Development of a organ dose measuring system to investigate exposure dose to pediatric patient by diagnostic x rays

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The objective of this study was to devise a convenient dosimetry system for measuring organ doses of pediatric patients undergoing clinical x-ray examinations and particularly CT scans delivering high exposure doses, and to investigate the level of doses deposited to pediatric patients by medical exposure from diagnostic x-rays.1. The dosimetry system was constructed using newly developed photodiode dosimeters installed in an anthropomorphic phantom realizing standard six-year-old Japanese children, 20 kg in weight and 115 cm tall. Spherical silicon photodiode dosimeters, 32 in number, were implanted at the positions of the tissues or the organs assigned in the ICRP's definition of the effective dose within the phantom. Electronic circuits were devised, which converted current signal generated in each dosimeter to the signal proportional to the dose deposited through exposure to x-rays. Also developed was a computer program which could read out dosimeter signals to a personal computer through analog-to-digital converters and convert the signals to absorbed doses for soft tissue calibrated by using standard ion chamber dosimeter to calculate organ and the effective doses.2. Exposure dose measurements were carried out using the new organ dose measuring system in routine pediatric chest, abdomen and head CT examinations by using multislice helical CT scanners of recent or the latest models from typical manufacturers as Siemens (Germany) and Toshiba (Japan). Using our new system we could obtain a large amount of data to explicate the present dose levels for pediatric patients in x-ray CT examinations. The data obtained indicated the effectiveness of dose reducing technique adopted by the recent CT scanners and clarified the reduction of organ doses by the use of tube current modulation mechanism adopted by these CT scanners.