P16.04USE OF 18F-FLUOROMETHYLCHOLINE PET IN EARLY TREATMENT RESPONSE ASSESSMENT IN GLIOBLASTOMA PATIENTS

Early detection of effectiveness of radiation therapy and concomittant temozolomide (TMZ) in glioblastoma (GB) patients is important and currently evaluated using magnetic resonance imaging (MRI) only. However, pseudo-progression on MRI makes accurate assessment of treatment response difficult. As metabolic changes are likely to precede anatomical changes, positron emission tomography (PET) with [18F]-fluoromethyl-dimethyl-2-hydroxyethylammonium (18F-fluoromethylcholine, 18F-FCho) may be a tool for GB treatment monitoring. METHODS: In this study 10 GB patients without resection or debulking of the tumor only, who received concomittant radiation therapy (RT) and TMZ, are included in the study. RANO criteria were used to define responders (R) versus nonresponders (NR) 1 month after completion of RT. Dynamic PET with 18F-FCho scans were performed before the start of RT, during RT (at week 2, 4 and 6) and 1 month after the completion of RT. At each time point a metabolic tumor volume (MTV) was defined as 40% SUVmax within the 95% isodose. Mean and maximal standard uptake values (SUVmean and SUVmax), mean and maximal lesion to normal ratios (LNRmean and LNRmax) and the % change of these variables between all time points were assessed. Mann-Whitney U test was performed to identify the PET variables that were able to predict response. RESULTS: Using the RANO criteria, 6 patients were categorized as NR and 4 patients as R. Mann-Whitney U test revealed no statistically signifcant difference in SUVmean and SUVmax between R and NR pre-RT. MTV and MTVxSUVmean at week 6 (both p = 0.032) and at 1 month after the completion of RT (p = 0.032 and p = 0.016, respectively) were statistically significantly lower in R than in NR. The % change in SUVmax (p = 0.038), % change in SUVmean (p = 0.038), % change in MTV (p = 0.010) and % change in MTVxSUVmean (p = 0.010) between pre-RT and 1 month after the completion of RT were statistically significantly lower in R than in NR. Also, % change of SUVmax between week 4 and 6 of RT was significanlty lower in R than in NR (p = 0.032). CONCLUSION: Based on our results, pre-RT 18F-FCho PET cannot discriminate R from NR. Discrimination between R and NR according to RANO criteria applied 1 month after the completion of RT, can at the earliest be made during RT, namely by assessing % change in SUVmax between week 4 and 6.