Radiation Benefit and Risk Assessment Health Physics Society

Radiation Benefit and Risk Assessment ©Health Physics Society

Risk Probability of harmful effects on a human

Risk Assessment n “Health risks of radiation exposure can only be estimated with a reasonable degree of scientific certainty at radiation levels that are orders of magnitude greater than levels established by regulators for protection of the public. ” n Radiogenic cancer elevated risk is currently only consistently able to be demonstrated in those groups of study populations exposed to highdose radiation (>1 Sv). Health Physics Society Position Statement. Risk Assessment. 1995. Available at www. hps. org.

Risk Assessment n “Cancer and other health effects have not been observed consistently at low doses (<0. 1 Sv) because the existence of a risk is so low as to not be detectable by current epidemiological data and methods. ” Health Physics Society Position Statement. Risk Assessment. 1995. Available at www. hps. org.

Risk Assessment n “In the absence of direct observations, estimation of radiogenic health risks at low doses must be viewed with caution. ” n Extrapolation of risk estimates to low doses where the mechanism of effect may not be the same as at high doses may not be valid. Health Physics Society Position Statement. Risk Assessment. 1995. Available at www. hps. org.

Risk Assessment n “The Health Physics Society recommends that assessments of radiogenic health risks be limited to dose estimates near and above 0. 1 Sv. Below this level, only [actual] dose is credible and statements of associated risk are more speculative than credible. ” Health Physics Society Position Statement. Risk Assessment. 1995. Available at www. hps. org.

Risks from Low-Dose Radiation n Methodological difficulties inherent in low- dose epidemiological studies suggest that precisely quantifying cancer risks at doses below 0. 1 Sv is unlikely. Brenner, et al. Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know. PNAS 24(100): 13, 761 -13, 766; 2003.

Risks from Low-Dose Radiation n Reasonable evidence for an increased cancer risk is shown at acute doses greater than 5 m. Sv. n Good evidence of an increased cancer risk is shown at acute doses greater than 50 m. Sv. n Reasonable evidence for an increased cancer risk is shown for protracted doses greater than 50 m. Sv. n Statistically significant evidence for an increased cancer risk is shown for protracted doses greater than 100 m. Sv. Brenner, et al. Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know. PNAS 24(100): 13, 761 -13, 766; 2003.

Risks from Low-Dose Radiation n “…epidemiological studies are generally unable to provide clear evidence of the effects of protracted low doses of radiation of less than about 50 -100 m. Sv. ” n The implication of the LNT model supported by ICRP, NCRP, UNSCEAR, the BEIR Committees, and others is that low doses are low risk. Wall, Kendall, Edwards, Bouffler, Muirhead, and Meara. What are the risks from medical x-rays and other low dose radiation? BJR 79: 285 -294; 2006.

Risks from Low-Dose Radiation n In a sense, there is a dose, although not zero, that can be considered safe for the risks to be ignored. Above this, there are doses where the risk is still small but can be justified because of the receipt of benefit. n As the dose increases, then, the benefit should also increase. n Wall, Kendall, Edwards, Bouffler, Muirhead, and Meara. What are the risks from medical x-rays and other low dose radiation? BJR 79: 285 -294; 2006.

Risks from Low-Dose Radiation n The fact that risks cannot be directly estimated at low doses does not imply that risks do not exist. Brenner, et al. Cancer risks attributable to low doses of ionizing radiation: Assessing what we really know. PNAS 24(100): 13, 761 -13, 766; 2003.

Benefits n There is no restriction on levels of exposures used in medicine, however: Exposures must be justified in terms of expected improvement in the clinical management of the patient. n All reasonable steps must be taken to keep exposures low without compromising the procedure (optimization). n International Commission on Radiological Protection Publication 60, Vol. 21, No. 1 -3 (1991), and 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n System of Protection - Justification n No practice should be adopted unless it produces sufficient benefit (societal or individual). n n The net benefit must be positive. If a practice no longer provides sufficient benefit to offset detriment, withdrawal of the practice should be considered. International Commission on Radiological Protection Publication 60, Vol. 21, No. 1 -3 (1991), and 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n System of Protection - Optimization n The radiation dose in justified practices should be kept as low as possible without diminishing diagnostic quality. n Practices should be limited only to those who will receive benefit. International Commission on Radiological Protection Publication 60, Vol. 21, No. 1 -3 (1991), and 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n “If the practice is justified and the protection optimized, the dose to the patient will be compatible with the intended medical purpose. ” International Commission on Radiological Protection Publication 60, Vol. 21, No. 1 -3 (1991), and 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n Justification is the responsibility of the referring physician and the physician who carries out the exam. There must be clinical indications for the exam. n There must be expected diagnostic yield. n Results should be expected to influence diagnosis and medical care. n International Commission on Radiological Protection Publication 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n “The physician who carries out the exam has the responsibility for the control of all aspects of the conduct and extent of the exam. ” [Optimization] International Commission on Radiological Protection Publication 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n “For most diagnostic examinations, the associated radiation hazards are typically much lower than the benefits from the acquired information. ” n “Regardless of this, care should be taken in the selection of the examination in order to be sure that the most appropriate examination has been selected and that the examination techniques have been optimized. ” International Commission on Radiological Protection Publication 62, Vol. 22, No. 3 (1993). Pergamon Press.

Benefits n “The degree of safety [of radiation exams in medicine] is now high and an examination, recommended on the basis of the clinical judgment of a qualified physician, generally brings to the patient a benefit that outweighs the unavoidable radiation risk. ” International Commission on Radiological Protection Publication 62, Vol. 22, No. 3 (1993). Pergamon Press.