Impact of Proton Beam Irradiation of an Anatomic Subsegment of the Liver for Hepatocellular Carcinoma.

PURPOSE: The objective of this research was to elucidate the impact on the prognosis, including the survival prognosis, resulting from proton beam irradiation of an anatomic subsegment of the liver (ASPT) for the treatment of hepatocellular carcinoma (HCC). METHODS AND MATERIALS: A total of 110 patients who received a diagnosis of HCC were analyzed in this retrospective study. Definitive proton beam therapy was delivered at a dose of 76 Gy (relative biological effectiveness) in 20 fractions between January 2008 and December 2015. When the HCC widely abutted blood vessels or when multiple HCC tumors occurred within the same liver subsegment, the clinical target volume was outlined as an anatomic subsegment of the liver, according to the portal territory, containing the tumor. In the remaining cases, the clinical target volume was delineated by adding a 5-mm margin around the gross tumor volume. The overall survival (OS), progression-free survival (PFS), and local control rates and adverse events were assessed. A review of the medical charts assessed adverse events that occurred during and after the treatment and were classified according to the Common Terminology Criteria for Adverse Events version 4.0. RESULTS: The median follow-up duration was 36.5 months (range, 1-90.6 months). The median age of the patients was 73 years (range, 48-90 years). ASPT was performed in 31 patients (28%). Three-year OS, PFS, and local control rates were 74.2%, 40.4%, and 91.7%, respectively. Multivariate analysis identified ASPT as a factor that significantly improved PFS (P = .049) but not OS (P = .79). No association was found between ASPT and the frequency of grade ≥3 acute/late adverse events. CONCLUSIONS: ASPT was associated with a reduction in the rate of tumor progression and no significant toxicity but was not associated with OS.