Mortality of british radiologists: a lecture note.

The precautions introduced after the first 23 years experience of the use of x-rays for medical diagnosis proved adequate to eliminate the acute hazards of exposure, but it was much longer before it was realized that small doses that did not produce any acute effect could increase the risk of cancer. British radiologists who took up the specialty at different periods have, therefore, been studied to see if the risk has now been adequately controlled. Four groups have been studied starting respectively before 1921, in 1921-34, 1935-54, and 1955-77, corresponding approximately to periods when different limits of exposure were applied. Altogether 2698 male radiologists have been identified and all but 27 followed successfully to emigration, death, or survival to January 1st 1997. Of the 1198 who had died, 228 are known to have died of cancer. Two problems arise in evaluating the carcinogenic hazard to which they were exposed: the assessment of the doses received and the selection of an appropriate control group with which to compare their mortality. The most appropriate comparison group would seem to be medical practitioners in general. In comparison with them, radiologists entering in the first 3 periods had increased risks of death from cancer though appreciably less than would have been predicted from the expected effect of the radiation they had received. Those who joined in the latest period had a relatively reduced risk, irrespective of any effect of the small dose of radiation they are likely to have received. Independent evidence suggests, however, that since 1951 radiologists have smoked less than other doctors and the lower than predicted risk in the groups exposed since 1920 is limited to smoking related cancers, the mortality from other cancers being higher than in doctors generally. In assessing the risk of occupational exposure to radiation, life-style has to be taken into consideration, as well as dose of radiation.