Proton beam therapy for patients with distal cholangiocarcinoma: a multicenter prospective registry study (Influence of age factor).

This study aimed to investigate the role of proton beam therapy (PT) in patients with unresectable distal cholangiocarcinoma (dCCA), with a special focus on elderly patients. We analyzed data from an updated multi-institutional prospective registry that included all Japanese proton beam facilities. The endpoints were local control (LC), progression-free survival (PFS), overall survival (OS) and toxicity. We included 36 patients with unresectable dCCA who were treated with PT at a median prescribed dose of 60 Gy (RBE) in 30 fractions. With a median follow-up of 12.4 months, the median survival time was 18.9 months, and the 1-year OS were 68.8%. The 1-year LC and PFS rates were 80.6 and 42.7%, respectively. The 1-year OS, LC and PFS rates for elderly patients (aged ≥80 years) were 65.6, 82.3 and 40.9%, respectively, showing no significant difference compared to younger patients (OS: 74.1%, P = 0.853; LC: 78.7%, P = 0.708; PFS: 45.5%, P = 0.654). However, four patients (11.1%) experienced grade ≥3 PT-related adverse reactions, exclusively among elderly patients (4/24 = 16.6% vs. 0/12 = 0% in younger patients, P = 0.278). These reactions were significantly higher with prescribed doses of equivalent 2-Gy fractions (EQD2)>60 Gy (3/6 = 50%) than with EQD2 ≤ 60 Gy (1/30 = 3.3%, P = 0.0104). PT showed good efficacy and acceptable toxicity for unresectable dCCA, even in patients aged ≥80 years, who showed outcomes similar to those of their younger counterparts. However, for elderly patients, a higher prescribed dose of EQD2 ≥60 Gy should be used with caution.