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Is Radiation Risk Assessed Properly?
Posted by 19 Dec 2014 at 11:50 GMTon
We have some comments and concerns regarding the article "How Safe Is Safe Enough? Radiation Risk for a Human Mission to Mars", by Cucinata et al. (Cucinotta FA, Kim MH, Chappell LJ, Huff JL. How Safe Is Safe Enough? Radiation Risk for a Human Mission to Mars? PLoS One. 2013;8(10):e74988.)
To emphasize our vision of the importance of human missions to Mars, we would like to quote from the article “What's the use of basic science?” by Llewellyn Smith , CERN Director-General in 1994-1998:
"Our lives are enriched, and our outlook changed, by (e.g.) knowledge of the heliocentric system, the genetic code, how the sun works, why the sky is blue, and the expansion of Universe. The point was elegantly, if arrogantly, made by Bob Wilson (first Director of Fermilab, a large particle physics/accelerator laboratory near Chicago) who, when asked by a Congressional Committee “What will your lab contribute to the defence of the US?”, replied “Nothing, but it will make it worth defending”.
Our point is that endeavors on the forefront of science are often worth pursuing, even when expensive, experimental or potentially risky. This includes a manned mission to Mars. However, the true radiation risks of such an effort might not be as hazardous as portrayed by Cucinotta et al.
NASA guidelines suggest that astronauts should not be exposed to more than 1,000 mSv of radiation in a lifetime. Data from Mars Science Laboratory's Radiation Assessment Detector [Zeitlin, 2013] indicate that a 180-day flight to Mars, a 500-day stay and a 180-day return flight to Earth would expose astronauts to a cumulative radiation dose of about 1000 mSv (based on 0.64 mSv per day on the Martian surface and 1.84 mSv per day on the space flight). Such figures would exceed NASA current 3% excess cancer risk limit. It should be mentioned, however, that actual exposure of the astronauts may prove to be only half the above value, as hinted by recent results of the MATROSHKA experiment [Puchalska et al., 2014].
NASA guidelines of 1000 mSv life-time limit are associated with a 5% increase in alleged risk of developing a fatal cancer. We are concerned with some very basic assumption regarding this association – namely the linear no-threshold (LNT) model of radiation-induced negative health effects. With the LNT model, it is assumed that each ionizing radiation dose increment, no matter how small, corresponds to an increase in the cancer risk to humans. However, the scientific validity of this model has never been proven and has been seriously questioned and debated for many decades.
It should be mentioned, that for about 20 years (~1920-1940) the accepted radiation exposure limit for radiologists was 2 mSv per day – higher than the estimated exposure level for space flight. No adverse health effects for those radiologists were reported – see, e.g., the study of Smith and Doll . There is no direct evidence for any adverse health effect of low doses of ionizing radiation – doses relevant to medical scanning or space travel – though acute 1000 mSv exposure is undoubtedly carcinogenic [Socol and Dobrzyński, 2014]. The recent memorandum [Gonzalez et al., 2013] of a Task Group of ICRP (International Commission on Radiological Protection), one of the main bodies promoting the LNT model, states:
While prudent for radiological protection, the LNT model is not universally accepted as biological truth, and its influence and inappropriate use to attribute health effects to low dose exposure situations is often ignored...
Speculative, unproven, undetectable and ‘phantom’ numbers are obtained by multiplying the nominal risk coefficients by an estimate of the collective dose received by a huge number of individuals theoretically incurring very tiny doses that are hypothesized from radioactive substances released into the environment (highlights are by the Comment's authors).
On the opposite side of the debate, numerous studies (experimental, epidemiological, and ecological) have shown that low doses of ionizing radiation might have a beneficial health effect. For example, in an epidemiological study of cancer among nuclear industry workers, the rate of cancer mortality (as well as overall mortality) among the workers was substantially lower than in the reference population [Sponsler and Cameron, 2005]. The low-dose radiation benefits mentioned above and numerous others constitute emerging scientific support for the application of radiation adaptive response for a variety of health benefits.
Discussion of such uncertainties in low-dose risk estimation is totally absent in the referenced paper. If the risk estimates presented in the paper were adopted in mission planning, they would unfortunately render the human mission to Mars essentially impossible. Importantly however, the paper also implicitly promotes radiophobia – an irrational fear of radiation hazards – by applying the LNT model at low doses, contrary to the advice of international advisory bodies. Other negative impacts of radiophobia include:
* "Predictions of hypothetical cancer incidence and deaths ... cause some patients and parents to refuse medical imaging procedures, placing them at substantial risk by not receiving the clinical benefits of the prescribed procedures" [AAPM, 2011].
* Radiophobia significantly dissuades the study of low-dose radiation therapies for beneficial effects in medicine, whereas such treatment has been successfully used to treat inflammatory diseases [Erickson, 2007] and even cancers [Sakamoto, 2004]. Animal studies have shown potential for treatment of diseases for which presently no treatments are available, e.g., AIDS [Shen et al., 1997] or Alzheimer's disease [Wei et al., 2012].
* At Fukushima, the compulsory relocation (on the basis of LNT-based ICRP recommendations) resulted in more than 1,000 non-radiogenic, disaster-related premature deaths among the evacuated population during the first year following the accident (Saji, 2013). If not evacuated, these people would have received low doses of radiation that likely would have had no detrimental health effects or at most, according to the LNT model, led to shortening of life expectancy by less than one week (Socol et al. 2013).
