Dosimetric comparison between the microSelectron HDR (192)Ir v2 source and the BEBIG (60)Co source for HDR brachytherapy using the EGSnrc Monte Carlo transport code

Manufacturing of miniaturized high activity (192)Ir sources have been made a market preference in modern brachytherapy. The smaller dimensions of the sources are flexible for smaller diameter of the applicators and it is also suitable for interstitial implants. Presently, miniaturized (60)Co HDR sources have been made available with identical dimensions to those of (192)Ir sources. (60)Co sources have an advantage of longer half life while comparing with (192)Ir source. High dose rate brachytherapy sources with longer half life are logically pragmatic solution for developing country in economic point of view. This study is aimed to compare the TG-43U1 dosimetric parameters for new BEBIG (60)Co HDR and new microSelectron (192)Ir HDR sources. Dosimetric parameters are calculated using EGSnrc-based Monte Carlo simulation code accordance with the AAPM TG-43 formalism for microSlectron HDR (192)Ir v2 and new BEBIG (60)Co HDR sources. Air-kerma strength per unit source activity, calculated in dry air are 9.698×10(-8) ± 0.55% U Bq(-1) and 3.039×10(-7) ± 0.41% U Bq(-1) for the above mentioned two sources, respectively. The calculated dose rate constants per unit air-kerma strength in water medium are 1.116±0.12% cGy h(-1)U(-1) and 1.097±0.12% cGy h(-1)U(-1), respectively, for the two sources. The values of radial dose function for distances up to 1 cm and more than 22 cm for BEBIG (60)Co HDR source are higher than that of other source. The anisotropic values are sharply increased to the longitudinal sides of the BEBIG (60)Co source and the rise is comparatively sharper than that of the other source. Tissue dependence of the absorbed dose has been investigated with vacuum phantom for breast, compact bone, blood, lung, thyroid, soft tissue, testis, and muscle. No significant variation is noted at 5 cm of radial distance in this regard while comparing the two sources except for lung tissues. The true dose rates are calculated with considering photon as well as electron transport using appropriate cut-off energy. No significant advantages or disadvantages are found in dosimetric aspect comparing with two sources.