(Key words: radiation, cancer, doses, ionizing radiation, risk)

 

AMERICAN  JOURNAL OF PHYSICS

 

Resource Letter EIRLD-2:
 Effects of Ionizing Radiation at Low Doses

 [DOI: 10.1119/1.3661997] Am. J. Phys. 80(1); 2011.
 (Received 2 September 2011; accepted 27 October 2011)

Richard Wilson

Harvard University, Cambridge, MA 02138


(Updated on November 14th 2011)


 

This Resource Letter provides a guide to the literature on the effects of ionizing radiation on people at low doses. Journal articles, books and web pages are provided for the following: data at high dose levels, effects of moderate to high doses, (leukemia, solid cancer, lung cancer, childhood cancer and non‑cancer outcomes), effects of dose rate, relationship to background, supra linearity and hormesis, and policy implications.


 

Introduction

 

That ionizing radiation can have serious adverse effects on people was obvious to the first experimenters 110 years ago. The primary use of radiation was in the medical profession. The advantages of using an X ray for diagnosis is so great that it outweighed the disadvantages. It took 50 years for the medical profession to realize that the disadvantages could be dramatically reduced (100 fold) by careful measurement and wise use of technology. This was the province of the new discipline of medical physics including radiation protection. There exist data on effects of high levels of radiation from excessive medical exposures, unwise use of radiation in treatment, and since 1945 in the effects of the atomic bombs at Hiroshima and Nagasaki and the effects of nuclear power accidents at Three Mile Island, Chernobyl and Fukushima. This Resource Letter will mostly address what we can discern from direct epidemiological measurements upon people. There are a large number of references to data on the effects of radiation at high doses. These are mostly in books and compilations (refs. 1‑37).


 

I.  Journals are listed in the following order. General journals, Cancer and Environment journals, and Radiation specific journals. Many of the most important results are published in the general journals, but detail is usually found in the radiation‑specific journals:

 

General

 

Nature

Lancet

Science

American Journal of Epidemiology

Journal of the American Medical Association

British Medical Journal

 

Cancer and Environment

 

Cancer Research

New England Journal of Medicine

Science of the Total Environment

Journal of the National Cancer Institute

Journal of Radioanalytical and Nuclear Chemistry

 

Radiation Specific journals

 

Applied Radiation and Isotopes

Health Physics

International Journal of Radiation Biology

Journal of Environmental Radioactivity

Radiation and Risk (from Obninsk, Russia)

 

Radiation Protection

 

Radiation and Environmental Biophysics

Radiation Research



 

II.  Books and Major Compilations

 

Of the six books listed, the first is intended for physicians. Nonetheless, there is a lot of physics therein, and all can be read by physicists with great profit. The second is the classic text and the third a more recent text on radiation protection.

 

1. Medical Effects of Ionizing Radiation, edited by F.A.Mettler and A. C. Upton, 3nd edition. (W.B. Saunders, Philadelphia, 2008). (I)

2. Principles of Radiation Protection, K.Z. Morgan and J.E. Turner, (Wiley, New York, 1967). (E)

3. Radiation Protection: A Guide for Scientists and Physicians, J. Shapiro, 4th edition (Harvard University Press, Cambridge, MA, 2002). (E)

4. Radiation Carcinogenesis: Epidemiology and Biological Significance, J.D. Boice, Jr. and J.F. Fraumeni, Jr. (Raven Press, New York, NY, 1984). (I)

5. Health Effects of Low‑Level Radiation, S. Kondo. (Kinki University Press, Osaka, Japan, 1993). (E)

6. Health Effects of Exposure to Low‑Level Radiation, edited by W.R. Hendee and F.M. Edwards. (Institute of Physics Publishing, Bristol, UK, 1996). (E)

 

The reports of the United Nations Scientific Committee on the Effects of Atomic Radiation (abbreviated and pronounced UNSCEAR) are voluminous. They include reports on exposures from many countries and a summary of much of the scientific literature. Although in general the reader should look at the latest report first, they are not completely repetitive and earlier volumes contain some information not present in the later ones. In addition, a study of the changes helps the reader to follow the changes in scientific understanding.

 

7. Sources and Effects of Ionizing Radiation, Report of the United Nations Scientific Committee on the Effects of Atomic Radiation. United Nations, General Assembly Official Records: 13th Session, Suppl. 17 (A/3838), (UNSCEAR, 1958). (I)

8. Effects of Atomic Radiation, United Nations Scientific Committee on the Sources and Effects of Ionizing Radiation, Report E. 77. (UNSCEAR, 1977). (I)

9. Atomic Radiation Sources and Biological Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Ionizing Radiation, Report to the General Assembly, United Nations, New York. (UNSCEAR, 1982). (I)

10. Genetic and Somatic Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, with Annexes. United Nations, New York. (UNSCEAR, 1986). (I)

11. Sources, Effects, and Risks of Ionizing Radiation, United Nations Scientific Committee on the Effects of Ionizing Radiation, Report to the General Assembly, United Nations, New York. (UNSCEAR, 1988). (I)

12. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, including annexes, United Nations, New York. (UNSCEAR, 1993). (I)

13. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, with scientific annexes, United Nations Sales Publication E.94.1X.11, United Nations, New York. (UNSCEAR, 1994). (I)

14. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, with scientific annexes, United Nations Sales Publication E.08.IX.6, United Nations, New York. (UNSCEAR, 2006). (I)

15. Sources and Effects of Ionizing Radiation, United Nations Scientific Committee on the Effects of Atomic Radiation, Report to the General Assembly, with scientific annexes, United Nations Sales Publication E.10.XI.3, United Nations, New York. (UNSCEAR, 2008). (I)

 

The US National Academy of Sciences has a Committee on the Biological Effects of Ionizing Radiation (abbreviated and pronounced BEIR) that regularly surveys the literature on the effects of ionizing radiation. In contrast to the UNSCEAR reports, which are mainly a compilation of data, BEIR reports are judgmental.

