Analysis of biological effect and clinical result of radiosurgery

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Radiosurgery is closed-skull destruction of a precisely defined intracranial target using ionizing irradiation. Compared to conventional fractionated radiotherapy, the biological effect of radiosurgery on each of pathological entities are not well known. In order to analyze the factors influencing the clinical results of radiosurgery, we evaluate the technique, and treatment parameters of consecutive 562 patients who underwent gamma knife radiosurgery between June 1990 and February 1996. Concerning cerebral arteriovenous malformations (AVMs), the lesion volume has been believed to be the primary factor influencing the obliteration rate. We found the rate does not depend on the volume under dose planning with precise 3-D information. However, radiation-induced brain edema occurred in proportion with treatment volume. Radiation-induced neurological deterioration was mainly depends on the location of the lesions. Concerning intracranial benign tumors, such as acoustic neurinomas or meningiomas, neoplasmic progression was observed only 7-9% after radiosurgery. Treatment-associated neurological morbidity of skull base tumors, especially, hearing preservatio rate in patients with acoustic neurinomas, was significantly better than microsurgical resection. In conclusion, sterotactic radiosrugery prove to be a effective and less invasive managment of selected cerebral AVMs and small benign brain tumors. However, longer follow-up and more detailed analysis of clinical outcome must be required to testify the future expanding role of this technique.