ANSI HPS N13.32-2008 Performance Testing of Extremity Dosimeters.pdf

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1、 ANSI/HPS N13.32-2008 American National Standard Performance Testing of Extremity Dosimeters Approved: November 2008 American National Standards Institute, Inc. ANSI/HPS N13.32-2008 ii Published by Health Physics Society 1313 Dolley Madison Blvd. Suite 402 McLean, VA 22101 Copyright 2008 by the Heal

2、th Physics Society. All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher. Printed in the United States of America ANSI/HPS N13.32-2008 iii Foreword (This foreword is not a par

3、t of the American National Standards Institute/Health Physics Society (ANSI/HPS) N13.32-2008.) This American National Standard provides a procedure for testing the performance of extremity personnel dosimetry systems used to monitor the personnel exposure to the extremities from ionizing radiation.

4、This is the first revision of the original standard, HPS N13.32-1995. Testing the performance of personnel dosimeters has been an active part of evaluation and quality assurance of personnel dosimetry systems. By ANSI policy, standards must be reviewed and, if necessary, revised every few years. The

5、 Health Physics Society working group that reviewed this standard held to three major objectives during revision: (1) as far as possible, maintain an approach to testing consistent with the practical application of extremity dosimeter systems without excluding current and developing techniques; (2)

6、attempt to achieve a measure of consistency with related national and international standards; and (3) base major changes in the approach and content of the standard on scientific fact. The group identified 12 major issues for consideration. The following paragraphs describe how the group resolved t

7、hese issues. Some of the issues are treated in greater detail in the appendices, which were written to provide greater insight and convenience. The working group made the most significant changes in the areas of test categories and test criteria. The working group attempted to harmonize the test cat

8、egories with those in the whole-body dosimetry testing standard, ANSI/HPS N13.11-2001. Particularly, the photon test categories in the protection level dose range were combined so that the previous test categories for low-energy and high-energy photons, Categories II and III, are now both included i

9、n test Category II for photons. In addition, the number of x-ray fields available for testing in the photon category was increased from four x-ray fields and one high-energy photon field to six x-ray fields and two high-energy photon fields. The beta category now included as Category III remains unc

10、hanged except for the addition of 85Kr as a replacement for 204Tl. The working group considered the inclusion of a neutron-testing category based on the recommendation in the Journal of the ICRU, Volume 1, No. 3 (2001), “Determination of Operational Dose Equivalent Quantities for Neutrons.” At this

11、time, though, the working group felt that the theoretical basis of neutron dosimetry to extremities has not reached a sufficient level of national and international agreement to promote the practice of neutron extremity dosimetry by including a testing category. At the request of the dosimetry commu

12、nity, one additional test category was added to evaluate response to the beta/photon mixtures (new Category IV). This category was added to accommodate test participants submitting dosimeters with the ability to interpret Hp(0.07) in mixed fields or for dosimeters that are energy/exposure field-inde

13、pendent. If a test participant chooses to test in this category, then that participant will not be told which exposure fields (test sources) were used in any of the categories (Categories I through IV), with the exception that the participant would be told which dosimeters were exposed in the high-d

14、ose category (Category I). However, if the participant chooses the “General” subcategory in Category I he or she will not be told whether the irradiating field was 137Cs or M150. This is referred to as blind testing. There is no option to only blind-test in Category IV. Normal testing, as in the pre

15、vious version of the standard, is not done blindly and includes only Categories I through III. In this case, the testing source is identified to the participant beforehand for the purpose of allowing him or her to apply a specific correction factor to determine a more accurate personal dose (dose eq

16、uivalent). It is intended that this methodology would be consistent with the methodology for normal processing of personnel dosimeters. That is, the processor would have knowledge of the workers exposure field and be able to use this information during the determination of the dose equivalent. ANSI/

17、HPS N13.54-2008 iv The working group modified the ratios of delivered doses for the mixture category to approximate fields more normally found in the industry. The ratios of contributing shallow doses from betas and photons were modified to range from 1:1 to 5:1 (beta:photons). The working group als

18、o considered adding a photon mixture category comprising irradiations in high- and low-energy photon fields. However, based on the response of dosimetry materials to photons with energies above 100 keV, and with the addition of high-energy, broad-spectrum x-ray testing fields, the group considered t