 

16. The effects on populations of exposure to low levels of ionizing radiation, Report of the Advisory Committee on the Biological Effects of Ionizing Radiations (BEIR 1972) (National Academy Press, Washington, D.C., 1972). (I)

17. The effects on populations of exposure to low levels of ionizing radiation (BEIR III 1980) (National Academy Press, Washington, D.C., 1980). (I)

18. Health Risks of Radon and Other Internally Deposited Alpha Emitters (BEIR IV) (National Academy Press, Washington, D.C., 1988). (I)

19. Health Effects of Exposure to Low Levels of Ionizing Radiation (BEIR V, 1990) (National Academy Press, Washington, D.C., 1990). (I)

20. Health Effects of Exposure to Low Levels of Ionizing Radiation Health Effects of Exposure to Indoor Radon (BEIR VI, 1999) ( National Academy Press, Washington, D.C., 1999). (I)

21. Health Risks from Exposure to Low Levels of Ionizing Radiation (BEIR VII Phase2, 2006) (National Academy Press, Washington, D.C., 2006). (I)

 


The National Council of Radiological Protection and Measurements (NCRPM) has produced over 100 reports. Most are too detailed to be of general interest, but I list the following particularly useful ones here.

 

22. Influence of Dose and Its Distribution in Time on Dose‑Relationships for Low‑LET Radiation, National Council on Radiation Protection and Measurements, Report No. 64 (NCRPM, Bethesda, MD, 1980). (I)

23. Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States, National Council on Radiation Protection and Measurements, Report No. 78, (NCRPM, Bethesda, MD, 1984). (I)

24. Induction of Thyroid Cancer by Ionizing Radiation, National Council on Radiation Protection and Measurements, Report No. 80, (NCRPM, Bethesda, MD, 1985). (I)

25. Ionizing Radiation Exposure of the Population of the US, National Council on Radiation Protection and Measurements, Report No. 93 (NCRPM, Bethesda, MD, 1987). (E)

26. Exposure of the Population of the US and Canada from Natural Background Radiation, National Council on Radiation Protection and Measurements, Report 94 (NCRPM Bethesda, MD, 1987). (I)

27. Risk Estimates for Radiation Protection, National Council on Radiation Protection and Measurements, Report No. 115 (NCRPM), Bethesda, MD, 1994). (E)

28. Research Needs for Radiation Protection, National Council on Radiation Protection and Measurements, Report No. 117 (NCRPM, Bethesda, MD, 1993). (E)

29. Principles and Application of Collective Dose in Radiation Protection, National Council on Radiation Protection and Measurements, Report No. 121 (NCRPM, Bethesda, MD, 1995). (E)

30. Sources and Magnitude of Occupational and Public Exposures from Nuclear Medicine Procedures, National Council on Radiation Protection and Measurements, Report No. 124 (NCRPM, Bethesda, MD, 1996). (E)

31. Uncertainties in Fatal Cancer Risk Estimates Used in Radiation Protection, National Council on Radiation Protection and Measurements, Report No. 126 (NCRPM, Bethesda, MD, 1997). (E)

32. Management of Terrorist Events involving Radioactive Materials, National Council on Radiation Protection and Measurements, Report No. 138 (NCRPM, Bethesda, MD, 2001). (E)

 

International Commission on Radiological Protection (ICRP). Although no specific reports are referred to here, this commission, started in 1928, issues many reports.

 



III.  Conference Proceedings

 

The International Atomic Energy Agency, a UN agency set up to promote peaceful uses of nuclear energy, and more recently to monitor (and aid in controlling) military uses, regularly holds conferences and issues a number of reports. The conference on low doses of radiation is particularly important since it contains reports from a number of people with divergent views.

 

33. International Conference: One decade after Chernobyl: Summing up the consequences of the accident, International Atomic Energy Agency, Vienna (1996). (E)

34. International Conference: Low Doses of Ionizing Radiation: Biological Effects and Regulatory Control, International Atomic Energy Agency, Seville, Spain, IAEA‑TECDOC‑976, IAEA‑CN‑67/63, 223‑226 (1997). (I)

35. Chernobyl, 10 Years After: Health Consequences, Epidemiologic Reviews 19(2), (1997).(E)

36. Catalogue of studies on human health effects of the Chernobyl accident, 1995 update. In: WHO European Center for Environment and Health. Rome, Italy: World Health Organization (1995).(I)

37. Radiation Research: State of the Service Science Twenty Years after Chernobyl, American Statistical Association Conference on Radiation and Health, Radiation Research 167(3), 338-360 (2007).(A)

 

One crucial feature of the data is that radiation does not seem to cause any medical or biological effect that cannot also occur naturally. It merely increases the probability of the effect. This fact is very important both for understanding possible dose‑response curves and for deciding what if anything to do about radiation at low doses. It also leads us to ask a general question. Does radiation add an additional probability of developing cancer (an absolute-risk model) or does it multiply the probability that is there from natural or other causes (a relative-risk model). Although both are discussed in all the BEIR reports, it is noteworthy that the emphasis has changed from the absolute risk model in BEIR I (1970) to the relative risk model in BEIR III,   BEIR V and BEIR VII.

 



IV.  Websites

 

38. http://www.rerf.jp/index_e.html

Radiation Effect Research Foundation successor to the Atomic Bomb Casualty Committee (ABCC) with numerous reports.

39. http://www.iaea.or.at/  International Atomic Energy Agency.
40.
http://www.hpa.org.uk/Publications/Radiation/HPARPDSeriesReports/

Radiation Protection Division of the Health Protection Agency (HPARPI) is the successor to the National Radiological Protection Board (NPRB) in the UK.

41. http://www.elseveier.com/wps/find/homepage.cws_home

42. http://www.ncrponline.org/

These sites all have information on important reports and papers on radiation from RERF, IAEA, NRPB/HPARPD, ICRP and NCRPM respectively. Some of the more recent can be downloaded.

43.  http://www.new.ans.org/pi/resources/dosechart/

The American NuclearSociety maintains this interactive webpage so that anyone may estimate his or her integrated dose. The author's dose in the previous 12 months was 2.4 Rems (0.024 Sv) mainly due to medical exposures.

 



V.  What is the effect at moderate to high doses?

 

44. "Hazards of Ionising Radiation: 100 Years of Observations on Man," R. Doll, Br. J. Cancer 72, 1339‑1349 (1995). (E)

This very important review paper by the leading epidemiologist Sir Richard Doll discusses the effects that one might expect from general biological principles and the general status of the field. It is a good start to studying the subject. He asks several questions:

(1) Does radiation exposure lead to cancer?

(2) Does radiation exposure lead to heart disease?

(3) Does radiation exposure lead to other diseases?

(4) Does radiation exposure lead to genetic anomalies passed to following generations?

(5) Does radiation exposure lead to birth defects?

 

Most of the studies address only (1) cancer, and the data do indeed suggest that cancer induction is the dominant adverse effect of radiation. The data are better than for the other outcomes largely because the observed effects are greater. Several groups of radiation‑induced cancer can be distinguished with different characteristics.



