Abstract
The risk of radiation exposure associated with mammography in breast cancer screening must be considered. In this study, we re-evaluated the benefit vs. risk of the mammographic procedure used for breast cancer screening in Japan, assuming a screening interval of 2 years with 2 mammography views for women aged 40-49 years and１view for those aged 50 years or more. We also used a new breast tissue weighting factor defined by ICRP 2007 and the life-time mortality coefficient defined by BEIR. The effective radiation dose used in mammography was assumed to be 0.72 mSv and 0.36 Sv for women aged 40-49 and 50 years or more respectively. The risk was expressed as loss of life expectancy (person-day) due to a single screening test. On the other hand, the benefit of screening was calculated on the basis of the number of lives saved by a stage shift of breast cancer detected by screening and then multiplying by the average life expectancy. Thus the benefit was expressed as the gain of life expectancy (person-day) due to a single screening. Finally, the benefit/risk ratio was obtained as: gain of life expectancy/loss of life expectancy as a function of age at which the benefit/risk ratio exceeded 1.0. In this study we showed that the benefit/risk ratio exceeds 1.0 from age of 25 years old or more in Japanese breast cancer screening, and so our screening is justified because the lowest age for the screenee is set at 40 years old.
