ISO/ASTM 51261:2013

Practice for calibration of routine dosimetry systems for radiation processing

ISO/ASTM 51261:2013 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).

Pratique d'étalonnage des appareils de mesure dosimétrique routinier pour le traitement par irradiation

General Information

• Status: Published
• Publication Date: 21-Mar-2013
• 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: 9599 - Withdrawal of International Standard
• Start Date: 04-Apr-2025
• Completion Date: 30-Oct-2025

Relations

• Consolidated By: ISO 2417:2016 - Leather — Physical and mechanical tests — Determination of the static absorption of water
• Effective Date: 06-Jun-2022
• Revises: ISO/ASTM 51261:2002 - Guide for selection and calibration of dosimetry systems for radiation processing
• Effective Date: 06-Aug-2011

Standards Content (Sample)

INTERNATIONAL ISO/ASTM
STANDARD 51261
Second edition
2013-04-15
Practice for calibration of routine
dosimetry systems for radiation
processing
Practique d’étalonnage des appareils de mesure dosimétrique
routinier pour le traitement par irradiation
Reference number
© ISO/ASTM International 2013
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ii © ISO/ASTM International 2013 – All rights reserved

Contents Page
1 Scope . 1
2 Referenced documents . 1
3 Terminology . 1
4 Significance and use . 2
5 Dosimeter system calibration overview . 3
6 Requirements for a routine dosimetry system calibration . 3
7 Requirements for measurement instruments calibration and performance verification . 3
8 Requirements for the sampling of calibration dosimeters . 4
9 Calibration of dosimetry systems . 4
10 Minimum documentation requirements . 6
11 Keywords . 6
Annexes . 7
Bibliography . 18
© ISO/ASTM International 2013 – All rights reserved iii

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 pilot project between ISO and ASTM International has been formed to develop and maintain a group of
ISO/ASTM radiation processing dosimetry standards. Under this pilot project, ASTM Committee E61,
RadiationProcessing,isresponsibleforthedevelopmentandmaintenanceofthesedosimetrystandardswith
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 51261 was developed by ASTM Committee E61, Radiation Processing,
through Subcommittee E61.01, Dosimetry, and by Technical Committee ISO/TC 85, Nuclear energy, nuclear
technologies and radiological protection.
iv © ISO/ASTM International 2013 – All rights reserved

An American National Standard
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 E178 Practice for Dealing With Outlying Observations
E2628 Practice for Dosimetry in Radiation Processing
1.1 This practice specifies the requirements for calibrating
E2701 Guide for Performance Characterization of Dosim-
routine dosimetry systems for use in radiation processing,
etersandDosimetrySystemsforUseinRadiationProcess-
includingestablishingmeasurementtraceabilityandestimating
ing
uncertainty in the measured dose using the calibrated dosim-
2.2 ISO/ASTM Standards:
etry system.
51607 Practice for Use of an Alanine-EPR Dosimetry Sys-
NOTE 1—Regulations or other directives exist in many countries that
tem
govern certain radiation processing applications such as sterilization of
51707 Guide for Estimating Uncertainties in Dosimetry for
healthcare products and radiation processing of food requiring that
Radiation Processing
absorbed-dose measurements be traceable to national or international
2.3 International Commission on Radiation Units and
standards (ISO11137-1, Refs (1-3) ).
Measurements Reports:
1.2 The absorbed-dose range covered is up to 1 MGy.
ICRU Report 85a Fundamental Quantities and Units for
1.3 The radiation types covered are photons and electrons
Ionizing Radiation
with energies from 80 keV to 25 MeV.
2.4 ISO Standards:
1.4 This document is one of a set of standards that provides
ISO 11137-1 Sterilization of health care products—
recommendations for properly implementing dosimetry in
Radiation—Requirements for the development, validation
radiation processing, and describes a means of achieving
and routine control of a sterilization process for medical
compliance with the requirements of ASTM E2628 “Practice
devices
for Dosimetry in Radiation Processing” for the calibration of
2.5 ISO/IEC Standards:
routinedosimetrysystems.Itisintendedtobereadinconjunc-
17025 GeneralRequirementsfortheCompetenceofTesting
tion withASTM E2628 and the relevantASTM or ISO/ASTM
and Calibration Laboratories
standard practice for the dosimetry system being calibrated
2.6 Joint Committee for Guides in Metrology (JCGM)
referenced in Section 2.
