Faculty Bibliography

OBJECT: The recently introduced Leksell Gamma Knife (LGK) Perfexion is an entirely new system with a different beam geometry compared with the LGK 4C. The new Perfexion system has 192 cobalt-60 sources that are fixed on 8 sectors (each sector has 24 sources). Each sector can be moved independently of the others and can be set to 1 of 5 different positions: 3 positions defining collimator sizes of 4, 8, and 16 mm; an off position (sources are blocked); and a home position. The purpose of this study is to compare the dosimetric characteristics of the GK 4C and the Perfexion models. This comparison is important especially for the treatment of functional disorders when only a single shot with the 4- or 8-mm collimator is used. METHODS: A 160-mm-diameter spherical polystyrene phantom was used for all measurements and calculations. The irradiation geometry consisted of the placement of a single shot at the center of this phantom. Comparisons were made among different dosimetric parameters obtained from calculations performed using Leksell GammaPlan v. 8.0 and measurements performed using film dosimetry. The dosimetric parameters investigated were dose profiles for all collimators in all 3 stereotactic planes (x, y, and z) including the full width at half maximum and the penumbra for each profile, cumulative dose-volume histograms, the volume encompassed by the 50% isodose surface, the mean doses delivered to a defined matrix volume, and relative output factors for all collimator sizes. RESULTS: There was excellent agreement between the dosimetric parameters of GK 4C and Perfexion for the 4- and 8-mm collimators. CONCLUSIONS: The results of this study suggest that consistent treatments of functional disorders will be delivered using either GK 4C or Perfexion.

BACKGROUND: Metastases to the brain from ovarian and endometrial carcinoma are uncommon and to the authors' knowledge consensus regarding optimal management is lacking. Stereotactic radiosurgery (SRS) has proven useful for the treatment of many benign and malignant brain tumors. In the current study, the authors evaluated outcomes after SRS in patients with ovarian and endometrial carcinoma. METHODS: Twenty-seven patients with brain metastases underwent gamma-knife SRS. Six patients had endometrial carcinoma, whereas 21 patients had ovarian carcinoma. Eighteen patients also received whole-brain radiotherapy. A total of 68 tumors were treated with gamma-knife SRS. RESULTS: At the time of last follow-up, 1 patient was still alive and 26 had died. The median survival was 7 months after the initial diagnosis of brain metastasis and 5 months after SRS. The 1-year survival rate after radiosurgery was 15% and that from the diagnosis of brain metastases was 22%. On final imaging, all tumors were controlled without further growth. Two patients (7.4%) developed new or progressive neurologic deficits after SRS. CONCLUSIONS: SRS is an acceptable choice for the treatment of brain metastases resulting from ovarian and endometrial carcinoma, and provides local tumor control with limited morbidity. Careful patient selection is warranted in the setting of patients with uncontrolled systemic disease in whom a limited survival benefit is expected.

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: 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.