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To describe population characteristics, efficacy, safety, and to identify prognostic factors associated with efficacy and safety of all patients treated by hepatic Cyberknife stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC) in our regional comprehensive cancer care center.

We retrospectively analyzed the data of 335 patients with 440 HCC treated in our center between June 2007 and December 2018. Patients had received SBRT as a first-line treatment or after other local or systemic therapies. Efficacy was estimated in terms of overall survival, progression-free survival and local control. Acute and late toxicities were described according to the 5th version of CTCAE. We used a Cox model to evaluate prognostic factors of overall survival, and logistic regression models to evaluate prognostic factors of toxicity. Finally, we collected pathological results of explanted livers for patients who had undergone liver transplantation after SBRT to evaluate response to irradiation.

Median follow-up was 70.2 months. Nearly one third of the population had received previous local treatment for the targeted HCC. The high majority of patients were treated with 45 Grays in 3 fractions. Median GTV volume was 20.3 cc (range 0.4-700.1), median CTV volume was 60.5 cc (2.5-999.4) and median PTV volume was 87.0 cc (2.6-1,067.6). Overall survival at 12, 24 and 60 months were respectively 72% (95%CI 67-77%), 45% (39-50%) and 10% (6-14%). Relapse-free survival at 12, 24 and 60 months were respectively 62% (55-67%), 28% (22-35%) and 12% (7-19%). Local control rates at 12, 24 and 60 months were respectively 97% (94-98%), 95% (91-97%) and 95% (91-97%).  Half of patients experienced acute toxicity, and 39% late toxicity. No toxicity higher than grade 3 was observed. We identified Child-Pugh score B-C, high BCLC score, the existence of portal thrombosis, and a high GTV volume and higher PTV volume reported on total hepatic volume ratio as significantly associated to the risk of death. High GTV volume and high PTV volume reported on total hepatic volume ratio  were significantly associated with the occurrence of acute toxicity. Low albumin levels before treatment and high GTV volumes were significantly associated with the occurrence of late toxicity. The analysis of 11 explanted livers showed 6 complete and 5 partial responses, but the existence of out-field disease in 8 patients.

SBRT is efficient for the management of hepatocellular carcinoma, with a favorable toxicity profile. Outcome is highly related to the natural evolution of underlying cirrhosis. This therapy can be considered in the same way as other local modalities such as transarterial chemoembolization and radiofrequency for unresectable HCC or as a bridge to transplantation.