Evaluation of patient dose for barium enemas and CT colonography in Japan

The objective of this study was to assess patient doses for examinations of the lower digestive tract (barium enemas and CT colonography) in Japan. These doses were evaluated from in-phantom dose measurements using a dosemeter-implanted anthropomorphic phantom and from the knowledge of procedures of these examinations. For barium enemas, the doses, which were the sums of doses for various projections in the procedure, were separately derived for fluoroscopy and for analogue and digital radiography. For CT colonography, the doses were evaluated for the prone and the supine positions, each including the doses by scout imaging, and a single abdominal scan for routine and low-dose set-ups. For barium enemas, maximum local skin doses were less than 100 mGy despite relatively long average fluoroscopy times of 8 min; organ doses ranged from 9-26 mGy in the abdomen. The effective dose of 10.7 mSv for analogue radiography decreased by 12% when digital radiography was used, although more than 80% of the dose was due to fluoroscopy. In routine CT colonography performed using a relatively high mean effective mAs of 119 for the accurate detection of colorectal cancer and extra colonic lesions, organ doses within the primary X-ray beam were between 30 mGy and 44 mGy for paired scans whereas, in a low-dose set-up with an effective mAs of 27, they were approximately 10 mGy. Effective doses for routine and low-dose CT colonography of 23.4 mSv and 5.7 mSv were about double and half of the doses for barium enemas, respectively.