Radiation damage to the normal monkey brain: experimental study induced by interstitial irradiation

Area of Science:

• Neuroscience
• Radiation Oncology
• Radiology

Background:

• Interstitial brachytherapy, particularly with iridium-192 seeds, is a crucial treatment modality.
• Understanding radiation-induced normal brain tissue damage is essential for optimizing treatment and minimizing side effects.

Purpose of the Study:

• To sequentially evaluate radiation damage to normal brain tissue following interstitial irradiation with iridium-192 seeds.
• To compare the efficacy of computed tomography (CT) and magnetic resonance imaging (MRI) in detecting radiation-induced brain injury.
• To establish a reliable animal model for studying delayed radiation necrosis.

Main Methods:

• 14 mature Japanese monkeys underwent interstitial irradiation with iridium-192 seeds.
• Radiation damage was assessed using serial computed tomography (CT), magnetic resonance imaging (MRI), and histological examination.
• Dosimetry confirmed doses ranging from 200-260 Gy to the experimental area.

Main Results:

• Coagulative necrosis was observed in irradiated areas, with macrophage infiltration at the periphery.
• MRI detected necrotic lesions starting 1 week post-irradiation, with stable size over 6 months and characteristic ring enhancement.
• Delayed and sustained edema surrounding lesions was noted, peaking at 1 week and recurring after 1 month.
• Histology revealed neovascularization, vascular hyalinization, and gliosis in the macrophage-infiltrated periphery.
• CT showed similar findings to MRI, including calcification, but with less clarity.

Conclusions:

• MRI is a sensitive tool for detecting and monitoring radiation-induced brain necrosis and associated edema.
• The observed pathological changes, including vascular damage and glial response, contribute to delayed radiation necrosis.
• This primate model provides a valuable platform for basic research into brachytherapy and radiation necrosis.