A.  Leukemia

 

Although there have been studies of the effects of radiation on people for 100 years, the most important studies are the studies of the consequences of the Hiroshima and Nagasaki atomic bombs. This study of the survivors has involved many good scientists, and considerable effort and expense. The exposures occurred over 50 years ago, but an increase in cancers over that expected in the general population is still occurring. Therefore the most recent of these papers are the important ones to read. In addition, the radiation dose to which the population was exposed is uncertain. It was derived from measurements at other (similar) explosions, and for the neutron dose by measuring long‑lived radioactivity in the region.


45. "Studies of the Mortality of Atomic Bomb Survivors Report 12, Part I. Cancer:1950‑1990," D.A. Pierce, Y. Shimizu, D.L. Preston, M. Vaeth, K. Mabuchi, Radiation Research 146, 1‑27 (1996). (I)


Leukemia was the first cancer to be noticed in the atomic-bomb survivors. Leukemias began to appear 5 years after the exposure and continued to appear for another 20 years, after which the number of leukemias (almost) ceased. Radiation induces leukemias more readily than other cancers. Therefore leukemias are often considered to be a "marker" for radiation effects. But the variation with age is clearly in great contrast to that of the "solid" cancers, and at old age even an "absolute-risk" model would overpredict the number of leukemias.


A small  increase of leukemia has been seen in children of workers near nuclear sites such as Sellafield (U.K.) and Douneray (U.K.). Although statistical significant it is hard to reconcile the numbers with the measured doses. Reference 46 reviews the data. Kinlen found a bigger effect at Glenrothes new town north of Edinburgh (with no nuclear facilities), and postulates that the observed effect is a viral effect of a new population.

 

46. "Epidemiologic Studies of Leukemia among Persons under 25 Years of Age Living Near Nuclear Sites," D. Laurier and D. Bard, Epidomiologic Reviews 21(2), 188-206 (1999). (E)

47. "Evidence for an Infective Cause of Childhood Leukemia: Comparison of a Scottish New Town with Nuclear Reprocessing Sites in Britain," L. Kinlen, The Lancet 332(8624), 1323-1327 (1988).

 

 

 

B.  Solid Cancers (other than lung)

 

Also in reference 45 are data on cancers in tissues of the body (other than those connected with blood), hereinafter called solid cancers. These do not appear until 20 years after the exposure and have continued to appear for 50 years. The increase of cancer with radiation dose seems to follow a "Relative-Risk" pattern whereby the risk, after the latent period of 20 years, is increased by a constant fraction relative to the background at that age.

 

48. Solid Cancer Incidence among the Chernobyl Emergency Workers Residing in Russia: Estimation of Radiation Risks," V.K. Ivanov et al., Radiation and Environmental  Biophysics 43, 35-42 (2004).(I)

 

For the considered dose interval (1-300 mSv) and for the period 1991-2001, the spontaineous incidence rate of solid cancer among emergency workers agrees, within confidence intervals, with that for the general Russian population. The presented estimates of radiation risk should be treated as preliminary because the follow-up period is rather short and the number of cases considered in the analysis is relatively small.

 

49. "The Chernobyl Disaster: Cancer following the Accident at the Chernobyl Nuclear Power Plant," M. Hatch et al., Epidemiologic Reviews 27, 56-66 (2005).(E)

 

 

C.  Lung Cancers

 

Lung cancers have a special place because the lung is also the point of entry for a major exposure route. One of the surprises of the atomic age (i.e. since 1945) was that an excess of lung cancers appeared among uranium miners. In some of the early studies, they seemed to appear only among Caucasian miners and not among native Americans (Indians). There was some speculation of a racial difference in sensitivity. This speculation was rejected and the data somewhat resolved by further follow up, but also by the observation that there are fewer tobacco smokers among the Indian miners. Most analysts have assumed that the lung cancers are due to radon rather than to any other pollution in the mines (dust, etc.) although there is still room to question this. The main concern is that inhaled particles or radionuclides might cause lung cancer. For example radon gas in uranium mines produces lung cancers by alpha particle irradiation to the lung. This is reviewed in references 18 (BEIR IV,1988) and 23 (NCRPM,1984).


The work in this paper summarizes the evidence for the idea that radiation is synergistic with tobacco smoking, in that the effects multiply and do not merely add. This makes some intuitive sense since both smoke and radiation are highly irritant to the lung tissue. This idea can therefore be used to guide the questions which are asked of the data at low doses.

 

50. "Lung Cancer Mortality Among U.S. Uranium Miners: a Reappraisal," A.S. Whittemore and A. McMillan, Journal of the National Cancer Institute 71, 489‑499 (1983). (I)  

 


D.  Childhood Cancers


Children in the age group 0‑8 seem to develop leukemia naturally at a greater probability than children and adults a little older. It is usually accepted that these leukemias are caused by something that happened in utero. In the period 1940‑1970 it was common to give an X ray to pregnant women to discover any problems with the infant fetus. This gave doses to the fetus approaching 1 Rem. This classic study (the Oxford study) showed that the probability of developing childhood leukemia increased with the number of X rays.


51. "Radiation Dose Effects in Relation to Obstetric X rays and Childhood Cancers," A. Stewart and G.W. Kneale, Lancet 295, 1185‑1188 (1970). (E)

52. "Cancer Mortality Among Atomic Bomb Survivors Exposed in utero or as Young Children (1950‑1992)," R.R. DeLongchamps, K. Mabuchi, Y. Yamamoto, D.L. Preston, Radiation Research 147, 385‑395 (1997). (E)

53. "Risk of Childhood Cancer from Fetal Irradiation," R. Doll and R. Wakeford, Br. J. Radiol. 70, 130‑139 (1997). (I)

54. "Childhood Leukemia in Belarus Before and After the Chernobyl Accident," E.P. Ivanov, G.V. Tolochko, L.P. Shuvaeva, S. Becker, E. Nekolla and A.M. Kellerer, Radiat. Environ. Biophys. 35(2), 75-80 (1996). (E)

 

The Chernobyl accident is now 25 years old and childhood cancers (leukemias, ref. 54, and thyroid, ref. 56 and 57 ) should have been seen within a few years. The lack of leukemias in the general population is consistent with a linear extrapolation from higher doses. But although the idea that X rays increase leukemia is generally accepted, it is still possible that causality works in the other direction, and that the reason for the X rays was a medical problem associated in some way with a latent leukemia. For that reason it is especially interesting to look at the pregnant women who were exposed at Hiroshima or at a radiation accident such as at Chernobyl. A small effect is seen. It is not larger than and could be smaller than the effect suggested by Stewart and Kneale (ref. 51).

