Description: Publication date: Available online 26 December 2016 Source: Radiotherapy and Oncology Author(s): Dae Yong Kim, Joong-Won Park, Tae Hyun Kim, Bo Hyun Kim, Sung Ho Moon, Sang Soo Kim, Sang Myung Woo, Young-Hwan Koh, Woo Jin Lee, Chang-Min Kim Purpose To evaluate clinical effectiveness and safety of simultaneous integrated boost-proton beam therapy (SIB-PBT) in hepatocellular carcinoma (HCC) patients with tumour vascular thrombosis (TVT). Material and methods Forty-one HCC patients with TVT underwent SIB-PBT using three dose-fractionation schemes: if gross tumour volume 〈1 cm ( n = 27), 1–1.9 cm ( n = 7), and ⩾2 cm ( n = 7) from gastrointestinal structures, 50 GyE (EQD2, 62.5 GyE 10 ), 60 Gy (EQD2, 80 GyE 10 ), 66 Gy (EQD2, 91.3 GyE 10 ), respectively, in 10 fractions was prescribed to planning target volume 1 (PTV1), and 30 GyE (EQD2, 32.5 GyE 10 ) in 10 fractions was prescribed to PTV2. Results Overall, treatment was well tolerated, with no grade toxicity ⩾3. Median overall survival (OS) was 34.4 months and 2-year local progression-free survival (LPFS), relapse free survival (RFS), and OS rates were 88.1%, 25%, and 51.1%, respectively. Patients treated with EQD2 of ⩾80 GyE 10 tended to show better TVT response (92.8% vs. 55.5%, p = 0.002) 2-year LPFS (92.9% vs. 82.5%, p = 0.463), RFS (28.8% vs. 19%, p = 0.545), and OS (58.4% vs. 46.8%, p = 0.428) rates than those with EQD2 of 〈80 GyE 10 . Multivariate analysis showed that TVT response and Child Pugh classification were independent prognostic factors for OS. Conclusions SIB-PBT is feasible and promising for HCC patients with TVT.