Abstract
The increasing use of ionizing radiation in hospitals makes medical exposure an important source to the public dose. According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the contribution from medical exposure to the public dose by man-made radiation is over 98 %. The National Radiological Protection Board (NRPB) has conducted a survey of patient dose. The variation of patient dose for the same examination at different hospitals was very large. Computed tomography images with excellent resolution and high contrast of soft tissue have led to significant advances in medical radiology. Growth of this technique has taken place without full appreciation of the relatively high patient dose involved. The increasing use of computed tomography has drawn much attention to the international medical physics and radiation protection organizations. To provide better health care and keep patient dose to a minimum value, assessments of the typical computed tomography patient doses and the quality assurance activities are important and required.Dose distributions were measured by thermoluminescent dosimeters. Analyses of computed tomography single-scan dose profiles were made in terms of a Gaussian function for primary radiation and a Lorentzian function for scattered radiation. The contribution of primary and scattered radiation within the computed tomography dosimetry phantoms was determined and discussed. Those two functions which represent single-scan dose profiles were applied to calculate the organ-specific average dose and to predict the dose profiles of multiple scans. Computed tomography dose index and beam quality were measured by a pencil-type ionization chamber. According to the questionnaires of large-scale survey, technical factors used by computer tomography centers were compared. Organ doses and effective doses of different examinations were assessed. Computed tomography dose index and dose length product were calculated to derive the reference dose levels based on optimization considerations involving the cost-effectiveness analysis. A simple and easy way to obtain effective dose was developed. The results of this study were very valuable to understand the computed tomography radiation dose in Taiwan.