Faculty Bibliography

OBJECT: Nonfunctioning pituitary adenomas comprise approximately 30% of all pituitary tumors. The purpose of this retrospective study was to evaluate the efficacy and role of gamma knife surgery (GKS) in the treatment of these lesions. METHODS: The authors conducted a review of cases in which GKS was performed at the University of Pittsburgh between 1987 and 2001. Forty-six patients with nonfunctioning pituitary adenomas and with at least 6 months of follow- up data were identified. In 41 of these patients some form of prior treatment such as transsphenoidal resection, craniotomy and resection, or conventional radiation therapy had been conducted. Five patients were deemed ineligible for microsurgery, and GKS served as the primary treatment modality. Endocrinological, ophthalmological, and radiological responses were evaluated. The mean radiation dose to the margin was 16 Gy. In all patients with microadenomas and 91% of those with macroadenomas tumor control was demonstrated after radiosurgery. Gamma knife surgery had essentially equal efficacy in terms of achieving tumor control in cases of adenomas with cavernous sinus invasion and suprasellar extension. No new endocrinopathies were noted following radiosurgery. In two patients, however, tumor growth and decline in visual function occurred. CONCLUSIONS: Gamma knife surgery is safe and effective in treating nonfunctioning pituitary adenomas. Radiosurgery may serve as a primary treatment modality in some or as a salvage treatment in others. Treatment must be tailored to meet the patient's symptoms, overall health, and tumor morphometry.

OBJECT: This study was conducted to examine the role of radiosurgery in the management of patients with recurrent or unresectable low-grade astrocytomas. METHODS: During a 13-year interval, 49 patients underwent stereotactic radiosurgery as part of multimodal treatment of their recurrent or unresectable low-grade astrocytomas. Thirty-seven of these patients (median age 14 years) harbored pilocytic astrocytomas and 12 patients harbored World Health Organization (WHO) Grade II fibrillary astrocytomas (median age 25 years). Tumors involved the brainstem in 22 cases, cerebellum in four, thalamus in six, temporal lobe in five, frontal lobe in four, and parietal lobe in three, as well as the hypothalamus, corpus callosum, insular cortex, optic tract, and third ventricle in one patient each. Each diagnosis was confirmed with the aid of stereotactic biopsy sampling in 17 patients, open biopsy sampling in five, partial resection in 13, and near-total resection in 14. Multimodal treatment included fractionated radiotherapy in 14 patients, stereotactic intracavitary irradiation in five, chemotherapy in two, cyst drainage in eight, ventriculoperitoneal shunt placement in five, and additional cytoreductive surgery in five. Tumor volumes ranged from 0.42 to 45.1 cm3. The median radiosurgical dose to the tumor margin was 15 Gy (range 9.6-22.5 Gy). After radiosurgery, serial neuroimaging demonstrated complete tumor resolution in 11 patients, reduced tumor volume in 12, stable tumor volume in 10, and delayed tumor progression in 16. No procedure-related death was encountered. Forty-five of 49 patients are alive at a median follow-up period of 32 months after radiosurgery and 63 months after diagnosis. Sixteen patients participated in follow-up review for more than 60 months. Three patients died of local tumor progression. CONCLUSIONS: Stereotactic radiosurgery is a potential alternative or adjunctive intervention in the management of selected patients with pilocytic or WHO Grade II fibrillary astrocytomas, usually performed for small-volume tumors in an attempt to avoid larger-field fractionated radiotherapy.

Management options for patients with vestibular schwannomas (acoustic neuromas) include observation, tumor resection, stereotactic radiosurgery, and fractionated radiotherapy. In this report the authors review their 15-year experience with radiosurgery and discuss indications and expectations in relation to the different approaches. They conducted a survey of neurosurgeons to determine management preferences in two different cases of intra- and extra-canalicular tumor presentations. Patient decisions must be based on quality information derived from peer-reviewed literature.

Stereotactic radiosurgery provided clinicians the ability to administer high single-doses of radiation to intracranial targets with relative safety. Analysis of clinical outcome from radiosurgery calls into question some of the radiobiological principles that have guided conventional fractionated radiotherapy in the past. The response of the tumor or target tissue being irradiated, as well as the response of the surrounding normal tissue, seems predominantly determined by the tumor or target vasculature. Injury to the tumor or target vasculature appears to contribute to the probability of developing normal tissue complications. Estimations of alpha/beta values from radiosurgical dose-response data consistently yield values that conflict with values from fractionated radiotherapy and with linear-quadratic theory. This indicates that projections from high-dose single-fractions to fractionated dose-equivalents made using the linear-quadratic formula are unreliable. Radiobiological analysis of clinical data from radiosurgery provides models for guiding treatment to achieve desired effects and provide reliable estimates of complications.