P05.05 Post whole-brain radiotherapy hippocampal volumetry and neuronal changes measured by MR spectroscopy

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Abstract Although cognitive impairment after radiotherapy is likely multifactorial, hippocampus (Hipp) is believed to be particularly sensitive to radiation injury due to presented neuronal stem cells involved in memory formation. Biomarkers of radiation injury can help elucidate the mechanism of post WBRT cognitive decline. In our previous prospective study, we demonstrated Hipp MR spectroscopy to be feasible and sensitive method for non-invasive measurement of radiotherapy injury. We observed decline in Hipp concentration of N-acetyl aspartat (NAA), the marker of neuronal viability and density, within left as well as right Hipp 4 months after WBRT. Herein, we present pilot data of Hipp volumetry in this patients cohort. METHODS: Structural MRI of patients involved in our previous study, where we measured Hipp NAA concentrations before and 4 months after WBRT, were retrieved. Left and right Hipp was contoured by experienced radiation oncologist and neuroradiologist. Volumes of Hipp were compared pre and post WBRT and changes were correlated to NAA concentrations. First 15 patients from our previous study were included in this pilot volumetry study (10 mens, median age 58 years, 26% renal cancer, 20% NSCLC, median overall survival 14.6 months). Mean NAA concentration in the right Hipp significantly decreased by 12% from 8.53mM to 7.43mM (0.001). Corresponding concentrations within left Hipp are 8.58mM and 7.69mM leading to significant decrease by 10.5% (0.004). Volume of right Hipp decreased by 9.2% (from median 2.52cc to 2.47cc; not significant) and left Hipp by 5.6% (from median 2.42cc to 2.27cc, not significant). DISCUSSION: We observed non significant decrease in volume of Hipp after WBRT. With no known normative standards, it is not possible to estimate an effect of small sample size to calculated p values. Remarkable difference in Hipp contouring results was observed within this pilot study. Hipp volumetry after WBRT may shed more lights into brain radioinjury, however more robust volumetry approach is needed for valid final results including correlations between volumetric data and concentrations. CONCLUSION: Significant decrease in mean Hipp NAA concentrations and non significant decrease in median Hipp volumes was observed in our patients cohort, four months after WBRT. Although presented pilot data are hypothesis generating, more patients as well as more robust approach in Hipp volumetry is needed for drawing valid conclusions.