Antinuclear

Australian news, and some related international items

Low dose radiation and cancer – the Linear No Threshold model holds good

The public, legislators, and journalists are often at a loss to deal with the charges and counter charges that surface in the debate over low-level radiation exposures. It does not help to listen to industry leaders, nuclear activists, or individual researchers, who, one after another, propound their competing images of the underlying truth.

It is now reasonably clear that protracted exposure does not protect against radiation-induced cancer. Rather, it is the cumulative radiation exposure from all sources that must be examined. 

There is no longer a convenient excuse to avoid using the LNT to estimate consequences from real or projected releases of radioactive materials, even when the dose of concern is below 0.1 Sv. 

The scientific jigsaw puzzle: Fitting the pieces of the low-level radiation debate http://bos.sagepub.com/content/68/3/13.full Bulletin of the Atomic Scientists,  May/June 2012, Jan Beyea   “…..One of the biggest paradoxes in the low-level radiation debate is that an individual risk can be a minor concern, while the societal risk—the total delayed cancers in an exposed population—can be of major concern…..

Deconstructing the debate The debate over radiation risks has many tentacles that extend into the fields of biology, epidemiology, medicine, sociology, and political science. The biggest tentacle penetrates directly into the political sphere, wrapping itself around arguments on energy policy and the consequences of radioactive releases like those at Chernobyl and the Fukushima Daiichi Nuclear Power Station….

analysis of the atomic-bomb dose data presents a clear picture that a linear no-threshold (LNT) model—the theory that
radiation risk declines in proportion to dose, but never goes to zero—holds for a large range of survivor doses (see Figure 1).

Figure 1. Solid cancer-incidence dose response for atomic-bomb survivors.  Source: Preston et al. (2007). This figure is reproduced with permission from the Radiation Research Society.

The horizontal access on the chart refers to colon dose, which is taken as a surrogate for the tissue dose to all organs; this may differ slightly. Each small tick mark corresponds to 0.2 Gy; half of this is what is considered to be low-dose radiation today. The vertical axis has units of excess relative risk (ERR) that have been found to fit radiation data better than absolute risk models.6 It is important to note that this figure illustrates a dose response for an entire population.

http://bos.sagepub.com/content/68/3/13/F1.expansion.html

…..The LNT theory predicts that background radiation exposure and medical diagnostic exposures slightly increase a population’s future cancer rates. The cancers don’t appear immediately but are diagnosed five years to more than 50 years after exposure. Delayed cancers are the usual focus of the low-level radiation debate, but delayed stroke and
heart disease account for “about one third as many radiation-associated excess deaths as do cancers among atomic bomb survivors” (Shimizu et al., 2010).

Protracted exposures above the dividing line
……..15-country nuclear worker data
It all started when epidemiologist Elaine Cardis and 46 colleagues
surveyed some 400,000 nuclear workers from 15 countries in North
America, Europe, and Asia—workers who had experienced chronic
exposures, with doses measured on radiation badges (Cardis et al.,
2005). The prediction of total excess cancers for these nuclear
workers was striking: Cancer deaths in this population increased by 1
to 2 percent, making past nuclear work a rather dangerous industrial
occupation relative to others. …… This study revealed a higher
incidence for protracted exposure than found in the atomic-bomb data,
representing a dramatic contradiction to expectations based on expert
opinion. Further, this challenged the relevance of cell dose-rate
experiments to human epidemiology….
UK radiation workers
A second major occupational study appeared a few years later,
delivering another blow to the theory that protracted doses were not
so bad. This 2009 report looked at 175,000 radiation workers in the
United Kingdom, and was an update to earlier reports of the same data
set. Sufficient diseases had appeared since the previous assessment,
making the cancer risk statistically significant and the same as in
the atomic-bomb data. Again, protracted exposures did not turn out to
be less dangerous than acute exposures.
12 worker studies combined
After the UK update was published, scientists combined results from 12
post-2002 occupational studies, including the two mentioned above,
concluding that protracted radiation was 20 percent more effective in
increasing cancer rates than acute exposures (Jacob et al., 2009). The
study’s authors saw this result as a challenge to the cancer-risk
values currently assumed for occupational radiation exposures. That
is, they wrote that the radiation risk values used for workers should
be increased over the atomic-bomb-derived values, not lowered by a
factor of two or more.
If history is any guide, it is questionable that this analysis and the
results of other studies will lead to actual changes in what defines
worker-exposure limits. Industry pushback is very strong….

Hormesis theory
Though it still is a pet topic of enterprising journalists, the
radiation hormesis theory is no longer of much interest to
researchers. The BEIR VII report, published in 2006, discounted the
concept;…. Given the increase in radiation from medical diagnostics
and the interest in protracted exposure, the possible existence of a
threshold or hormetic effect for public policy appears to be a moot
issue for developed countries when it comes to future exposures. Even
if the level of medical diagnostic exposures does not increase in the
future, over the course of 40 years most people in developed countries
will receive an average of 0.1 Sv from medical procedures, alone. With
this in mind as a dose starting point for millions of people, it is
fair to say that any exposure to radioactive elements from a nuclear
accident or a dirty bomb would definitely contribute to their delayed
cancer risk…..

The public, legislators, and journalists are often at a loss to deal with the charges and counter charges that surface in the debate over low-level radiation exposures. It does not help to listen to industry leaders, nuclear activists, or individual researchers, who, one after another, propound their competing images of the underlying truth.

Given the complexities, the only alternative for most people is to rely on scientific committees, like the BEIR committee and UNSCEAR, recognizing that the scientific jigsaw puzzle is incomplete. Not all pieces fit correctly, but a reasonable idea of the true situation emerges from the recognizable image visible from the pieces already assembled.

It is now reasonably clear that protracted exposure does not protect against radiation-induced cancer. Rather, it is the cumulative radiation exposure from all sources that must be examined. In developed countries, the average accumulated dose from medical procedures is now so high that a significant percentage of the
population in these countries will be above 0.1 Sv.

Therefore, this population will be primed for radiation-induced, delayed cancers from releases from nuclear reactors or dirty bombs, even using the hypothetical dose-response models of the LNT dissenters. There is no longer a convenient excuse to avoid using the LNT to estimate consequences from real or projected releases of radioactive materials,
even when the dose of concern is below 0.1 Sv.  http://bos.sagepub.com/content/68/3/13.full

October 11, 2021 - Posted by | Uncategorized

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