Hypofractionated proton beam therapy for centrally located lung cancer

Introduction: To clarify the efficacy and safety of hypofractionated proton beam therapy (PBT) for centrally located lung cancer.

Methods: We retrospectively reviewed 39 patients who received hypofractionated [≧3 Gy (relative biological effectiveness: RBE)/fraction] PBT for centrally located cT1-2N0M0 (8th edition) lung cancer between 1999 and 2015. A tumour within 2 cm of the proximal bronchial tree was defined as a centrally located tumour.

Results: Twenty-four patients (62%) were treated with 80 Gy (RBE) in 20 fractions (112 Gy₁₀ ), whereas eight (21%) were treated with 66 Gy (RBE) in 10 fractions (109.56 Gy₁₀ ). The median follow-up period for censored patients was 48 months (range: 4-140). The 2-year progression-free survival (PFS) and overall survival (OS) rates were 86 and 100% for T1 disease and 56 and 94% for T2 disease, respectively. Patients who received 110 Gy₁₀ or higher showed significantly better PFS than those who received less than 110 Gy₁₀ , while no significant difference was noted in OS between the two groups. The sites of the first progression were local in six patients (27%), regional in seven (32%), distant in seven (32%), and local and distant in two (9%). Among the 13 patients with loco-regional recurrence, only two (15%) received treatments with curative intent. Dyspnoea of grade 3 was noted in one patient (3%), and pneumonitis of grade 2 was noted in four patients (10%).

Conclusion: Hypofractionated PBT may be a very safe and effective treatment option for centrally located early lung cancer.