Long-term outcomes of concurrent chemo-proton therapy for unresectable stage III non-small cell lung cancer: a Japanese national registry study.

[BACKGROUND AND PURPOSE] We aimed to analyze the data from the Japan Association for Radiation Oncology Particle Beam Therapy Committee's prospective registration database to evaluate the clinical efficacy and safety of concurrent chemo-proton therapy (CCPT) for unresectable stage III non-small cell lung cancer (NSCLC).

[MATERIALS AND METHODS] The data of patients with histologically confirmed unresectable stage III NSCLC who received CCPT between May 2016 and June 2020 were extracted. Dose fractionation within the unified standard of 60-74 Gy relative biological effectiveness over 30-37 fractions and irradiation range to lymph node regions was determined at the discretion of the attending radiation oncologists. Immune checkpoint inhibitor (ICI) as adjuvant therapy was mostly administered after the provision of insurance coverage in August 2018. Toxicities were evaluated using the Common Terminology Criteria for Adverse Events version 4.0.

[RESULTS] A total of 170 patients were enrolled, of whom 156 met the eligibility criteria, including 10 patients (6.4 %) with interstitial pneumonia and 31 patients (20 %) who were ineligible for definitive chemo-radiation using x-rays due to exceeding normal dose constraints. Sixty-six patients (42 %) received ICI as adjuvant therapy. The median follow-up duration was 49.0 months, 2 and 5-year overall survivals were 72.9 % (95 % confidence interval: 66.2-80.4) and 43.7 % (35.8-53.3), and 2 and 5-year progression-free survivals were 35.4 % (28.5-43.8) and 21.3 % (15.0-30.1), respectively. Grade 2 or 3 radiation pneumonitis was observed in 19.9 % and 3.2 % of the patients, respectively, and there were no grade ≥ 4 late toxicities. In the 31 patients who were not eligible for definitive chemo-radiation using x-rays, the 2 and 5-year overall survivals were 58.1 % (43.1-78.3) and 27.5 % (14.2-53.4), respectively.

[CONCLUSION] CCPT for unresectable stage III NSCLC is considered safe and effective. Definitive treatment was possible even in patients who were not eligible for photon thoracic radiotherapy.