Algorithm Development of Designing a Patient-Specific Block for MC-Based Dose Calculation in Electron Beam Therapy for Breast Cancer

摘要

In order to investigate accurate dose to heart and lung in electron beam therapy for breast cancer, an algorithm for designing patient-specific electron block was developed. A voxel phantom, consisting of 5×5×5 mm~3 voxels (61×39×75) filled with four pre-defined materials including air, lung, soft tissue, and bone, was generated from a patient's CT images. Dose distribution of the patient-specific phantom by using MCNPX was calculated for the electron beam with energy of 9 MeV, and compared to that by using a conventional treatment planning system. The algorithm for designing patient-specific block of electron beam therapy for breast cancer was developed. The algorithm could simulate a patient-specific electron block from DICOM-RT. The differences between dose distributions from MC-based dose calculation and the conventional treatment planning system were investigated at the same depth. The results, from the MC-based dose calculation for the electron beam, estimated 10% less than those from the conventional treatment planning system at the same depth, due to the limitation of the conventional algorithm in accurate modeling of electron scattering in heterogeneous phantom. It is expected that the algorithms can be directly applied to MC-based dose and output factor calculation for patient-specific block in electron beam radiotherapy.