Failure rate of contemporary low-dose radiosurgical technique for vestibular schwannoma Clinical article

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The decline in cranial nerve morbidity after radiosurgery for vestibular schwannoma (VS) correlates with dose reduction and other technical changes to this procedure. The effect these changes have had on tumor control has not been well documented.


The authors performed a retrospective review of 293 patients with VSs who underwent radiosurgery between 1990 and 2004 and had a minimum of 24 months of imaging follow-up (90% of the entire series). The median radiation dose to the tumor margin was 13 Gy. Treatment failure was defined as progressive tumor enlargement noted on 2 or more imaging studies. The mean postradiosurgical follow-up was 60.9 ± 32.5 months.


Tumor growth was noted in 15 patients (5%) at a median of 32 months after radiosurgery. Radiographically demonstrated tumor control was 96% at 3 years and 94% at 7 years after radiosurgery. Univariate analysis revealed 2 factors that correlated with failed radiosurgery for VS: an increasing number of isocenters (p = 0.03) and tumor margin radiation doses ≤ 13 Gy (p = 0.02). Multivariate analysis showed that only an increasing number of isocenters correlated with failed VS radiosurgery (hazard ratio 1.1, 95% CI 1.02–1.32, p < 0.05). The tumor margin radiation dose (p = 0.22) was not associated with tumor growth after radiosurgery.


Distortion of stereotactic MR imaging coupled with increased radiosurgical conformality and progressive dose reduction likely caused some VSs to receive less than the prescribed radiation dose to the entire tumor volume.

Abbreviations used in this paper:CPA = cerebellopontine angle; HR = hazard ratio; IAC = internal auditory canal; IQR = interquartile range; NF2 = neurofibromatosis Type 2; PIV = prescription isodose volume; VS = vestibular schwannoma.

Article Information

Address correspondence to: Bruce E. Pollock, M.D., Department of Neurological Surgery, Mayo Clinic, Rochester, Minnesota 55905.

Please include this information when citing this paper: published online May 1, 2009; DOI: 10.3171/2009.3.JNS08949.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Axial post-Gd MR images obtained in a 74-year-old man, showing a right-sided VS. The tumor margin radiation dose was 12 Gy. A: Image obtained 12 months after radiosurgery. B: Image obtained 43 months after radiosurgery. C: Image obtained 58 months after radiosurgery. Along the petrous axis, the tumor measured 18 (A), 20 (B), and 23 mm (C).

  • View in gallery

    Graph showing tumor control rates in patients who underwent VS radiosurgery between January 1990 and March 1997 (88 patients, solid line) compared with those who underwent radiosurgery between April 1997 and December 2004 (205 patients, dashed line).

  • View in gallery

    Images from a dose plan for a patient undergoing radiosurgery for a right-sided VS. Left: Coronal reconstruction of a post-Gd MR image showing the 50% isodose line. Nine isocenters of radiation were used to cover a PIV of 307 mm3. The tumor margin radiation dose was 12 Gy, and the maximum radiation dose was 24 Gy. Right: Coronal reconstruction of the stereotactic CT showing the 50% isodose line shifted ~ 1 mm superior in the z plane. The radiation dose to the inferior portion of the IAC ranges from 6.1–7.1 Gy.


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