Fig. 3

A 64-year-old woman was treated with 76 (relative biological effectiveness [RBE])/20 fractions of proton beam therapy for cholangiocarcinoma. Despite no pathological diagnosis, the patient was diagnosed with cholangiocarcinoma based on clinical, including imaging, findings. Chronic liver disease was not observed, and liver reserve was noted with Child–Pugh class A. The tumor is large, 134 × 128 × 125 mm, and shows hyperintense signals on magnetic resonance imaging fat-suppressed T2-weighted images (a). We diagnosed the patient with a T4N0M0 stage IIIB (Union for International Cancer Control 8th edition) cancer. Isodose lines are observed on treatment planning computed tomography (b). The proton therapy plan was prepared and incorporated two beams of 200° and 315°, and 76 relative biological effectiveness/20 fractions was prescribed. Eight months after proton beam therapy, a tendency for local recurrence was observed, and 10 months after proton beam therapy, the patient developed dyspnea due to right-sided predominant pleural effusion and was intubated (grade 4 Common Terminology Criteria for Adverse Events version 5.0)