[Survey of CT practice in Japan and collective effective dose estimation].

Computed tomography(CT) has been established as an important diagnostic tool in clinical medicine and has become a major source of medical exposure. A nationwide survey regarding CT examinations was carried out in Japan in 2000. CT units per million people in Japan numbered 87.8. The annual number of examinations was 0.1 million in those 0-14 years old, 3.54 million for those 15 years old and above, and 3.65 million in total. Eighty percent of examinations for those 0-14 years old were examinations of the head, as were 40% for those 15 years old and above. The number of examinations per 1000 population was 290. The collective effective dose was 295 x 10(3) person.Sv, and the effective dose per caput was evaluated as 2.3 mSv.