[Risk-benefit analysis for mass screening of breast cancer utilizing mammography as a screening test].

Incidence of breast cancers in Japanese women is increasing steadily. Mass screening of breast cancer was started in Japan under auspices of Adult Health Promotion Act of the Japanese Government from 1987. As the first screening method, the palpation of breasts is employed at present, but it is expected to be replaced by the mammography. In this report, the risk-benefit analysis is presented between risk of breast carcinogenesis due to radiation and benefit of mass screening of breast cancer. The benefit of mass screening is taken as the net elongation of average life expectancy of women due to survival from breast cancers. The risk of mammography is taken as the net loss of average life expectancy of women due to breast carcinogenesis. In the latter, the latency time and plateau period of radiation carcinogenesis were taken into consideration in the calculation. The results show that the ages at which the benefit and risk become equal are between 30 and 35 years old when dose equivalent of mammography is between 10 and 20 mSv, that are conventionally used. However, the critical age will be reduced to 20 years old if the dose equivalent becomes 1 mSv. Therefore, it is strongly recommended that a low dose mammographic system should be developed in order to achieve 1 mSv for the mass screening of breast cancer of Japanese women. In author's opinion, this is quite feasible by employing a new digital radiography with imaging plate.