To determine if proton radiotherapy (PT), compared to intensity modulated radiotherapy (IMRT), delayed time to cognitive failure in patients with newly diagnosed glioblastoma.


Eligible patients were randomized unblinded to PT vs. IMRT. The primary endpoint was time to cognitive failure. Secondary endpoints included overall survival (OS), intracranial progression-free survival (PFS), toxicity, and patient-reported outcomes.


A total of 90 patients were enrolled and 67 were evaluable with median follow-up of 48.7 months (range 7.1-66.7). There was no significant difference in time to cognitive failure between treatment arms (HR, 0.88; 95% CI, 0.45 to 1.75; P=0.74). PT was associated with a lower rate of fatigue (24% vs. 58%, P=0.05), but otherwise there were no significant differences in patient-reported outcomes at 6 months. There was no difference in PFS (HR, 0.74; 95% CI, 0.44 to 1.23; P=0.24) or OS (HR, 0.86; 95% CI, 0.49 to 1.50; P=0.60). However, PT significantly reduced the radiation dose for nearly all structures analyzed. The average number of grade 2 or higher toxicities was significantly higher in patients who received IMRT (mean 1.15, range 0-6) compared to PT (mean 0.35, range 0-3; P=0.02).


In this signal seeking phase II trial, PT was not associated with a delay in time to cognitive failure but did reduce toxicity and patient reported fatigue. Larger randomized trials are needed to determine the potential of PT such as dose escalation for glioblastoma and cognitive preservation in patients with lower grade gliomas with a longer survival time.