 

55. "Leukemia Following the Chernobyl Accident", G.R. Howe, Health Physics Society 93(5), 512-515 (2007). (A)

56. "Chernobyl‑Related Thyroid Cancer in Children of Belarus: A Case‑Control Study," L.N. Astakhova, L.R. Anspaugh, G.W. Beebe, A. Bouville, V.V. Drozdovitch, V. Garber, Y.I. Gavrilin, V.T. Khrouch, A.V. Kuvshinnikov, Y.N. Kuzmenkov, V.P. Minenko, K.V. Moschik, A.S. Nalivko, J. Robbins, E.V. Shemiakina, S. Shinkarev, S.I. Tochitskaya, M.A. Waclawiw, Rad. Research 150, 349‑356 (1998). (I)

 

The childhood thyroid cancers from Chernobyl, while mostly non‑fatal are numerous. They were a surprise although in retrospect they should not have been.

 

57. "Risk of Thyroid Cancer After Exposure to 131I in Childhood," Cardis et al., Journal of the National Cancer Institute 97(10), 724-732 (2005).

58. "Thyroid Disease 60 years after Hiroshima and 20 years after Chernobyl," John Boice, Journal of the American Medical Association (JAMA) 295(9), 1061-1062 (2006). (E)

59. "Radiation-induced Thyroid Cancer - Whats New?", J.D. Boice, Journal of the National Cancer Institute 97(10), 703-705 (2005).(I)

 

 

E.  Medical Exposures


It might be expected that people already being treated with radiation would be examined more carefully than others. This makes a study of such patients particularly interesting. The following studies are typical. They are often interpreted as consistent with a linear dose response relationship with a usual slope. But they can also be interpreted as showing evidence for a threshold. The increase of heart problems after treatment for Hodgkin's disease is a particularly interesting (and troubling) effect.


60. "Mortality from Breast Cancer After Irradiation During Fluoroscopic Examination in Patients Being Treated for Tuberculosis," A.B. Miller, G.R. Howe, G.J. Sherman, J.P. Lindsay, M.J. Yaffe, P.J. Dinner, H.A. Risch, and D.L. Preston, N. Engl. J. Med. 321, 1285‑1289 (1989). (I)

61. "Radiation dose and Leukemia Risk in Patients Treated for Cancer of the Cervix," J.D. Boice, M. Blettener, R.A. Kleneman et al., J. Nat. Cancer Inst. 79,1295‑1311 (1987). (I)

62. "An Affair of the Heart", J.D. Boice, Journal of the National Cancer Institute 99(3), 185-187 (2007).(I)

 


F.  The Other Outcomes

 

Shimuzu et al. (ref. 63) found an increase in several other medical outcomes as a result of the lower levels of exposure. In particular, heart disease appears with a frequency about one third of the frequency of cancer. Boice (ref. 62) and references therein discuss how radiation for cancer treatment can cause cardiac problems.

 

63. "Studies of the mortality of A bomb survivors: non cancer mortality based upon revised doses DS86," Y. Shimuzu, H.Kato, W.J. Schull and D.G. Hoel, Radiation Research 130, 249‑266 (1992). (I)

64. "Cardiac Exposure in Breast Cancer Radiotherapy: 1950s-1990s," Taylor, C.W., F.R.C.R., Nisbet, A., McGale, P., Darby, S.C., International Journal of Radiation Oncology, Biology and Physics 69(5), 1484-1495 (2007).(I)

65. "Cardiac Dose from Tangential Breast Cancer Radiotherapy in the Year 2006," Taylor, C.W., F.R.C.R., Povall, J.M., Nisbet, A., McGale, P., Dodwell, D., Smith, J.T., Darby, S.C., International Journal of Radiation Oncology, Biology and Physics 72(2), 501-507 (2008).(I)


Careful search has been made in the Radiation Effects Research Foundation (RERF, reference 38) data for genetic effects, which are so often portrayed in science fiction as dominant effects of radiation. Reference 66 shows that are very small. Statistically significant effects are not observed.


66. "The Children of Parents Exposed to Atomic Bombs: Estimates of the Genetic Doubling Doses of Radiation for Humans," J.V.Neel, W.J. Schull, A.A. Awa, C. Satoh, H. Kato, M. Otake, and Y. Yoshimoto, Amer. J. Human. Genet. 46, 1053‑1072 (1990). (A)                                                                                


One statistically significant effect has been found in the RERF data on children whose parents were irradiated while they were in utero. Those whose parents were exposed within 1500 m of the hypocenter of the Hiroshima bomb were on average 2.25 cm shorter, 3 kg lighter and 1.1 cm smaller in head circumference than those exposed further away. This has not been seen in other data sets although there seems to have been no careful look.


67. "The Growth and Development of Children Exposed in utero to the Atomic Bombs in Hiroshima and Nagasaki," J.W. Wood, R.J. Hoehn, S. Kawamoto and K.G. Johnson". Amer. J. Public Health 57, 1374‑1380 (1967). (A)

 

Another effect that is perhaps associated with or a consequence of the reduction in head size is a statistically significant reduction in Intelligence Quotient (IQ) among children exposed in utero. In other cases there is severe mental retardation. Although these effects are generally believed to have a threshold, the data on reduction in IQ are consistent with a linear relationship between reduction and dose.


68. "Threshold for Radiation‑Related Severe Mental Retardation in Prenatally Exposed A‑bomb Survivors: a Reanalysis," M. Otake, M.J. Schull, and Lees Brit. J. Radiation Biology 70(6), 755‑763 (1996). (A)

 



V.  The Effects of Dose Rate

 

From general principles one might guess that a high radiation dose given at a low rate over a period of years might have a different (probably smaller) effect from the same dose given in a short time, although the very use of a total DOSE summed over a long time period, of the order of a lifetime implies that the difference is unlikely to be large. Data from animal exposures to shows that there is a reduction in cancers (for the same total dose) at low dose rates. A Dose Rate Reduction Factor (DRRF) is usually introduced to describe this. The following papers can be used to address this directly.

