Evaluation of BEBIG HDR ⁶⁰Co system for non-invasive image-guided breast brachytherapy

Purpose: HDR ⁶⁰Co system has recently been developed and utilized for brachytherapy in many countries outside of the U.S. as an alternative to ¹⁹²Ir. In addition, the AccuBoost® technique has been demonstrated to be a successful non-invasive image-guided breast brachytherapy treatment option. The goal of this project is to evaluate the possibility of utilizing the BEBIG HDR ⁶⁰Co system for AccuBoost treatment. These evaluations are performed with Monte Carlo (MC) simulation technique.

Material and methods: In this project, the MC calculated dose distributions from HDR ⁶⁰Co for various breast sizes have been compared with the simulated data using an HDR ¹⁹²Ir source. These calculations were performed using the MCNP5 code. The initial calculations were made with the same applicator dimensions as the ones used with the HDR ¹⁹²Ir system (referred here after as standard applicator). The activity of the ⁶⁰Co source was selected such that the dose at the center of the breast would be the same as the values from the ¹⁹²Ir source. Then, the applicator wall-thickness for the HDR ⁶⁰Co system was increased to diminish skin dose to levels received when using the HDR ¹⁹²Ir system. With this geometry, dose values to the chest wall and the skin were evaluated. Finally, the impact of a conical attenuator with the modified applicator for the HDR ⁶⁰Co system was analyzed.

Results: These investigations demonstrated that loading the ⁶⁰Co sources inside the thick-walled applicators created similar dose distributions to those of the ¹⁹²Ir source in the standard applicators. However, dose to the chest wall and breast skin with ⁶⁰Co source was reduced using the thick-walled applicators relative to the standard applicators. The applicators with conical attenuator reduced the skin dose for both source types.

Conclusions: The AccuBoost treatment can be performed with the ⁶⁰Co source and thick-wall applicators instead of ¹⁹²Ir with standard applicators.