Fractionated stereotactic radiosurgery for patients with skull base metastases from systemic cancer involving the anterior visual pathway

Abstract

Background: To analyze the tumor control, survival outcomes, and toxicity after stereotactic radiosurgery (SRS) for skull base metastases from systemic cancer involving the anterior visual pathway.

Patients and methods: We have analyzed 34 patients (23 females and 11 males, median age 59 years) who underwent multi-fraction SRS for a skull base metastasis compressing or in close proximity of optic nerves and chiasm. All metastases were treated with frameless LINAC-based multi-fraction SRS in 5 daily fractions of 5 Gy each. Local control, distant failure, and overall survival were estimated using the Kaplan-Meier method calculated from the time of SRS. Prognostic variables were assessed using log-rank and Cox regression analyses.

Results: At a median follow-up of 13 months (range, 2-36.5 months), twenty-five patients had died and 9 were alive. The 1-year and 2-year local control rates were 89% and 72%, and respective actuarial survival rates were 63% and 30%. Four patients recurred with a median time to progression of 12 months (range, 6-27 months), and 17 patients had new brain metastases at distant brain sites. The 1-year and 2-year distant failure rates were 50% and 77%, respectively. On multivariate analysis, a Karnofsky performance status (KPS) >70 and the absence of extracranial metastases were prognostic factors associated with lower distant failure rates and longer survival. After multi-fraction SRS, 15 (51%) out of 29 patients had a clinical improvement of their preexisting cranial deficits. No patients developed radiation-induced optic neuropathy during the follow-up.

Conclusions: Multi-fraction SRS (5 x 5 Gy) is a safe treatment option associated with good local control and improved cranial nerve symptoms for patients with a skull base metastasis involving the anterior visual pathway.

Figure 1

Prescription isodose distribution in axial and coronal views of a skull base metastasis compressing the optic chiasm (contoured in yellow). The planning target volume (contoured in blue) was created by the geometric expansion of tumour plus 1 mm. The patient was treated with a linear accelerator (LINAC) multi-fraction stereotactic radiosurgery (5 x 5 Gy) with the use of 8 noncoplanar conformal beams. The dose was prescribed to the 87% isodose line normalized to the maximum dose, with a minimum PTV coverage of 98%. The isodose curves showing dose levels delivered to surrounding tissues and adjacent critical structures are represented.

Figure 2

Kaplan-Meier estimate of local control.

Figure 3

Kaplan-Meier estimate of distant disease-free survival.

Figure 4

Kaplan-Meier estimate of overall survival.