APPLICATION OF THE MONTE-CARLO INTEGRATION (MCI) METHOD FOR CALCULATION OF THE ANISOTROPY OF IR-192 BRACHYTHERAPY SOURCES

Source anisotropy is a very important factor in the brachytherapy qual ity assurance of high-dose rate (HDR) Ir-192 afterloading stepping sou rces. If anisotropy is not taken into account then doses received by a brachytherapy patient in certain directions can be in error by a clin ically significant amount. Experimental measurements of anisotropy are very labour intensive. We have shown that within acceptable limits of accuracy, Monte Carlo integration (MCI) of a modified Sievert integra l (3D generalization) can provide the necessary data within a much sho rter time scale than can experiments. Hence MCI can be used for routin e quality assurance schedules whenever a new design of HDR or PDR Ir-1 92 is used for brachytherapy afterloading. Our MCI calculation results are compared with published experimental data and Monte Carlo simulat ion data for microSelectron and VariSource Ir-192 sources. We have sho wn not only that MCI offers advantages over alternative numerical inte gration methods, but also that treating filtration coefficients as rad ial distance-dependent functions improves Sievert integral accuracy at low energies. This paper also provides anisotropy data for three new Ir-192 sources, one for the microSelectron-HDR and two for the microSe lectron-PDR, for which data are currently not available. The informati on we have obtained in this study can be incorporated into clinical pr actice.