Opinion
Opinion On "Conservative" Estimates of Radiation Hazards 1 Harold M. Swartz, M.D., Ph.D. The problem of extrapolating radiation hazard risks from high doses to low doses is analyzed in regard to the controversy surrounding mammography in screening women under age 50 for breast cancer. The problem of faulty risk/benefit analysis based on an erroneously high estimate of risk is discussed. The author concludes that a conservative view of risk/benefit ratios is not possible, because equal risk may be associated with performing or not performing a particular radiological procedure. INDEX TERMS:
Mammography, radiation hazard. Radiations, injurious effects
RadIology 126:267-268, January 1978
C
ONTRARY to frequently expressed comments, it is
not possible to take a "safe," conservative position in considering risk-benefit ratios for the use of radiation. An erroneously high estimate of risk can result in a loss of the medical benefit; therefore, the erroneous estimate itself causes harm. A possible case in point is the current controversy over the use of mammography in screening women under age 50 for breast cancer. As long as there are no apparent benefits from this procedure, e.g., the "H.I.P." study (1), demonstration of some associated risk will discredit the use of mammographic screening of women under age 50. Precise quantitation of the risk is not necessary in this situation. Data exist, however, that indicate there may be benefits of screening younger women (2). Therefore, we need to know the risk resulting from the associated radiation exposure, including a realistic assessment of the uncertainties of that risk. Using the data of the "BEIR" report (3) plus recently revised data on which the report is based, Upton et a/. (4) concluded that 8 cancers/ tn" patient years at risk (PYR)/ rad is a reasonable estimate of risk. They felt that the estimate might be slightly low in view of recent data that indicate an even higher rate of breast cancer in some heavily irradiated women. Also, a plausible departure from linearity in the dose-response curve could make the estimate a factor of 2 to 3 times too high. This is a well documented, thoughtful report which treats the material in an evenhanded manner, but the authors accepted the basic risk estimate in the BEIR report; I regret that they did not turn their attention to a quantitative assessment of it. A recapitulation of the basis of the risk calculations in the BEIR report is instructive. The risk factor in the BEIR report apparently is based particularly on data from the fluoroscopic examinations in Nova Scotia. The following assumptions were made in the use of the data:
(a) The dose-response curve is linear over a range that includes the radiation exposures of the women in the Nova Scotia study, and the exposures in mammography. (> 1,000 rads to
Opinion On "Conservative" Estimates of Radiation Hazards 1 Harold M. Swartz, M.D., Ph.D. The problem of extrapolating radiation hazard risks from high doses to low doses is analyzed in regard to the controversy surrounding mammography in screening women under age 50 for breast cancer. The problem of faulty risk/benefit analysis based on an erroneously high estimate of risk is discussed. The author concludes that a conservative view of risk/benefit ratios is not possible, because equal risk may be associated with performing or not performing a particular radiological procedure. INDEX TERMS:
Mammography, radiation hazard. Radiations, injurious effects
RadIology 126:267-268, January 1978
C
ONTRARY to frequently expressed comments, it is
not possible to take a "safe," conservative position in considering risk-benefit ratios for the use of radiation. An erroneously high estimate of risk can result in a loss of the medical benefit; therefore, the erroneous estimate itself causes harm. A possible case in point is the current controversy over the use of mammography in screening women under age 50 for breast cancer. As long as there are no apparent benefits from this procedure, e.g., the "H.I.P." study (1), demonstration of some associated risk will discredit the use of mammographic screening of women under age 50. Precise quantitation of the risk is not necessary in this situation. Data exist, however, that indicate there may be benefits of screening younger women (2). Therefore, we need to know the risk resulting from the associated radiation exposure, including a realistic assessment of the uncertainties of that risk. Using the data of the "BEIR" report (3) plus recently revised data on which the report is based, Upton et a/. (4) concluded that 8 cancers/ tn" patient years at risk (PYR)/ rad is a reasonable estimate of risk. They felt that the estimate might be slightly low in view of recent data that indicate an even higher rate of breast cancer in some heavily irradiated women. Also, a plausible departure from linearity in the dose-response curve could make the estimate a factor of 2 to 3 times too high. This is a well documented, thoughtful report which treats the material in an evenhanded manner, but the authors accepted the basic risk estimate in the BEIR report; I regret that they did not turn their attention to a quantitative assessment of it. A recapitulation of the basis of the risk calculations in the BEIR report is instructive. The risk factor in the BEIR report apparently is based particularly on data from the fluoroscopic examinations in Nova Scotia. The following assumptions were made in the use of the data:
(a) The dose-response curve is linear over a range that includes the radiation exposures of the women in the Nova Scotia study, and the exposures in mammography. (> 1,000 rads to
