[ RadSafe ] When Radiation Isn’t the Real Risk
jjshonka at shonka.com
jjshonka at shonka.com
Wed Sep 23 15:09:19 CDT 2015
Mohan Doss said: “In summary, I would suggest dividing radiation use into two categories. One where the workers/public would likely be exposed to low doses only and there is no or little chance of exposure to high doses. For such use of radiation, there should be no regulation. Of course no ALARA. For radiation uses that have a potential for high radiation doses, the current regulations should be applied, so that no one is exposed to high radiation doses.”
While I agree with that statement, if you have a non-linear model, all sources of exposure become critical. How you implement what Mohan suggests is the issue that I am having trouble understanding.
So, how do you regulate non-LNT? For 80% of the people, as Mohan said, if the limit is high enough, there is no need for limits, regulations or ALARA with non-LNT. Most of the push for reconsideration of LNT is from people who believe we don’t need limits. How do we know who the 80% are? Does everyone still get dosimetry and HP? and what about the 20% who might have a problem? Do we have to track everyone to find the critical ones who are in the 20% “outliers”?
For example, an aircrew member who routinely gets 6 mSv per year from galactic cosmic radiation, but last year had medical problems and needed 50 mSv of diagnostic tests from a nuclear stress test using thallium (rather than technicium) that is required by the FAA for certain stress test results as a condition to continue working. He may have also undergone cardiac catheterization. He also had a few CAT scans because he used to be a fighter pilot and has medical issues in his back from performing high G maneuvers for the airforce (beyond the aircrew dose he also got in the Air Force from flying). Maybe he also got 100 mSv from a terrestrial gamma flash three years ago while working for a different airline. Maybe he had thyroid cancer a few years ago and had a thyroidectomy using radioactive iodine. He gets AML, with a greater than 50% POC. At some point, the last dose (or last few doses) pushed him up into the positive dose response region of the curve. Prior to the threshold, there wasn’t an issue. After you reach the threshold, the curve is even steeper, so the risk per rem is higher than a LNT model. Whose dose is responsible for the cancer? The last dose that pushed you into the positive response region? How do you determine when you are getting close? Does the employer have to keep track of background, medical and historical exposures, including past employers, in order to decide whether to limit this employee’s exposure or not? And who (which dose) do you have pay workman’s compensation and the medical costs of the cancer treatment? Do we have to track all 300,000 aircrew to find this guy, even if many, or even most of other aircrew are not an issue? We can’t simply pay off all AML cases for aircrew because most AML cases are not radiogenic.
It may be that more HPs will be required to design and implement radiation protection for a non-linear model. If we have to capture other sources of exposure, including medical, background, etc. the effort may exceed the LNT world we live in.
Joseph J. Shonka, Ph.D.
Shonka Research Associates, Inc.
119 Ridgemore Circle
Toccoa, GA 30577
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