KS03.5.A COMPARING VOLUMETRIC GROWTH-RATE AND RANO CRITERIA IN DETERMINING THE RESPONSE OF MENINGIOMA TO BEVACIZUMAB THERAPY

Abstract INTRODUCTION Meningioma is the most prevalent primary tumor in the central nervous system (CNS). Although mostly benign, 15- 20% are aggressive and tend to recur and progress despite surgery and adjuvant radiation. Recent publications show that bevacizumab, a vascular endothelial growth factor inhibitor, effectively treats these refractory meningiomas. The standard method to monitor treatment’s effect on imaging is Response Assessment in Neuro-Oncology criteria (RANO). Recently, an alternative tool called 3D volumetric growth rate (3DVGR) has emerged as a result of significant advancements in the accuracy of volumetric measurement techniques. Our aim is to compare the effectiveness of conventional RANO criteria and the emerging 3DVGR measure in evaluating the response to bevacizumab treatment in patients with refractory meningiomas. We will also assess their correlation with clinical outcomes over a period of up to 9 months. METHODS 68 MRI scans of 20 patients with aggressive meningiomas that progressed after radiation therapy and then received Bevacizumab were evaluated. Scans were obtained from two tertiary cancer centers. For each tumor both RANO and 3DVGR were conducted in two subsequent head MRI studies acquired prior to the initiation of bevacizumab treatment and then in at least one exam within 6 months post-treatment. Measurements were obtained using PACS and BRAIN LAB software by two radiologists. RESULTS A total of 43 lesions derived from 13 males and 7 females were included in the final analysis. The mean age was 65.5; mean number of pre-radiation treatments was 2.66; mean number of pre-surgical treatments was 2.7 and mean number of bevacizumab cycles was 22.7. All lesions showed a decrease or stabilization in growth rate compared to baseline. More specifically, 34 out of 43 lesions (79%) showed a negative growth rate value indicating decrease in tumor size. Comparison of treatment response using RANO criteria was not always in concordance with the 3DVGR measurement and showed inaccurate correlation with clinical outcome. CONCLUSIONS Although widely accepted for treatment response evaluation, RANO criteria are not an accurate technique for irregularly shaped lesions. As shown in our study, for atypical meningiomas, the 3DVGR measure seems to be more precise compared to RANO criteria. Furthermore, our results show great promise for treatment of refractory meningiomas with bevacizumab.