Outpatient gamma knife surgery for vestibular schwannoma: definition of the therapeutic profile based on a 10-year experience

Abstract

Object. The purpose of the study was to define the therapeutic profile of outpatient gamma knife surgery (GKS) for vestibular schwannoma (VS) by using sequential tumor volumetry to quantify changes following treatment. Methods. A total of 111 patients met the inclusion criteria. The median follow-up duration was 7 years (range 5–9.6 years). Thirty-seven patients (33%) had undergone surgery before GKS and 10 (9%) had neurofibromatosis Type 2 (NF2). The median VS volume was 1.6 cm3 (range 0.08–8.7 cm3). The actuarial 6-year tumor control rate after a single GKS treatment was 95%. Tumor swelling was observed in 43 patients (38.7%). Recurrence was significantly associated with NF2 (p < 0.003) and the reduced dose (p < 0.03) delivered to these tumors. The incidence of facial nerve neuropathy was mainly determined by surgery prior to GKS (p < 0.0001). Facial nerve radiation toxicity was mild and transient. No permanent facial nerve toxicity was observed. Trigeminal neuropathy occurred in 13 patients, and this was correlated with the VS volume (p < 0.02). The median hearing loss was −10 dB (range + 20 dB to −70 dB). The risk of hearing loss was correlated with age and transient tumor swelling (p < 0.05) but not with dose parameters or NF2. Conclusions. Outpatient GKS is feasible, effective, and safe. Its therapeutic profile compares favorably with that of microsurgery.

Long-term follow-up results of linear accelerator-based radiosurgery for vestibular schwannoma using serial three-dimensional spoiled gradient-echo MRI

“…A meta-analysis of the tumor control rates in 3677 patients from 37 recently published studies reported an overall local control rate of 91.1% (95% confidence interval, 90.4-93.7) [26]. Recently, gamma knife facilities have reported tumor control rates of 87-98.5% [5,[27][28][29]. This is largely consistent with the 88.6% tumor control rate observed at the final MRI in our study.…”

“…The incidence of this transient growth pattern has been reported to range from 3% to 80% [5,8,9,16,25,[29][30][31][32][33][34], and one reason for this disparity is thought to be the method for evaluating enlargement. It is necessary to determine whether tumors that enlarge early after treatment will continue to grow or instead begin to shrink.…”

A simple dose gradient measurement tool to complement the conformity index

“…In an arbitrary selection of 10 papers 4,6,9,[11][12][13]20,21,28,31 published since 2000 in which the treatment of vestibular schwannoma by GKS was described, prescription isodoses varied between 30% and 94%, 4,20 although some centers (in three of 10 papers) reported strict adherence to the 50% isodose line, 12,13,21 and one group reported strict adherence to the 65% isodose line. In an arbitrary selection of 10 papers 4,6,9,[11][12][13]20,21,28,31 published since 2000 in which the treatment of vestibular schwannoma by GKS was described, prescription isodoses varied between 30% and 94%, 4,20 although some centers (in three of 10 papers) reported strict adherence to the 50% isodose line, 12,13,21 and one group reported strict adherence to the 65% isodose line.…”

Intracochlear Hemorrhage After Gamma Knife Radiosurgery

“…On the other hand, the tumor may recur, especially in NF2 patients and when reduced doses are used (20). Moreover, tardive malignant transformation may occur, especially in young and/or NF2 patients, but this eventuality is widely overlooked (21).…”