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.