Published in the Green Journal, this study by Memorial Sloan Kettering Cancer reported early outcomes of postmastectomy proton radiation including clinical efficacy and toxicities. 42 patients who received mastectomy were treated with adjuvant chest wall and regional nodal proton therapy. With median followup of 35 months, there was one local failure, which occurred on the chest wall within the radiation field, approximately 2.5 years after the completion of radiation; zero regional nodal failure; and six distant failures.

The 3-year rate of locoregional disease-free survival was 96.3%, metastasis-free survival was 84.1%, and overall survival was 97.2%. All patients developed grade 1 or 2 acute skin toxicity and there was no grade 3 or 4 acute skin toxicity. Proton radiation is able to achieve excellent target coverage with median PTV V95 over 95% and heart sparing with median mean heart dose less than 1 Gy (RBE). The authors concluded that post-mastectomy proton radiation has shown excellent locoregional control rates and favorable toxicity profile. Long-term adverse effect of heart-sparing radiation will require longer follow-up time and randomized clinical trials.