The Study: Even if you’re a devoted IMN believer and always include them in regional nodal irradiation volumes, you’ve undoubtedly encountered anatomic scenarios that tested your faith. This single-arm phase 2 trial of protons at Mass General was designed to address just those scenarios. Enrolled patients were a highly select group for who photon-planning resulted in: 1) inadequate target coverage due to reconstruction, 2) a heart volume ≥5% receiving ≥20 Gy, or 3) a left anterior descending coronary artery max dose of ≥20 Gy. Given the selection criteria, we’re not surprised the vast majority (94%) had left sided or bilateral tumors and nearly 10% had gross IMN disease. Regardless of selection criteria, we’re not surprised selected patients overwhelmingly were <50 years old and had insurance that covered protons. Prescriptions were standard at 45-50.4 Gy, with protons achieving a median of 48.8 Gy to the IMNs and a median mean heart dose of just 0.5 Gy. Here’s where we get into the weeds. Despite enrollment criteria mainly related to cardiac dosimetry, the primary endpoint was grade 3+ pneumonitis, which no patient experienced. Ok, sure. We all know no small phase 2 trial could ever show us a meaningful clinical cardiac outcome over a short period of time, but they did note no changes in stress echo or cardiac biomarkers. The ongoing RadCOMP trial, on the other hand, is actually designed to compare major cardiac event outcomes between proton and photon breast radiation.
TBL: Among mostly young women with left-sided breast cancer receiving regional nodal irradiation, proton therapy produces excellent target coverage with miniscule cardiac doses and low rates of lung toxicity. | Jimenez, J Clin Oncol 2019