19、he testing provided in Category II to be adequate for mixed photon fields. The selection method for irradiation levels remains unchanged from the previous version of this standard (i.e., the choice of the use of logarithms to increase the number of irradiations at the lower personal dose equivalents

20、). The working group agreed to the adoption of the personal dose equivalent at 0.07 mm depth or in mass thickness 7 mg cm2. Research has shown that the dose rate at 0.07 mm used for beta particles incident on the slab phantom is applicable for use with the rod and pillar phantoms (ISO 2006). In sele

21、cting personal dose equivalent at 0.07 mm, the working group chose to exclude a discussion of lens dose equivalent (LDE). The group concluded that it was inappropriate to include LDE dose as part of a standard addressing extremity dose. Conversion coefficients for photons, listed in ISO 4037-3 (ISO

22、1999), were used with digitized spectra of the National Institutes of Standards and Technology (NIST) x-ray beams to determine coefficients to convert air kerma to personal dose equivalent for the x-ray testing fields. Considering the uncertainties in estimating the extremity exposure in the field,

23、the added uncertainty from this difference in computed conversion factors from air kerma to dose is insignificant. For practical purposes, the polymethylmethacrylate (PMMA) rod phantom will continue to be used for testing of finger dosimeters. The working group considered several different designs i

24、n selecting a pillar phantom for testing of wrist/ankle dosimeters. They conducted an experiment to determine the differences in the amount of backscatter among designs. Extremity dosimeters were irradiated on a solid PMMA pillar, a water-filled PMMA pillar, an aluminum-core PMMA pillar, and a Styro

25、foam pillar. Only small differences in dosimeter response were observed among these phantom designs. Therefore, for practical reasons, a solid PMMA phantom, of the same dimensions, was chosen to replace the aluminum-core PMMA phantom described in the previous version of this standard. The study is s

26、ummarized in Appendix A6. In the Unites States, performance test criteria for personal extremity dosimeter systems have historically used a systematic approach (i.e., testing the performance of a group of dosimeters rather than basing the test on individual dosimeter results). This philosophy was co

27、ntinued in the current revision of the standard, and as before there are no individual dosimeter failure criteria to pass. However, the approach to determining group failure criteria has been modified. In the past, group failure criteria were based on (1) not exceeding the tolerance level (L) by the

28、 performance index, defined as the sum of the absolute value of the bias (|B|) and standard deviation (S) of 15 dosimeters irradiated in a single test category and (2) not exceeding individual limits on the |B| and S in a single test category. In this revision of the standard a new testing model was

29、 adopted in which the performance index is redefined as the square root of the sum of the squares of the B and S, consistent with current theory in statistical quality control (see Wheeler and Chambers 1992, in Appendix I of this standard). The resulting performance index is compared to a criteria l

30、imit determined by either (1) setting the new performance models area of acceptable performance equivalent to the previous models area of acceptable performance or (2) limiting the acceptable values of B and S to historical levels. There are several notable differences in the two models that could a

31、ffect the evaluation of performance of dosimetry systems compared to past results. For the high-dose test category, the limit was chosen so the area of acceptable performance was equal to the previous area of acceptable performance (i.e., by equating the area of the triangle formed by L = |B| + S to

32、 the area of the half-circle formed by L2 = B2 + ANSI/HPS N13.32-2008 v S2). This is illustrated in Fig. D1 and results in (1) lowering the maximum allowable individual S and |B| from 0.30 in the old model to 0.24 in the new model and (2) two identical small areas on the graph where the allowable su

33、m of the |B| and S would be greater than 0.30. The probability that a dosimeter system would perform in the affected area of acceptable performance is extremely small. Further, the maximum |B| + S in these small areas for the quadrature model was determined to be 0.34, which is only slightly above t

34、he value of 0.30 for |B| + S allowed by the previous model. For the protection level categories, the quadrature model was also adopted and the limit was chosen so the maximum acceptable individual value of the |B| and S would be 0.35, consistent with the previous testing criteria. The maximum |B| +

