Investigation report on causes of radiation underexposure accident at Yamagata University Hospital and Prevention of Similar accident

The accident in the title was announced on February 18, 2004 by the hospital, which asked its investigation immediately. The group based on 4 academic societies concerned, thereby started investigations of the in-house reports on the accident and of subsequent hospital visit in March, which involved hearing from personnel concerned, physical/technological examinations and clinical evaluation, with respect to the hospital system for radiation treatment, flow of the treatment, accident details, estimation of the actual expose dose and classification of patients. The investigational group found for the actual number of patients underexposed to be 36 (63, in the in-house report) in 1,377. The cause of the accident was thought essentially the input error for the correct power coefficient 1.032 to be a wrong one 1.320 for 15 x 15 cm 4 MV X-ray. The error had been overlooked by the contract operator from the introduction of the treatment planning equipment in 1999. For prevention, setting up of quality assurance (QA) program by the hospital, the user itself, was pointed out necessary. Making the guideline for introducing the new equipment was conceivably an important work of the trader. (N.I.)