An Assessment Of Failure Rates And Complications Following Contemporary Reduced Dose Gamma Knife Radiosurgery For Vestibular SchwannomaCaroline Hayhurst1, Zadeh Gelareh11Gamma Knife Centre, University Health Network, Toronto/ Canada Keywords: vestibular schwannoma, outcome, gamma knife, complications, recurrent disease
With a prescription dose of 16Gy for vestibular schwannoma (VS) tumour control was reported between 96 -98%. Therefore, very few non NF-2 patients would require salvage therapy. However, the incidence of facial and trigeminal dysfunction approached 30% with this regime. The reduction in prescription dose to 12 -13 Gy has resulted in fewer cranial neuropathies, but whether it remains an effective dose for tumour control in the long term has not been clearly defined in the literature.
We aim to define long-term outcomes with a 12Gy marginal dose and assess the impact of treatment plan characteristics on outcome.
We have reviewed the Gamma Knife database at our institution for patients treated with radiosurgery for VS. 41 patients were treated between September 2005 and 2006. 39 of these have complete clinical and radiological follow up for 3 years.
All patients received a prescription dose of 12Gy.Volumetric analysis of tumour response was performed. Tumour response is classified as stable, initial increase followed by stability and growth requiring salvage treatment. All treatment plans were reviewed for 12Gy volume, conformality index, isocenter number, brainstem, trigeminal nerve and cochlear dose.
28 patients (72%) have stable tumours at 3 years. 8 (20%) show an initial increase in size, which then stabilized. 3 patients (7.7%) required salvage therapy. 8 (20%) patients developed oedema within the cerebellar peduncle and 10 patients (26%) developed complications (hydrocephalus 3, ataxia 4, trigeminal dysfunction 7, facial weakness 1). There were no significant differences in the conformality index, isocenter number or radiation dose to adjacent structures in those patients with complications. Treatment volume is the most important predictor of adverse radiation effects.
This is a retrospective study.
Whilst the numbers of treatment failures overall is low, consideration of retreatment with either repeat radiosurgery or microsurgery may be necessary in increasing numbers over time when using a 12Gy marginal dose.
Radiation induced complications do not appear dependent on actual dose to the brainstem or adjacent cranial nerves but on total 12Gy volume. Project Roles:
C. Hayhurst (), Z. Gelareh ()