Abstract
Proton therapy reduces the integral dose received by normal tissues due to its physical properties of dose deposition in the Bragg peak. In a small but significant percentage of patients requiring adjuvant radiotherapy (RT) for left-sided breast cancer, photon-based RT can lead to cardiac complications during long-term follow-up. The risk of cardiac complications is correlated with the dose to the coronary arteries and to the general 'mean heart dose'. Dosimetric comparison analysis has identified advantages of proton therapy in accomplishing sparing of the heart with increasing target complexity while permitting uncompromised target coverage of the chest wall ± breast plus draining lymphatics. Early clinical data indicate good clinical tolerance to proton therapy without unexpected complications. Several clinical trials are presently ongoing to prospectively confirm a clinical benefit and to identify the subgroup of patients benefitting most from proton therapy for breast cancer.