[ RadSafe ] More LNT-based phantom cancer risks related to Fukushima

[Miller, Mark L]

Dear All,

Comments below relate to LNT-hypothesis-based phantom thyroid cancer risks in the recent paper: Jacob P, Kaiser JC, and Ulanovsky A. Ultrasonography survey and thyroid cancer in the Fukushima Prefecture.  Radiat Environ Biophys DOI 10.1007/s00411-013-0508-3, published online 09 January 2014.

The researchers assessed the expected thyroid cancer prevalence in the Fukushima Prefecture ultrasonography group based on an ultrasonography survey of Ukrainians (i.e., cross-population extrapolation) who were initially exposed to Chernobyl released I-131 at an age up to 18 years. By using a fudge-factor approach (e.g., screening factor), difference in equipment and ultrasonography study protocol differences were supposedly adjusted for.

Based on findings, the researchers expect that the ultrasonography survey of residents of Fukushima Prefecture will lead to a dramatic increase in the measured thyroid cancer incidence (mainly non-radiogenic) when compared to the incidence recorded in 2007.

Thyroid cancer attributed to radiation exposure was assessed using an LNT risk model where in order to obtain the excess absolute risk rate per unit dose, the excess relative risk per unit dose (evaluated based on A-bomb survivor data and related follow-up-time- and gender-dependent model) was multiplied by the population-specific average baseline incidence rate. Because the baseline thyroid cancer incidence rate for males was less than 0.000001 per year for those younger than 15 years, no radiogenic cases would be expected among males during the first 15 years after radiation exposure as infants.  Because of this (called an error), the authors then modified the LNT model employed to allow for a weighted average baseline term that allows for earlier occurrence of thyroid cancer cases when exposed as infants.

For an average thyroid dose of 20 mSv for the most exposed in the surveyed Japanese population, the researchers estimate that in the early time period about 10 percent and in the late time period about 5 percent of the reported thyroid cancer incidence will be attributed to radiation exposure related to Fukushima. However, this is just another example of LNT-based phantom cancer risks from low radiation doses (much lower than for Chernobyl victims that developed presumed radiogenic thyroid cancer).

The authors point out that the present assessment includes large uncertainties caused by uncertainties in the thyroid cancer risk function (LNT type) for the a-bomb survivor Life Span Study, the impact of the ultrasonography survey, and the transfer of risk from a-bomb survivors to the Fukushima Prefecture group.

A very important uncertainty, model uncertainty, was not considered by the authors. This relates to uncertainty about what is the appropriate risk model to apply to thyroid cancer induction by very low doses of low-LET radiation delivered at low rates.  Threshold and hormetic models also need to be considered (Sasaki et al.  2013) and would lead to very different conclusions about radiogenic cancer among persons exposed to radiation from the Fukushima accident. With these models, possibly, no radiogenic thyroid cancers would be expected when the average dose to the thyroid is 20 mSv (20 mGy low-LET radiation) or even somewhat higher for the most heavily exposed group. Another important uncertainty that was also neglected (as pointed out by Ludwik Dobrzynski) is uncertainty about the occult thyroid cancer rate.

Best wishes,
Bobby
B. R. Scott
Lovelace Respiratory Research Institute
Albuquerque, NM, USA
Member: Scientists for Accurate Radiation Information (SARI), www.radiationeffects.org<http://www.radiationeffects.org/>

Sasaki MS, et al. Cancer risk at low doses of ionizing radiation: artificial neural networks inference from atomic bomb survivors. Journal of Radiation Research, 2013, pp 1-16, doi: 10.1093/jrr/rrt133. [This new paper shows evidence for threshold and hormetic dose-response relationships for cancers among a-bomb survivor data as well as evidence for significant neglected internal radiation dose from fission products for the indicated population]







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