 

69. "Cancer Mortality Among Techa River Residents and Their Offspring," M.M. Kossenko, Health Physics 71, 77‑82, (1996). (E)

70. "Issues in the Comparison of Risk Estimates for the Population in the Techa River Region and Atomic Bomb Survivors," M.M. Kossenko, M.O. Degteva, O.V. Vyushkova, D.L. Preston, K. Mabuchi, and V.P. Kozheurov, Radiation Research 148, 54‑63 (1997). (I)

71. "Studies on the Extended Techa River Cohort: Cancer Risk Estimation", M.M. Kossenko; D.L. Preston; L.Y. Krestinina; M.O. Degteva; N.V. Startsev; T. Thomas; V.P. Vyushkova; L.R. Anspaugh; B.A. Napier; V.P. Kozheurov; et al., Radiation and Environmental Biophysics 41(1), 45‑8 (2002). (I)                 

72. "Protracted Radiation Exposure and Cancer Mortality in the Techa River Cohort", Krestinina, L.Y., Preston, D.L., Ostroumova, E.V., Degteva, M.O., Ron, E., Vyushkova, O.V., Startsev, N. V., Kossenko, M.M. and Akleyev, A.V., Radiation Research 164(5), 602-611 (2005). (E)

 

In 1955‑56 radionuclides spilled from the reservoir in Lake Karachay into the Techa River. Villagers drank the water and ingested many radionuclides. For 40 years the health of 30,000 villagers around the Techa River has been studied. The exposures were mostly internal exposure from the bone seeker strontium 90. The doses can be moderately well determined by subsequent examination of radioactivity of teeth and other bones. This then enables a bone marrow dose to be determined, which is the appropriate organ dose for describing leukemia incidence. In contrast, the "solid" cancers depend upon external doses which are far less well determined. There are fewer leukemias than a linear plot from the Hiroshima-Nagasaki data. This could be a DRRF of 3 with a large error band  from 2 to 6 or a quadratic relationship of effect with dose. The dose rate reduction factor for solid cancers is about 1 with a much larger error band.

 

72. "Radiation Doses and Cancer," A. Shlyakhter and R. Wilson, Nature 350, 25 (1991). (E)

 

For many years it had been rumored that the workers at the MAYAK atomic bomb plant in the Urals received large radiation doses. Attempts from the western countries to discover what they were fruitless until 1991 when a description was published in Russian in the journal Priroda. In this paper, these data are discussed and show that the cancer rate was less than suggested by the Japanese atomic bomb data by a Dose Rate Reduction Factor of about 3.

 

73. "Verification of Occupational Doses at the First Nuclear Plant in the Former Soviet Union," A. A. Romanyuka, D. Regulla, E. K. Vasilenko, A. Wierser, E.G. Drozhko, A. F. Lyzlov, N. A. Koshurnikova, N. S. Shilnikova, and A. P. Panfilov Appl. Radiat. Isot. 47, 11‑12, 1277‑1280 (1996). (A)

74. "Mortality Among Workers with Chronic Radiation Sickness," N. S. Shilnikova, N. A. Koshurnikova, M. G. Bolotnikova, N. R. Kabirova, V. V. Kreslov, A F. Lyzlov, and P. O. Okatenko., Health Physics 71(1), 86‑89 (1996). (A)

 

The doses to the MAYAK workers are in principle well determined by personal monitors. Personal monitors even at that early date were reliable in the USA. In principle it should be possible to determine a dose rate reduction factor both for leukemia and for the principal solid cancers.

 

75. "Lung Cancer in Radiochemical Industry Workers",V. Hohryakov and S. Romanov, The Science of the Total Environment 142, 25‑28, Elsevier Science B.V. (1994). (A)

76. "Cancer Mortality Risk among Workers at the Mayak Nuclear Complex", N.S. Shilnikova, D.L. Preston, E. Ron, E.S. Gilbert, E.K. Vassilenko, S.A. Romanov, I.S. Kuznetsova, M.E. Sokolnikov, P.V. Okatenko, V.V. Kreslov and N.A. Koshurnikova, Radiation Research 159, 787-798 (2003). (A)

 

An interesting subsidiary set of data comes from the MAYAK workers. This is because the workers were exposed to plutonium by inhalation and might be expected to develop lung cancer in the same way that uranium miners develop lung cancer from uranium. These are the only workers exposed to plutonium (239 mostly) at doses high enough to have an appreciable incidence of lung cancer. While the first studies suggested that the dose‑response relationship is quadratic with dose (in qualitative agreement with animal data) and therefore a low dose effect approaching zero seemed to make sense, a more careful look at the data suggests that a linear dose response relationship fits the data better. However the doses are not low and a threshold or reduced effect at low doses is possible.


77. "Estimated Long Term Health Effects of the Chernobyl Accident," E. Cardis, G. Anspaugh, V.K. Ivanov, et al., presented to the IAEA Conference: One Decade after Chernobyl: Summing up the Consequences of the Accident, International Atomic Energy Agency, Vienna (1996). (E)




VI.  Low and Very Low Doses

 

A.  The One-Hit Theory

 

The physicist Geoffrey Crowther produced the first theory of radiation‑induced cancer of which this author is aware. The idea is that when a cell was ionized by radiation it would initiate a cancer. The probability of ionizing a cell in a given time is clearly proportional to the radiation intensity and hence one gets a theory that cancer induction is linear with dose even at low doses. But this theory in its simplest form cannot be true. Cosmic rays and background radiation ionize millions of cells every day and yet lifetime cancer incidence is only about 30% in the US population. Other effects must modify this idea drastically. Cells can be repaired; they can be excreted without leading to a cancer, and so on. Whether cancer incidence is linear with dose depends therefore on whether these important mechanisms are constant with dose or otherwise.  The concept that even small amounts of radiation can induce cancer is deeply embedded in the public consciousness and influences public policy and legal actions. It is often called the One-Hit Theory. This cannot be tested directly and remains an unprovable  hypothesis. But it is vitally important to realize that the inverse is demonstrably false. Every cell ionization does not lead to a cancer. It becomes necessary to discuss what is the lowest level that is known to cause increases in cancer.

 

 

B.   What is low dose?

   

The concept of what constitutes a low dose changed after 1945. A typical chest X ray gave a dose of 1 Rem (0.01 Sv) and at least one jurisdiction (UK) went as far as to propose mandating such an X ray every year. (The bill died in the House of Lords because of the objections of the physicist Lord Cherwell.) In contrast, in 1987 a proposal of the U.S. Nuclear Regulatory Commission to call a radiation exposure that gave no more than 1 milliRem (0.00001 Sv) to any person "Below Regulatory Concern" was withdrawn after some vocal public opposition. Yet natural background exposures are a few hundred milliRems or 100 times this amount. Thus "low dose" now means doses as low as, and usually well below background.