Reports:
1.5 This standard does not purport to address all of the
JCGM 100:2008, GUM 1995, with minor corrections,
safety concerns, if any, associated with its use. It is the
Evaluation of measurement data – Guide to the Expres-
responsibility of the user of this standard to establish appro-
sion of Uncertainty in Measurement
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
3. Terminology
3.1 Definitions:
2. Referenced documents
3.1.1 approved laboratory—laboratory that is a recognized
2.1 ASTM Standards:
nationalmetrologyinstitute;orhasbeenformallyaccreditedto
E170 TerminologyRelatingtoRadiationMeasurementsand
ISO/IEC 17025; or has a quality system consistent with the
Dosimetry
requirements of ISO/IEC 17025.
3.1.1.1 Discussion—Arecognized national metrology insti-
tute or other calibration laboratory accredited to ISO/IEC
This guide is under the jurisdiction of ASTM Committee E61 on Radiation
Processing and is the direct responsibility of Subcommittee E61.01 on Dosimetry,
17025 should be used in order to ensure traceability to a
and is also under the jurisdiction of ISO/TC 85/WG 3.
national or international standard. A calibration certificate
Current edition approved Aug. 16, 2012. Published April 2013. Originally
published asASTM E1261–88. Last previousASTM edition E1261–00.ASTM
ϵ1
E 1261–94 was adopted by ISO in 1998 with the intermediate designation ISO
15556:1998(E). The present International Standard ISO/ASTM 51261:2013(E) is a Available from International Commission on Radiation Units and Measure-
major revision of ISO/ASTM 51261:2002(E), which replaced ISO 15556. ments, 7910 Woodmont Avenue, Suite 800, Bethesda, MD 20814, USA.
2 5
The boldface numbers given in parentheses refer to the bibliography at the end Available from International Organization for Standardization (ISO), 1, ch. de
of this guide. la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
For referenced ASTM and ISO/ASTM standards, visit the ASTM website, www.iso.ch.
www.astm.org, or contact ASTM Customer Service at [e-mail]. For DocumentproducedbyWorkingGroup1oftheJointCommitteeforGuidesin
Annual Book of ASTM Standards volume information, refer to the standard’s Metrology (JCGM/WG 1). Available free of charge at the BIPM website (http://
Document Summary page on the ASTM website. www.bipm.org).
© ISO/ASTM International 2013 – All rights reserved
provided by a laboratory not having formal recognition or for routine absorbed dose measurements, including dose map-
accreditation will not necessarily be proof of traceability to a ping and process monitoring.
national or international standard. 3.1.16 traceability—propertyoftheresultofameasurement
or the value of a standard whereby it can be related to stated
3.1.2 calibration—set of operations that establish, under
references, usually national or international standards, through
specified conditions, the relationship between values of quan-
an unbroken chain of comparisons all having stated uncertain-
tities indicated by a measuring instrument or measuring sys-
ties.
tem,orvaluesrepresentedbyamaterialmeasureorareference
3.1.16.1 Discussion—Measurementtraceabilityisarequire-
material, and the corresponding values realized by standards.
ment of any measurement management system (see Annex
3.1.3 calibration curve—expression of the relation between
A4).
indication and the corresponding measured quantity value.
3.1.17 transfer standard dosimetry system—dosimetry sys-
3.1.4 charged-particle equilibrium (referred to as electron
tem used as an intermediary to calibrate other dosimetry
equilibrium in the case of electrons set in motion by photon
systems.
beamirradiationofamaterial)—conditioninwhichthekinetic
3.1.18 type I dosimeter—dosimeter of high metrological
energy of charged particles (or electrons), excluding rest mass,
quality, the response of which is affected by individual influ-
entering an infinitesimal volume of the irradiated material
ence quantities in a well-defined way that can be expressed in
equals the kinetic energy of charged particles (or electrons)
terms of independent correction factors.
emerging from it.
3.1.19 type II dosimeter—dosimeter, the response of which
3.1.5 dosimeter batch—quantity of dosimeters made from a
isaffectedbyinfluencequantitiesinacomplexwaythatcannot
specific mass of material with uniform composition, fabricated
practically be expressed in terms of independent correction
in a single production run under controlled, consistent condi-
factors.
tions, and having a unique identification code.
