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ICRP: Free the Annals!

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Submitted by Bernd Lorenz, ENISS
   Commenting on behalf of the organisation
Document Operational Quantities for External Radiation Exposure
 

ENISS recognizes the joint effort of ICRU and ICRP in the preparation of these recommendations which is aimed to replace the previous definitions which have been successfully used in more than 30 years and became part of everyday practical radiation protection. The newly proposed operational quantities are an attempt to better approximate the unmeasurable protection quantities.  The proposal offers a more direct way for demonstration of compliance with regulations on occupational exposures. The arrangement of physical, operational and protection quantities will be perhaps more intuitive and transparent and could lead to a better understanding of operational quantities. The question is, what benefits result with respect to practical radiation protection which is at a high standard today worldwide and the result is a dose level of real exposure that is less a tenth of the limits. The measurement of doses and the demonstration of compliance with the protection quantities is of more importance when doses are near the protection limits. This is not the case today. From this it is less important to have a higher accuracy in the definition of operational quantities.


    


Thus, there are issues of severe concerns with the introduction of new operational dose quantities.


 


The implementation of new operational quantities in radiation protection will have a significant impact on radiation protection. The measurement of radiation is one of the cornerstones of practical radiation protection. There are several Millions of measuring devices used by several Millions of occupationally exposed workers worldwide. Further, a change in measurement does not only affect the numerical value measured, but also the development of the means of the measurements (detectors) and the traceability of the measurement results (calibration methods and procedures, practices in accredited standard laboratories). In addition, documents have to be updated at least due to name change and training modules have to be revised. It is therefore important to address the upcoming costs in relation to the benefits for radiation protection before redefined quantities are considered. There is lacking evidence in this respect in the new recommendation. It is not convincing to introduce new dose quantities only based on science but not taking into account the consequences for the daily practice of Millions of occupationally exposed people.


 


A comparison of the dose conversion factors for the old quantities with those in the proposed recommendations shows that there is a better approximation for photons with low and high energies. However this will not have any significant practical effect for occupationally exposed workers in the nuclear industry since the majority of the dose results from photons in the energy range where the dose conversion factors will not change significantly. The benefit of the proposed change in quantities due to a better estimation of the protection quantity does therefore not exist.


 


Since there is no need to haste these recommendations, we urge that an analysis of the consequences, from a user perspective, is performed before the adoption of these recommendations; with the specific objective to understand the impact on the set of instrument in operation today and on the calibration procedures used at dosimetry facilities, standard laboratories and in practices. In the analysis the impact of different transition times should be included, bearing in mind that measuring devices may work properly more than ten years. Such an analysis will obviously show no justified benefit for safety.


 


Summing up we urge ICRP/ICRU to withdraw this recommendation. If a change is wanted at all, this would be at best placed in connection with the next basic recommendation on the system of radiation protection which is expected perhaps in 2020 or so.


 


Specific comments:


 



  • The proposed recommendations have excluded the specific depth in the definition of personal doses for total body, for the lens of the eye and for the skin. This is not discussed in the recommendations and the consequences of this are unclear. Manufacturers of personal dosimeters may leave the current harmonized practice of designing personal dosimeters, since this is no longer a condition in the definitions of the operational quantities.


 


ICRP and ICRU are therefore encouraged to include in the recommendations that ICRU and ICRP continue to recommend (or see as a good practice) (or do not oppose) that depths 10 mm, 3 mm and 0,07 mm to be used in the manufacture of the personal dosimeters, for the determination of the doses for total body, lens of the eye and local skin.


 



  • Irrespective of whether the proposed definitions of operational quantities require recalibration of all calibration rooms and all personal dosimeters, which will undoubtedly result in a significant effort of time and human resources, the main proposed change is that personal doses will not be defined on the basis of the equivalent doses, but on the effective dose, and for that reason the joint effort of ICRU and ICRP with this publication is recognized: Paragraph 215 “The previous operational quantities were based on the dose equivalent that would be produced at a depth in the hypothetical ICRU 4-element sphere, and on dose equivalent in soft tissue at a point in the body” and paragraph 1261 “The recommendations of operational quantities in terms of conversion coefficients to  ambient dose, directional absorbed dose in the lens of the eye, directional absorbed dose in local skin, personal dose, personal absorbed dose to the lens of the eye, and personal absorbed dose to local skin, are a clean break from the existing recommendations for operational quantities that are based on dose equivalent in the ICRU 4-element sphere and at a depth in the body, and will give a better estimate of the protection quantities”.


However, the calibration of personal dosimeters in the present operational quantity of the personal dose equivalent at the depth of 10 mm has an important advantage that will be lost; it overestimates the effective dose and it do not underestimates, in relevant exposure situations. An example may help to understand this better.


For the Cs-137 gamma energy, the air kerma, physical quantity, conversion factor to personal dose equivalent Hp (10) is 1.21 Sv/Gy (ICRP-74 table A.23 and ISO-4037, Part 3, Table 33), while the air kerma conversion factor to effective dose is 1.02 Sv/Gy (ICRP-116, Table A-2). That is, calibrating personal dosimeters in Hp (10) has a certain operating margin of 1.21/1.02 = 1.186 for not to underestimate the effective dose. As proposed, the conversion factor of the personal dose Hp is defined as a function of the effective dose, the margin of maneuver is lost, and given the high uncertainties that arise in personal dosimetry, as also recognized in the ICRP document "For doses below dose constraints or investigation levels, in common practice, the protection quantities are assessed in terms of the operational quantities” there is no guarantee that the reading of personal dosimeters will underestimate the most important protection quantity, the effective dose.


 


Even if one can think that the problem is solved by maintaining the calibration of personal dosimeters with the old definition the personal dose equivalent to a depth of 10 mm, Hp (10), which will soon be obsolete, this will not be possible because future national or international intercomparisons, where the new definition of personal dose would be used, would leave users calibrating their personal dosimeters in Hp (10) in a poor position or situation, at least 18.6% above the actual effective doses used in the intercomparison.


 



  • It would be convenient to include an image or drawing to clarify and thus better understand the definition of "Charged-particle equilibrium".


 



  • The paragraph beginning on line 333 requires clarification because it is not understood: “Although the conversion coefficients from fluence or air kerma are to values of protection quantities that are not point quantities but are averaged over an organ or tissue, or the sum of these averages, the operational quantities that are recommended are point quantities.”