Short-term CT and MR changes in brain tumors following 125I interstitial irradiation.

ABSTRACT

PURPOSE: The study was undertaken to assess characteristic short-term CT and MR changes in brain tumors following 125I interstitial irradiation. METHOD: Sixteen patients were included who had both CT and MR control examinations at regular intervals over a period of 18 months following treatment. Two groups were distinguished low grade tumors (11 cases) and high grade malignancies (5 patients). 125I seeds were used as temporary implants. The cumulative dose was 50-60 Gy. RESULTS: In some patients of both groups, a low attenuation spheric structure with a contrast-medium-enhanced ring and a diameter of 6-8 mm was observed. There was no edema around the structure, which represents a zone of tissue necrosis at the site of the temporary 125I implant. Tumors in both groups were completely destroyed, some decreased in size, and others were unchanged. Pseudotumor necrosis with accompanying edema occurred in two patients with low grade astrocytoma, the diameter of which was > 4 cm. CONCLUSION: The behavior of cerebral tumors and their appearance on CT and MR images after interstitial irradiation seem to be variable. Decrease in tumor size may take place at different intervals after therapy. Brachytherapy of tumors with a diameter of > 4 cm may produce space-occupying radionecrosis.