Organ dose measurement in x-ray CT and other diagnostic radiology by using novel photodiode dosimeters installed in an anthropomorphic phantom

Dosimetry system for measuring organ doses of the patients undergoing clinical x-ray examinations was devised by using newly developed photodiode dosimeters installed in an anthropomorphic phantom realizing standard Japanese adult body. The system was constructed using pin silicon photodiode dosimeters, 32 and extra two in number, inserted at the positions of tissues or organs assigned in the ICRP's definition of the effective dose within the phantom, where the phantom was composed of tissue substitutes for soft tissue, cortical bone and lung. Dosimeter signals were read out on a personal computer to calculate organ and the effective doses with a minimum detectable absorbed dose for soft tissue of 0.01 mGy. Dose measurements were carried out in routine CT examinations with single-slice helical and multi-detector row CT scanners currently used. In thoracic CT examinations effective doses calculated from measured organ doses were 4.8 times ranged from 3.9 to 18.6 mSv among the scanners with a maximum organ dose of approximately 50 mGy at thyroid. In the CT examinations of upper-abdomen the effective doses were 3.5 times ranged from 3.9 to 13.8 mSv among the scanners with a maximum organ dose of approximately 40 mGy at stomach. Organ dose measurements in body radiography in which six different examinations were carried out using routine examination conditions indicated that organ doses greater than 1 mGy were not observed and the range of the effective doses was between 0.06 mSv in chest-PA and 0.24 mSv in thoracic spine-AP examinations. Comparison between the present results and the Japanese data of the UNSCEAR 2000 report indicates that the effective dose by UNSCEAR in lumbar spineAP examination was ten times greater than that obtained in the present study, while the doses by UNSCEAR in chest-PA and abdomen-AP examinations were coincided with our results.