With the national cancer database, a total of 724,492 patients were identified: 871 received PRT and 723,621 received non-PRT. The factors found to be significant for receipt of PRT (all p < 0.05) include academic facility, South and West location, left-sided, ER-positive and mastectomy.

This study reported that PRT was not associated with OS for all patients. PRT remained not significant after stratifying for subsets likely associated with higher heart radiation doses, including: left-sided, inner-quadrant, mastectomy, node positivity, N2-N3 disease, and lymph node irradiation (LNI). This study concluded that further studies are required to determine non-OS benefits of PRT. In the interim, given the high cost of protons, only well-selected patients should receive PRT unless enrolled on a clinical trial.