小児X線CT検査における実効線量の評価

X-ray computed tomography (CT) images are used for diagnostic and therapeutic purposes in various medical disciplines. In Japan, the number of facilities that own diagnostic CT equipment, the number of CT scanners, and the number of CT examinations increased by approximately 1.4-, 1.5-, and1.6-fold between 2005 and 2014, respectively. CT operators (medical radiological technologist, medical physicist, and physician) must understand the radiation exposuredoses for examinations at their own institutions and carefully approach each examination. In addition, the patients undergoing the examination (as well as his/her family) must understand the effective dose of each examination in the context of the cumulative dose. The numbers of pediatric patients (aged 0-5 years) and total patients who underwent CT at Hirosaki University Hospital between January 2011 and December 2015were surveyed, and effective doses administered to children aged 0, 1 and 5 years were evaluated. Age-and region-specific conversion factors and dose-length products obtained from the CT scanner were used to estimate the effective doses. The numbers of CT examinations performed in 2011, 2012, 2013, 2014, and 2015were 16,662, 17,491, 17,649, 18,242，and 18,206, respectively, of which1,052(1.2 %) of the overalltotal involved children aged 0-5 years. The estimated effective doses per examination to children aged 0, 1, and 5 years were 5.6 ± 4.1, 4.4 ± 3.1, and 2.9 ± 2.8mSv, respectively. This large variation was attributed to several factors associated with scan methods and ranges in actualsetting. In conclusion, the need for individual patient prospective exposure management systems and estimations of low-dose radiation exposure should be considered in light of the harmful effects of exposure.This study will encourage medical staffs to recognize and understand the effective dose estimation and help to the necessity and introduction of radiation dose management system for each child