Surgery is the standard treatment of adrenal tumours, but it's full of potential difficulties, particularly in cases of intracaval extension. Aim of this study was to evaluate the technical feasibility and therapeutic efficacy of adrenal tumour ablation using hypofractionated volumetric modulated arc stereotactic radiotherapy (VMAT) in dogs with vascular invasion.

Ten dogs suffering from adrenal tumours with vascular invasion were treated using a LINAC with micromultileaf collimator. The VMAT plans were computed using a Monte Carlo statistic algorithm and the Monaco 3.0 treatment planning system. Dose constraints have been derived from AAPM TG 101. The plan has been evaluated for quality assessment with Dosimetry Check. The prescription dose was 33–39 Gy in 3 fractions. The followup provided biochemical exams and CT/MRI. According to RECIST criteria, 7 partial responses and 3 stable diseases were obtained, but all patients showed a better performance status. Ascites disappeared immediately after the treatment completion. At 1 year, all patients are alive. In 3/4 dogs with an elevated cortisol level, a value normalization was obtained. According to VRTOG criteria, a grade I pancreatitis and a focal renal cortical atrophy were observed.

Results of this study are better than the median survival time reported in literature. Stereotactic hypofractionated VMAT may be an option in cancer treatment and control of endocrine clinical signs in dogs suffering from adrenal tumors with vascular invasion, with low morbidity and mortality rates. Further studies of dose escalation are suitable.