Interpretation of biossay data

Draft document: Interpretation of biossay data
Submitted by Bertrand Theriault, Canadian Nuclear Safety Commission
Commenting on behalf of the organisation

1. General Comments Overall the draft provides a comprehensive treatment of the interpretation of bioassay monitoring data for the purpose of assigning doses to workers. The proposed systematic approach for assessing dose is scaled to the level of risk, i.e., the effort in the assessment is proportional to the estimated dose. Once finalized, this ICRP document will most likely be a valuable tool for internal dosimetry and radiation protection specialists. In addition, its use will likely help to harmonize internal dose assessment carried out by the internal dosimetry services in Canada. Its publication is timely, given that CNSC regulatory standard S-106 Rev. 1 (“Technical and Quality Assurance Requirements for Dosimetry Services”, May 2006) has introduced new requirements for internal dosimetry services, namely submitting for approval by the CNSC their method of assessing dose to workers on the basis of bioassay data, and participating in dose intercomparison exercises in order for the CNSC to gauge the capability of licensees in assessing worker doses on the basis of bioassay monitoring data. The CNSC has not yet provided guidance on an acceptable method of assessing such doses. Hence, it would be of value for the CNSC to consider the method proposed in the subject document as a basis for future guidance to its licensees. 2. Specific Comments 1. Section 2.4: The basis on which the "reasonable probability" of exceeding 1 mSv be determined should be addressed. 2. Section 2.4: In the case of the potential for exposures to many different radionuclides, on what basis should a decision be made as to which radionuclides to monitor (e.g., screening for Ce-144 in urine to assess the potential for intakes of actinides)? 3. Section 2.4: On page 10, the list of work situations where experience has shown that it is necessary to give consideration to routine individual monitoring does not include the mining of uranium ores. Also, the last bullet refers to exposures to Rn+ in mines. Should this statement be construed as "in any mine"? 4. Section 2.5: Page 11, 4th paragraph: it may be of value to add that individual specific dose assessments may be carried out not only when a dose limit could be exceeded, but also, when an investigation level could be exceeded. Also, it is not clear in this paragraph whether changes in dosimetric assumptions refer to the use of individual-specific (HRTM) absorption parameters. 5. Section 2.7: A reference to where guidance exists should be provided on the modification of dose coefficients and biokinetics of radionuclides for female workers during pregnancy or lactation. 6. Section 3.4: Last sentence: is the intent here to say " no specific models are recommended by ICRP for calculating doses from beta-emitting radionuclides absorbed through intact skin" ? 7. Section 3.10: In the 2nd paragraph it may also be worthwhile noting that radioiodine uptake has been observed to be significantly less than that the ICRP default of 30% in some cases (see for example G.H. Kramer et al, Radiation Protection Dosimetry, Vol. 102, No. 2, pp. 129 - 135 (2002)). The effect of thyroid function (e.g., hypothyroidism) on radioiodine uptake and biological half-time in the thyroid may also be noted here (c.f., reference cited above). 8. Section 7.2: Given that Level 2 tasks apply to situations where the CED is expected to be 1 to 6 mSv/a, it may be helpful to address the issue of DIL (in terms of bioassay quantity measured) to help in deciding whether a group of workers should be dealt with as Level 2 (i.e., for whose dose assessments workplace-specific data should be collected). 9. Section 7.2: It should be noted that the use of z(t) to assess E(5) should apply only to Level 1 situations as Levels 2 and 3 would use site and/or individual specific data. 10. Section 7.3: On page 54, 1st paragraph, it is indicated that it is desirable to use condition-specific parameters above Level 0, however, the discussion on Level 1 on page 52 suggests the latter is not intended for use with condition-specific data. To avoid confusion, the text of page 54 should reflect that on page 52 on the structure of “Levels of Task”. 11. Section 7.6.3: This section appears to address situations of multiple measurements that are part of a special monitoring program as opposed to multiple measurements made in a single individual routine monitoring program. It would be of use to briefly discuss the latter in this section. 12. Section 8.1.1: This section suggests that for routine monitoring there typically is one measurement relating to each intake. This is often not the case, in particular when chronic intakes occur. Is the intent to say that either only one acute intake is assumed to occur at the mid-point in the monitoring period, or a chronic intake is assumed to occur throughout the monitoring period? 13. Section 8.2.2, Step 1.1: the note "see Chapter 8" should be more specific (e.g., see section 8.x.x). Also, reference should be made to types of monitoring and the selection of monitoring period (as these are the subject of this paragraph). 14. Section 8.2.3, Step 2.0; Clarification should be given to the phrase "do some simple hand calculations", e.g., what should be calculated at this point, using which method ? 15. Section 8.2.3, Step 2.2: Clarification should be given as to how far back one should go in accounting for previous intakes. Past chronic intakes should also be considered. 16. Section 8.2.3, Step 2.3: the first line should say "... then there is at least a 95% probability ...". 17. Section 8.2.3, Step 2.4: Large SF values could result in large missed doses over a year - this should perhaps be mentioned as a point of caution. 18. Section 8.2.4, Step 3.3: The assumption of an acute intake at the mid-point in the monitoring period may over or under estimate dose when there is a significant prompt component to excretion or retention. Perhaps the assumption of chronic intake should be considered where the assumption of acute intake at T/2 results in an error of greater than a factor of 3. 19. Section 8.2.4, Step 3.3: The assumption of AMAD = 5um should be used only where it is known that the compounds taken are not vapors, e.g., one would not use the assumption of 5 um AMAD in the case of HTO intakes. Also, this section implies that for radioiodine intakes, one should assume their form to be particulates while an assumption of vapor may be conservative. Some clarification here would be beneficial. 20. Section 8.2.5, Stage 4: The first paragraph addresses situations where there is evidence for a CED greater than 1 mSv. Based on the description of the Level of Task (page 52) one would assume this to mean 1 mSv/a. This should be clarified.