Abstract

Proton beam therapy is an external beam radiotherapy modality that offers potentially similar efficacy and reduced toxicity compared with photon radiotherapy due to little to no exit dose of radiation beyond the intended target. Improvements in radiotherapy from two-dimensional, to three-dimensional, to intensity-modulated radiation therapy have offered comparable to improved efficacy of radiation therapy with progressive reductions in toxicity. Proton beam therapy may offer further improvements, with multiple dosimetric studies demonstrating potential reductions in exposure of normal tissue to radiation, particularly bowel and bone marrow. Proton beam therapy offers avenues for dose escalation or re-irradiation, which were previously not feasible with photon radiotherapy. Although early clinical data generally demonstrate safety, feasibility, and efficacy in a few series, prospective clinical trials are limited and needed to better define who might benefit from proton therapy. In this review, we discuss the history, dosimetry, available clinical data, and technical needs to deliver high-quality proton therapy.