Published in the Red Journal, this study reported the safety data from the first multicenter phase I trial investigating the use of hypofractionated proton therapy with concurrent chemotherapy for patients with stage II or III NSCLC. This study followed a stepwise 5+2 dose-intensification protocol with the following dose arms: (1) 2.5 GyRBE/fraction to 60 GyRBE; (2) 3.0 GyRBE/fraction to 60 GyRBE; (3) 3.53 GyRBE/fraction to 60.01 GyRBE; and (4) 4.0 GyRBE/fraction to 60 GyRBE. Eighteen patients were treated, including 5 patients on arms 1 and 2, 7 patients on arm 3, and 1 patient on arm 4.

Two SAEs occurred among 7 patients treated at 3.53 GyRBE/fraction; however, per outside expert review, both were attributed to chemotherapy and unrelated to radiotherapy. Although this study closed early due to slow accrual and competing enrollment in NRG 1308 before accrual was met, the authors concluded that hypofractionated proton therapy delivered at 2.5-3.53 GyRBE/fraction to a dose of 60 GyRBE with concurrent chemotherapy has an acceptable toxicity profile.