Short-term results of treatment outcome and toxicities following gamma knife surgery in cerebellopontine angle tumors

Abstract

Introduction: About 5% to 10% of all intracranial neoplasms are located at the cerebellopontine (CP) angle. The most common of these is the vestibular schwannoma (VS). Aims and Objectives: The primary objective was to assess treatment outcomes in CP angle tumor post-Gamma Knife radiosurgery (GKS). Secondary objectives were the assessment of dose conformity and gradient indices for target coverage and organs-at-risk sparing along with the assessment of hearing function preservation post-GKS. We also assessed facial and trigeminal nerve function and quality of life (QoL) post-GKS. Materials and Methods: This was a retrospective study carried out in a tertiary care center of North India for 2 years and 3 months. All patients were followed up for 24 months posttreatment with a minimum follow-up at least 12 months. Tumor expansion was assessed post-GKS along with hearing preservation rates, facial and trigeminal nerve function and QoL. Results: No significant relationship between age, sex, and study variables was made out. The target tumor coverage ranged from 94% to 100%, with a mean of 97.24%. The conformity index ranged from 1.17 to 1.92, and the gradient index ranged from 1.35 to 1.73. Tumor expansion occurred in 52% of the patients (13) 6 months after GKS, though the increase in size was minimal with a standard deviation of 0.59 and did not result in any clinical deterioration of patients. Positive correlation was seen between maximum tumor size and loss of hearing function. The hearing preservation rate at 12 months post-GKS is 80%. This study also showed that GKS for VS has little impact in the deterioration of the function of the trigeminal and facial nerve and the general QoL. Conclusion: The radiation changes after GKS are generally seen after 6–12 months post-GKS and about 3–5 years are required to ascertain tumor control and any meaningful change in hearing levels and other toxicities. Thus, a longer period of follow-up is needed to validate the findings of this study.