carried by the product
eters should be used at discontinuities in composition or
throughtheirradiationzone(23).Enoughdosimetersshouldbe
density to evaluate any possible dose gradients.
used to obtain statistically significant results.
11.4.2 Variation in absorbed dose:
11.4.7 Routine Monitoring Positions—Establish the routine
11.4.2.1 When dose mapping a specific product loading
monitoring locations based on the analysis of the dose map
configuration, consideration should be given to possible varia-
data. If the locations of absorbed dose extremes identified
tions in the absorbed doses measured at similar locations in
during the dose mapping procedure are not readily accessible
different process loads.
during production runs, alternative locations (external or inter-
11.4.2.2 To evaluate the extent of this dose variability, nal to the process load) may be used for routine product
dosimeter sets should be placed in the expected regions of the processing dosimetry. The relationships between the absorbed
doses at these alternative routine monitoring positions and the
minimum and maximum absorbed doses in several (at least
three) process loads and irradiate them under the same condi- absorbed dose extremes shall be established, shown to be
reproducible, and documented.
tions. The measured variations in the absorbed-dose values
11.4.8 Target Dose Values—Becauseofthestatisticalnature
reflect,forexample,variationsinproductloadingconfiguration
of the absorbed-dose measurement and the inherent variations
(due to shifts in the contents of the process load during its
in the radiation process, it is necessary to set the operating
movement through the irradiator), small differences in bulk
parameters to deliver, on average, an absorbed dose greater
density of the process loads, fluctuations in operating param-
than any prescribed minimum dose and smaller than any
eter values, and the uncertainty in the routine dosimetry
prescribed maximum dose (24, 25). These doses may be
system.
referred to as “target dose values.” Generally, these target dose
11.4.3 Partial Loading—For partially-loaded process loads,
values should be chosen so that there is a low probability of
the same performance qualification requirements as for fully-
irradiating the product or part of the product with doses lower
loaded process loads shall be followed. Dose mapping shall
than the required minimum product dose specification or
ensure that the absorbed-dose distributions are adequately
higher than the allowed maximum product dose specification.
characterized and are acceptable. Variations to the dose distri-
For further discussion on determination of the target dose
butionfrompartialloadingmayinsomecasesbeminimizedby
values, see Refs (26, 27).
the use of phantom material placed at appropriate
...