Tumor response on CT following hypofractionated stereotactic ablative body radiotherapy for small hypervascular hepatocellular carcinoma with cirrhosis.

OBJECTIVE: The purpose of this study is to evaluate the CT appearances of tumor responses following hypofractionated stereotactic ablative body radiotherapy for small hypervascular hepatocellular carcinomas (HCCs) and to assess the relationship between tumor responses and local control.
MATERIALS AND METHODS: Among 277 HCC tumors treated with stereotactic ablative body radiotherapy (35 or 40 Gy per five fractions), we selected enhanced lesions on arterial phase CT performed before stereotactic ablative body radiotherapy. Radiographic findings after stereotactic ablative body radiotherapy were evaluated during a 2-year follow-up period with the modified Response Evaluation Criteria in Solid Tumors. Local control and survival rates were calculated with the Kaplan-Meier method.
RESULTS: Forty-two tumors with a median size of 2.1 cm (range, 1.0-3.8 cm) were selected with a median follow-up of 23.3 months (range, 9-56 months). Local recurrence was observed in two tumors after achieving a complete response (CR). The 2-year local control rate was 97%, and the overall survival rate was 81%. CR increased from 10 (24%) to 28 (67%) to 30 (71%) tumors at 3, 6, and 12 months after stereotactic ablative body radiotherapy. Overall CR at maximum follow-up was 39 tumors (93%), yet three enhanced tumors persisted for more than 2 years. The median time to achieve CR was 5.9 months (range, 1.2-34.2 months).
CONCLUSION: The CR rate in hypervascular HCCs after hypofractionated stereotactic ablative body radiotherapy increased during the 2-year follow-up period. Cautious and continuous observation until tumor regrowth is considered relevant to evaluate a true effect of this treatment. Further studies for the optimal evaluation of treatment outcome after stereotactic ablative body radiotherapy are warranted.