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Stereotactic radio-surgery (SRS) is routinely used to treat Vestibular Schwannoma’s (VS) to avoid the need for surgical intervention.  However, some VS can remain indolent and given that SRS carries a risk of toxicity without guarantee of long term hearing preservation, timing of intervention remains debated. The objective of this analysis was to assess toxicity and long term outcomes using CyberKnife SRS.

All patients undergoing SRS for VS at a regional centre were identified from a prospective database. Patients with progressive growth on an observation programme, or presenting with a tumour ≥2cm, and minimum 5 year follow up were included. Patients with prior surgical intervention were excluded.  The prescription dose was either 12 Gy in 1 fraction to 100% of PTV, or 18Gy in 3 fractions. The primary endpoint was progression defined as need for surgical salvage. Secondary endpoints included any grade of facial and trigeminal nerve toxicity. All other CTCAEv4 grade 3 or 4 toxicity events were recorded.  All patients were given a key worker contact number to report toxicity events.

130 patients were included for analysis.  126 were treated with a single fraction and 4 were treated with 3 fractions. Mean size was 1.78cc (range 0.14cc-9.44cc).  7 patients required surgery for progression.  All patients with failure received a single fraction.  In patients requiring surgery the mean tumour volume was 3.11cc (0.6cc-5.28cc) vs.  1.70cc (0.14cc-9.44cc) in those who did not (p=0.035). 9 patients experienced some form of acute facial nerve toxicity and 2 (1.5%) were persistent.  There was no association between volume and acute facial nerve toxicity (p=0.37).  20 patients had acute trigeminal toxicity, all of which received treatment in a single fraction and 3 persisted beyond 2 years.  4 additional patients developed late trigeminal toxicity, 2 of which persisted leaving a total of 5 patients with persistent trigeminal nerve toxicity (3.8%).  In patients with acute trigeminal toxicity the mean volume was 2.63cc (0.49cc-6.67cc) vs 1.63cc (0.14cc-9.44cc) in those who did not have toxicity (p=0.016).  Similarly the mean trigeminal nerve dose was 1085cGy vs 872cGy in those with/without toxicity (p=0.01).

The trend of increased risk of failure for larger volume VS should be considered when following a policy of observation.  Although long term toxicity rates were low, significant levels of temporary nerve irritation were seen. Consideration should also be given to whether the trigeminal nerve constraint will still be achieved if delaying SRS.