A prospective data analysis of radiosurgical patients has been undertaken since 2004 using objective assessment of volume change. This demonstrated some unexpected differences in response between vestibular schwannoma and meningioma which required analysis.

     Between 2004 and 2006, 51 vestibular schwannomas and 27 meningiomas were included in this study. 

     Patients were assessed at 2 years after radiosurgery by tumour volume measurement using the fiducial markers of the MR indicator box and Leksell Gamma Plan 5.2 (Del Valle et al. 2005). The process of volume measurement is identical to that performed on the day of treatment and carried out by the same doctors.

     For meningiomas the mean prescription dose was 13.5 Gy (10-16 Gy) and the mean volume after 2 years was 62.7% of the pre treatment volume with a range of 19-145%. Only one of 27 tumours increased in size (success rate 96.3%). For vestibular schwannomas the mean prescription dose was 11.7 Gy (11-14 Gy) and the mean volume after 2 years was 110.7% of the pre treatment volume (i.e. a mean increase of 10.7%) with a range of 0-382%. Surprisingly 21 of 51 tumours increased in size (success rate only 58.8%). The chance of failure in vestibular schwannomas was statistically greater later in the observation period (p=0.010) and the reason for this will be addressed in another study.

     This is a retrospective study.

     Precise volumetric follow up has revealed an interesting difference in response between vestibular schwannoma and meningioma.   

      It is recommended that all analyses of outcome in radiosurgery should be objective. A 5 year volumetric follow up is now in process.