Linac-based stereotactic radiation therapy for canine non-lymphomatous nasal tumours: 29 cases (2013-2016).

Twenty-nine dogs were treated with linac-based stereotactic radiation therapy (SRT) for non-lymphomatous nasal tumours. Only dogs with a follow-up time >365 days were included in this retrospective analysis. No dogs had evidence of distant metastasis at diagnosis. Treatment was planned and a total of 30 Gy in 3 daily 10 Gy fractions was delivered using intensity-modulation, cone-beam CT-based image guidance and a robotic treatment couch. Clinical signs improved in all cases. Nineteen dogs had CT scans 3-4 months post-SRT and all had partial or complete tumour response. Minimal acute toxicities were detected. Clinically significant late toxicities included oronasal or nasocutaneous fistulas (N = 3) and biopsy-confirmed fungal rhinitis with no evidence of tumour progression (N = 2). The median progression-free survival (PFS) was 354 days, with 49% and 39% progression-free at 1 and 2 years post-SRT, respectively. The median survival time (ST) was 586 days, with 69% and 22% alive 1 and 2 years post-SRT, respectively. Neither the clinical parameters evaluated (modified Adams' stage, histopathology, presence of intracranial extension of the tumour) nor dosimetric data were predictive for PFS or ST. This SRT protocol appears to be well tolerated, and PFI and ST are comparable or superior to those reported in other definitive-intent radiotherapy protocols.