Evaluation of NCRP Report No. 49 assumptions on workloads and use factors in diagnostic radiology facilities

A survey of modern medical institutions has been performed to measure the workload and primary beam use factors used in diagnostic x-ray installations in comparison to those suggested in Report 49 of the NCRP. Seven types of radiology installations were investigated, namely general radiographic rooms, general fluoroscopic and radiographic rooms (fluoroscopic and radiographic tubes surveyed separately), chest radiographic rooms, mammographic suites, and cardiac and peripheral angiographic suites. The radiologic technique (kVp and mAs) for each exposure performed on a total of 2396 patients was recorded either manually or by a commercially-available invasive electronic sensing system. Additionally, the direction of the primary beam during the exposure was recorded. The kVp distribution of the workload data was determined and normalized per patient for each of the seven types of installations. The total average workload per patient surveyed in each type of installation is 2.5, 13, 1.5, 0.22, 6.7, 160, and 64 mA min per patient for the above installation types. For general radiographic rooms the primary beam was directed at the floor for 69% of the total workload, with the remaining 21.5%, 6.5% and 1.6% of the workload directed toward three walls. When multiplied by the average number of patients examined weekly in each type of installation, the mean weekly workloads observed are 270, 230, 35, 44, 320, 3100, and 1400 mA min for the above-listed types of installations. Additionally, a significant fraction of the observed workloads occur at potentials much less than the kVp values typically assumed for radiation shielding.