Abstract: We have analyzed the delivery of a novel form of radiation therapy for the treatment of breast cancer: modulated electron beam radiation therapy (MERT). The perturbations introduced by a realistic collimator system have been assessed using Monte Carlo radiation transport simulations. The changes in the electron and photon fluence have been quantified and found to be non-trivial. In particular the electron beam penumbras may be changed by interaction with the electron multileaf collimator, and photon contamination contributes significantly to the total energy fluence. An optimization system for correcting for these perturbations has been developed and reported. We propose a two stage optimization, in which the first stage selects leaf positions, while the second stage sets segment weights. This system satisfies two key requirements: the treatment plan is optimized with the inclusion of knowledge of realistic delivery effects, and the computed fluence is an accurate representation of the delivered fluence. The accuracy of the computed fluence model is necessary for any beam verification system for MERT.This is used to deliver electron radiation therapy to cancer patients. The shape of the patient's tumor determines the irregular shape of the opening on the right side. The block with the opening is custom made for each patient; it is made of a lead alloy.
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