Abstract
The paper on the risk of cancer from diagnostic X-rays appeared in the Lancet (363: 345-351,2004) by Prof. Darby and his colleague in Oxford University described the highest attributable risk estimate of cancer in Japan, 3.2% among the UK and 14 other countries. The present paper will make a comment on the risk estimate and its understanding on low dose risk. The risk estimate from medical exposure may contribute to judgment whether a diagnostic radiology can be justified. However, the role of the risk estimate in the paper of the Lancet is quite different since it describes the attributable risk from all the medical exposure in each country. The risk should be characterized by other aspects which can not be expressed by a single value of probability, because the risk characterization in previous radiological protection has contributed to a preventive approach but has failed to communicate with the public. The epidemiological data in the atomic bomb survivors in Hiroshima and Nagasaki show the fundamental facts that we can not detect excess cancer deaths under about 10-50 mSv if high dose rate is received. It should be stressed that these risk estimates are calculated risk not authentic one just like car accidents that are evaluated by statistics, and also that the radiation risk from a low dose can not be detected even if exposed patients would be followed up.