 

 

C .  Variation of Cancer Incidence with Background Exposure

 

One way of attempting to understand the effect of radiation on people at low doses is to understand the variation of cancer mortality with natural radiation exposure. In many studies cancer mortality seems to be lower in areas with high radiation dose.

 

78. "Altitude, Radiation, and Mortality from Cancer and Heart Disease," C.R. Weinberg, K.G. Brown, and D.G. Hoel, Radiat. Res. 112, 381‑390 (1987). (E)

79. "Natural Background Radiation and Cancer Death in Rocky Mountain States and Gulf Coast States," J. Jagger, Health Physics 75(4), 428‑430 (1998). (E)

 

The radiation levels in the Rocky Mountain states are higher than in the Gulf states, yet the cancer rate is lower. This effect may be seen throughout the U.S. and Canada (see ref. 26), but confounding factors may exist. Many Mormons live in Utah and mountain states who do not smoke or drink alcohol or coffee and seem to have half the cancer rate of their non‑Mormon neighbors. In New Jersey also there is much (presumably polluting) industry. Thus many analysts conclude that the only fact of importance from these studies of geographical variation is that radiation at these levels (a few hundred milliRems per year of 10‑20 Rems per lifetime) is not an important factor in developing human cancers compared to other factors.


High background radiation in China does not seem to lead to high cancer rates. It is unclear how much this is due to life style factors or other pollutant effects.


80. "High Background Radiation Research in China", L. Wei, et al., Atomic Energy Press, Beijing, China (1996). (I)

 



D.  The Relationship of Low Dose Effects and Background - Cancer Modeling.

 

When doses were called low even when they were more than background dose, it was possible to discuss logically the effects of radiation independently of whatever causes the background. Now that low means radiation doses 100 times smaller than background, it is necessary to consider them together. However, very few scientists and scientific papers do this logically.  It is necessary to use theoretical models to suggest what the effects can be. The discussion below is primarily about cancer induction.

 

81. "Fundamental Carcinogenic Processes and their Implications for Low Dose Risk Assessment," K.S Crump, D.G. Hoel, C.H. Langley and R.Peto, Cancer Research 36, 2973‑2979 (1976). (E)

In the first of these papers, Guess, Crump and Peto point out that whatever the basic biological process relating a dose to cancer, a differential linearity results provided that the radiation dose and the background act on the biological system in the same way. Indeed this is implied in Doll and Armitage's well-known multistage theory of cancer. Since pathologists cannot distinguish the cancers produced by radiation and those produced by background, this is an assumption that has not been refuted. Crawford and Wilson went further and pointed out that the argument is a general one and can apply to other outcomes than cancer, and other causes than radiation such as respiratory problems caused by air pollution or cigarette smoking.

 

82. "Uncertainty Estimates for Low Dose Rate Extrapolation of Animal Carcinogenicity Data", Guess, H., Crump, K., Peto, R., Cancer Research 37, 3475-3483 (1977). (A)   

83. "Low‑Dose Linearity: the Rule or the Exception?," M. Crawford and R. Wilson, Human and Ecological Risk Assessment 2(2), 305‑330 (1996). (E)

 

There is a possibility that the cancers from radiation and background can be distinguished, by DNA analysis for example. In which case the above argument might not apply. Rowley and Le Beau (ref. 84) have shown that the chromosome structure of an Acute Myelogenous Leukemia (AML) occurring subsequent to and presumably caused by radiotherapy was appreciably different from those that occur naturally. If this turns out to be a general result, the low dose extrapolation arguments of references 81, 82 and 83 must be drastically reconsidered.


84. "Cytogenetic and Molecular Analysis of Therapy‑Related Leukemia," J.D. Rowley and M.M. Le Beau, Ann. N.Y. Acad. Sci. 567, 130‑140 (1989). (A)

 

 

E. Epidemiological studies of Low Dose Behavior


The following paper addresses the few epidemiological studies with a large enough data sample, and with systematic errors well enough controlled, that can be used to discuss directly the shape of the dose response curve below a total dose of 50 Rems (0.5 Sv). The paper focuses on the data on atomic-bomb survivors.


85.
"Threshold Models in Radiation Carcinogenesis", D. G. Hoel and P. Li, Health Physics 75(2), 241‑250 (1998). (I)

 

There have been various studies of the cancer rates among workers in nuclear power plants and other nuclear facilities. The most detailed study in the United States was in reference 87. But a more recent collaborative study in 15 countries (ref. 88) shows a small effect. This is not merely a "meta‑analysis" of several papers but a combined study of those groups where the data are deemed reliable. The additional number of leukemias seen is consistent with an extrapolation from the number at higher doses (but the lower 95th percentile of the number is close to zero). The number of additional "solid " cancers is close to zero but the upper 95th percentile is close to the linear extrapolation from higher doses. Taken together these data suggest that much larger numbers suggested in references 88 and 89 can be excluded.


86. "A Mortality Study of Employees of the Nuclear Industry in Oak Ridge, Tennessee," E.L. Frome, et al., Rad. Res. 148, 64‑80 (1997). (I)

87. "Cancer in Populations Living Near Nuclear Facilities: A Survey of Mortality Nationwide and Incidence in Two States," S. Jablon, Z. Hrubec, J. D. Boice, Jr., J. Amer. Med. Assoc. 265(11), 1403‑1408 (1991). (E)

88. "The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: Estimates of Radiation-Related Cancer Risks", Cardis et al., Radiation Research Society 167, 396-416 (2007). (E)

 

Only recently have there been studies of the effects of radon on people in residential situations. There are two types of study. One, an "ecological" study, compares the average lung cancer rate in a community with the average radon concentration in the houses of that community. There are several early studies but the most important and most careful are in references 89-97. The average lung cancer rate falls with increasing radon concentration. It would be a logical non sequitur to derive directly from such a study the relationship of the probability of an individual person succumbing to cancer with the radon concentration to which that individual is exposed (the dose‑response relationship). To make such a conclusion is sometimes called "the ecological fallacy." However, Cohen argues that it is legitimate to compare any set of data with a theory and if the data do not fit, the theory must be wrong. In particular, he claims that the particular linear dose response relationship espoused by U.S. Environmental Protection Agency cannot be correct.

