Gamma knife radiosurgery for skull base chordomas: a 13 year review from a single institution

Purpose/Objective: We retrospectively evaluated the efficacy of gamma knife radiosurgery (RS) in the treatment of skull-base chordomas. Materials/Methods: Data collected between September 1998 and July 2001 from a series of 20 patients with skull base chordomas treated with gamma knife radiosurgery at The University of Pittsburgh Medical Center were retrospectively reviewed. Patients were followed annually after RS, with MRI of the brain, and clinical evaluation detailing any new symptoms and signs. A pathological biopsy proven diagnosis was established in 18 patients, and an imaging based diagnosis suggested in 2 patients. Median follow up time was 28 months (range:4–94 months). A median tumor margin dose of 16.5 Gy (range:11–25 Gy) was prescribed to the 50% isodose line in 19 patients, and the 70% isodose line in 1 patient. The median number of isocenters used was 7 (range:1–13), and the median treatment volume was 4.6cc (range:1.0–19.2cc). Results: Five year overall survival was 29% (range:5–53%), and five year disease specific survival was 57% (range:32–82%). 2 patients died of disease progression at 35 and 57 months, and 1 died from metastatic brain lesions stemming from a primary non-small cell lung cancer. Significant morbidity newly occurring after the RS procedure was appreciated in only 1 patient which consisted of diminished ipsilateral hearing corresponding to visualized tumor extension in the internal auditory canal. 45% (9/20) of patients demonstrated interval shrinkage, 25% (5/20) no change, and 30% (6/20) interval progression on follow up brain MRIs. 10% (2/20) developed infield failure, and 20% (4/20) developed out of field failure. From the latter group, 3 of 4 patients had a repeat stage II RS. Conclusions: Gamma knife radiosurgery is a safe and reasonable treatment option for skull base chordomas. In this retrospective analysis, out of field or marginal misses were a problem in at least 20% of patients. The outcome of salvage treatments needs to be further evaluated. Larger series of patients with longer follow up times will be needed to better evaluate gamma knife RS for the treatment of skull base chordomas.