[Hemodynamic and pathological changes in the normal rabbit brain after linac stereotactic irradiation].
A number of clinical reports on stereotactic radiosurgery using a linear accelerator have been published. So far, however, basic studies using the experimental animals have been comparatively few in number. Changes of cerebral hemodynamics and pathohistology in the animal brain after stereotactic, large dose irradiation was studied in this experiment. Fourteen pure imbred Japanese white rabbits, weighing approximately 5 kg, were used. As the landmark for irradiation targeting, a small silicone ball, 2 mm in diameter, was implanted aseptically in the right frontal bone. A month after placing the landmark, stereotactic irradiation was given in a single dose of 100 Gys by a linear accelerator with a 10 mm collimator. In all animals, dynamic CT was carried out before and immediately after irradiation, and thereafter, it was repeated at various intervals. Time density curve which has two parameters of peak-time (PT) and peak-height (PH), was drawn with the help of Sprine function. The ratios of PT, PH, and CBF were calculated for their values in the irradiated area/values in the contralateral corresponding area. Two animals were sacrificed immediately, 1, 3, 7, 21, 90 and 180 days respectively after irradiation, and one animal was killed 1 year after radiation followed by another animal killed 2 years after irradiation. Brains were removed and formalin-paraffin sections were made. All sections were stained with hematoxylin-eosin and GFAP (glial fibrillary acidic protein). In the brain of day 3, cerebral hemorrhage and an increase of astrocyte were demonstrated in the irradiated area. The increase of astrocyte had persisted for approximately 3 weeks. On the other hand, neurons and vessels appeared intact, even i the brain of day 90. In the brain of day 180, brain necrosis had developed in the irradiated area and necrosis had become wider and more prominent in the brains of 1 and 2 years after irradiation. Fibrinoid degeneration of capillaries was evident in the irradiated area and its adjacent areas. Regional cerebral blood flow (r-CBF) in the irradiated area decreased for 3 days and continued to remain at a lower level for a week. However, r-CBF increased thereafter again at 3 weeks. Then it gradually continued to decrease and finally it became unmeasurable at one or 2 years after irradiation. To interpret the fact that there is a biphasic time course for r-CBF, the early decrease was attributed to local edema, and the later decrease was attributed to changes in the wall of vessels.
Ohtsuka
T
T
Department of Neurosurgery, Toho University School of Medicine.
D000818:Animals; D001921:Brain / Q000473:pathology / Q000528:radiation effects*; D002560:Cerebrovascular Circulation / Q000528:radiation effects*; D009336:Necrosis; D011817:Rabbits; D016634:Radiosurgery