Faculty Bibliography

OBJECTIVE: One of the key limitations of gamma knife surgery arises from the radiation safety tolerance limit of the brainstem. The authors conducted an analysis of patients with intra-axial brainstem lesions and documented the incidence of adverse radiation imaging effects (ARIE) and new neurological deficits after gamma knife surgery. METHODS: Thirty-eight patients (39 lesions) with intra-axial brainstem astrocytomas or vascular malformations underwent gamma knife surgery during a 6-year interval. Brainstem exposure volume was calculated by subtracting the volume within the 12-Gy isodose line (12 Gray volume) from the prescription volume. ARIE was defined as a new parenchymal signal alteration on follow-up magnetic resonance imaging sequences. RESULTS: The average prescription volume was 1.46 cm, 12 Gy volume was 2.03 cm, and brainstem exposure volume was 0.57 cm. Seven (18.4%) patients developed ARIE. ARIE correlated only with the presence of new neurological deficits and age younger than 40 years. Three (7.9%) patients developed minor residual deficits without any ARIE. There was no mortality. CONCLUSION: Exposure of the brainstem to more than 12 Gy at volumes as low as 0.1 cm can produce ARIE and new neurological deficits. The tolerance of the brainstem to radiosurgery is related to patient age, lesion volume, and pathology. Analysis of the exposed volume of brainstem tissue may be useful in radiosurgical planning for individual patients.

OBJECTIVE: To report the results of gamma knife radiosurgery (GKR) for treatment resistant choroid plexus papillomas. METHODS: Six patients (median age 55 years; range 29-75) with residual (n = 2) or recurrent (n = 4) choroid plexus papillomas underwent GKR. All failed prior surgery and one failed prior proton beam radiation therapy. These six patients had a total of 11 locally or distant recurrent intracranial tumors. The median and mean tumor volumes were 2.7 and 3.9 cc (range, 0.23-21.1). A median margin dose of 12.0 Gy (range, 11.5-15) was prescribed to the tumor margin. RESULTS: The progression-free periods varied from 7 to 108 months (mean: 36.9). Four tumors were stable after GKR but seven showed progression. Four recurrent tumors in two patients were managed with repeat radiosurgery and three were observed. At the second GKR, the tumor volume varied from 1.3 to 12.4 cc, and the marginal radiation dose varied from 11 to 14 Gy. The overall survival after the first GKR varied from 15 to 120 months. Four patients were alive at the end of the study period. CONCLUSIONS: Radiosurgery represents an additional management strategy for patients who progress despite surgical removal. It may especially be useful for patients with small deep seated residual choroid plexus papillomas, and for tumors that recur at a site distant from their origin.

OBJECTIVE: To evaluate the role of stereotactic radiosurgery (SRS) in the management of recurrent or residual intracranial hemangioblastomas, we assessed tumor control, survival, and complications in 32 consecutive patients. METHODS: We retrospectively reviewed records of 32 consecutive hemangioblastoma patients (74 intracranial tumors) who underwent gamma knife SRS. The median patient age was 43.8 years (range, 21.3-79.4 yr). Thirty-one patients had undergone previous surgical resections. Nineteen patients had sporadic lesions (22 tumors), and 13 patients had von Hippel-Lindau disease-associated hemangioblastomas (52 tumors). The median SRS target volume was 0.72 mL (range, 0.08-16.6 mL), and the median marginal dose was 16.0 Gy (range, 11-20 Gy). RESULTS: At a median of 50.1 months (range, 6.0-165.4 mo), seven patients had died from disease progression, and one patient had died secondary to heart failure. The overall survival after radiosurgery was 100%, 94.4%, and 68.7% at 1, 3, and 7 years, respectively. Follow-up imaging studies demonstrated tumor control in 68 tumors (91.9%). The progression-free survival after SRS at 1, 3, and 5 years was 96.9%, 95.0%, and 89.9%, respectively. Factors associated with an improved progression-free survival included von Hippel-Lindau disease-associated hemangioblastoma, solid tumor, lower tumor volume, and greater marginal dose. CONCLUSION: SRS is an important tool in the management of hemangioblastomas and is associated with a high tumor control rate and a low risk of adverse radiation effects.