164. 1H-MR Spectroscopy of normal brain tissue before and after postoperative radiotherapy for primary brain tumors

Abstract

Purpose The aim of the study was to reveal the impact of postoperative radiotherapy (pRT) on normai brain tissue metabolism and find out, if proton magnetic resonance spectroscopy (1 HMRS) can help in delineating tumor recurrence area. Methods and Material Spectra of 43 patients treated with pRT for glial tumors assessed by 1H-MRS were analyzed. Patients were treated with conformal 3D techniques using 6–20 MV photons to the total dose dr 60 Gy given in 30 fractions. Control group consisted of spectra registered for 30 healthy volunteers. Spectra were taken from tumor bed and from control region before pRT and from a 3 uninvolved regions 9–12 months after the end of pRT. Voxels were located in the region of low, medium and high total dose. Relative intensities of the signals due to N-acetyl aspartate (NAA), choline based compounds (Cho), mio-lnositol (ml), lactate (Lac) and lipids (Lip) were obtained. The statistical difference between means was calculated using Mann-Whitney U-test for independent samples or paired Wilcoxon test for the different dose levels for one patient. Results Spectra taken after pRT were significantly different from those obtained from healthy volunteers and those acquired before radiotherapy. The lactate and lipids signals were strong and not correlated with absorbed dose. NAA/Cr ratios were significantly lower than before pRT even for the low dose regions. These differences were increasing with radiation dose. Cho/Cr and Cho/NAA ratios increased significantly in medium and high dose area. Conclusion 1H-MRS can not help in delineating tumor recurrence area after pRT. Surgery and pRT cause alteration of brain metabolism even in regions far from the postoperative tumor bed that received relatively low total radiation dose.