OBJECTIVES: I. Evaluate the toxic effects of gadolinium texaphyrin administered to patients receiving cranial radiotherapy for glioblastoma multiforme. II. Determine the maximum tolerated dose of this regimen in these patients. III. Determine the pharmacokinetic profile of this regimen in these patients. IV. Determine the biodistribution of gadolinium texaphyrin in both neoplastic tissue and normal brain parenchyma. V. Evaluate the effect and accumulation of this regimen in normal brain parenchyma and neoplastic tissue by following the change in enhancing volume and percent change in signal intensity over time.