* After Chernobyl, radiophobia resulted in more than 100,000 unnecessary abortions of pregnancies among females that received negligible radiation doses (or no dose at all) associated with the reactor accident [Ketchum, 1987].
* Finally, radiophobia contributes to motivating radiological terrorism and promoting nuclear proliferation.
More background and extensive bibliography are given in a recent paper [Socol et al., 2014].
We believe the decision on whether or not to proceed with a manned mission to Mars should consider potential benefits as well as real risks, as opposed to speculative estimates. In light of the above, we strongly recommend that Cucinotta et al. include critical scientific review of these risks, rather than solely using the LNT model.
With best regards,
On behalf of Scientists for Accurate Radiation Information (SARI)
Dr. Yehoshua Socol
Hanevel 13/1 Karney Shomron, 4485500 Israel
Dr. Jerry M. Cuttler
Cuttler & Associates Inc.
1781 Medallion Court, Mississauga, ON Canada, L5J2L6
Prof. Ludwik Dobrzyński
Director, Education & Training Division
National Center for Nuclear Research
Andrzeja Sołtana 7, 05-400 Otwock, Świerk, Poland
Prof. Mohan Doss
Associate Professor, Diagnostic Imaging
Fox Chase Cancer Center
Philadelphia, PA 19111, USA
Prof. Ludwig E. Feinendegen,
Professor emeritus, Nuclear Medicine
Heinrich-Heine University, 40204 Düsseldorf, Germany
Dr. Krzysztof W. Fornalski
Polish Nuclear Society (PTN), Warszawa, Poland
Mr. Mark L. Miller, CHP
Sandia National Laboratories
PO Box 5800, MS-0729
Albuquerque, NM 87185, USA
Dr. Brant Ulsh, Ph.D, CHP
Principal Health Physicist
M.H. Chew & Associates
897 Baccarat Drive, Cincinnati, OH 45245, USA
Dr. Alexander Vaiserman
Head, Laboratory of Epigenetics
Institute of Gerontology
Vyshgorodskaya st. 67, Kiev 04114, Ukraine
Dr. James Welsh
Northern Illinois University, DeKalb, IL and Fermi National Accelerator Laboratory, Batavia, IL, USA
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Erickson, B.E. (2007), The therapeutic use of radon: a biomedical treatment in Europe; an alternative remedy in the United States. Dose-Response 5:48–62.
Gonzalez, A. J., et al. (2013), Radiological protection issues arising during and after the Fukushima nuclear reactor accident, J Radiol Prot, 33(3), 497–571.
Ketchum, L. E. (1987), Lessons of Chernobyl: SNM members try to decontaminate world threatened by fallout. Part II, J Nucl Med, 28(6), 933-942.
Llewellyn Smith, C. H. (1997), What's the use of basic science? [online] http://cds.cern.ch/record... Accessed 24.11.2013
Puchalska, M., P. Bilski, T. Berger, M. Hajek, T. Horwacik, Ch. Körner, P. Olko, V. Shurshakov, G. Reitz (2014) Radiation and Environmental Biophysics 53:719–727; DOI 10.1007/s00411-014-0560-7
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Shen, R. N., L. Lu, H. E. Kaiser, and H. E. Broxmeyer (1997), Murine AIDS cured by low dosage total body irradiation. Adv Exp Med Biol 407:451–458.
Smith PG and Doll R. (1981), Mortality from cancer and all causes among British radiologists. British Journal of Radiology 54:187–194.
Socol Y. and L. Dobrzyński (2014), Atomic bomb survivors life-span study: insufficient statistical power to select radiation carcinogenesis model. Dose-Response (Pre-Press) DOI: 10.2203/dose-response.14-034.Socol
Socol, Y., L. Dobrzyński, M. Doss, L.E. Feinendegen, M.K. Janiak, M.L. Miller, C.L. Sanders, B.R. Scott, B. Ulsh, and A. Vaiserman. (2014), Commentary: ethical issues of current health-protection policies on low-dose ionizing radiation, Dose Response, 12: 342–348, DOI: 10.2203/dose-response.13-044.Socol
Socol, Y., M. Yanovskiy, and I. Zatcovetsky (2013), Low-dose ionizing radiation: scientific controversy, moral-ethical aspects and public choice. Int J of Nuclear Governance, Economy and Ecology, 4:59–75.
Sponsler, R., and J. R. Cameron (2005), Nuclear shipyard worker study (1980–1988): a large cohort exposed to low-dose-rate gamma radiation, Int. J. of Low Radiation 1: 463-478. Available at: http://radiationeffects.o...
Wei, L. C., Y. X. Ding, Y. H. Liu, L. Duan, Y. Bai, M. Shi, and L. W. Chen (2012), Low-dose radiation stimulates Wnt/beta-catenin signaling, neural stem cell proliferation and neurogenesis of the mouse hippocampus in vitro and in vivo, Curr Alzheimer Res, 9(3), 278–289.
Zeitlin C, Hassler DM, Cucinotta FA, et al. (2013), Measurements of energetic particle radiation in transit to Mars on the Mars Science Laboratory. Science. 340(6136), 1080–1084.