Clinical Outcome Of Gamma Knife Radiosurgery For Residual Skull Base Meningiomas After Surgery: Preservation Of Cranial Nerve Function And Recurrence Rates

Masahito Kobayashi1, Takayuki Ohira2, Tadashige Kano2, Kazunari Yoshida2, Takeshi Kawase2

1Saitama Medical University 2 Keio University

Keywords: gamma knife, outcome, meningioma, radiosurgery, skull base

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     After surgery for skull base meningiomas, cranial nerves may be vulnerable due to tumor compression and surgical intervention.
     This study is aimed to evaluate long-term outcome of residual skull base meningiomas after gamma knife (GK) radiosurgery with our strategies, conservatively avoiding excessive irradiation to cranial nerves.
     This study included 68 patients (51 women, mean age 57.9 y/o).
      Fifty-five of them underwent surgery before GK. The mean follow-up period was 36.0 months (11 to 100). The mean tumor volume was 5.74ml (0.2-25.6). Forty-eight patients had residual tumors in the cavernous sinus region. The mean marginal and maximal doses were 13.2 and 26.4 Gy (range of marginal dose: 10-15Gy). To prevent cranial nerve injuries, the dose for the lateral wall of the cavernous sinus was set below 13 Gy without overlaying 50% isodose lines of each shot in the lateral part of the sinus, and the dose near the superior orbital fissure was set less than 80 % of the maximum dosage. The Kaplan-Meier method and a stepwise regression analysis were used to evaluate tumor control rates and possible predictors of the risk of regrowth.
     The mean d95% was 13.0 Gy. The tumor regrowth was observed in four patients and additional treatments were done in three; repeated surgery for two with large-sized residual tumors (>18 ml) and repeated GK for one with the tumor embedded in the pons. No regrowth was observed in the patients without preceding surgery. The actuarial progression free survival rate was 92.0%, and the actuarial tumor volume decrease rate was 45.3 % at 7years.  Malignant transformation and outside recurrence were not observed. One patient (1.5%) had worse preexisting abducens nerve paresis. Improvement of visual or oculomotor function was observed in four patients. Tumor volume > 10ml was significantly associated with tumor regrowth. There were no other risk factors for tumor progression, including the prescribed dose.
     This is a retrospective study.
     Gamma knife radiosurgery with the conservative planning for lateral wall of cavernous sinus and skull base foramen is safe and effective over the long term for skull base meningiomas.
     Close observation should be recommended for large-sized residual tumors.


Project Roles:

M. Kobayashi (), T. Ohira (), T. Kano (), K. Yoshida (), T. Kawase ()