In an effort to both reduce and improve the monitoring of radiation dose delivered to patients during computed tomography (CT) procedures, the Dosimetry Group has an ongoing project that involves the characterization of clinical dosimeters and reference quality ionization chambers.
The goal of this project is to provide guidelines to users of these instruments for performing QA checks. The project involves use of the x-ray beam calibration facility and NIST PET/CT unit, as well as other medical/research CT facilities. Multiple CT chambers are being calibrated to determine their energy dependence and the applicability of the current reference radiation techniques dedicated for CT use. The chamber response will be used to determine the NIST proficiency test parameters for CT, including uncertainty expectations. The CT chamber data will serve as a foundation for the evaluation of the transfer of currently used reference radiation techniques for air-kerma calibration coefficients to medical CT units. Dose measurements are being performed using radiochromic film and OSL dosimeters.