The use of the cyberknife stereotactic radiosurgery system for the treatment of intracranial and extracranial residual or recurrent chordoma

Abstract

Objectives: Chordomas are relatively rare primary malignant bone tumors that arise from remnants of the notochord along the craniospinal axis. They tend to be locally invasive around the clival or sacro-coccygeal regions and critical neurological structures are often involved. Complete surgical excision is rarely possible and post-resection radiation enhances local control of the disease. The CyberKnife is a frameless imageguided LINAC radiosurgical system that allows treatment of both intracranial and extracranial lesion. We review here the methodology of the system and present our experience of treating skull base and spinal chordomas. Methods: Between 1994 and 2008, 22 patients with a histological diagnosis of a chordoma underwent stereotactic radiosurgery (SRS) at Stanford University Hospitals. 17 patients underwent frameless SRS at the Stanford CyberKnife Center. A retrospective and prospective review of these patients was undertaken by obtaining clinical and radiological information from an institutional review board-approved prospective database. Results: There were 11 males and 6 females with an average age of 42 years (range 10-73). 12 lesions were in the clivus, 3 in the cervical spine below C2, 1 lumbar and 1 sacral region. All but one patient had prior surgery. 9 had undergone one resection, 5 had two and 2 had three resections. Three patients had prior radiation or proton beam therapy. The average tumor volume treated was 10.9 cm3 (range 1.9-31.6 cm3), with a mean radiation dose of 29.3 Gy (range 18-50 Gy), and a mean maximum intratumoral dose of 41.0 Gy (range 24.1-67.6 Gy). Patients were followed up for an average of 4 years. Tumor control was achieved in 12 out of the 17 cases (70.6%). 5 of the 12 patients showed tumor size reduction. However, 5 out of the 17 cases showed progression with one developing a new lesion at a lower cervical vertebra despite good local control. None of the patients with tumor control developed new neurological deficits, but 4 of the 5 cases with tumor progression showed worsening neurological deficits. There was no radiation associated complications. Conclusions: Good tumor control rates can be achieved with no significant morbidity with CyberKnife based stereotactic radiosurgery. Cases with poor control tended to have complexmultiple surgical resections. Longer follow-up in larger series is required to adequately compare this technique with other forms of radiation therapy.