2525 - Memory Tract Sparing Using Diffuse Tensor Imaging in Radiation Planning of Primary Brain Tumor

O. Haisraely¹, M. ben-Ayun², A. Mayer³, M. Jaffe⁴, and Y. Lawrence²; ¹Chaim Sheba Medical Center, Ramat Gan, Israel, ²Radiation Oncology Department, Sheba Medical Center, Ramat Gan, Israel, ³SHEBA MEDICAL CENTER, RAMAR GAN, Israel, ⁴UNIC medical school, haogen, Israel

Purpose/Objective(s): Radiation therapy is an effective treatment of primary brain tumors. post radiotherapy cognitive deterioration is a major concern. The hippocampus plays important roles in the consolidation of information from short-term memory to long-term memory, and spatial memory. Most of the focused is on the avoidance of radiation to the hippocampus grey matter. The primary purpose of this study is to shown that white matter tracts (memory fibers) of hippocampal function mapped by DTI can be delineate and incorporate into RT planning as an avoidance structure without compromising PTV coverage. In addition to the purpose of this study is to show that with that approach we can minimize damage to the brain thus preserving memory function and decrease cognitive decline secondary to brain radiotherapy. DTI Diffusion tensor imaging (DTI) is an MRI imaging method that allows for imaging of the random diffusion motion of water molecules inside brain’s tissues. Integration of DTI into radiation treatment planning has been done in the past and was shown to be feasible and beneficial.. Materials/

Methods: This is a prospective trial of single cohort that been approved by the IRB . RT was deliver to a total dose of 54-60Gy in -27-30 fractions according to guidelines. During MRI simulation and before radiation therapy a diffuse sequence was performed. Two different radiation plan were performed by two different independent physicists. One with constrains on all memory fibers tract outside the PTV and one with only to the hippocampi as institution guidelines. In this trial we used the Montreal Cognitive Assessment for cogentive and memory evaluation.
Results: Recruitment was completed with 12 patients were analyzed for this analysis. The average age was 56 (42-71) with KPS>80. Dosimetrist analysis The memory fibers and Hippocampi were successfully contoured in all 12 cases. Volumetric modulated arc therapy spared the memory avoidance structures; with the mean dose to the memory fibers structures was 15.2 Gy (range, 9.4-19.1 Gy) and a maximum dose (D0.03 cm³) range of 25.1-39.8 Gy. For the hippocampi Target coverage was achieved for all plans. For comparison a 2^nd plan was created and analyzed with an independent physics without constrains to the Memory fibers. The mean dose was 18.4Gy (range 18.1-26.9 Gy) and a maximum dose (D0.03 cm³) range of 43.4 Gy (40.1-55.6), p=0.04 Cognitive analysis All 12 patients completed the MoCA test before the beginning of RT and 4 month after. The average score was 27.1 (23-30) and 26.4 (21-30) respectively, p-0.07.
Conclusion: MRI planning using DTI to detect memory fibers and incorporate into RT planning using VMAT techniques allow for sparing of the hippocampi and the white fibers that connecting into and out to the hippocampus with plausibility for memory fibers avoidance without affecting PTV coverage. Phase 2 study will open soon with primary end point for cognitive preservation with new patients cohort.