Development of radiation necrosis in rat brains and its evaluation with MRI

Radiation brain damage, especially radiation necrosis, is most critical and well-known sequelae after cranial irradiation. However, the etiology of radiation necrosis has not been fully understood. In order to characterize and to investigate the pathogenesis of radiation necrosis, the experimental techniques in small animals and the evaluation methods should be refined. The authors developed focal radiation brain damage in rats utilizing protons of a single dose of 60 Gy with superior dose distribution and demonstrated the lesions caused by radiation on MRI with 2T magnet. The damaged lesion was not uniform within the radiation field 5 months after radiation. The corpus callosum was the most vulnerable site which showed low intensity on T1 weighted spin echo images with marked enhancement after Gd-DTPA administration. These MRI findings are common in patients with radiation necrosis. Discrepancy between the area of Gd-DTPA enhancement on MRI and that of Evans blue extravasation on excised brain might be attributed to the different response and pathological conditions in different brain structures following a single dose of radiation of 60 Gy. Further investigation on radiation brain damage in rats can be encouraged with the elegant methods of both protons radiation and high resolution MRI described here. (author)