SUMMARY: Proton Radiotherapy (PRT) unlike external beam radiotherapy uses energy from positively charged particles called protons and has the ability to precisely localize the radiation dose to the tumor site, minimizing collateral damage. In this retrospective analysis, data on 27,647 Medicare beneficiaries who received PRT or IMRT (Intensity-Modulated RadioTherapy) for prostate cancer, was reviewed, during 2008 and/or 2009. At 12 months post-treatment, there was no statistical difference in genitourinary and gastrointestinal toxicity for patients who had received PRT compared to those who were treated with IMRT. With PRT almost twice as expensive as IMRT, it remains to be seen if PRT will be reimbursed by third party payors. It is interesting to note that in this study, patients receiving PRT were relatively younger, healthier, and lived in more affluent areas than patients receiving IMRT. Yu JB, Soulos PR, Herrin J, et al. J. Natl. Cancer Inst. 2013;105:25-32