3.1.20 uncertainty (of measurement)—parameter associated
3.1.6 dosimeter stock—partofadosimeterbatchheldbythe
with the result of a measurement that characterizes the disper-
user.
sion of the values that could reasonably be attributed to the
3.1.7 dosimetry system—system used for measuring ab-
measurand or derived quantity.
sorbed dose, consisting of dosimeters, measurement instru-
3.1.21 uncertainty budget—quantitative analysis of the
ments and their associated reference standards, and procedures
component terms contributing to the uncertainty of a measure-
for the system’s use.
ment, including their statistical distribution, mathematical
3.1.8 electron equilibrium—charged particle equilibrium
manipulation and summation.
for electrons. (See charged-particle equilibrium.)
3.2 validation (of a process)—establishmentofdocumented
3.1.9 influence quantity—quantity that is not the measurand
evidence, which provides a high degree of assurance that a
but that affects the result of the measurement. specified process will consistently produce a product meeting
its predetermined specifications and quality attributes.
3.1.10 in-situ/in-plant calibration—calibration where the
3.3 verification—confirmation by examination of objective
dosimeter irradiation is performed in the place of use of the
routine dosimeters. evidence that specified requirements have been met.
3.3.1 Discussion—In the case of measuring equipment, the
3.1.10.1 Discussion—In-situ/in-plant calibration of dosim-
result of verification leads to a decision either to restore to
etry systems refers to irradiation of dosimeters along with
service or to perform adjustments, repair, downgrade, or
reference or transfer standard dosimeters, under operating
declare obsolete. In all cases it is required that a written trace
conditions that are representative of the routine processing
of the verification performed be kept on the instrument’s
environment, for the purpose of developing a calibration curve
individual record.
for the routine dosimetry systems.
3.4 Definitions of other terms used in this standard that
3.1.11 measurand—specific quantity subject to measure-
pertain to radiation measurement and dosimetry may be found
ment.
in ASTM Terminology E170. Definitions in ASTM Terminol-
3.1.12 measurement management system—set of inter-
ogy E170 are compatible with ICRU Report 85a; that docu-
related or interacting elements necessary to achieve metrologi-
ment, therefore, may be used as an alternative reference.
cal confirmation and continual control of measurement pro-
cesses.
4. Significance and use
3.1.13 primary standard dosimetry system—dosimetry sys-
4.1 Ionizing radiation is used to produce various desired
tem that is designated or widely acknowledged as having the
effects in products. Examples of applications include the
highest metrologial qualities and whose value is accepted
sterilization of medical products, microbial reduction, modifi-
without reference to other standards of the same quantity.
cation of polymers and electronic devices, and curing of inks,
3.1.14 reference standard dosimetry system—dosimetry
coatings, and adhesives (4).
system, generally having the highest metrological quality
4.2 Absorbed-dose measurements, with statistical controls
available at a given location or in a given organization, from
and documentation, are necessary to ensure that products
which measurements made there are derived.
receive the desired absorbed dose. These controls include a
3.1.15 routine dosimetry system—dosimetry system cali- program that addresses requirements for calibration of routine
brated against a reference standard dosimetry system and used dosimetry system.
© ISO/ASTM International 2013 – All rights reserved
4.3 A routine dosimetry system calibration procedure as tainty together with their methods of estimation, statistical
described in this document provides the user with a dosimetry distributions and magnitudes.
system whose dose measurements are traceable to national or
5.3.3 Examples of components of uncertainty in the dosim-
international standards for the conditions of use (see Annex
etry system calibration include inherent variation in dosimeter
A4). The dosimetry system calibration is part of the user’s
response, uncertainty in the calibration irradiation dose, uncer-
measurement management system.
tainty in the calibration curve fit and uncertainty in dosimeter
response correction parameters such as dosimeter thickness,
5. Dosimeter system calibration overview
dosimetermass,unirradiatedresponseandirradiationtempera-
ture.
5.1 Calibrationofaroutinedosimetrysystemconsistsofthe
5.3.4 Additional components of uncertainty might be pres-
following:
entwhentheconditionsofusearedifferentthantheconditions
5.1.1 Selection of the calibration dosimeters from the user
of calibration. In these instances, a calibration verification is
stock (see Section 8).
conducted to quantify a component of uncertainty to account
5.1.2 Irradiation of the calibration dosimeters (see 9.1 and
for these differences (see 9.1.8 and 9.2.9).
9.2).
5.1.3 Calibration and/or performance verification of mea-
6. Requirements for a routine dosimetry system
surement instruments (see Section 7).
calibration
5.1.4 Measurement of the calibration dosimeters response
(see 9.1.6 and 9.2.5.1).
