Meningiomas are the most common intracranial tumours of dogs. The aims of this study were to quantify tumour volume reduction (TVR) after surgical treatment and radiotherapy and to assess the association of TVR with survival time. The clinical database (2001-2006) of the Animal Health Trust was searched for dogs with a histologically confirmed diagnosis of intracranial meningioma. Dogs that had undergone hypofractionated radiotherapy 1-3 months after intracranial surgery and at least one follow-up MRI scan 2-4 months post-radiation were included. Tumour volume was measured on gadolinium-enhanced T1-weighted MR images using a commercial software program (Able software 3D-doctor^TM). Follow-up was obtained from the medical records and telephone interview with the owners. Survival time was calculated from the date of diagnosis by MRI. Survival analysis using Cox proportional hazards regression was used to examine the effect of TVR on survival. Kaplan-Meier estimates of the median survival time (MST) are reported with 95% confidence intervals.

Nine dogs met the inclusion criteria. The median TVR at the first re-scan was 828 mm3 (735 to 5961). The median TVR expressed as a percentage was 100% (-19 to 100). The MST from date of diagnosis by MRI was 695 days (221 to 1169). There was no association of TVR with survival (P>0.1). Based on these pilot data it is estimated that this retrospective study had 55% power to detect a statistically significant difference with 95% confidence (alpha=0.05). A larger prospective study is being planned with repeat MRI scans scheduled at regular intervals post therapy.