Radiation Exposure from CT Examinations in Japan

Data-sheets were sent to all 126 hospitals and randomly selected 14 (15%) of 94 clinics in Gunma prefecture which had CT scanner(s). Data for patients undergoing CT during a single month (June 2008) were obtained, along with CT scan protocols for each institution surveyed. Age and sex specific patterns of CT examination, the variation in radiation exposure from CT examinations, and factors which were responsible for the variation in radiation exposure were determined.An estimated 235.4 patients per 1,000 population undergo CT examinations each year, and 50% of the patients were scanned in two or more anatomical locations in one CT session. There was a large variation in effective dose among hospitals surveyed, particularly in lower abdominal CT (range, 2.6-19.0 mSv). CT examinations of the chest and upper abdomen contributed to approximately 73.2% of the collective dose from all CT examinations. It was estimated that in Japan, approximately 29.9 million patients undergo CT annually, and the estimated annual collective effective dose in Japan was 277.4 *103 Sv person. The annual effective dose per capita for Japan was estimated to be 2.20 mSv.There was a very large variation in radiation exposure from CT among institutions surveyed. CT examinations of the chest and upper abdomen were the predominant contributors to the collective dose.Since computed tomography (CT) was introduced to medical practice, this diagnostic X-ray technique has provided great benefits for health care. In most circumstances, the risk to an individual patient of developing a malignant tumour because of CT is low and acceptable compared to the substantial benefit, although there is a large uncertainty in risk estimates at these dose levels. However, the large number of people exposed means that even small individual risks could translate into a considerable number of cancer deaths [1,2]. In the UK (2005-2006), approximately 60% of the total radiology collective effective dose was from CT [3]. In