EVOLUTION IN TECHNIQUE FOR VESTIBULAR SCHWANNOMA RADIOSURGERY AND EFFECT ON OUTCOME

Purpose: To define changes in treatment technique for vestibular schwa nnoma radiosurgery and to relate them to changes in outcome, a large s ingle institution experience was reviewed. Methods and Materials: Two hundred seventy-three patients with unilateral vestibular schwannomas underwent Gamma knife radiosurgery: 118 with computed tomography (CT) treatment planning during 1987-1991, and 155 with magnetic resonance i maging (MR) treatment planning in 1991-1994, Mean treatment parameters differed between the CT and MR groups: minimum tumor dose (D-min) was 17 vs, 14 Gy, number of isocenters was 3.4 vs. 5.8, and volume was 3. 5 vs, 2.7 cc., respectively. Results: The actuarial 7-year clinical tu mor control rate (no requirement for surgical intervention) for the en tire series was 96.4 +/- 23%, with a radiographic tumor control rate o f 91.0 +/- 3.4%; these rates were similar for the CT and MR groups, Si gnificantly lower rates of postradiosurgery facial, trigeminal, and au ditory neuropathy were observed in the MR group compared to the CT gro up, Multivariate analyses found significant independent correlations o f increasing rates of facial and trigeminal neuropathy with increasing transverse tumor diameter and D-min, as well as with CT treatment pla nning (compared to MR). Decreased hearing was similarly correlated wit h diameter and CT planning but not with D-min. Conclusions: Changes in radiosurgery technique and the use of lower doses improved the outcom e after vestibular schwannoma radiosurgery by decreasing cranial neuro pathy rates, MR-based treatment planning appears to have significantly contributed to this improvement, Despite decreases in radiation dose, no change in the high rate of tumor control has yet been observed. Co pyright (C) 1996 Elsevier Science Inc.