Intrahepatic cholangiocarcinoma is the second leading primary hepatic tumors, accounting for 5% of all hepatic tumors. The curability depends on the operability; however, the difficulty of early diagnosis and late clinical presentation account for the poor prognosis. Therefore, development of a novel therapeutic option and a method to determine the viability of the primary tumor, which hinder the assessment of the impact of other therapies, including chemotherapy and radiotherapy are needed. Although FDG-PET has been used to detect distant metastases of ICC, which are present in 20% of patients at the initial diagnosis, little is known about the efficacy of FDG-PET of the primary lesion of ICC. Here, we present the case of a 31-year-old male diagnosed with unresectable ICC and successfully treated with carbon-ion radiation, and present the usefulness of fluorodeoxyglucose-positron emission tomography in the determination of the viability of the tumor.