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

[Scott, Bobby]

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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