Study objectives: To determine the efficacy and toxicity of high-dose hypofractionated proton beam radiotherapy for patients with clinical stage I lung cancer.
Design: A prospective phase 2 clinical trial.
Setting: Loma Linda University Medical Center.
Patients: Subjects with clinical stage I non-small cell lung cancer who were medically inoperable or refused surgery.
Interventions: All patients were treated with proton beam radiotherapy. The target included the gross tumor volume as seen on CT scan, with additional margin to allow for respiratory motion. A multibeam treatment plan was generated. Delivered treatment was 51 cobalt Gray equivalent (CGE) in 10 fractions over 2 weeks to the initial 22 patients; the subsequent 46 patients received 60 CGE in 10 fractions over 2 weeks.
Results: Sixty-eight patients were analyzed for this report, with a median follow-up time of 30 months. No cases of symptomatic radiation pneumonitis or late esophageal or cardiac toxicity were seen. The 3-year local control and disease-specific survival rates were 74%, and 72%, respectively. There was significant improvement in local tumor control in T1 vs T2 tumors (87% vs 49%), with a trend toward improved survival. Cox regression analysis revealed that patients with higher performance status, female gender, and smaller tumor sizes had significantly improved survival.
Conclusion: High-dose hypofractionated proton beam radiotherapy can be administered safely, with minimal toxicity, to patients with stage I lung cancer. Local tumor control appears to be improved when compared to historical results utilizing conventional radiotherapy, with a good expectation of disease-specific survival 3 years following treatment.