6.1 Dosimetry system calibration shall be conducted for
5.1.5 Analysis of the calibration dosimeter response data
each new dosimeter batch.
(see 9.1.7 and 9.2.6).
NOTE 4—The response of different dosimeter stocks purchased at
5.1.6 Verification of the calibration curve for conditions of
different times from a given dosimeter batch should be verified to ensure
use, if appropriate (see 9.1.8 and Note 2).
equivalent response.Astatistical test should be used to determine if there
5.1.7 Estimation of the combined uncertainty for the condi-
is any significant difference between the stocks. This should be repeated
tions of use (see 9.1.10 and 9.2.7).
at several doses over the calibration dose range.
5.1.8 Verification of the calibration curve at a time other
6.2 Routinedosimetrysystemsshallbecalibratedusingone
than calibration for assessment of continuing validity of the
of the methods described in 9.1 and 9.2.
calibration curve (see 9.1.11, 9.2.9, and Note 2).
6.3 Therationaleforselectingamethodforcalibrationshall
NOTE 2—Calibration verification is conducted as part of the calibration
be documented (see 9.1.4 and 9.2.3).
when the calibration irradiation conditions are different from the condi-
6.4 Recalibration of an existing batch or stock shall be
tions of use (5.1.6). Calibration verification is also conducted between
conducted at a frequency specified by the user based on the
calibrations to ensure continued suitability of the calibration curve for the
known characteristics of the dosimetry system.
conditions of use (5.1.8).
6.4.1 Additional calibration or calibration verification may
5.2 Calibration Irradiation Methods—There are two meth-
be required to determine if changes have occurred that affect
ods for irradiating dosimeters for calibration:
thecalibration.Examplesarechangesinthevaluesofinfluence
5.2.1 Calibration irradiations performed at an approved
quantities, such as temperature or humidity, changes in the use
laboratory followed by a calibration verification exercise.
of the dosimetry system and change in response due to
5.2.2 In-situ/in-plant calibration irradiations of routine do-
dosimeter aging. Changes in influence quantities can result
simeters along with transfer standard dosimeters issued and
from seasonal changes in ambient conditions or changes in
analyzed by an approved laboratory.
source activity or distribution.
NOTE 3—Valid in-situ/in-plant calibration irradiations result in a cali-
6.5 Calibration curves are specific to the measurement
bration curve generated under conditions that are representative of the
instrument used to generate them. They shall not be used with
routineprocessingenvironment.Anin-situ/in-plantcalibrationmaynotbe
otherinstrumentsunlessithasbeendemonstratedthatthedose
valid or may require calibration verification if the calibration conditions
measurements agree within user defined limits.
can not be maintained during routine use. For example, the calibration
6.6 All software associated with dosimetry system and
irradiations are carried out as a single exposure, but the dosimeter is used
for dose measurement of fractionated irradiations. calibration data analysis shall be validated for its intended use.
5.3 Uncertainties:
7. Requirements for measurement instruments
5.3.1 Allmeasurementsofabsorbeddoseneedtobeaccom-
calibration and performance verification
panied by an estimate of uncertainty (see ISO/ASTM 51707,
7.1 All measurement instrumentation associated with the
Refs (5,6) and GUM).
5.3.2 All components of uncertainty should be included in dosimetry system shall either be calibrated, or have its perfor-
mance verified, before use. Performance checks and/or recali-
the estimate, including those arising from calibration, dosim-
brationshallbecarriedoutatuser-specifiedintervals,basedon
eter reproducibility, instrument stability and the effect of
the known characteristics of the instrument.
influencequantities.Afullquantitativeanalysisofcomponents
of uncertainty is referred to as an uncertainty budget and is 7.1.1 Where recognized standards exist, the calibration of
often presented in the form of a table. Typically, the uncer- the instrument shall be traceable to national or international
tainty budget will identify all significant components of uncer- standards.
© ISO/ASTM International 2013 – All rights reserved
7.1.2 Where recognized standards do not exist, the perfor- 9.1.3 Transport of Calibration Samples—The effect of in-
mance of the instrument shall be verified in accordance with tended transportation on dosimeter response shall be evaluated
industry or manufacturer recommended practices and proce- toestablishcriteriaforacceptablepackagingandtransportation
dures. of calibration dosimeters. The evaluation should be based on
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
spin reference such as irradiated alanine dosimeters, pitch sample, or for the calibration target dose levels, their spacing and irradia-
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 perfor-
9.1.4.1 Forexample,fordoserangesoflessthanonedecade
mance, instrument performance shall be verified and, if neces-
(factor of ten), dose levels should be distributed arithmetically
sary, 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
as ‘calibration dosimeters’.
doses. The absorbed dose is usually specified in terms of
8.2 Calibration dosimeters shall be labelled to ensure seg-
absorbed dose to water.
regation and identification throughout the calibration exercise.
