Veterinary and comparative oncology | 2021
Retrospective assessment of radiation toxicity from a definitive-intent, moderately hypofractionated image-guided intensity-modulated protocol for anal sac adenocarcinoma in dogs.
Abstract
A recent calculation study predicted acceptable toxicity in pelvic organs at risk for a new definitive-intent, moderately hypofractionated radiation therapy (RT) protocol (12 x 3.8 Gy), when used with image-guided intensity-modulated radiation therapy (IG-IMRT). We hypothesized this protocol to result in clinically acceptable radiation toxicities. Dogs diagnosed with and irradiated for anal sac adenocarcinoma (ASAC) were retrospectively assessed. Eleven dogs were included, six had prior surgery. Before any therapy, staging according to Polton et al. resulted in the following distribution: stage 1 (n=1), stage 2 (n=1), stage 3a (n=6), stage 3b (n=3). We scored radiation toxicities at the end of therapy, at weeks 1, 3, and every 3 months after RT according to VRTOG radiation toxicity criteria. Clinical follow-up was maintained on regular intervals combined with computed tomography (n=3). Median follow-up time for dogs still alive was 594\u2009days (range: 224-972\u2009days). Within 1 week post treatment, 8 dogs (73%) developed grade 2 and 4 dogs (36%) grade 1 acute toxicity in the perianal region. All acute toxicities resolved or improved to grade 1 within 3\u2009weeks after treatment. Late toxicity, e.g. chronic colitis/diarrhea, ulcerations, strictures or myelopathies was not observed in any patient. Five dogs were euthanized 105, 196, 401, 508 and 908\u2009days after RT and six dogs were still alive, one in spite of progressive disease. The median PFS was 908\u2009days (95%CI: 215;1602). The previous theoretically described definitive-intent, moderately hypofractionated protocol using IG-IMRT for the treatment of advanced ASAC showed clinically acceptable acute and late toxicities.