Neurologic improvement and tumor shrinkage after radiotherapy in dogs with imaging-based intracranial neoplasia

Background Traditional measures of treatment success for radiotherapy in dogs with intracranial neoplasia include progression-free and overall survival time. Although important, these measures do not reflect neurologic function. Hypothesis/Objectives Assess tumor shrinkage by follow-up imaging and outcome using 2 neurodisability scoring systems—1 validated and 1 simplified. Animals One hundred six dogs with imaging-diagnosed intracranial tumors treated with 10-fraction definitive-intent radiotherapy. Methods Data were collected from 2 randomized trials. Neurologic function was prospectively assessed using a validated score, and a retrospective simplified score was added. Imaging was recommended every 6 months or upon clinical decline. Results Diagnoses included extraparenchymal tumors (45.3%), intraparenchymal tumors (35.8%), and pituitary tumors (18.9%). Median follow-up was 581 days. The neurodisability score improved significantly before radiotherapy (median 1.0, P = .04) because of medical management, and again during treatment (median 0.0, P < .01). At peak response, 76% of dogs had no or only mild neurologic deficits. Tumor volume significantly decreased at 6 and 12 months (P < .01): median shrinkage at 6 months was −39% (extraparenchymal tumors), −83% (intraparenchymal tumors), and −47% (pituitary tumors). A moderate correlation between tumor reduction and neurodisability score was seen only at 6 months (r = 0.395, P = .002). Results were consistent across protocols. Conclusions and clinical importance Radiotherapy led to lasting neurologic improvement and substantial tumor reduction. Neurologic function did not always correlate with tumor volume shrinkage, emphasizing the importance of incorporating and prioritizing neurologists’ functional assessments in posttreatment evaluation.