Monte Carlo calculation of shielded colpostat effect on rectum received dose in high dose rate brachytherapy with Cobalt-60 sources

Abstract

Background: In the current study the effect of shielded colpostat on rectum received dose was calculated in cervical brachytherapy using Monte Carlo (MC) method. Materials and Methods: Two 60 Co sources of GZP6 brachytherapy unit used for intracavitary treatments were simulated using MCNPX Monte Carlo code. Also the two types of colpostats including shielded and unshielded were simulated inside a water phantom. The radial dose func'on, depth doses and dose distribu'on around sources were calculated with spa'al dose resolu'on of 2×2×2 mm. The effect of tungsten shields on rectum dose was studied. Moreover, the accuracy of treatment planning system (TPS) was verified comparing to MC results. Results : Our results showed that shielded colpostats reduce the rectum dose up to 7% according to the MC calcula'ons. Also, it was found less than 3% dif ference between TPS and MC results in percentage depth dose and radial doses for unshielded case. Conclusion: It can be concluded that the applica'on of shielded colpostats provide a rela'vely mild protec'on (7% reduc'on in dose) for the rectum in intracavitary brachytherapy due to the higher energy of 60 Co