Clinical Outcomes Following Proton and Photon Stereotactic Body Radiation Therapy for Early-Stage Lung Cancer.

We aimed to report the clinical outcomes following stereotactic body radiation therapy (SBRT) using photon or proton equipment in early-stage lung cancer. We retrospectively reviewed 202 cT1-2N0M0 lung cancer patients who underwent SBRT with 60 Gy in four consecutive fractions between 2010 and 2019 at our institution: 168 photon SBRT and 34 proton SBRT. Patients who underwent proton SBRT had relatively poor baseline lung condition compared to those who underwent photon SBRT. Clinical outcomes were comparable between treatment modalities: 5-year local control (90.8% vs. 83.6%, p = 0.602); progression-free survival (61.6% vs. 57.8%, p = 0.370); overall survival (51.7% vs. 51.9%, p = 0.475); and cause-specific survival (70.3% vs. 62.6%, p = 0.618). There was no statistically significant difference in grade ≥ 2 toxicities: radiation pneumonitis (19.6% vs. 26.4%, p = 0.371); musculoskeletal (13.7% vs. 5.9%, p = 0.264); and skin (3.6% vs. 0.0%, p = 0.604). In the binary logistic regression analysis of grade ≥3 radiation pneumonitis, poor performance status and poor baseline diffusion capacity of lung for carbon monoxide were significant. To summarize, though patients with high risk of developing lung toxicity underwent proton SBRT more frequently, the SBRT techniques resulted in comparable oncologic outcomes with similar toxicity profiles. Proton SBRT could be considered for patients at high risk of radiation pneumonitis.