Half‐Body Radiation Therapy Results in a Prolonged Progression‐Free Interval in Canine High‐Grade Lymphoma After First Remission

Abstract

ABSTRACT An optimal protocol of adding wide‐field irradiation to multi‐agent chemotherapy for dogs with lymphoma has not been established. The aim of this retrospective case–control study was to evaluate the efficacy of a protocol combining chemotherapy and half‐body irradiation (HBI) for dogs with high‐grade lymphoma. Dogs in the treatment group received cranial HBI 2 weeks after completing the second cycle of the multi‐agent chemotherapy protocol. The radiation therapy protocol consisted of 4 Gy/fraction once per day for 2 consecutive days for the cranial half body, followed by the same protocol for the caudal half 2 weeks later. The control group only received multi‐agent chemotherapy. All patients were required to have cytological confirmation of high‐grade lymphoma and achieve complete remission after two cycles of multi‐agent chemotherapy. Fourteen patients receiving HBI and 11 patients in the control group were included. The median progression‐free interval (PFI) in the HBI group (1143 days) was significantly longer than that in the control group (316 days, p = 0.004). In the HBI group, dogs with T cell lymphoma had statistically shorter PFI (292 days) than dogs with B cell lymphoma (2127 days, p = 0.0013). The median survival time in the HBI group (1924 days) was significantly longer than that in the chemotherapy‐only group (566 days, p = 0.0077). The predictive factors for longer PFI and ST were found in the patients who received HBI and chemotherapy (p = 0.0062 and 0.0252, respectively). For chemotherapy‐responding patients that completed a multi‐agent protocol, HBI significantly prolonged the time to tumour relapse compared with the chemotherapy‐only group.