P17.37SMALL INCREASES IN ENHANCEMENT ON MRI MAY PREDICT SURVIVAL POST RADIOTHERAPY IN PATIENTS WITH GLIOBLASTOMA

INTRODUCTION: To determine the rate of pseudoprogression (PsP) in glioblastoma patients (GBM) receiving chemoradiotherapy (CRT) using both modified RANO and novel volumetric analysis techniques. METHODS: Patients ≥17 years with WHO grade IV glioma managed with CRT between June 2008 and November 2011 were included. Patients with incomplete MRI image sets for all study time points were excluded. Modified RANO and two different volumetric calculations (Volumetric versus Rim analyses) were performed on post-operative MRI, and MRIs at 1 month (M + 1), 3 months (M + 3), 5 months (M + 5), 7 months (M + 7), and 12 months (M + 12) post completion of RT. Overall survival was months post definitive surgery. Modified RANO technique involved measurement of the surgical cavity with surrounding enhancement on T1 gadolinium enhanced MRI and compared subsequent scans with the baseline post-operative scan to determine response. Two novel volumetric techniques used the ARIA Eclipse radiotherapy planning software to calculate the volume (cm3) of cavity plus surrounding enhancement (Volumetric) versus the enhancement only (Rim). RANO definitions of response were implemented for all three techniques. RESULTS: 52 patients were included, with median age at diagnosis of 50 years. Seven patients were still alive at time of analysis and median survival was 18 months (95% CI 15-23). Concordance between the measurement techniques was an average of 62% agreement for RANO and Volumetric analysis, 55% for RANO and Rim analysis, and 86% for Volumetric and Rim analysis. Pseudoprogression was defined as progressive disease at M + 1, M + 3, or M + 5, with subsequent stable disease or partial response by M + 12. Using RANO technique we identified four patients (8%) with pseudoprogression. There were four patients with volumetric analysis (only one in common with RANO technique), and two patients (4%) with rim analysis (both in common with the volumetric group although none in common with RANO). Using the volumetric analysis we examined the difference in overall survival for patients that had a ≥5% increase in enhancement versus <5% at the time points M + 1, M + 3, and M + 5. There were 17 patients (33%) at M + 1 with ≥5%, 28 (54%) at M + 3, and 26 patients (50%) at M + 5. There was no significant difference at M + 1 (19 v 18 months, p = 0.548) but at M + 3 and M + 5 there was a significant improvement in survival for those with <5% increased volume: M + 3 23 v 15 months (p = 0.005), and M + 5 26 v 15 months (p = 0.004). CONCLUSION: This series of 53 patients demonstrated low rates of pseudoprogression (4-8%). An increase in the volume of the surgical cavity and enhancement of ≥5% at M + 3 and M + 5 post completion of RT was associated with reduced survival compared with patients who had <5% increase. This suggests that increase in radiological abnormality of <25% may predict survival. Further studies are required with larger sample sizes to confirm these results.