Transit dose comparisons for 60Co and 192Ir HDR sources.

Abstract

The goal of this study is to evaluate the ambient dose due to the transit of high dose rate (HDR) 60Co sources along a transfer tube as compared to 192Ir ones in a realistic clinical scenario. This goal is accomplished by evaluating air-kerma differences with Monte Carlo calculations using PENELOPE2011. Scatter from both the afterloader and the patient was not taken into account. Two sources, mHDR-v2 and Flexisource Co-60, (Elekta Brachytherapy, Veenendaal, the Netherlands) have been considered. These sources were simulated within a standard transfer tube located in an infinite air phantom. The movement of the source was included by displacing their positions along the connecting tube from z  =  -75 cm to z  =  +75 cm and combining them. Since modern afterloaders like Flexitron (Elekta) or Saginova (BEBIG GmbH) are able to use equally 192Ir and 60Co sources, it was assumed that both sources are displaced with equal speed. Typical HDR source activity content values were provided by the manufacturer. 2D distributions were obtained with type-A uncertainties (k  =  2) less than 0.01%. From those, the air-kerma ratio 60Co/192Ir was evaluated weighted by their corresponding typical activities. It was found that it varies slowly with distance (less than 10% variation at 75 cm) but strongly in time due to the shorter half-life of the 192Ir (73.83 d). The maximum ratio is located close to the tube. It reaches a value of 0.57 when the typical activity of the sources at the time when they were installed by the vendor was used. Such ratio increases up to 1.28 at the end of the recommended working life (90 d) of the 192Ir source. 60Co/192Ir air-kerma ratios are almost constant (0.51-0.57) in the vicinity of the source-tube with recent installed sources. Nevertheless, air-kerma ratios increase rapidly (1.15-1.29) whenever the 192Ir is approaching the end of its life. In case of a medical event requiring the medical staff to access the treatment room, these ratios indicate that the dosimetric impact on the medical team will be lower, with a few exceptions, in the case of 60Co-based HDR brachytherapy as compared to 192Ir-based one when typical air-kerma strength values are considered.

Cite this paper

@article{GimnezAlventosa2016TransitDC, title={Transit dose comparisons for 60Co and 192Ir HDR sources.}, author={Vicent Gim{\'e}nez-Alventosa and Javier Vijande and Facundo Ballester and Jos{\'e} P{\'e}rez-Calatayud}, journal={Journal of radiological protection : official journal of the Society for Radiological Protection}, year={2016}, volume={36 4}, pages={858-864} }