35、S for the protection level categories was determined to be 0.495, which is only slightly less than the value of 0.50 for |B|+S allowed by the previous model. This is illustrated in Fig. D2. The performance criterion for the General Beta test (Category IVC in the previous version of the standard and

36、Category IIIA in the current version of the standard) was modified from having no limit on |B| and S in the previous version to a value of 0.35 in the current version as a result of applying the quadrature model to all categories. The working group modified the required ancillary tests to further di

37、stinguish between type tests and periodic performance tests. The requirements for the lower limit of detection (LLD) and angular response testing were removed from this standard because they constitute one-time tests that should be performed upon the initial implementation or modification of a dosim

38、eter system. Recommended protocols for those studies are described in the attached appendices. In addition to those studies, the working group modified the standard to also recommend the study of uncertainty for each dosimeter system. Based on the U.S. Guide to the Expression of Uncertainty in Measu

39、rements, guidance is given in the appendices for the approach to uncertainty analysis (see ANSI/NCSL 1997, in Appendix 1 of this standard). Suggestions for improving this standard are welcome. Suggestions should be sent to the Health Physics Society, 1313 Dolley Madison Blvd., Suite 402, McLean, VA

40、22101. ANSI/HPS N13.54-2008 vi This standard was consensus-balloted and approved by the ANSI-accredited HPS N13 Committee on November 6, 2007. At the time of balloting, the HPS N13 Committee had the following membership: Chairperson Tracy Ikenberry American College of Occupational and Environmental

41、Medicine Bryce Breitenstein American Industrial Hygiene Association Irene Patrek American Iron and Steel Institute Anthony LaMastra American Mining Congress Scott C. Munson American Nuclear Insurers Bob Oliveira American Nuclear Society Nolan E. Hertel Conference of Radiation Control Program Directo

42、rs Shawn Seeley Council on Ionizing Radiation Msmts the foot and leg below the knee (NRC 2008). Extremity dosimetry system: A system used to assess dose equivalent resulting from external radiation to the extremities. The extremity dosimetry system includes the dosimeter, the dosimeter processing sy

43、stem and the system used to ensure the quality of the dosimetry result. Half-value layer: The thickness of material that reduces the intensity of a radiation beam by one-half. Homogeneity coefficient: The ratio of the first half-value layer to the second half-value layer, times 100. ICRU tissue: A t

44、issue-equivalent (TE) material defined in the ICRU Report 33 (ICRU 1980) having a density of 1,000 mg cm3and a composition by mass of 76.2% O, 10.1% H, 11.1% C, and 2.6% N. Irradiating laboratory, IL: A laboratory possessing radiation sources, calibration equipment, and associated facilities that is

45、 able to irradiate dosimeters from the test sample to radiation quantities known to a high degree of certainty. Performance quotient, Pi: The relative difference of the absorbed dose or personal dose equivalent reported by the test participant from the delivered absorbed dose or personal dose equiva

46、lent, which for the ithdosimeter is defined as (Eq. 7) where Hiis the personal dose equivalent assigned by the IL to the i thirradiated dosimeter and Hi is the corresponding personal dose equivalent reported by the test participant. For tests of high-dose dosimetry, the same definition applies with

47、the absorbed dose, D, replacing the personal dose equivalent, H. Personal dose equivalent, Hp(d): The dose equivalent dose in soft tissue as defined in ICRU 51 (ICRU 1993) below a specified point on the body at an appropriate depth d. Note 1: The unit of the personal dose equivalent is joules per ki

48、logram (J kg1) with the special name sievert (Sv). Note 2: Any statement of personal dose equivalent should include a specification of the depth, d, expressed in millimeters. Note 4: Shallow dose equivalent is defined as the personal dose equivalent at a depth of 0.07 mm in ICRU tissue and is denote

49、d by Hp(0.07). Processor: A supplier of personnel dosimetry services. These services include (1) furnishing dosimeters to the user, (2) evaluating the readings of the dosimeters after their return in terms of the absorbed dose or personal dose equivalent as prescribed in this standard, (3) recording the results, and (4) reporting them to the user. Protection levels: For this standard, protection levels are considered to be below 0.1 Gy (10 rad). The upper end of the regulatory range of protection dosimetry levels is addressed in the “high-dose levels” categories. Radi