[ RadSafe ] LNT and the WHO guidance on red meat
PHILIP.KARAM at nypd.org
Sun Nov 1 00:29:13 CDT 2015
I guess there's something else to consider, then, when we talk about medical radiation - the benefit (and risk reduction) from the medical exposure. Taking your example of an x-ray to avoid exploratory surgery, I think it would be very reasonable to compare the risk from undergoing surgery to the risk from receiving an x-ray or CT scan. Similarly, I'm guessing we could also compare the risks of, say, chemotherapy-only instead of chemo + radiation therapy versus the risk to one's health from the scattered radiation (or, in the case of I-131 therapy, risk to non-thyroid tissues from the I-131 uptake). In the case of diagnostic and interventional radiology my guess is that, when properly used, the risk of NOT having the diagnostic information exceeds the risk from the procedure - in the case of therapeutic radiation I suspect you'd have to look at the time post-irradiation to have a good understanding of the overall radiological risk.
But we should also remember that many medical conditions can kill you in minutes, hours, or days while radiation-induced cancer shows up years to decades later. Even if a diagnostic procedure eventually gives me cancer, I'd still consider it a net reduction in risk if it made it possible for me to survive those extra years or decades.
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of jjshonka at shonka.com
Sent: Wednesday, October 28, 2015 9:14 PM
To: The International Radiation Protection (Health Physics) Mailing List
Subject: Re: [ RadSafe ] LNT and the WHO guidance on red meat
I appreciate the humor, but my question was serious.
The EPA sets guidelines for all federal agencies, including the NRC. EPA published Guidelines for Carcinogen Risk Assessment in 2005 ( http://www2.epa.gov/risk/guidelines-carcinogen-risk-assessment ). I am trying to understand when regulators should use linear extrapolation from POD (point of departure, where you have data and uncertainty bounds) and when non-linear can be used. I think EPA makes a conservative assumption that carcinogens that directly affect DNA can cause cancer regardless of the dose. The non-linear approach (to extrapolation from known data to lower levels) is only used when the agent is non-mutagenic ( my reading of Section 3.3.1 of that report). For EPA, linearity is considered health protective.
As an aside, if one limits the consumption of farm raised fish for PCB concerns, and consumers substitute red meat as a protein source, cardiovascular disease (instead of cancer) from the red meat may cause more deaths than are saved by avoiding fish with PCBs. Thus, linearity might, at times, be non-protective. Hormesis aside, radiation does not seem to fall into that category since there would be no substitution if a source of radiation exposure is avoided. (use of surgery instead of x-ray imaging is not a realistic option).
There seems to be a complication for radiation. If EPA accepts that non-linearity has been observed for radiation, a reference dose based on a threshold, a daily exposure that would not cause harm, might be established using the 2005 approach. That is what some are advocating. Unlike potential exposure pathways such as airborne contamination of carcinogens, radiation has many exposure pathways and it would be difficult to prevent a sum of exposures exceeding any reference dose.
If one assumes that a reference dose for radiation is 1 mSv/a, there are many sources whose sum exceed that reference dose. The sum (and variability) of three sources alone: natural background at ground level, medical exposure, exposure from flight, (as well as what seems to be trivial exposures from most licensed uses of radiation such as nuclear power) can easily exceed 10 mSv/a for some individuals (not the average). How does one control that sum and which element contributing to the sum has to be subject to further controls? In my view, a reference dose of at least 100 mSv would be needed to avoid conflict between various low level contributors to exposure, but that value (100 mSv) is unlikely to be accepted. Or is the reference dose only applied to the average exposure, with outlier individuals not provided that protection?
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