Clinical Outcomes of Patients with Recurrent Lung Cancer Reirradiated with Proton Therapy on the Proton Collaborative Group and University of Florida Proton Therapy Institute Prospective Registry Studies.

PURPOSE: We sought to assess clinical outcomes and toxicities of patients enrolled on two prospective registry trials with recurrent lung cancer reirradiated with PBT.

MATERIALS/METHODS: Seventy-nine consecutive patients were reirradiated with PBT at 8 institutions. Conventionally fractionated radiotherapy was used to treat the previous lung cancer in 68% of patients (median equivalent dose in 2 Gy fractions (EQD2) 60.2 Gy) or hypofractionated/stereotactic body radiation therapy in 32% (median EQD2 83.3 Gy). Nine (11%) patients received ≥2 courses of thoracic irradiation prior to PBT. ECOG performance status was 2-3 in 13%. Median time from prior radiotherapy to PBT was 19.9 months. PBT was delivered with conventional fractionation in 58% (median EQD2 60 Gy), hyperfractionation in 3% (median EQD2 62.7 Gy) or hypofractionation in 39% (median EQD2 60.4 Gy). Twenty-four (30%) patients received chemotherapy concurrently with PBT.

RESULTS: All patients completed PBT as planned. At a median follow-up of 10.7 months after PBT, median overall survival (OS) and progression-free survival (PFS) were 15.2 months and 10.5 months, respectively. Acute and late grade 3 toxicities occurred in 6% and 1%, respectively. Three patients died after PBT from possible radiation toxicity. On multivariate analysis, ECOG performance status of ≤1 was associated with OS (HR 0.35 [0.15-0.80], p=0.014) and PFS (HR 0.32 [0.14-0.73], p=0.007).

CONCLUSION: This is the largest series to date of PBT reirradiation for recurrent lung cancer, showing that reirradiation with PBT is well tolerated with acceptable toxicity and encouraging efficacy. ECOG performance status was associated with OS and PFS.