Calibration of New High Dose Rate 192Ir Sources

The increased popularity of high dose rate (HDR) brachytherapy in the treatment of neoplastic disease has resulted in the introduction of new or redesigned 192Ir sources by various manufacturers. In order to provide accurate clinical dosimetry, accurate calibration of these sources is required. In this work, two new sources are calibrated with the standard, NIST traceable, in-air calibration technique. These sources are the Varian VariSource (VS2000) and the newly redesigned Nucletron MicroSelectron source. An uncertainty budget was performed to determine the overall uncertainty of the measurement, and a total relative expanded uncertainty (k = 2) of 2.15% was calculated. The results of the source calibration using the in-air technique and that obtained based upon the 1991 standard calibration all lie well within this uncertainty. In addition to the in-air calibration, contact autoradiographs of the sources were made with International Specialty Products model HD810 radiochromic film to demonstrate the sources relative dose distributions.