Radiation-induced brain metabolic changes in the acute and early delayed phase detected with quantitative proton magnetic resonance spectroscopy

Objective: Quantitative proton magnetic resonance spectroscopy (MRS) was performed before and after radiation therapy to estimate its usefulness for evaluating radiation-induced metabolic brain changes. Methods: Twenty patients with multiple brain metastases not having received any previous brain radiation were selected for the study. The total radiation dose varied from 40 (20 fractions) to 50 (25 fractions) Gy, with an opposition technique. MRS was performed just before irradiation, during the acute phase (n = 20, 8.5 +/- 4.6 days) and in the early delayed phase (n = 15, 3.6 +/- 0.5 months) after radiation. The concentration of N-acetyl-L-aspartate (NAA), choline-containing substance (Cho), and creatine/phosphocreatine (Cr) was quantified. Results: The concentration of NAA decreased (P = 0.05 versus before radiation), and the concentration of Cho increased (P = 0.006 versus before radiation) during the early delayed phase. The concentration of Cr was not changed before or after radiation. Conclusions: Radiation-induced changes in brain metabolism were well detected with quantitative MRS in the early delayed phase. Quantitative MRS is a novel tool for estimating radiation-induced neurotoxicity.