Comparison of calibration procedures of iridium-192 sources used in high dose rate brachytherapy system

Calibration of iridium-192 high dose rate (HDR) brachytherapy sources has been compared by using two independent systems. Two types of calibration systems, well-type chamber (SDS), and field dosimeter (0.6 cc graphite thimble) with nucletron calibration jig have been compared. A number of measurements have been performed to calibrate the six iridium-192 sources according to national/international protocol during the clinical half-life of the iridium-192 source. All influencing factors like room-scattering, positional errors and accuracy of source position etc. have been taken care of, because the accuracy of source position itself within the applicator can lead to an error of +/-1.2% for the radial distance of 10 cm used in the calibration jig. Taking the 0.6 cc graphite thimble results as reference, percentage root mean square error (RMS) value of 0.33% for well-type chamber has been observed. It has been found that, both the calibration systems are equally good and can, determine accurate and quick source calibration with careful measurements. Further, it should be mandatory to calibrate the source, prior to use of the source for the treatment of patients.