[ RadSafe ] Hypothetical post-LNT Rad Limits and Regs
Mohan.Doss at fccc.edu
Mon Sep 28 12:40:10 CDT 2015
The A-bomb survivor data (generally accepted to be the most important data for estimating radiation effects) do not show increased cancer risk for doses greater than 100 mSv, contradicting your statement that 100 mSv is the threshold dose accepted by many. Their published data (Ozasa et al., 2012) is faulty because they used the invalid LNT model as an integral part of the analysis to extract the Excess Relative Risks (ERRs). An indication why their analysis based on the LNT model is wrong is the curvature in dose response, i.e., when the dose increases from ~0.2 Gy to ~0.5 Gy, ERRs go down rather than up, violating the LNT model which they assumed in the analysis. If we apply a correction for the likely negative bias in their low dose data due to hormesis, the corrected ERR has a hormetic J-shaped dose response with a threshold dose of ~800 mGy. (This view, that the A-bomb survivor data do not support the LNT model any longer, is being accepted explicitly and implicitly by many other scientists, who used to quote these data to raise concerns about low dose radiation.) Based on 800 mGy threshold dose, applying safety factors and accounting for uncertainties, I have suggested a dose guidance value of 100 mGy for acute exposures. This would be in the hormetic zone and so no dose limit is required at this value but only guidance not to exceed this value significantly (e.g. by a factor of 2) to ensure safety. You can see the discussion of this in my presentation on the Future of Radiation Protection Regulations available at: https://goo.gl/gw4xAG . We have already harmed the public by low dose limits that have prevented the use of low-dose radiation to prevent cancer. A brief report available at https://goo.gl/rPghvr shows how the regulations which have claimed to protect the public have likely harmed them by increasing cancers.
The data in the above report show a significant reduction of cancers at low doses. Genetic differences would result in a (e.g.) Gaussian distribution for the reduction in cancers centered at the mean. It is quite a stretch of imagination to say some will have a significant positive increase in risk at low doses due to genetic variations, when the mean shows significant reduction of cancers. If you have any evidence for such increased risk at low doses, please state it. Otherwise it would be pure speculation.
To say we don’t know the effects of low-dose radiation after decades of intense study disregards all the work that has been done so far. Though there are many studies that have claimed increased risk of cancer following low-dose radiation, invariably there are major flaws in such studies (that get identified later) making the claims not credible. Once we dismiss such publications, the definitive conclusion is that low-dose radiation reduces cancers. So we do know the effects of low-dose radiation.
You expressed concerns about error-free repairs from low-dose radiation induced stochastic damage. There is much more damage happening in the cells from natural processes, and the enhanced defenses due to low-dose radiation would reduce the natural damage, resulting in reduced overall damage and improved health. So there is indeed a definitive deterministic improved health following low-dose radiation exposure.
To involve the public in discussions on this subject, the first step we need to take is to give them the correct information. ICRP, etc. have failed to do this. If we inform the public about the observed health effects of low-dose radiation, that they are beneficial, there would be no more concerns regarding low radiation exposures. If we keep stating wrongly that the risks are too low to be worried about, or that we do not know the effects of low dose radiation or that there is acceptable risk from low radiation exposures, people would be quite concerned.
With best regards,
Mohan Doss, Ph.D., MCCPM
Associate Professor, Diagnostic Imaging,
Fox Chase Cancer Center,
333 Cottman Avenue,
Philadelphia, PA 19111-2497.
Phone: 215 214-1707
From: radsafe-bounces at agni.phys.iit.edu [mailto:radsafe-bounces at agni.phys.iit.edu] On Behalf Of parthasarathy k s
Sent: Sunday, September 27, 2015 1:01 AM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] Hypothetical post-LNT Rad Limits and Regs
Hunting for a threshold dose was never successful so far.You may recall that The French Academy which raised formal objection to the scientific validity of LNT conceded that it could not get evidence for any threshold. Additionally, if there is a threshold dose it is likely to be different for different individuals.There is still unsettled debate on the lowest dose which causes cancer. Most critics accept a value of 100 mSv single short term dose. Now the question is what should be the safety factor taken.There may also be some agreement that the safety factor can be more for members of the public which includes sensitive and vulnerable sections such as pregnant women, infants and children. we have accepted a safety factor of 5 for occupational workers; ICRP accepted 100 mSv in consecutive 5 years with occasionally 50 mSv/year.Whether we have to accept one mSv or 5 mSv for public is an equally important debate depending on how conservative we have to go.In all this arguments we seldom indicate to members of the public that there is judgement exercised by scholarly bodies such as the ICRP and NCRP.
Most important factor in these arguments is how to carry all stakeholders in the process of decision making. A few years ago, ICRP realized it.The fact that the members of the public need not necessarily accept the decisions of a dozen specialists however highly regarded was probably an eye opener. The publication of ICRP recommendations on its website, gathering views of all stake-holders, discussing them threadbare were all part of the democratization process.
The perception that everyone on either side of the aisle has an agenda is influencing impartial observers. Rather than naively assuming that public will not understand complex arguments, specialists must develop the tools for effective communication WE must not deny the public a chance to participate in decision making; may be specialists have not yet developed such tools. Let us grudgingly accept that the true nature of interaction of low doses of radiation with living tissue is not exactly known. So long as interactions at low dose levels are statistical in nature, it will be very difficult to accept error free repairs of the micro damages of tissue at molecular level.A totally maverick approach to the issues is not likely to be acceptable.At the present level of knowledge, it will be foolhardy to believe that deterministic answers must be obtained for purely probabilistic questions.The way forward is to accept and publicize the fact that the risks, if any, at low levels of radiation are too low to be worried about.
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