9.1.5.1 The approved laboratory shall report deviations
8.3 The number of dose levels required for developing the
from the conditions specified by the user (see 9.1.4).
calibration curve depends on the range of utilization. At least
9.1.6 Dosimeter Response Measurement—The performance
five dose levels shall be used for each factor of ten span of
of measurement instrumentation shall be verified (see 7.1).
absorbed dose (for example, choose five dose levels fora5to
9.1.6.1 Measure the calibration dosimeter response upon
50 kGy range).
return from the approved laboratory in accordance with the
8.3.1 The minimum number of dose levels to be used in the
users calibration and measurement procedures.
calibration can be determined as follows: divide the maximum
9.1.7 Analysis of Dosimetry Data:
dose (D ) of the dose range by the minimum dose (D )of
max min 9.1.7.1 If required, each dosimeter response shall be ad-
the dose range; calculate log (base 10) of this ratio: Q =
justed for dosimeter parameters such as dosimeter thickness,
log(D /D ).If Qisequaltoorgreaterthan1,calculate5 3
max min mass or unirradiated dosimeter response following established
Q, and round this up to the nearest integer value. This value
measurement practice.
representstheminimumnumberofdoselevelstobeused.If Q
9.1.7.2 The individual dosimeter response, the sample stan-
is less than 1 use five dose levels.
dard deviation and the coefficient of variation of the replicate
8.4 Aminimum of four dosimeters for each dose level shall
measurements at each dose level shall be determined and
be used. However, using a larger number of dosimeters per
documented.
dose level may reduce the uncertainty associated with the
NOTE 6—In general, if the coefficient of variation at any dose level is
calibration.
greater than a user-defined limit, a re-determination of the data should be
9. Calibration of dosimetry systems considered (for example, perform a visual inspection to identify potential
dosimeter damage, repeat the calibration irradiation at the dose level or
9.1 Calibration of Dosimetry Systems using irradiations at
perform an outlier test).
an approved laboratory:
9.1.7.3 Derivethecalibrationcurveinmathematicalform, y
9.1.1 Overview—TheroutinedosimetermaybeaTypeIor
= f(x), where dosimeter response is the dependent variable (y)
Type II dosimeter. The calibration irradiation at an approved
and absorbed dose is the independent variable (x). Choose an
laboratory has the advantage that the dosimeters are irradiated
analytical form (for example, linear, polynomial, or exponen-
to known doses under well-controlled and documented condi-
tial) that provides an appropriate fit to the measured data. The
tions. However, when conditions of use (in-situ/in-plant) differ
ease of deriving dose from measured dosimeter response (the
from calibration conditions, significant uncertainties may be
mathematical inverse of the analytical form) may also be a
introducedinthecombineduncertaintyoftheroutineabsorbed
consideration in selecting the analytical form (see Annex A2
dosemeasurement.Transportofthedosimeterstoandfromthe
and Annex A3).
approvedlaboratorymayalsointroduceuncertaintiesfrompre-
9.1.7.3.1 The resulting calibration curve shall be evaluated
and post-irradiation influence quantities that are difficult to
characterize. for goodness of fit within user defined limits.
9.1.2 Post Irradiation Response—Post-irradiation response 9.1.8 Calibration Verification (as part of calibration)—
characteristics of the routine dosimeter shall be determined Prior to implementation of a calibration curve, a calibration
prior to calibration irradiation and incorporated into the cali- verification shall be performed to assess the suitability of the
bration procedure. calibration curve for the conditions of use. This is usually
© ISO/ASTM International 2013 – All rights reserved
achieved by in-situ/in-plant irradiation of transfer standard 9.1.11 Stability Verification—The suitability of the calibra-
dosimeters supplied by an approved laboratory alongside tioncurveshallbeverifiedoveritsperiodofuseinaccordance
with the requirements of 6.4.1.
