The effects of fractionated doses of fast neutrons or photons on the canine brain: evaluation by computerized tomography and evoked response recording

High-dose single-fraction brain irradiation: MRI, cerebral blood flow, electrophysiological, and histological studies

Radiation-induced alterations in cerebrovascular and metabolic function form the basis for the radiosurgical treatment of selected intracranial vascular malformations and tumors in human patients. However, the underlying mechanisms, temporal progression, and modifying factors involved in the radiosurgical obliteration of these intracranial lesions as well as the risks of delayed radiation injury to surrounding normal brain remain poorly understood. In this report, the rabbit brain was used as an animal model to examine the effects of high-dose single-fraction X-irradiation on magnetic resonance imaging (MRI) appearance, neurophysiologic function, and histological integrity. At approximately 10 weeks following left-hemisphere irradiation with 60 Gy (225 kVp) X rays, MRI studies showed radiation-induced changes including blood-brain barrier (BBB) perturbations in the white matter regions and the hippocampus. Significant reductions in regional cerebral blood flow (rCBF) ratios were found in the hippocampus and certain regions of the cortex in irradiated animals. However, no changes in somatosensory evoked potentials (SEP) were observed. Histological studies demonstrated telangiectatic vessels, spreading edema in the white matter, and focal regions of necrosis and hemorrhage in the irradiated cortices and hippocampi. These results demonstrate that the irradiated rabbit brain may be used as an experimental model to correlate the spatiotemporal pattern of functional changes with radiologic and histological changes in delayed radiation injury.

Neutron interstitial brachytherapy for malignant gliomas: a pilot study

Fifty-six patients with malignant glioma were treated with implantation of the neutron-emitting element californium-252 (252Cf) within 2 weeks after surgical debulking of the tumor. Implantation was performed using computerized tomography-guided placement of afterloading catheters, and the 252 Cf sources were removed after approximately 300 neutron rads were delivered. Patients then received 6000 to 7000 conventional photon rads by external beam. The total photon-equivalent dose to the tumor ranged from 8100 to 9100 rads. The median survival time was 10 months, with 18-and 24-month survival rates of 28% and 19%, respectively. The results of reoperation or autopsy showed that patients had recurrence of the tumor but that radiation necrosis was restricted to the area of the original tumor. Serious complications occurred in five patients (9%) and consisted of wound infections in three, cerebral edema in one, and radiation necrosis beyond the original tumor margin in one. Previous studies using external-beam neutron radiation have shown that neutrons are capable of totally eradicating malignant gliomas; however, in most cases, unacceptable widespread radiation necrosis has resulted. Neutron implants are a logical way to increase the dose to the tumor and decrease the dose to normal brain. Interstitial neutron radiation can be given safely with 252Cf, and the survival results achieved by radiation alone using relatively low doses of interstitial neutron radiation from 252Cf implants plus conventional photon radiation were equal to the results attained with any currently available conventional therapy.

The application of evoked potentials in the diagnosis and follow-up of children with intracranial tumors

Somatosensory and brainstem auditory evoked potentials (SSEPs and BAEPs) provide sensitive measures of the central conduction functions of the auditory and somatosensory input systems at different levels of the central nervous system. The contribution of SSEPs and BAEPs in the primary diagnosis and follow-up of 26 children with infra- and supratentorial tumors were reviewed. The SSEPs, especially the specific complex, showed a latency increase in patients with supratentorial and brainstem mass lesions involving directly or distantly the somatosensory tracts. The BAEPs were sensitive for supratentorial pressure effects and for local and distant posterior fossa tumor effects. In the follow-up of children, evoked potentials offer a good method of detecting tumor recurrence, whereas neuroradiological procedures may be obscured by surgical or radiation artifacts.