89. "Radon Levels in United States Homes by States and Counties," B.L. Cohen, R.S. Shah, Health Physics 60, 243‑259 (1991). (E)

90. "Relationship Between Exposure to Radon and Various Types of Cancer," B.L. Cohen, Health Physics 65(5), 529‑531 (1993). (E)

91. "Dose‑response Relationship for Radiation Carcinogenesis in the Low‑dose Region," B.L. Cohen, Int. Arch. Occup. Environ. Health 66, 71‑75 (1994). (I)

92. "Test of the Linear‑no Threshold Theory of Radiation Carcinogenesis for Inhaled Radon Decay Products," B.L.Cohen, Health Physics 68, 157‑174 (1995). (I)

93. "Problems in the Radon vs. Lung Cancer Test of the Linear No‑Threshold Theory and a Procedure for Resolving Them", B.L. Cohen, Health Physics 72, 623‑628 (1997). (I)

94. "Indoor Radon and Lung Cancer: Risky or Not?," J.M. Samet, J. Nat. Cancer Inst. 86, 1813‑1814 (1994). (E) A distinguished epidemiologist challenges Cohen's studies and implicitly all other "ecological" studies.

 

These are "retrospective cohort" studies in which a group of people are followed and the individual doses estimated. These are free from the ecological fallacy but there are no data in the low dose region where 90% of Americans are exposed. It is important to realize that any conclusion about the risk at low doses (that is doses below natural background) derived from these studies is dependent upon an extrapolation, which may not be in direct disagreement with the ecological study of Cohen.


95. "Residential Radon Exposure and Lung Cancer among Nonsmoking Women," M.C.R. Alavanja, R.C. Brownson, J.H. Lubin, J. Chang, C. Berger and J.D. Boice, Jr., J. Natl. Cancer Inst. 86, 1829‑1837 (1994). (A)

96. "Lung Cancer Risk from Residential Radon: Meta‑analysis of Eight Epidemiologic Studies," J.H. Lubin and J.D. Boice, Jr., J. Natl. Cancer Inst. 89, 49‑57 (1997). (I)

 

The following paper summarizes of the evidence that suggests that the mining cancer data underestimate the risk of uranium miners. Such an underestimate would be even harder to reconcile with the data of Cohen.

 

97. "Radon‑exposed Underground Miners and Inverse Dose‑rate (protraction enhancement) Effects," J.H. Lubin, J.D. Boice, Jr., C. Edling, R.W. Hornung, G. Howe, E. Kunz, R.A. Kusiak, H.I. Morrison, E.P. Radford, J.M. Samet, et al., Health Physics 69(4), 494‑500 (1995). (A)

 


 

F.  Larger Effects than Establishment

The following is the foremost and most logical of a set of claims that the effect of a low dose is greater than the "establishment" wisdom. At the time the "establishment" used an absolute risk model which gives a smaller effect than the relative risk model now accepted for solid cancers.  But Gofman's estimate was still 5 times the relative risk model. Although primarily concerned with radiation exposures from peaceful nuclear energy, Gofman is consistent in also pointing out high medical exposures although he is clearly less eager to oppose them.

 

98. Radiation and Human Health, J.D. Gofman (Sierra Club Books, San Francisco, 1981). (I)

 

99. ECRR 2010 Recommendations of the European Committee on Radiation Risk The Health Effects of Exposure to Low Doses of Ionizing Radiation, C. Busby, R. Bertell, I. Schmitz‑Feuerhake, M. S. Cato, A. Yablokov (Regulators Edition, Green Audit, August 2010). (E)

This multinational group is the latest in the idea that the effect of the dose is undetermined.

 

The following paper discusses several claims that at radiation doses at or below the background cancers are produced. These reports often select data or otherwise fall into statistical "traps" or errors. Rarely (Gofman is an exception) is there a discussion of the effect of the background and why many more people are not dying naturally from cancer in high radiation areas, which would be expected if their claims were true.

 

100. "Is there a Large Risk of Radiation? A Critical Review of Pessimistic Claims," A. Shihab‑Eldin. A.S. Shlyakhter and R. Wilson, Environmental International 18, 117‑151 (1992). (E)

 


G.   Is radiation good for you?


The idea that the effect of radiation is linear with dose at low doses dominates most discussions. But there is also a  movement in the opposite direction, suggesting that radiation at low doses and low dose rates is good for you. This paper is typical of several papers in this conference report that address this proposition. In addition, this view is strongly supported in reference 5.

 

101. "Health Effects of Low‑dose Radiation: Molecular, Cellular, and Biosystem Response," M. Pollycove, and C.J. Paperiello, in: Low Doses of Ionizing Radiation: Biological Effects and Regulatory Control, International Atomic Energy Agency, Vienna, IAEA‑TECDOC‑976, IAEA‑CN‑67/63, 223‑226 (1997). (A)

 

It is important to realize that there are many other possibilities. It is possible, for example, that radiation cures a commonly occurring cancer while increasing the less common ones. Although there are no good data on radiation effects this possibility has been suggested for the chemically induced effects. Also it is possible that radiation cures an infectious disease (such as by killing the bacteria) while increasing cancer. A clear example of a substance that is beneficial at low doses and very deleterious at higher ones is ethyl alcohol.

 

Alcohol is a substance which has been studied for a much longer period (millenia) than radiation. In this paper Sir Richard Doll points out that at low doses it reduces the risk of stroke, while it is carcinogenic also (especially in conjunction with tobacco smoking) and at even higher doses the narcotic effects can cause many adverse effects such as car accidents. The implication here is that the same mixture of outcomes can occur with radiation.


102. "The Benefit of Alcohol in Moderation," R. Doll, Drug and Alcohol Review 17, 353-363 (1998). (A)

 



H. Policy Implications: Man Rems (Person‑Sievert) or Rems/man (Sv/Person)?

 

The first imperative is to understand what question you are asking. The relevant policy may be different for different questions. 


The following paper described why health physicists often use collective dose. This was originally measured in Man Rems but allowing both for political correctness and also for a change in units, it is measured in Person‑Sieverts. If a linear dose response relationship is assumed, multiplying the collective dose by the slope of the dose response curve (from BEIR VII Table 1) gives the overall calculated societal effect which can be compared to other total societal impacts.  However, this can also obscure the fact that an individual decision or decision of a small group, is best discussed using the individual dose.

 

103. "Principles and Application of Collective Dose in Radiation Protection", National Council on Radiation Protection and Measurements, Report No. 121 (NCRPM, Bethesda, MD, 1995). (E)

 

In 1978 Dr. Dunster, while head of the Health and Safety Executive of the U.K., stated:  " all politicians would prefer a dead body to a frightened voter." A dead body does not vote: a person who fears he may have cancer does. This dramatically brings out a potential bias in these discussions. 

