SHORT-TERM CT AND MR CHANGES IN BRAIN-TUMORS FOLLOWING I-125 INTERSTITIAL IRRADIATION

Purpose: The study was undertaken to assess characteristic short-term CT and MR changes in brain tumors following I-125 interstitial irradia tion. Method: Sixteen patients were included who had both CT and MR co ntrol examinations at regular intervals over a period of 18 months fol lowing treatment. Two groups were distinguished: low grade tumors (11 cases) and high grade malignancies (5 patients). I-125 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 I-125 implant. Tumors in both groups were completely destroyed, some decreased in size, and oth ers were unchanged. Pseudotumor necrosis with accompanying edema occur red in two patients with low grade astrocytoma, the diameter of which was >4 cm. Conclusion: The behavior of cerebral tumors and their appea rance on CT and MR images after interstitial irradiation seem to be va riable. Decrease in tumor size may take place at different intervals a fter therapy. Brachytherapy of tumors with a diameter of >4 cm may pro duce space-occupying radionecrosis.