1. 8/15/2015 Linear Non-Threshold p. 1 of 15 Illinois Institute of Technology Physics 561 Radiation Biophysics Lecture 13: The Linear Non-threshold Hypothesis 15 July 2014 Andrew Howard

2. 8/15/2015 Linear Non-Threshold p. 2 of 15 Lecture 16 Plans u The LNT hypothesis – What it says – Evidence for it – Evidence against it – Scientific Consequences of it – Regulatory Consequences u What do we do with it?

3. 8/15/2015 Linear Non-Threshold p. 3 of 15 Linear non-threshold hypothesis u Asserts that the population dose-response to a toxicant at low doses is linear from the origin up to the lowest value for which reliable data can be derived u On the causal side, this hypothesis can be applied to chemical toxicants as well as ionizing radiation u On the effect side, this is usually applied to cancer risk but it can apply to other (usually chronic) conditions

4. Dose-response curves: LNT hypothesis 8/15/2015 Linear Non-Threshold p. 4 of 15 Risk Average dose to population, mSv Experimental or Epidemiological Data Risk with No Exposure LNT

5. Dose-Response Curves: Weak-Form Hormesis 8/15/2015 Linear Non-Threshold p. 5 of 15 Risk Average dose to population, mSv Experimental or Epidemiological Data Risk with No Exposure LNT Hormesis: Weak Form

6. Dose-Response Curves: Strong-Form Hormesis 8/15/2015 Linear Non-Threshold p. 6 of 15 Risk Average dose to population, mSv Experimental or Epidemiological Data Risk with No Exposure LNT Hormesis: Weak Form Hormesis: Strong Form

7. Is this a new idea? u Of course not… u It underlies much of the regulatory machinery in this country and elsewhere for ionizing radiation and other risks u Goes back to before WWII u In recent years it’s been called into question 8/15/2015 Linear Non-Threshold p. 7 of 15

8. American Nuclear Society 2001 report u Emphasizes lack of evidence for any deleterious effects of ionizing radiation below 1 Sv u Brings forward numerous studies that suggest beneficial effects at low doses and harm from artificial lowering of background u Authors assert that LNT is unlikely for cancer given cancer’s multi-step, complex causality u Numerous references 8/15/2015 Linear Non-Threshold p. 8 of 15

9. ICRP Publication 99: a 2005 report u Committee includes many researchers whose work we have cited in this course: Little, Kellerer, Ullrich u Considers epidemiological, mechanistic, and animal studies u Explicitly takes error analysis into account u Concludes that there is no universal threshold but is willing to concede that there might be thresholds for cancers of specific tissues, maybe all of them 8/15/2015 Linear Non-Threshold p. 9 of 15

10. The ALARA concept u Advocated by ICRP itself as well as by NRC, DOE u As low as reasonably achievable: u But who decides what is reasonable u WNS points out that one should take economic and social factors into account u Is that what really happens, though? 8/15/2015 Linear Non-Threshold p. 10 of 15

11. Rutherford’s discussion u A patient pedagogical approach u Already organized into a PDF that is PowerPoint-like, so I will simply show it to you directly 8/15/2015 Linear Non-Threshold p. 11 of 15

12. World Nuclear Society 2013 report u This is a trade organization, not a governmental body u Report looks at risks associated with radiation in the context of other risks u Specifically examines Fukushima and argues that the aggressive measures taken to protect the public from radiation at Fukushima caused considerable suffering (physical and psychic) and several deaths u Discusses Chernobyl and suggests that most of the health effects arose from fear and dislocation 8/15/2015 Linear Non-Threshold p. 12 of 15

13. Regulatory consequences of LNT u Clearly the prospect of a threshold would relax the exposure limits, i.e. they’d be higher than they are now u As it is: – Nuclear power plants have difficulties operating – Researchers have to jump through hoops to use radionuclides or X-ray generators – Hospitals have to keep extremely careful records of the nuclides they use and the X-ray sources they employ u Clearly there are costs associated with this! 8/15/2015 Linear Non-Threshold p. 13 of 15

14. Acceptable Risk: LNT 8/15/2015 Linear Non-Threshold p. 14 of 15 Average dose to population, mSv Experimental or Epidemiological Data LNT Risk with No Exposure Acceptable Risk LNT-based dose limit

15. Acceptable Risk: LNT vs Hormetic Models 8/15/2015 Linear Non-Threshold p. 15 of 15 Average dose to population, mSv Experimental or Epidemiological Data LNT Risk with No Exposure Acceptable Risk LNT-based dose limit Hormesis-based dose limit