Cyberknife Stereotactic Radiosurgery for Intracranial Chordomas

Introduction: Intracranial chordomas are rare malignant skull base tumors representing less than 1% of all intracranial neoplasms. Chordomas are locally aggressive with high recurrence rates regardless of the treatment. As a more convenient alternative to 8 weeks of standard post-operative fractionated radiotherapy we present the Stanford experience with skull base chordomas treated with CyberKnife (CK) stereotactic radiosurgery (SRS).

Methods: We retrospectively reviewed the outcomes of 16 patients with intracranial chordoma treated at Stanford CK Center between the years 2000 and 2012. Nine males and 7 females (7 patients with primary adjuvant SRS and 9 for salvage of recurrent tumor) underwent 21 SRS procedures. The median age was 49 years (range: 10–78 years). All had pathological confirmation of the diagnosis. For primary treatments, a median tumor volume of 8.5 cm3 (range: 2.4–17.4 cm3) was treated in 3 (to 33–43.5 Gy) or 5 (to 35–40 Gy) fractions. For salvage treatments, a median tumor volume of 9.3 cm3 (range: 3.2–27 cm3) was treated in 3 (to 24–33Gy) or 5 (to 25–50Gy) fractions. We report the clinical and radiological outcomes following SRS. Local control was defined as imaging stability and no need for further treatment.

Results: Median imaging follow-up was 33 months (range:17 - 94 months) for primary and 28 months (range: 8–153) for salvage patients. Crude local control was achieved in 100% of primary and 45% of salvage treatments. Of the with 12 tumors with local control following treatment, tumor shrinkage was only seen in 29% (2/7) of the primary SRS, 11% (1/11) of salvage SRS patients. 11% (2/16) of patients had worsening of pre-existing symptoms (facial pain, diplopia). One patient (5%) experienced asymptomatic, imaging-defined radionecrosis of the temporal lobe.

Conclusion: With relatively short follow-up, this largest single institution experience with CyberKnife SRS for intracranial chordomas found an excellent local control rate for primary adjuvant treatment and represents an alternative to conventionally fractionated radiotherapy. Tumor stability is seen more often than tumor shrinkage. Salvage rates for recurrent chordomas remain poor and means for intensification of treatment should be investigated.