Review on ICRP Report “Cancer Risk from Exposure to Pu and U”
The Report follows the series of reviews of carcinogenic effects related to incorporation of radionuclides. The undoubted value of the report lies in a very detailed review of all the presently existing results of plutonium cancer risk estimates among nuclear workers. A detailed coverage of dosimetry issues regarding estimation of doses from incorporated plutonium is an important advantage of the report.
We would like to note the following points as our suggestions for improving the part of the report related to plutonium:
The fact that the report is limited to data on occupational exposure, moreover, on plutonium inhalation at workplaces, requires explanation.
Validity of using such concepts as “detriment” in estimation of absorbed doses raises certain doubts. It seems that dose to the whole lung obtained from multiplying the sum of doses to different parts of the lung (BB, bb, AI) by coefficient 1/3 that is indicated in paragraph (50) line 638 should be regarded as some average value without mentioning such a concept as “detriment”. Using the “detriment” concept results in turn in the need to change the naming of the dose from absorbed to equivalent, as well as to change the units from Gy to Sv.
We consider necessary to cite the data from Labutina (2013) regarding radiation risk assessment for certain histological types of liver cancer in 2.3. Epidemiological studies 2.3.1. Mayak Workers 2.3.1.3. Results by organ in paragraph 122 lines 1314-1319:
Among workers monitored for plutonium, the morphological analysis indicated that hepatocellular cancer was the most common type of liver cancer diagnosed (18 cases). There were also six confirmed cases of cholangiocarcinoma and eight cases of hemangiosarcoma (Table 7). The risk for hepatocellular cancer was best described by the LQ or the pure quadratic (Q) models than a linear model (L) in relation to internal plutonium liver dose. For the LQ model, the linear term was 0.95 (95% CI: j4.91; 9.53), and the quadratic term was 2.5 (95% CI: 0.4; 10.9). Although it was not feasible to examine a dose response relationship for other morphological types of liver cancer, seven of the eight hemangiosarcomas were observed for workers with plutonium doses of above 4 Gy, and all six cases of liver cholangiocarcinoma were confirmed for workers with doses less than 0.5 Gy.
Describing the data on leukemia risk it would be useful to mention the manuscript by Gillies M., Haylock R., Hunter N., Zhang W. Risk of Leukemia Associated with Protracted Low-Dose Radiation Exposure: Updated Results from the National Registry for Radiation Workers Study. Radiation Research. 2019. Vol. 192(5), P. 527-537. doi: 10.1667/RR15358.1, that states the following:
… internal dose assessments are not currently routinely available for the cohort; however, supplementary analyses found no evidence of a difference in ERR estimates between workers monitored and not monitored for internal exposures (P = 0.28). This finding tallies with the expectation that internal doses will generally be low in this cohort and suggests that the confounding effect of internal exposures may not be large for leukemia end points.
The declared objective of the document was to discuss “how results presented relate to the assumptions currently used for protection against alpha radiation” (lines 8-9). However, no comparison with the existing limits and standards were presented in the text.
There is a mistake in Table 2.2: in the study by Labutina (2013) ERR/Gy for males was estimated as 7.1 (95% CI: 4.5; 10.9).
For consistency purposes it is desirable to adjust all the numerical values indicated in the tables – dose values, risk assessments – to a common form, for example, with one figure after a decimal point.
It seems relevant to rubricate Future Plans as a separate point in Executive Summary, as well as in the document itself. Further study regarding dose estimates in various parts of the lung seems to be essential as the goals of future dosimetric studies, along with studying the uncertainty of dose estimates, the kinetics of plutonium in various tissues and organs in the course of inhalation of various chemical forms. Further study of simultaneous effect of smoking and radiation exposure to lung cancer as well as continued study of cancer effects in organs and tissues that are not the organs of main plutonium deposition seem to be essential for epidemiological research purposes.