Simultaneous integrated boost and protection proton beam therapy approach for hepatocellular carcinoma

Although simultaneous integrated boost and protection with proton beam therapy (SIB-PBT) facilitates tumor dose escalation while maintaining organ-at-risk (OAR) dose constraints, clinical outcomes are limited. This study assessed the safety and efficacy of using the SIB-PBT technique in hepatocellular carcinoma (HCC) patients.

We reviewed 47 patients with HCC who underwent SIB-PBT between 2014-2021. The radiation dose ranged from 36-67.5 Gy(RBE) in 15 fractions. SIB-PBT was used for the following reasons: minimize high-dose exposure to organs-at-risk (OARs) (n = 22, 47 %), treat targets with different dose levels (n = 6, 13 %), or both (n = 19, 40 %). Survival, local control, and toxicities were assessed using Kaplan-Meier, Fine-Gray cumulative incidence, and descriptive statistics, respectively.

Forty-one patients (87 %) had tumors located ≤2 cm from luminal gastrointestinal (GI) OARs. The median tumor diameter was 9.2 cm (range, 2.0-21.5 cm). The median EQD2 D50%, D95% and D99% of gross tumor volume were 79.8 (range, 51.1-85.9), 66.7 (range, 36.9-84.6) and 50.2 (range, 34.1-83.6) Gy(RBE)₁₀, respectively. Most patients (91 %) received a D0.5 cc of <45 Gy(RBE) to luminal GI OARs. At a median follow-up of 22 months (range, 0.8-77.0 months), the 2-year cumulative incidence of local failure was 12 %. The 2-year progression-free survival and overall survival rates were 12 % (95 % CI 4.7-23.4 %), and 49 % (95 % CI, 33.2-63.2 %), respectively. One patient experienced grade 3 acute nausea/vomiting. No GI bleeding/ulcers or grade 4 + toxicity were observed. CP + 2 occurred in 5 patients.

SIB-PBT enables OAR protection along with heterogeneous tumor dose escalation and is a safe and effective treatment for HCC tumors.