Effect of treatment plan quality on outcomes after radiosurgery for vestibular schwannoma.

Object: The goal in this study was to review the effects of treatment plan quality on outcomes after radiosurgery for vestibular schwannoma (VS).

Methods: Between July 1988 and August 2005, 390 patients were treated. The results of this experience have been published recently. In this study the authors looked at dosimetry variables: conformity of treatment plan and steepness of dose gradient, in the same group of patients. Over the duration of this study, dosimetry evolved from a single isocenter with marginal conformity to multiple isocenters with high conformity. Multivariate statistics were used to determine the effects of these variables on tumor control and on two types of complication, facial weakness and facial numbness.

Results: The 5-year actuarial tumor control was 91%. Dosimetry had no effect on tumor control. Eighteen patients (4.6%) reported new-onset facial weakness and 14 (3.6%) reported new-onset facial numbness. Since 1994, when peripheral treatment doses were lowered to 1250 cGy, only three (1%) of 298 patients have experienced facial weakness and two (0.7%) of 298 have experienced facial numbness. Statistical analysis confirms, as in the prior study, that treatment volume and treatment dose are significant predictors of both facial weakness and facial numbness. In this model, prior tumor growth was also significant. Dosimetry, however, is definitely not a significant predictor of either complication.

Conclusions: Treatment dose appears to be much more important than treatment plan quality in the prevention of facial numbness or weakness after radiosurgery for VS.