Perfusion and Volume Response of Canine Brain Tumors to Stereotactic Radiosurgery and Radiotherapy

Background Stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) are highly conformal, high‐dose radiation treatment techniques used to treat people and dogs with brain tumors. Objectives To evaluate the response to SRS‐ and SRT‐treated tumors using volume and perfusion variables and to measure the survival times of affected dogs. Animals Prospective study of 34 dogs with evidence of brain tumors undergoing stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT). Methods Computed tomography and MRI imaging were used to calculate tumor volume and perfusion at baseline, and at 3 months and 6 months after treatment. Survival analysis was performed to evaluate treatment efficacy. Results Mean tumor volume significantly declined from baseline to the first recheck by −0.826 cm3 (95% CI: −1.165, −0.487) (P < .001); this reduction was maintained at the second recheck. Blood flow and blood volume declined significantly in the tumor after treatment. Median survival was 324 days (95% CI: 292.8, 419.4), and 4 dogs survived longer than 650 days. Neither actual tumor volume (hazard ratio = 1.21, P = .19) nor the change in tumor volume from the baseline (hazard ratio = 1.38, P = .12) significantly affected the hazard of death because of the tumor. Conclusions and Clinical Importance Stereotactic radiosurgery and SRT are effective treatments for reducing tumor volume, blood flow, and blood volume. Treated dogs surviving for more than 1 year are more likely to die from other causes than of their primary brain tumor. SRS and SRT should be considered for noninvasive treatment of intracranial brain tumors.