Utility of Early Posttreatment PET/CT Evaluation Using FDG or 18F-FCH to Predict Response to 90Y Radioembolization in Patients With Hepatocellular Carcinoma

BACKGROUND. Assessment of hepatocellular carcinoma (HCC) treatment response after transarterial radioembolization (TARE) is challenging, because response by conventional imaging criteria may not become apparent until 6 months after treatment. Though HCC exhibits variable avidity for FDG, some cases of HCC without avidity for FDG show avidity for ¹⁸F-fluorocholine (¹⁸F-FCH). OBJECTIVE. The purpose of this study was to evaluate the utility of early posttreatment evaluation by PET/CT using FDG or ¹⁸F-FCH to predict 6-month treatment response and survival after TARE in patients with HCC. METHODS. This retrospective study included 37 patients (mean age, 67 years; 34 men, three women) with documented HCC treated by TARE who underwent both pre-treatment FDG PET/CT and ¹⁸F-FCH PET/CT and early FDG PET/CT and/or ¹⁸F-FCH PET/CT 4-8 weeks after treatment; FDG PET/CT and ¹⁸F-FCH PET/CT examinations were performed on separate dates. Only one of 73 initially identified potentially eligible patients was excluded because of lack of HCC avidity for both FDG and ¹⁸F-FCH. Response assessment by modified RECIST (mRECIST) on multiphase CT or MRI was performed at 1 month and 6 months in 23 patients. Early responses seen on PET/CT and 1-month mRECIST response were assessed as predictors of 6-month mRECIST response. Univariable and multivariable predictors of overall survival (OS) were identified. RESULTS. On pretreatment PET/CT, 28 (76%) patients were FDG-positive (showed visual uptake on FDG PET/CT and tumor-to-normal liver ratio > 1.15), 15 (41%) were FCH-positive (showed visual uptake on ¹⁸F-FCH PET/CT), and six (16%) were both FDG-positive and FCH-positive. Twelve of 28 FDG-positive HCCs exhibited early response by FDG PET/CT; seven of 15 FCH-positive HCCs exhibited early response by ¹⁸F-FCH PET/CT. Twelve (52%) patients exhibited 6-month mRECIST response. Response seen on early posttreatment PET/CT exhibited 100% (12/12) sensitivity and 100% (11/11) specificity for 6-month mRECIST response, whereas 1-month mRECIST response exhibited 67% (8/12) sensitivity and 100% (11/11) specificity for 6-month mRECIST response. Response seen on early posttreatment PET/CT was a significant independent predictor of OS on univariable (hazard ratio [HR], 0.4; 95% CI, 0.2-0.9; p = .03) and multivariable (HR, 0.2; 95% CI, 0.1-0.8; p = .01) analyses. CONCLUSION. Early evaluation after TARE by PET/CT using FDG or ¹⁸F-FCH may pre dict 6-month response and OS in patients with HCC. CLINICAL IMPACT. Early posttreatment evaluation with PET/CT could help more reliably identify true nonresponders after TARE, which in turn could prompt early response-adapted therapeutic management.