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There is increasing evidence supporting the efficacy of stereotactic body radiation therapy (SBRT) in the treatment of hepatocellular carcinoma (HCC). However, the role of SBRT has not yet been well defined within the treatment guidelines. We hypothesized that SBRT for HCC has a durable effect on tumor control and can be delivered safely. The research protocol and patient consent form were approved by the Medical Ethics Review Committee. Patients included in this retrospective study have been treated at our institution between January 2008 to December 2022. Eligibility criteria were diagnosis of HCC, case review in a multidisciplinary liver board, BCLC stage 0-A-B, noncirrhotic liver or liver with cirrhosis Child-Pugh class A, and a maximum of three lesions with a cumulative diameter of ≤ 6 cm. SBRT was considered for patients not suitable for resection or thermal ablation but eligible for TACE. Patients with relapses after surgery, thermal ablation or TACE or patients awaiting transplant were also candidates for SBRT. Exclusion criteria were uncontrolled portal hypertension and active hepatitis infection. SBRT was delivered in 6 fractions of 8 or 9 Gy applying a risk adaptive approach. The primary endpoint was local (target) control (LC). Secondary endpoints were time to (target and non-target) progression (TTP), overall survival (OS), best local response and toxicity. Treatment response was assessed for the purpose of this study on CT or MRI images by an expert radiologist using mRECIST criteria. Toxicity was defined as an SBRT related grade ≥ 3 event according to the CTCAE v4.03 scoring system. The Kaplan-Meier method was applied to analyze LC, TTP, and OS. A total of 52 patients received SBRT at our institution and 51 were included in this study. One patient objected to the use of his data and this patient was excluded. Median follow-up was 2.1 years (0.5–14.8) for tumor response and 2.3 years (0.5–14.8) for OS. Median tumor size was 26 mm (8–68). Median number of treated tumors per patient was 1 (1–3). Median LC was not reached. There was 1 local recurrence after 21 months. At 1, 2 and 5 years LC rates were 100%, 95% and 95% respectively. Median TTP was 45.6 months [95% CI, 16.1 to not reached]. Median OS was 7.1 years [95% CI, 4.9 to not reached]. Best local target response was 100%. None of the patients in this study have experienced SBRT related CTCAE grade ≥ 3 toxicity. Thirteen patients underwent a liver transplantation after SBRT with a median time interval between baseline and transplant of 7 months (3–16). SBRT resulted in excellent long-term local control rates and absence of severe toxicity in a group of HCC patients with well compensated liver cirrhosis, disease confined to the liver, limited size and number of treated tumors, and not eligible for surgery or thermal ablation but eligible for TACE. The reported outcomes compared favorably with other local therapies. SBRT should be considered as one of the available local treatment options for HCC. [ABSTRACT FROM AUTHOR]

Poster: Physics track: Treatment plan optimisation: algorithms PO-1435: Large treatment plan quality enhancement in robotic radiotherapy M. GiżyŠska, L. Rossi, W. Den Toom, M. Milder, L. Inrocci, K. De Vries, J. Nuyttens, B. Heijmen. [Extracted from the article]