Quantitative Neuroimaging and Neurocognitive Assessments to Determine Radiation Dosing Parameters to Memory Network Structures and Associated Memory Decline

Abstract

While much research has focused on radiation dose effects on the hippocampus and subsequent memory decline, identifying other structures in the memory network and associated radiation sensitivities is important. We investigated whether RT to the memory network, including hippocampus (HC), entorhinal cortex (EC), fornix, and cingulum affected verbal and non-verbal memory, with an objective of better determining dosimetric parameters to aid future RT planning. Volumetric neuroimaging was obtained on 27 patients with brain tumors prior to RT, as well as 3- and 6-months post-RT, in a prospective, observational trial. Radiation dosing parameters included minimum dose, maximum dose, mean dose, median dose, D2, D98, and V5-V60 in 5Gy increments. Memory tests included the Hopkins Verbal Learning Test (HVLT) for verbal memory and the Brief Visuospatial Memory Test (BVMT) for non-verbal memory. Reliable change indexes (RCIs) were calculated to determine significant baseline to 6-month memory changes. General linear modeling and univariate analyses were performed using SPSS. Alpha was set to 0.05 to determine significance for all analyses. From baseline to 6-months post-RT, mean HVLTtotal declined by 0.2907 (range of -0.305 to 1.52) and mean HVLTdelayed declined by 0.387 (range of -3.03 to 1.82). Significant dosimetric parameters included dose minimum (mean = 12.4 Gy, p = 0.022) and D2 (mean = 13.2 Gy, p = 0.016) to the left hippocampus. Dose minimum (mean = 13.3 Gy, p = 0.005), D2 (mean = 13.9 Gy), p = 0.007), and V35 (mean = 26%, p = 0.002), V40 (mean = 23.3%, p = 0.001), V45 (mean = 20.6%, p = 0.001), V55 (mean = 13.1%, p = 0.014), and V60 (mean 9.1%, p = 0.009) were significant for the left cingulum closest to the parahippocampal gyrus (CPG). Also, dose mean (mean = 17.4 Gy, p = 0.033) and dose maximum (mean = 31 Gy, p = 0.015) were significant for the left cingulum closest to the cingulate gyrus (CCG). See table 1 for results summary, including significant dosimetric parameters for structures involved in non-verbal memory. This longitudinal study and dosimetry analysis confirms the regional vulnerability of various structures in the memory network in contributing to both verbal and non-verbal memory decline following RT. Further investigation and analysis may help guide RT planning to better preserve memory function.Abstract 138; TableMemory testStructureRT Dosimetry ParametersParameter Meansp valuesHVLTL hippocampusDose minimum, D212.4 Gy, 13.2 Gy0.022, 0.016HVLTL cingulum closest to parahippocampal gyrusDose minimum, D2, V35, V40, V45, V55, V6013.3 Gy, 13.9 Gy, 26%, 23.3%, 20.6%, 13.1% 9.1%0.005, 0.007, 0.002, 0.001, 0.001, 0.014, 0.009HVLTL cingulum closest to cingulate gyrusDose mean, dose maximum17.4 Gy, 31 Gy0.033, 0.015BVMTR entorhinal cortexDose minimum, dose maximum, D2, D98, V35, V40, V4516.7 Gy, 37.4 Gy, 19.5 Gy, 35.4 Gy, 32.8%, 27.9%, 25.6%0.041, 0.032, 0.018, 0.009, 0.002, 0.003, 0.022BVMTR fornixV20, V25, V3042.3%, 39.2%, 27.2%0.006, 0.018, 0.024 Open table in a new tab