representative samples from the routine dosimeter stock under
9.2 In-situ/In-plant Calibration of Routine Dosimetry Sys-
the conditions of use. The dosimetry system being calibrated
tems in a Production Irradiator Using Transfer Standard
andthetransferstandarddosimetrysystemusedforcalibration
Dosimetry System:
verification should, if possible, be based on different types of
9.2.1 Overview—The routine dosimeter may be a Type I or
dosimeters. For example, if the dosimetry system being cali-
Type II dosimeter. The calibration irradiation of the routine
bratedisbasedonalaninedosimeters,andthetransferstandard
dosimeterstogetherwiththetransferstandarddosimetersinthe
dosimetry system is also based on alanine dosimeters, then the
production irradiator has the advantage that the influence
effect of an inappropriate correction for influence quantities,
quantityvaluerangeswillbeverysimilarinroutineapplication
such as temperature, will not be apparent as both systems will
and calibration, provided the calibration irradiation conditions
respond in the same way.
are chosen appropriately. This method takes into account the
9.1.8.1 The calibration verification shall be conducted at a
effect of the influence quantities of the conditions of use to the
minimum of three dose levels targeted near the extremes and
extent that the transfer standard dosimeter response can be
near the center of the calibration dose range.
corrected for the difference between the fixed influence quan-
9.1.8.2 The routine dosimeters for the calibration verifica-
tity values of its calibration and the production irradiation
tion shall be selected from the same dosimeter stock as the
influence quantities profile by the approved laboratory issuing
calibration dosimeters.
and analyzing the transfer standard dosimeters. Care must be
9.1.8.3 Theirradiationoftheroutinedosimetersandtransfer
taken to ensure that the routine dosimeters and transfer
standard dosimeters shall consist of complete pathways
standard dosimeters irradiated together receive the same ab-
through the irradiator.
sorbed dose.
9.1.8.4 The routine and transfer dosimeters shall be irradi- 9.2.2 Post-Irradiation Response—Post-irradiation response
atedsothatitisensuredthattheyreceivethesamedosewithin characteristics of the dosimeter shall be determined prior to
predetermined limits (see Annex A1). calibration irradiation and incorporated into the calibration
procedure.
NOTE 7—The temperatures associated with the calibration verification
9.2.3 Irradiation Conditions—A rationale for target dose
irradiations should be similar to those expected to be encountered during
levelsandirradiationconditionsforcalibrationirradiationshall
routine use of the dosimetry system.
be prepared and documented. The irradiation conditions se-
9.1.8.5 In a few instances it may be impossible to conduct
lected for calibration irradiation should be such that the
the calibration verification as described. In these instances, the
irradiation conditions are similar to those expected during the
user shall develop a verification method and rationale that is
intendeduseoftheirradiator,forexample,duringperformance
capable of demonstrating that the calibration curve of the
qualification and routine process monitoring.
routine dosimetry system is suitable for the conditions of use.
9.2.3.1 Forexample,fordoserangesoflessthanonedecade
The rationale for the need to use this alternative method shall
(factor of ten): dose levels should be distributed arithmetically
be documented.
uniformly (for example, 10, 20, 30, 40, 50 kGy). For dose
ranges of more than one decade, dose levels should be
9.1.8.6 Thecalibrationverificationresultsshallbeevaluated
to identify difference between the measured dose values of the distributedgeometricallyuniformly(forexample,1.0,1.5,2.3,
3.4, 5.1, 7.6, 11.4, 17.1, 25.6, 38.4, 57.7, 86.5 kGy).
routineandtransferstandarddosimetrysystemsandtoprovide
9.2.4 Dosimeter Irradiation—The calibration dosimeters
anestimateofoneofthecomponentsofcalibrationuncertainty
(see Annex A3). shallbeirradiatedwithtransferstandarddosimetersissuedand
analyzed by an approved laboratory. The irradiation phantom
9.1.9 Corrective Action—If the calibration verification re-
used to co-locate the calibration dosimeters and the transfer
sult exceeds a user defined acceptable limit, corrective action
standard dosimeters shall be characterized to ensure both the
inaccordancewiththemeasurementmanagementsystemshall
calibration dosimeters and the transfer standard dosimeters
be implemented.
receive the same absorbed dose (seeAnnexA1).The absorbed
9.1.9.1 Correctiveactionmayinclude:repeatingthecalibra-
dose is usually specified in terms of absorbed dose to water.
tion using more appropriate influence quantity conditions
during calibration irradiation, reducing the dose range of the NOTE 8—The temperatures of the routine dosimeters during calibration
irradiation should be similar to those expected to be encountered during
calibration curve, developing calibration curves for specific
routine use of the dosimetry system.
irradiator pathways, applying a correction factor to the routine
dosimeter response in cases where a single factor is applicable
9.2.5 Dosimeter Response Measurement—Verifytheperfor-
over the entire calibration curve, or calibrating using an
mance of the measurement instrumentation (see 7.1-7.1.3).
in-situ/in-plant calibration method (see 9.2).
