Repeat stereotactic radiosurgery for progressive vestibular schwannomas after previous radiosurgery: a systematic review and meta-analysis

Abstract

Vestibular schwannomas (VS) are slow-growing intracranial extraaxial benign tumors, developing from the vestibular part of the eight cranial nerves. Stereotactic radiosurgery (SRS) has now a long-term scientific track record as first intention treatment for small- to medium-sized VS. Though its success rate is very high, SRS for VS might fail to control tumor growth in some cases. However, the literature on repeat SRS after previously failed SRS remains scarce and reported in a low number of series with a limited number of cases. Here, we aimed at performing a systematic review and meta-analysis of the literature on repeat SRS for VS. Using PRISMA guidelines, we reviewed manuscripts published between January 1990 and October 2020 and referenced in PubMed. Tumor control and cranial nerve outcomes were evaluated with separate meta-analyses. Eight studies comprising 194 patients were included. The overall rate of patients treated in repeat SRS series as per overall series with first SRS was 2.2% (range 1.2–3.2%, p < 0.001). The mean time between first and second SRS was 50.7 months (median 51, range 44–64). The median marginal dose prescribed at first SRS was 12 Gy (range 8–24) and at second SRS was 12 Gy (range 9.8–19). After repeat SRS, tumor stability was reported in 61/194 patients, i.e., a rate of 29.6% (range 20.2–39%, I2 = 49.1%, p < 0.001). Tumor decrease was reported in 83/194 patients, i.e., a rate of 54.4% (range 33.7–75.1%, I2 = 89.1%, p < 0.001). Tumor progression was reported in 50/188 patients, i.e., a rate of 16.1% (range 2.5–29.7%, I2 = 87.1%, p = 0.02), rarely managed surgically. New trigeminal numbness was reported in 27/170 patients, i.e., a rate of 9.9% (range 1.4–18.3%, p < 0.02). New facial nerve palsy of worsened of previous was reported in 8/183 patients, i.e., a rate of 4.3% (range 1.4–7.2%, p = 0.004). Hearing loss was reported in 12/22 patients, i.e., a rate of 54.3% (range 24.8–83.8%, I2 = 70.7%, p < 0.001). Repeat SRS after previously failed SRS for VS is associated with high tumor control rates. Cranial nerve outcomes remain favorable, particularly for facial nerve. The rate of hearing loss appears similar to the one related to first SRS.

MRI Changes in Failed Radiosurgery for Vestibular Schwannomas

“…This treatment has been shown to be a valuable therapy with high and long-term efficacy and low complication rate [1,2,5]. However, treatment failure can occur [6]. So, radiological follow-up is a crucial issue in the follow-up of patients after radiosurgical treatment.…”

“…To reduce the risk of post-therapeutic complications, the radiation dose used has been reduced with time to obtain the best compromise between a high tumor control and a low morbidity [1]. So, from the doses of 20 Gy or more used in the early radiosurgery for VS to stop tumor growth, the radiation dose has been reduced to 11-12 Gy to minimize the risk of radiation-induced facial and cochlea-vestibular neuropathy [5][6][7][8]. Using these low doses, the tumor control rate ranged from 90% to 98% in the current series [6].…”

“…So, from the doses of 20 Gy or more used in the early radiosurgery for VS to stop tumor growth, the radiation dose has been reduced to 11-12 Gy to minimize the risk of radiation-induced facial and cochlea-vestibular neuropathy [5][6][7][8]. Using these low doses, the tumor control rate ranged from 90% to 98% in the current series [6]. For patients with obvious failure of tumor control after radiosurgery, a second irradiation could be proposed as an alternative to microsurgical removal of the tumor.…”

“…For patients with obvious failure of tumor control after radiosurgery, a second irradiation could be proposed as an alternative to microsurgical removal of the tumor. In the last decade, more and more articles have pointed out the interest of such salvage therapy after failed radiosurgery for VS [6,[9][10][11][12][13][14][15][16]. The criteria to decide that therapy has failed have necessitated a broader understanding of the patterns of tumor behavior observed during follow-up imaging after radiosurgery [17].…”

“…Some recent articles have reported patients who needed a second radiosurgical treatment to control the tumor [6,[9][10][11][12][13][14][15][16]. Unfortunately, these series were focused on the clinical and radiological outcome of the second radiosurgical therapy, and there was little information on the details of the radiological evolution between the two irradiation sessions.…”