Gamma knife radiosurgery for vestibular schwannomas: identification of predictors for continued tumor growth and the influence of documented tumor growth preceding radiation treatment.
OBJECTIVE
Gamma knife radiosurgery (GKRS) has become an important treatment modality for vestibular schwannomas. The primary aim of this study was to investigate whether tumor growth at the moment of GKRS has any correlation with the outcome. The secondary aim was to identify clinical predictors of radioresistance in vestibular schwannoma patients treated with GKRS.


METHODS
One hundred vestibular schwannoma patients, treated with GKRS, were divided into two groups: 1) proven tumor growth preceding GKRS; and 2) previous history of growth unknown. GKRS outcome was defined in two ways. According to the first definition, GKRS was said to have failed when additional treatment had taken place. According to the second one, a volume decrease >20% after 2 years marked successful treatment.


METHODS
Correlations between outcome and growth status were determined with SPSS software. Furthermore, the study assessed how different variables (patient data, history, tumor characteristics, imaging, and audiovestibular examinations) correlated with the outcome of GKRS.


RESULTS
No significant difference regarding success and failure of GKRS was found between the two patient groups. The mean reduction in tumor volume after GKRS was less pronounced in patients in whom tumor growth was demonstrated before treatment, but this finding was not significant. No significant predictors (P < .05) could be identified in this data set.


CONCLUSIONS
This study found no indication that growth at the moment of GKRS influences therapeutic outcome, nor did it identify any predictors of the outcome after GKRS in vestibular schwannoma patients.
Department of Otorhinolaryngology-Head and Neck Surgery, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands. f.timmer@kno.umcn.nl
Ferdinand C A
FC
Timmer
Jef J S
JJ
Mulder
Patrick E J
PE
Hanssens
J J
JJ
van Overbeeke
Rogier T
RT
Donders
Cor W R J
CW
Cremers
Kees
K
Graamans
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001301:Audiometry, Pure-Tone; D002150:Caloric Tests; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D009464:Neuroma, Acoustic / Q000473:pathology / Q000601:surgery*; D011237:Predictive Value of Tests; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*; D018709:Statistics, Nonparametric; D016896:Treatment Outcome