Role and Effectiveness of Hypofractionated Proton Beam Therapy and Combinations with Systemic Chemotherapy in Inoperable Extrahepatic Cholangiocarcinoma.

Purpose: This study aims to assess the clinical outcomes of hypofractionated proton beam therapy (PBT) for extrahepatic cholangiocarcinoma (EHCC) and to investigate the optimal sequencing for combining PBT with chemotherapy.

Materials and methods: We retrospectively analyzed fifty-nine consecutive patients with inoperable EHCC treated with PBT. The median prescribed dose of PBT was 50 GyE (range, 45-66 GyE) in 10 fractions. The combination sequences of PBT and chemotherapy were categorized as 'Pre-PBT chemo' (chemotherapy before PBT), 'Post-PBT chemo' (chemotherapy after PBT), and 'No pre-/post-PBT chemo' (no chemotherapy before or after PBT). Overall survival (OS), progression-free survival (PFS), and local progression-free survival (LPFS) were estimated using the Kaplan-Meier method.

Results: All patients completed the planned treatments without any interruptions, and ≥grade 3 acute adverse events were noted in 1.6% of the cases. The 1-year and 2-year FFLP rates were 86.1% and 66.4%, respectively, with a median time of FFLP of 30.9 months. The 1- and 2-year OS rates were 74.5% and 25.3%, respectively, with a median survival time of 16.7 months. For prognostic factor analysis, pre- or post-PBT chemo was associated with a significantly reduced hazard ratio of 0.473 (95% confidence interval 0.233-0.959, p=0.038) in the multivariate analysis. The median OS times for the groups receiving no pre-/post-PBT chemo, pre-PBT chemo, and post-PBT chemo were 14.6, 18.2, and 21.8 months, respectively (p<0.05 for each).

Conclusion: Hypofractionated PBT for inoperable EHCC has demonstrated promising FFLP and OS rates with a safe toxicity profile. The combination of PBT with chemotherapy shows potential to improve clinical outcomes.