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18 Comments

    1. This study doesn’t negate LNT, it supports LNT. In LNT, we apply the Dose and Dose Rate Effectiveness Factor (DDREF) because we’ve long observed that DNA repair mechanisms work better at low doses & with fractionated dose rates. We have continually revised the DDREF based on new data, and this will happen into the future.

      In order for there to be a threshold, one of two things has to happen (or both): radiation has to cause cell death 100% of the time or DNA repair has to be error-free 100% of the time. Otherwise, there will be a threshold-less risk of cancer, with linear or linear-quadratic or something similar dose response curves.

      The study doesn’t provide evidence of either of these constraints. The images provide great evidence in support of DDREF.

      1. But doesn’t this suggest that even if there isn’t a literal threshold, that the function would be an asymptotic curvie? That is, that after a certain point, it gets really close to zero and is really flat?

        At that point, if you could find a point on the dose curve where you would expect to, say, get one additional cancer in a population size which is greater than the population of earth, can’t we say it is *effectively* zero, and there is a practical “threshold”?

        1. You are almost describing a linear quadratic shaped curve. That is the appropriate curve for leukemia and we could use that curve for solid tumors. There is no statistical difference between LNT & LQ for solid tumors. However, the curve is probably not as flat and close to zero as you’re describing. See Figure ES-1 in BEIR VII.

          With LNT or LQ we can say the risk is “close to zero” depending on the dose. The approximate risk increase from 10 mrem is .001%. To some people that’s close to zero. It just depends on what one means by “close to zero”. But with billions of people on Earth, the current risk estimates would have to go way down.

          Note that there are super-linear dose response effects at play as well, which moderate supra-linear dose response effects. This study is just focused on one of many supra-linear phenomenon.

          1. IMHO – 0.001% is close enough to zero to ignore.

            You cannot convince me to worry just because you can multiply that number by a very large number to obtain something that sounds significant.

        2. So in other words LNT will never be wrong regardless. If evidence shows otherwise adjust the DDREF accordingly and insist that there needs be a hard bright line for a threshold to be deemed to exist. Never mind that this sort of thing is very rare in biological systems, LNT must be preserved at all costs.

        3. Bob, we know that LNT is a misnomer because in fact the function is linear quadratic, not linear. The assumption, which you repeat, is that the quadratic term is relatively insignificant to the extent that it is indistinguishable from a linear function.

          But the conclusion at the very end of the new paper is that the quadratic term is a lot more significant than expected.

          http://www.pnas.org/content/early/2011/12/16/1117849108.full.pdf+html

          “However, the amount of DSB clustering at 1 Gy suggests a much higher quadratic term for DSB misrejoining than expected. Therefore, extrapolating risk linearly from high dose as done with the LNT could lead to overestimation of cancer risk at low doses.”

          That is why the research is significant.

        4. @ Rod

          You are talking about collective dose here, and ICRP have specifically stated that it cannot and should not be used for estimating health effects from tiny individual doses in a large population.

      2. DDREF doesn’t support LNT. It supports the myth of no-threshold, but at the cost of discarding the linear-from-high-dose concept. It means that the model result has much less experimental justification than before, as it is now “linear” with no high-dose results at all.

        LNT/DDREF is a meaningless bodge of a model.

  1. I’ve pored over the Lawrence Berkeley study which was posted by the NAS with the trained eye of an old HP. I’ll add a few details to your above summation. First, when one drops exposure from 2 sieverts (the approximate lethal threshold for short term exposures)to 150 millisieverts, the DNA repair function actually increases by a factor of 20. They call the DNA repair function “Resistance Inducing Foci (factor)”, or RIF. It seems the DNA repair process in the living cell works best when it is not overwhelmed by a very high rate of damage. The “no-safe-level” (Linear/No Threshold hypothesis) concept’s supporting research has not allowed enough time for low dose radiation DNA repair to run to its conclusion. What’s worse, previous studies supporting LNT looked at RIF sporadically at precise intervals after exposure and missed the continuous process of DNA repair itself. RIF begins immediately upon then onset of DNA damage, and it seems that the rate of repair goes down with time because there are fewer and fewer DNA strands to repair with each passing moment. By observing the process continually, from beginning to end, the research team came across this paradigm-shattering discovery. CNN, AP, Fox News, and all the other major Press outlets should tell the world the good news…but they won’t because it might diminish radiophobic anxiety in the public and make nuclear energy a “less-newsworthy” topic.

