Radionecrosis after radiotherapy for brain tumor

The neurological deterioration after radiotherapy of brain tumor may depend on radionecrosis or regrowth of the tumor. In the present study, five patients with brain tumor were irradiated with doses of 3,900 to 6,800 rads. The neurological deterioration appeared 3.5 to 46 months after radiotherapy in three patients, who received 5,000 to 5,680 rads, immediately after radiotherapy in one patient, who received 6,800 rads, and during radiotherapy in one patient, who received 3,900 rads. Ring enhancement was observed on sequential CT scans. This enhanced area was surgically removed and the correlation between histology and CT scans and superimposed dose distributions was studied in order to differentiate radionecrosis from regrowth of tumor. The radionecrosis was confirmed at the second operation in five patients, but regrowth of the tumor was also observed in the brain adjacent to radionecrosis in three out of five patients. Coagulation necrosis and fibrinoid necrosis were observed microscopically at the rim of the ring enhancement and necrotic and hyalinized debri were observed in the central low density area of the ring enhancement. Viable tumor cells were noted in the enhanced area adjacent to the ring enhancement on CT scans. Both radionecrosis and regrowth of tumor were observed in the dose distribution area of 3,500 to 6,120 rads on CT scans. This suggested that the superimposed dose distributions could not differentiate radionecrosis from tumor regrowth. Forty-eight cases of cerebral radionecrosis gathered from the literature were reviewed. (J.P.N.)