Journal of Medical Physics
EDITORIAL
Year
: 2013  |  Volume : 38  |  Issue : 2  |  Page : 57--58

On the risk to low doses (<100 mSv) of ionizing radiation during medical imaging procedures - IOMP policy statement


AS Pradhan 
 Editor, JMP, India

Correspondence Address:
A S Pradhan
C/o AMPI, RP & AD, Bhabha Atomic Research Centre (CT & CRS), Mumbai - 400 094
India




How to cite this article:
Pradhan A S. On the risk to low doses (<100 mSv) of ionizing radiation during medical imaging procedures - IOMP policy statement.J Med Phys 2013;38:57-58


How to cite this URL:
Pradhan A S. On the risk to low doses (<100 mSv) of ionizing radiation during medical imaging procedures - IOMP policy statement. J Med Phys [serial online] 2013 [cited 2019 Nov 20 ];38:57-58
Available from: http://www.jmp.org.in/text.asp?2013/38/2/57/111307


Full Text

The science committee of International Organization for Medical Physics (IOMP) developed a policy statement on the predictions of radiation-induced cancers and cancer deaths in patients exposed to low doses (<100 mSv) of ionizing radiation during medical imaging; this statement has been approved by the IOMP council. In order to attract the attention of medical physicists, an editorial [1] titled "Risk of Medical Imaging" that includes the said statement has recently been published in Medical Physics journal of American Association of Physicists in Medicine (AAPM). As stated, [1] IOMP represents 80 national and 6 regional medical physics organizations and 18,000 medical physicists worldwide. The IOMP affiliated bodies/organizations in different countries (such as Association of Medical Physicists of India, AMPI) have been encouraged to reproduce the IOMP statement in their journals/newsletters for the benefit of larger community of medical physicists. The IOMP statement is reproduced below (readers may also go through the supportive literature listed in references [2],[3],[4],[5],[6],[7],[8],[9] ). It is hoped that this policy statement will have some deterrent influence on the continued propagation of unproven risk related to medical imaging procedures conducted with small doses.

 IOMP Policy Statement



This policy statement addresses predictions of induced cancers and cancer deaths in a population of patients exposed to low doses (<100 mSv) of ionizing radiation during medical imaging procedures.

Prospective estimates of cancers and cancer deaths induced by medical radiation should include a statement that the estimates are highly speculative because of various random and systematic uncertainties embedded in them. These uncertainties include dosimetric uncertainties; epidemiological and methodological uncertainties; uncertainties from low statistical power and precision in epidemiology studies of radiation risk; uncertainties in modeling radiation risk data; generalization of risk estimates across different populations; and reliance of epidemiological studies on observational rather than experimental data. Such uncertainties cause predictions of radiation-induced cancers and cancer deaths to be susceptible to biases and confounding influences that are unidentifiable. Paragraph A86 of Report 103 of the International Commission on Radiological Protection (ICRP) states that "There is, however, general agreement that epidemiological methods used for the estimation of cancer risk do not have the power to directly reveal cancer risks in the dose range up to around 100 mSv". Further, UNSCEAR Report A-67-46, approved in May, 2012, states that "The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels."Predictions of radiation-induced cancers and cancer deaths from medical imaging procedures should be accompanied by estimates of reductions in patient morbidity, mortality and cost resulting from the same medical imaging proceduresIf effective dose is used to generate predictions of cancers and cancer deaths, a statement should be included that the ICRP has expressed caution in the use of effective dose for purposes of estimating risks to individuals or populations exposed to ionizing radiation. Paragraph 151 of ICRP Report 103 states: "The use of effective dose for assessing the exposure of patients has severe limitations that must be considered when quantifying medical exposure", and "The assessment and interpretation of effective dose from medical exposure of patients is very problematic when organs and tissues receive only partial exposure or a very heterogeneous exposure which is the case especially with x-ray diagnostics."The essence of the statement is that the phobia of risk due to exposure to low level (<100 mSv of effective dose) radiation should not incite the patients to delay or defer any medical examination (medical imaging) that may otherwise cause risk to their health. It is suspected that media sometimes misuse the interpretations of the risks in developing print or electronic news that raise anxiety in patients and public at large and may restrain them from using imaging procedures involving ionizing radiation. Sometimes, this may also be obliviously inferred from the effusive deliberations of experts while embellishing radiation protection. Usually, the extracted risks for low level of radiation exposures are based on the unproven hypothesis of "linear non-threshold" (LNT) model (assumption of linearity of dose response from high doses to low doses). There appears to exist little possibility to prove or disprove LNT model in the near future in view of the indistinguishable excess risk of low level of radiation exposures over the risk prevalent because of causes other than radiation with large uncertainty. However, both supporting and opposing arguments for the validity of LNT model remains available. Even with the unproven LNT model, the probability of cancer risk at low doses is very small, e.g., 1 in 1 million in the case of a typical diagnostic X-ray examination (with effective dose <0.1 mSv or an organ dose ranging from 1 mGy to several mGy) and 100 in 1 million for a typical CT examination of head, chest, or abdomen. [10] This should be viewed in the light of usual and unavoidable risks in daily life. Even for breast cancer, the natural occurrences is about 1170 cases per million annually in USA, [10] albeit the improving curability of cancer with unabated advancements of medical sciences (International Agency for Research on cancer approximated about 2000 new natural cancer cases per million world population during 2008). One should also keep in mind that exposure to ionizing radiation prevalent in nature (from sources such as cosmic, terrestrial, and constituents of the human body) cannot be avoided, which contributes an average effective dose of about 2 mSv/y to each of us since inception until death. In fact, mankind has evolved with and continues to live with radiation. Therefore, there is no reason to deter from any justified medical examination involving exposure to ionizing radiation.

