The absorbed dose-to-water calibration coefficients ND,W of some ionization chambers were determined in terms of the secondary standard chambers in 60Co gamma-ray beam based on the TRS-398 protocol. The reference absorbed dose-to-water Dw were measured using secondary standard ionization chambers of model NE 2781#0537 (0.60 cm3 volume) and NE 2771#1205 (0.69 cm3 volume) which are traceable to the dosimetry laboratory of the International Atomic Energy Agency (IAEA). This study mainly focuses on the comparative assessment of the determined ND,W coefficients of twenty cylindrical ionization chambers from various user groups. The determined ND,W coefficients were compared with the manufacturer provided ND,W coefficients. The observed percentage of deviation between the measured and the manufacturer’s ND,W coefficients among all the chambers were found to be in the range of 0.019% and -2.263% as the least and highest, respectively. The observed percentage of deviations for studied chambers were found within the IAEA’s acceptance limit of 1.5% with an exception for three chambers. This observed discrepancy with the IAEA’s acceptance limit for the three chambers out of the twenty chambers, indicates the calibration necessity before using chambers in routine reference dosimetry. In ND,W measurement, the uncertainty Uc is reported with the coverage factor k=1 that providing a level of confidence of approximately 68%.
Absorbed Dose to Water Rate in a Cyberknife VSI System Reference Field Using Ionization Chambers and Gafchromic Films
