Impact of radiation dose in postoperative radiotherapy after R1 resection for extrahepatic bile duct cancer: Long term results from a single institution

Purpose: This study was conducted to evaluate the impact of radiation dose after margin involved resection in patients with extrahepatic bile duct cancer. Methods: Among the 251 patients who underwent curative resection followed by adjuvant chemoradiotherapy, 86 patients had either invasive carcinoma (n = 63) or carcinoma in situ (n = 23) at the resected margin. Among them, 54 patients received conventional radiation dose (40-50.4 Gy) and 32 patients received escalated radiation dose (54-56 Gy). Results: Escalated radiation dose was associated with improved locoregional control (5yr rate, 73.8% vs. 47.1%, p = 0.069), but not disease-free survival (5yr rate, 43.4% vs. 32.6%, p = 0.490) and overall survival (5yr rate, 40.6% vs. 29.6%, p = 0.348). In multivariate analysis for locoregional control, invasive carcinoma at the margin (HR 2.957, p = 0.032) and escalated radiation dose (HR 0.394, p = 0.047) were independent prognostic factors. No additional gastrointestinal toxicity was observed in escalated dose group. Conclusions: Delivery of radiation dose ≥ 54 Gy was well tolerated and associated with improved locoregional control, but not with overall survival after margin involved resection. Further validation study is warranted.