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Purpose: The purpose of this study was to determine whether a dose response exists for extrahepatic bile duct carcinoma (EBDC) when treated with increasingly higher radiation doses delivered via a combination of external beam radiation (EBRT) and high dose rate intracavitary brachytherapy (HDRIB). To establish the best tolerated dose of HDRIB.Methods and Materials: Eighteen patients with pathologically proven, locoregional but unresectable or incompletely resected EBDC were studied from 1991-1998 in this phase I/II trial. All patients received EBRT, delivered via megavoltage photons at standard fractionation schedules, for a total dose of 45 Gy. The HDRIB was delivered using the nucleotron HDR remote afterloading unit with a 10 Ci Ir192 source. Each treatment of HDRIB delivered 7 Gy at 1 cm depth. The first group of eight patients received one treatment of HDRIB (Group 1, total dose = 52 Gy). The second group of six patients received two weekly treatments (Group 2, total dose = 59 Gy). The last group of four patients received three weekly treatments of HDRIB (Group 3, total dose = 66 Gy). HDRIB was delivered once weekly concomitant with the EBRT. Acute adverse reactions were evaluated after for each group of patients before escalating to the next higher dose level of HDRIB.Results: The median follow up time for all 18 patients was 15 months. The median survival for all 18 patients was 12.2 months (range 2 to 79.6 months). Overall two-year survival was 27.8%. Three patients (16.7%) had survival of more than 5 years. Dose response is suggested by the median survival of the three groups (9, 12.2, and 20.3 months for Group 1, 2, and 3, respectively), although this did not reach statistical significance. Complete or partial response (>50% reduction in tumor size) was seen in 25% of patients receiving total of 52 Gy compared to 80% of patients (5 patients in Group 2 and 3 patients in Group 3) receiving greater than 59 Gy (P = 0.05). No patients developed Grade 4 complications. One patient in Group 2 developed Grade 3 toxicity after second treatment of HDRIB.Conclusion: High dose rate brachytherapy of 21 Gy in three divided weekly treatments, plus 45 Gy of external beam radiation is well tolerated. A dose response is shown with significant increase of PR and CR rate for dose >59 Gy. This modality of treatment appears to be safe and effective for inoperable extrahepatic biliary duct carcinoma. [ABSTRACT FROM AUTHOR]