Glucose metabolic changes in nontumoral brain tissue of patients with brain tumor following radiotherapy : A preliminary study

Purpose : Our goal was to measure the effect of radiotherapy on the brain glucose metabolism of tumoral and nontumoral tissue of patients with brain malignancies. Method : Fifteen patients with primary or metastatic brain tumors were studied with 2-deoxy-2-[ 18 F]fluoro-D-glucose and PET prior to radiotherapy, and nine of them were rescanned I week after completing radiotherapy. Results : Brain metabolism in patients (all brain regions except for tumoral and edematous tissue) was lower than that of matched controls (34.0 ± 8.3 vs. 46.5 ± 6.4 μmol/100 g/min ; p ≤ 0.0001). Five of the nine patients retested after radiotherapy showed decrements in tumor metabolism (47 ± 10% ; p ≤ 0.05) and increases in brain metabolism (10 ± 4% ; p ≤ 0.004), and the other four showed no changes in tumor or in brain metabolism. Radiotherapy-induced changes in tumor metabolism were negatively correlated with changes in brain metabolism (r = 0.85, p ≤ 0.004), but not with changes in tumor volume (assessed with MR images). Conclusion : The study indicates that radiotherapy-induced increases in metabolism of nontumoral tissue are secondary to decreased tumor metabolic activity and not just due to volume reduction.