It may also be noted that, for medical exposures, even in the principles of radiation protection of International Commission on Radiological Protection (ICRP), the dose limitation is not applicable to patients. [3],[11] However, due emphasis has been laid on the justification and optimization (As Low As Reasonably Achievable, ALARA) and the regulatory procedures to ensure the quality of equipment and the procedures to minimize the avoidable unnecessary radiation exposure. As an example of implementation of ALARA, in spite of the remarkable reduction in the tissue weighting factor 'wT ' for gonads and the heritable radiation risk, the recommendation for the use of gonad shields and other protection devices continue because there is no justification for allowing a controllable exposure. [12] Without compromising radiation protection procedures and the relevant regulatory recommendations, the medical practitioners/medical physicists/regulators/radiation safety personnel must avoid over emphasizing the apprehension of risk of low level of radiation exposures in the wider interest of patients.

References

1Hendee W. Risk of medical imaging. Med Phys 2013;40:1-2. ( http://dx.doi.org/10.1118/1.4794923 )
2National Research Council. Health risks from exposure to low levels of ionizing radiation: BEIR VII-Phase 2. Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation. Washington, DC: National Academies Press; 2006.
3The 2007 recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007;37:1-332.
4Health Physics Society. Position statement of the Health Physics Society. Radiation risk in perspective. July, 2010. Available from: http://hps.org/documents/risk_ps010-2.pdf [Last accessed on].
5American Association of Physicists in Medicine. Position statement of the American Association of Physicists in Medicine. Radiation risks from medical imaging procedures. December, 2011, affirmed November, 2012. Available from: http://www.aapm.org/org/policies/details.asp?id=318&type=PP [Last accessed on].
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7United Nations Scientific Committee on the Effects of Atomic Radiation. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation. 59th session (May 21-25, 2012. General Assembly Official Records. 67th session, Supplement No. 46. Available from: http://daccess-dds-ny.un.org/doc/UNDOC/GEN/V12/553/85/PDF/V1255385.pdf?OpenElement [Last accessed on].
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9 National Council on Radiation Protection and Measurements. Uncertainties in the Estimation of Radiation Risks and Probability of Disease Causation. NCRP Report 171. National Council on Radiation Protection and Measurements. Bethesda, Maryland; 2012. Available from: http://www.ncrponline.org/Publications/Press_Releases/171press.html [Last accessed on].
10 Martin CJ. Effective dose: How should it be applied to medical exposures? Br J Radiol 2009;80:639-47.
11Pradhan AS, Kim JL, Lee JI. On the use of "effective dose" (E) in medical exposures. J Med Phys 2012;37:63-5.
12Pradhan AS. Evolution of dosimetric quantities of International Commission on Radiological Protection (ICRP): Impact of the forthcoming recommendations. J Med Phys 2007;32:89-91.