P13.07.B LACTATE LEVEL OF MRS CAN PREDICT TUMOR VOLUME CHANGES OF INTRACRANIAL MENINGIOMAS AFTER GKRS

Abstract BACKGROUND In this prospective study, we set the focus on evaluating TV changes and MRS findings of meningioma in early period after GKRS. MATERIAL AND METHODS Serial multi-voxel proton MRS and conventional MR imaging of 68 intracranial meningiomas were performed 6-month or 1-year (initial) after GKRS and then annually (follow-up). Using volumetric tool contained in Leksell GammaPlan (Ver. 10.1.1), studied cases were classified into reduction group (more than 20% TV reduction, N=30), increased group (more than 20% TV increase, N=12), or non-changed group (N=26). The changes of several metabolites, such as choline, creatine, N-acetil-aspartate, lactate, choline/creatine ratio, and lactate/creatine ratio were estimated and statistically analyzed in these groups. RESULTS The mean prescription dose was 12 Gy (range 10-20 Gy). The mean initial TV of changed group was slightly larger than those of TV non-changed groups (8.3 vs. 5.9 cm3, p=0.302). The incidence of lactate peak at initial MRS was found in 81.0% of TV changed group (vs. 23.1% of non-changed groups, P<0.001). Mean lactate/creatine ratio of non-changed group was 0.8 at 6 months or 1 year after GKRS (vs. 2.0 in TV changed groups, P=0.05). In TV changed groups, normalized lactate peak was found in 82.6% of reduction group (vs. 0% of increase group, P<0.001). Mean lactate/creatine ratio of reduction group dropped from 2.0 to 0.8 on sequential follow-up MRS (vs. 2.8 in TV increase group, P<0.001). CONCLUSION Results of this study show that level of lactate on MRS can be a predictive factor for TV changes of meningiomas after GKRS. TV reduction is related increase of lactate level after GKRS, followed by drop to normal level. However, further long-term follow-up data are needed to evaluate the exact role of MRS on GKRS-treated meningiomas.