9.2.5.1 The calibration dosimeter response shall be mea-
9.1.10 Dosimetry System Measurement Uncertainty— sured in accordance with the users’ calibration and measure-
Prepare an estimate of the combined uncertainty in the mea- ment procedures.
sured dose using the calibrated dosimetry system for the 9.2.6 Analysis of Dosimetry Data—Ifrequired,eachdosim-
conditions of use (see Annex A3 and ISO/ASTM 51707). eterresponseshallbeadjustedforresponseparameterssuchas
© ISO/ASTM International 2013 – All rights reserved
dosimeter thickness, mass or unirradiated dosimeter response 9.2.9.1 Changes to the intended conditions of use of the
following established measurement practice. routine dosimetry system may render the calibration curve
9.2.6.1 The individual dosimeter response, the sample stan- unsuitable. An example of such a change is that of dose
dard deviation and the coefficient of variation of the replicate fractioning during the intended use when the calibration
measurements at each dose level shall be determined and irradiation consists of a single exposure. In such instances, the
documented. effect of the change shall be evaluated.
NOTE 9—In general, if any coefficient of variation is greater than a
NOTE 10—Performing a calibration verification is one method of
user-definedlimit,are-determinationofthedatashouldbeconsidered(for
evaluating the effect of changes to the conditions of intended use,
example, perform a visual inspection to identify potential dosimeter
reference 9.1.8 and Note 7.
damage, repeat the calibration irradiation at the dose level or perform an
outlier test).
10. Minimum documentation requirements
9.2.6.2 Derivethecalibrationcurveinmathematicalform, y
10.1 Document the dosimetry system being calibrated in-
= f(x), where dosimeter response is the dependent variable (y)
cluding the dosimeter manufacturer, type and batch number,
and absorbed dose is the independent variable (x). Choose an
and measurement instrumentation.
analytical form (for example, linear, polynomial, or exponen-
10.2 Document the rationale for the calibration method.
tial) that provides an appropriate fit to the measured data. The
10.3 Document the dosimetry system calibration data, irra-
ease of deriving dose from measured dosimeter response (the
diation parameters, irradiation date, transfer standard dosim-
mathematical inverse of the analytical form) may also be a
eters, and description of the irradiation facility used.
consideration in selecting the analytical form (see Annex A2
10.4 Document or reference a description of the radiation
and Annex A3).
source(s) used in calibration and processing, including the
9.2.6.3 Theresultingcalibrationcurveshallbeevaluatedfor
type, nominal activity or beam parameters, and any available
goodness of fit within user defined limits
information on the energy spectrum.
9.2.7 Dosimetry System Measurement Uncertainty—
10.5 Document irradiation temperatures and, if necessary,
Prepare an estimate of the combined uncertainty in the mea-
the relative humidity.
sured dose using the calibrated dosimetry system for the
10.6 Document the combined uncertainty in the measured
conditions of use (see Annex A3 and ISO/ASTM 51707).
dose using the calibrated dosimetry system.
9.2.8 Corrective Action—If the combined uncertainty ex-
10.7 Referencethemeasurementmanagementsystematthe
ceeds a user defined acceptable limit, corrective action in
radiation facility.
accordancewiththemeasurementmanagementsystemshallbe
implemented.
11. Keywords
9.2.8.1 Correctiveactionmayinclude:repeatingthecalibra-
tion using more appropriate calibration irradiation conditions, 11.1 absorbed dose; accredited laboratory; dosimeter; do-
reducing the dose range of the calibration curve, developing simetry system calibration; dosimetry system; electron beam;
calibration curves for specific irradiator pathways. gammaradiation;ionizingradiation;measurementtraceability;
9.2.9 Stability Verification—The suitability of the calibra- radiation processing; reference standard dosimetry system;
tioncurveshallbeverifiedovertheperiodofuseinaccordance routine dosimeter; transfer standard dosimetry system; Type I
with the requirements of 6.4.1. dosimeter; Type II dosimeter; X-ray; X-radiation
© ISO/ASTM International 2013 – All rights reserved
ANNEXES
(informative)
A1. PHANTOM GEOMETRY
A1.1 Aphantomofknownhomogenousmaterialisusedfor differences should be evaluated as part of the calibration
the irradiation of the dosimeters in order to minimize the procedure.