 

In this category are recommendations by the International Atomic Energy Agency (IAEA).


One criterion is for external acute exposure of 2.5 Gray at a depth of 0.5 cm in tissue. This criterion is more applicable to a localized radioactive source accident than for the effective whole body dose applicable to a nuclearor reactor or RDD device and must be used with caution.


104.
"Criteria for Use in Preparedness and Response for a Nuclear or Radiological Emergency General Safety Guide", Series No. GSG‑2, published Thursday, March 17, 2011.Table 2. (E)



105. "Manual of Protective Action Guides and Protective Actions for Nuclear Incidents", Environmental Protection Agency (EPA), May (1992). These guides have been the basis for action by other agencies including the U.S. Nuclear Regulatory Commission. (E)

 

There are few discussions, and none in the regulatory arena yet,  of how such important individual decisions or decisions of small groups work in practice. Obviously a sensible decision involves careful balancing of alternative non-radiation hazards work out. Three examples are :

 

106. "A Nuclear Explosion in a City or an Attack on a Nuclear Reactor," R.L. Garwin, The Bridge 40(2), 20-27 (2010). (E)

107. Analyzing Evacuation Versus Shelter-in-Place Strategies After a Terrorist Nuclear Denotation, L.M.Wein, Y. Choi, S. Denuit, Society for Risk Analysis (2010). (E)

108. "Medical Preparedness and Response to Nuclear Terrorism," G.C. Benjamin, The Bridge 40(2), 39-44 (2010).(E)

 

It is surprising that even 66 years after the detonations at Hiroshima and Nagasaki, mankind still has not come to grips with what might happen in another nuclear explosion. The above papers argue that an explosion at ground level, rather than the 500 feet altitude at Hiroshima and Nagasaki will increase the number of  radiation casualties. They also argue that merely running directly away from the site may be the wrong thing to do. Sheltering in place can cut our exposure for the first day, and when the direction of the wind blown plume is know, walking sideways from the plume is the best response.


There is much confusion in many public discussions between a explosion of a fission device and dispersal of a large radioactive source. There is a difference of roughly a factor of 10,000 in the amount of radioactive products released. While calculation and experience eith the theft and accidental dispersal of a source at Goiania, Brazil, suggest that the immediate casualties in such dispersal are small (less than 10) there is no consensus on when to reenter a contaminated area.

 

109. "Management of Terrorist Events involving Radioactive Materials", National Council on Radiation Protection and Measurements, Report No. 138 (NCRPM, Bethesda, MD, 2001). (E)

110. "Health Aspects of a Nuclear or Radiological Attack," Tenforde et al., The Bridge 40(2), 50-57 (2010).(E)

 

The following report discusses the evacuation decision at Fukushima and argues that it was deleterious to public health. It points out that as soon as there is an important adverse effect of any action then a risk-benefit comparison must take this into account. The IAEA and other guidance in the above references omit this in their documents and may therefore be deleterious to overall public health.    

 

111. "Lessons from History of Radiation use and Nuclear Accidents particularly Fukushima", R. Wilson, The 44th Seminar on Planetary Emergencies World Federation of Scientists, Erice Sicily (August 20th, 2011). To be available in a full volume of the papers of the seminar at World Scientific. (E)


In 1985, the U.S. Congress  requested a set of tables to determine the probability that a person's cancer was due to his radiation exposure. These tables assume a linear dose response relationship. The dose for which the probability of causation is greater than 50% (and therefore compensable by ordinary legal rules) is very high and very few people will receive it. However, there is a comples procedure administered by the U.S. Department of Labor. While nominally it is based on scientific principles a close examination shows the scientific basis is flawed. For example, a worker who was a heavy cigarette smoker and developed lung cancer is more likely to be compensated than a worker who did not know his smoking history.

             

112. "Report of the NCI-CDC Working Group to Revise the 1985 NIH Radioepidemiological Tables," U.S. Department of  Health and Human Services (2003).

 

In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 Rems (the Rem is a the unit of effective dose; in international units, 1 Rem = 0.01 sievert (Sv)) in one year or a lifetime dose of 10 Rems in addition to background radiation. "Risk estimation in this dose range should be strictly qualitative, accentuating a range of hypothetical health outcomes with an emphasis on the likely possibility of zero adverse health effects. The current philosophy of radiation protection is based on the assumption that any radiation dose, no matter how small, may result in human health effects, such as cancer and hereditary genetic damage. There is substantial and convincing scientific evidence for health risks at high dose. Below 10 Rems (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are "non‑existent."

113. "Policy Statement of the Health Physics Society," 1313 Dolley Madison Boulevard, Suite 402, McLean, VA 22101. (1996). (E)

 

The policy recommendation of the International Commission on Radiological Protection (ICRP) dating back to 1928 is that it is prudent to assume that a risk remains at low doses and that no exposure should be accepted without expectation of some benefit. This has led to the principle of ALARA ‑ that doses should be reduced to As Low As Reasonably Achievable (economic and other factors taken into account). This report outlines suggested procedures and on page 25 suggests that if doses can be reduced at a cost of $10 ‑ $1,000 per man Rem or less ($1000 ‑ $100,000 per person Sv) that should be done. The Nuclear Regulatory Commission in 1975 had already suggested a number at the high end $1,000 per Man Rem ‑ for nuclear activities under their purview.  NRC since updated this to $200,000 per person Sievert. This is approximately $6,000,000 per cancer (calculated with a linear dose response) and is consistent with a US EPA figure of $6,000,000 per "Statistical life." It is noteworthy that although for almost all individuals medical exposures are a large fraction of a person's individual dose, these are not under the purview of the Nuclear Regulatory Commission and there is no reliable monitoring of these medical doses.


114. "Implementation of the Principle of As Low As Reasonably Achievable (ALARA) for Medical and Dental Personnel, National Council on Radiation Protection and Measurements, Report No. 107 (NCRPM, Bethesda MD, 1990). (E)

 

This reference also recommend a de minimis level for an individual dose of 1 milliRem (100 m Sv). Another suggestion was to note that the difference in radiation exposure of about 50 mRem/year (0.5 MSv/year) between sea level and in the Rocky Mountains due to cosmic rays and increased terrestrial radioactivity is generally accepted without question.  Although the first was proposed by the NRC there were public political objections and the proposal was not finalized.  Many scientists believe that their time and that of the public is better spent in insisting that these guidelines be followed (and not exceeded) with a coherent risk/cost/benefit analysis rather than addressing the possibility of a threshold at low doses that may be impossible to prove rigorously.