Long-term Functional Outcome, Complications Of Radiosurgery For Vestibular Schwannomas Using Below 12 Gy For Tumor Marginal Doses

Yoshiyasu Iwai1, Kazuhiro Yamanaka2, Masaki Yoshimura2

1Osaka, Japan 2Osaka City General Hospital, Osaka, Japan

Keywords: gamma knife, outcome, vestibular schwannoma, dose planning, hearing function

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       Dose selection is important for vestibular schwannoma radiosurgery and in recent years lower doses have been used.
     We evaluated long-term follow-up results of low dose radiosurgery (<12 Gy) for vestibular schwannomas from the standpoint of functional hearing preservation and other complications.
     We encountered and followed up 194 patients of unilateral vestibular schwannomas treated by gamma knife radiosurgery and followed up, for 5 years those treated with below 12 Gy for the tumor margin between 1994 and 2003. 63 patients (33%) had surgical resection. The tumor volume range was 0.08 - 25.9 ml (median 2.2 ml) and the tumor marginal dose range was 8 - 12 Gy (median 12 Gy). The patients were able to be followed up to a median 8 years (range 5 - 15 years).
     We studied patients who received < 12 Gy to the tumor margin.
     5-year, 10-year and 15-year actuarial tumor growth control rates were 96 %, 92% and 90% respectively. 5-year, 10-year and 15-year actuarial tumor growth control rates without additional treatment were 96 %, 96% and 94% respectively. Hearing preservation was achieved in 58 % of the patients and useful hearing (below 50 dB) was preserved in 62% of the patients. 5-year, 10-year actuarial useful hearing preservation rates were 63% and 36%. The significant predictive factors concerning useful hearing preservation were age (below 50 years, p=0.02) and pre GKRS hearing level (below 20 dB, p=0.04). Facial neuropathy was suffered by one patient (0.5%) transiently. New trigeminal neuropathy was suffered by 5 patients (2.6%) and persisted in one patient (0.5%). 7 patients (3.6%) needed shunt surgery due to hydrocephalus. Intratumoral bleeding occurred in 6 patients (3.1%) and four patients were treated conservatively while two patients needed surgical resections.
     This was a retrospective study.
     Low dose radiosurgery (<12 Gy) for vestibular schwannomas is a useful treatment strategy from the standpoint of tumor growth control and functional preservations of hearing over a long term. 
     We must be aware of complications which require long-term follow-up.


Project Roles:

Y. Iwai (), K. Yamanaka (), M. Yoshimura ()