Multileaf Collimator for Modulated Electron Radiation Therapy for Breast Cancer

摘要

Irradiation is an effective adjuvant therapy to lumpectomy, mastectomy, and chemotherapy for breast cancers of different stages. However, the conventional tangential photon beam treatment has two major limitations. Firstly, part of the lung and heart (in the case of the left breast treatment) may be exposed to high radiation dose. Secondly, the contralateral breast may receive a significant amount of scatter dose. Consequently, irradiation-related complications such as arm edema, myocardial infarction, severe breast fibrosis, and secondary breast cancer may occur in the patients who have undergone conventional photon beam treatment. To reduce radiation dose to normal structures, we have investigated treating breast cancers using MERT. To deliver MERT plans effectively, we designed and manufactured a prototype EMLC based on the results of Monte Carlo simulations and a Varian 25 x 25 sq cm electron applicator. The performance of the EMLC was experimentally evaluated and the results were compared with those of Monte Carlo simulations and a PMLC. We have also developed a complete system of Monte Carlo-based inverse treatment planning system for MERT plans. The system incorporates the Monte Carlo simulated electron pencil beams into the inverse planning process. Additionally, we have characterized the EMLC using a multiple-source beam model for fast Monte Carlo simulation. Furthermore, we have also studied the effect of beam delivery on optimized modulated electron radiation therapy plans in the final dose calculation.