Tumor shrinkage after simultaneous proton therapy for multiple hepatocellular carcinomas

There are no reports on shrinkage of multiple hepatocellular carcinomas (HCCs) after simultaneous treatment with radiotherapy. The purpose of the study was to examine the relationship between tumor shrinkage and treatment outcomes for several HCCs irradiated simultaneously using proton beam therapy (PBT). The subjects were 46 patients with multiple HCCs (95 lesions) who received PBT between January 2008 and December 2018. Overall survival (OS), local control (LC) and complete+partial response (CR + PR) rates were determined using the Kaplan-Meier method. The median follow-up period was 29.2 months and the 3-year OS was 50.3%. For the 95 lesions, the 3-year LC rate was 90.4% and the CR + PR rate was 85.2% at 3 years. Three combination protocols (referred to as A, B and C) were used for different lesions in the same patient: A (66 Gray (Gy) Relative biological effectiveness (RBE) in 10 fractions (fr))-B (72.6 Gy(RBE) in 22 fr) (22 lesions), A-C (74 Gy(RBE) in 37 fr) (15 lesions) and B-C (2 lesions). The 1-year CR + PR rates were 75.8% for A and 56.4% for B in A-B cases (P = 0.14), and 62.5% for A and 57.1% for C in A-C cases (P = 0.35). In the B-C group, there was only one patient with 2 lesions. The lesion treated with the B protocol reached CR + PR, while that treated with the C protocol did not reach CR + PR. These results show that some cases can have differences in tumor shrinkage after concurrent PBT for multiple HCCs, and that there is no significant relationship between dose and tumor shrinkage.