Radiation exposure dose outside the irradiation field due to differences in pediatric head computed tomography scanning methods

The use of pediatric computed tomography (CT), a valuable imaging tool, has been increasing rapidly. The present study examined radiation exposure in non-irradiated fields of CT scans in pediatric patients using a 7-year-old child phantom. Radio-photoluminescence glass dosimeters were placed in the insertion ports of the phantom corresponding to the organs. For the helical and the non-helical scans, the doses to the head in the irradiation field were 54.6 mGy and 53.4 mGy, respectively. The dose measured for the helical scan was 2.3% higher than that for the non-helical scan. The largest dose was in the thyroid gland, and the doses for helical and non-helical scans were 5.37 mGy and 3.58 mGy, respectively. The difference in the dose between helical and non-helical scans was 1.79 mGy. The dose measured for the helical scan was 50% higher than that for the non-helical scan. The dose to which the thyroid gland was exposed outside the irradiation field in the head CT scan was 5.37 mGy using the helical scan method. The excess relative risk per gray increased by 3-5.5% if the excess relative risk per gray was 5-10. Decreasing the dose to the thyroid gland, which has a high risk of cancer after radiation exposure, is desirable. The dose to the thyroid gland was higher in the helical scan than in the non-helical scan. This is probably because overscanning, which is unique to helical scanning, increases the exposure dose outside the irradiation field.