SU-GG-T-57: Collimated Beams for HDR Brachytherapy Dosimetry

Abstract

Purpose: To construct and test a small 192Ir collimator for HDR brachytherapydosimetry purposes. Material and methods: The device is made up of a cerrobend cube to produce a collimated beam when a catheter from an HDR 192Ir source is inserted in the center of the cube. The cube is mounted in a calibration bench which allows the positioning of a 15 × 15 × 15 cm3 water and/or solid water phantoms in the central axis of the radiation beam at a fixed distance. The field size at the fixed calibration distance of 10 cm is 5 cm diameter. The radiation beam profile at this distance was measured with a gafchromic film, ionization chamber and calculated with the PENELOPE Monte Carlo code. Such code was also used to determine the spectra of radiation in air and at 0.5‐cm depth of both phantoms. Simulations were performed with 109 histories. Results: Calculated data have shown that both profiles (x and the z‐axis which is along the source) at a distance 10 cm away from the source is flat within 0.7%. This beam flatness was confirmed with the measurements done with the ionization chamber and with the gaphchromic film as well. Within the statistical uncertainty of the calculations (0.4%), there was no observable change in the mean energy of the input photon spectra and at 0.5‐cm depth in water phantom. Conclusion: The miniature irradiatior can be used for QA of HDR brachytherapy equipments. If the system is provided with a standard calibrated ionization chamber and appropriate phantoms, it can be used to calibrate HDR sources, TLDs films and to determine the Fricke chemical yield.