difference between the absorbed doses received by the routine
A1.3 When thick and thin dosimeters are irradiated to-
and transfer standard dosimeters. The phantom design should
gether, the thin dosimeters should be surrounded by sufficient
hold the two types of dosimeters so that they do not signifi-
polymericmaterialtoensurethattheattenuationcharacteristics
cantly influence each other and provide a geometry that is
are similar to the thick dosimeters and that the dosimeters
appropriate for the radiation source employed (see Fig. A1.1
receive the same dose.
and Fig. A1.2 for examples of such phantoms employed for
gamma or X-ray irradiation; see Fig.A1.3 for an example of a A1.4 Dose variation within the phantom can be character-
phantom suitable for high energy electron-beam irradiation).
ized by irradiating the phantom with the same type of dosim-
eter in all the dosimeter positions within the calibration
A1.2 Theuseofaphantomcanresultindifferentirradiation irradiationphantom.However,differenceingeometrybetween
temperature and temperature profile than the conditions of use the routine dosimeters and transfer standard dosimeters must
oftheroutinedosimeterwithoutaphantom.Theeffectofthese be taken into account.
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 2013 – All rights reserved
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
A2. CURVE FITTING
© ISO/ASTM International 2013 – All rights reserved
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
form(model)definesthedependentvariable(Y)intermsofthe
where:
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.
yˆ = themodelpredictedvalueofthedependentvariableat
i
the corresponding independent variable, and
A2.2 Regression models are either an empirical or a
w = assigned weight which in most cases is assumed to be
i
mechanistic model. The empirical model describes the general
1 unless a weighting is applied to compensate for a
shapeofthedataset.Theparametersoftheempiricalmodeldo
deviation of homoscedasticity (A2.3.1.3).
not correspond to an underlying biological, chemical or physi-
cal process. The mechanistic model is formulated to provide
NOTE A2.3—When the Gaussian distribution of error assumption is
insight or description of the process under study.
invalid due to appreciable tails in the residuals distribution, the assump-
tionthatleastsquaresprovidesthemaximumlikelihoodfitisalsoinvalid.
A2.3 The two basic types of regression analysis are linear
In these instances a robust method of minimization may be used. The
regression and non-linear regression. Linear regression is
essence of robust fitting is to use a minimization technique that is less
wheretheunknownparameters(coefficients)appearlinearlyin
influenced by potential outliers and the range of the dependent variable.
Several examples of nonlinear robust minimization are Least Absolute
the expression as in Eq A2.1. Non-linear regression is where
Deviation, Lorentzian, and Pearson.
theunknownparameters(coefficients)appearinanon-linearor
nested fashion as in Eq A2.2.
A2.5 Goodnessoffitdescribeshowwellthemodelfitsaset
2 3
y 5 a 1 bx 1 cx 1 dx (A2.1)
of data. Measures of goodness of fit typically summarize the
a
discrepancy between observed values (y) and the values
i
y 5 (A2.2)
c
x
predicted by the model (yˆ).Areview of a plot of the residuals
1 1
S D
b
is critical when assessing goodness of fit.The most commonly
usedstatisticsforassessinggoodnessoffitarethecoefficientof
NOTE A2.1—In the context of regression analysis, the terms linear and
determination, lack of fit sum of squares (F statistic), confi-
non-lineardonotrefertotheshapeoftheplottedcurve,forexample,both
Eq A2.1 and Eq A2.2 represent curved plots.
dence intervals of the fit coefficients, and the F test when
comparing fits between different models. Another powerful
A2.3.1 In both types of regression analysis (linear and
non-statistical evaluation method is a review of the plot of the
nonlinear) several assumptions are made:
residuals.
A2.3.1.1 X is known precisely and all error is in Y. (It is
sufficient that imprecision in measuring X is very small
A2.5.1 A plot of the residuals can reveal behaviour in the
compared to the variability in Y. Error refers to deviation from
data that is otherwise difficult to see in the curve fit.Aplot of
the average.)
the residuals should not demonstrate a form or trend. A
A2.3.1.2 Variability of Y at any X follows a known distri-
residuals plot may also indicate potential or suspect outliers
bution, typically assumed to be Gaussian or near Gaussian.
(see A2.6).
A2.3.1.3 Thestandarddeviationoftheresidualsisthesame 2
A2.5.2 Thecoef
...