NIMG-42. PENETRATION OF RADIOLABELED TEMOZOLOMIDE CORRELATES WITH CONTRAST ENHANCEMENT IN PATIENTS WITH RECURRENT GBM TREATED WITH BEVACIZUMAB

Abstract

Anti-angiogenic agents can decrease vascular permeability raising concern that these agents may also decrease blood brain barrier (BBB) penetration of concomitantly administered chemotherapy. We evaluated if the volume of contrast enhancement in recurrent glioblastoma (GBM) patients correlated with the volume of temozolomide penetration using MR-PET. After labeling temozolomide with the positron emitter [11C], we performed MR-PET scans in patients receiving bevacizumab 10mg/kg Q2weeks and temozolomide 50mg/m2 daily. Patients were scanned prior to bevacizumab (but after achieving steady state for oral temozolomide to minimize nonspecific binding), 1 day post first bevazicumab infusion, and prior to the third bevacizumab infusion. Tumor regions of interest were outlined on the T1-post contrast and FLAIR images. Volume of temozolomide delivery within the FLAIR hyperintensity (greatest potential extent of visible tumor) was determined by selecting all voxels above a threshold by using 3D Slicer software on the SUV map. This SUV volume was correlated to the volume of contrast enhancement and also correlated to the volume of FLAIR hyperintensity using Pearson correlation coefficient (PCC). Each visit was considered a separate data point even if it was from the same patient. Eight patients have been accrued to the study. A total of 9 MR-PET visits have been analyzed. The preliminary analysis showed the volume of contrast enhancement correlated with volume of PET uptake (PCC = 0.74) and the volume of FLAIR hyperintensity also correlated with volume of PET update (PCC = 0.86). These indicate that smaller volumes of radiolabeled temozolomide uptake corresponded to smaller contrast enhancing volumes and smaller FLAIR hyperintensity volumes. Volume of penetration of radiolabeled temozolomide correlates with contrast enhancement in patients with recurrent GBM treated with bevacizumab. Contrast enhancement may be a surrogate marker for concomitant drug delivery even with drugs such as temozolomide which penetrate an intact BBB.