  2. Rod Adams wrote:
    As long as people keep their short term doses below the levels at which their naturally evolved repair mechanisms are not overwhelmed, they should have no fear of radiation-caused cancers sometime in the distant future. That would be exceptionally good news for us all – except, of course, for those people who make their living by maintaining the fiction that our economy will be almost completely dependent upon hydrocarbon fuels for the foreseeable future.

    But burning fossil fuels releases radioactive substances into the open environment. During normal operation, nuclear power plants release less than coal-fired plants per unit of energy produced. It makes me wonder if all the accidental releases to date were also added in, would the total releases to the open environment still be lower than those from fossil fuels? I would not be surprised if the answer is ‘yes’.

    If this is so, then we have a case of the pot calling the kettle black. But the fossil fuel pot has had a lot more money to spend in its campaign against the nuclear kettle.

    1. @donb – perhaps I was being too subtle. The reason it would be bad news for people with financial ties to the fossil fuel industry is that a nuclear industry that is unshackled from excessive fears of radiation would be impossible for them to beat in the market. They would lose nearly every competitive battle that does not involve personal transportation or aviation.

      The power and money shift would be rather impressive – or depressing, depending on which side you are on – energy consumer or energy producer .

  3. That’s some really interesting study, and definitelly something to pay attention at. But then there are all those other studies just saying the opposite thing, for example all the data compiled in this youtube video:

    http://www.youtube.com/watch?v=ywKv0dj3UuY

    There are many serious studies and academys cited there: National Academy of Sciences Low-Dose Radiation Report, and studies such the “15-country study of nuclear-worker cancer risk”, all of them unveiling that even the LNTM used by ICRP is underestimating the real risk.
    Really I don’t know what to think, and I’d appreciate some light there. Thanks.

    1. The use of hypothetical syllogism in science is worthy of the Descartes era when one was trying to establish the existence of God through a trifecta of unrelated and orthogonal statements.

      This is not serious.

    2. Oh … I love how they refer to Jacob, et al. What an awful paper!

      My wife brought that paper to my attention when it was first published two years ago. I thought that it stunk then, and I think that it stinks now.

      For their “epi” evidence, they start with a dozen or so studies, of varying quality and conducted by numerous teams of researchers, who have corrected for who-knows-what confounding factors (or more importantly, have not corrected for them). They lump them together using a special formula to get an estimate of what the DDREF should be.

      Unfortunately for them, the error bars on their results are so large that nothing can be concluded with any certainty. So they reduce the error bars from the 95% that is the standard in this field to only 90%, which allows them to claim a (marginally) statistically significant result when compared to the larger value of DDREF=2 used by ICRP. BEIR VII’s DDREF value of 1.5 is clearly within the error bars.

      This is the evidence that they present to argue that the DDREF (which is used to account for the observation that low-dose and low-dose-rate exposures pose less risk per unit of exposure than accuse doses) is no longer needed. It’s a very weak argument, which is why it hasn’t received much attention outside of bad YouTube videos.

  4. I think there is an analogy with mechanical damage. Small cuts and bruises can be repaired completely by the body, and are not a risk to health.

    But if you fall into a threshing machine or step on a land mine, the machanical damage overwhelms the repair system, and you are left dead or maimed.

    If a linear dosage rule were applied to mechanical injury, all knives and hammers would be banned and heavily padded overalls would be compulsory at all times.

  5. Everyone knows the Linear no-threshold model is not applicable to real life, low dose exposure. The numbers have been saying so for years. The only uncertainty is by those that don’t want to believe them.

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