Clinical outcome after hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors

Surgical resection of skull base tumors can be associated with significant morbidity. In cases where the risks outweigh the benefits, radiation therapy can offer an alternative means to effectively control tumor growth. However, the optimal dose regime for radiation therapy remains controversial. The objective of this study was to assess the neurological outcome, local control rate and morbidity associated with a 5-fraction regime of hypofractionated stereotactic radiotherapy (HSRT) for benign skull base tumors.

Twenty-six patients presenting with two of the most prevalent benign skull base tumors were included in the study. The tumors comprised 16 meningiomas and 10 acoustic neuromas. All patients exhibited preserved cranial nerve function prior to treatment, and a detailed audiological assessment was performed pre- and post-treatment for those patients with acoustic neuroma. Stereotactic radiosurgery was administered with the frameless CyberKnife Robotic Radiosurgery System. In each case, a 5-fraction HSRT regime was used: a dose of 5 Gy × 5 = 25 Gy to 6 Gy × 5 = 30 Gy was prescribed for skull base meningiomas, and 5 Gy × 5 = 25 Gy was prescribed for acoustic neuromas.

The clinical and radiographic median follow-up was 22 months (range: 6-54 months). Radiological assessment showed local control in all 26 tumors (100%), and in 5/26 patients (20%) the tumor showed a decrease in size. Cranial nerve function was preserved in all cases thus far studied; however, 28% of patients had transient Grade II side effects, including fatigue, headaches, unsteadiness and transient subjective worsening of hearing. In two of these patients, the period of transient worsening of hearing was associated with a temporary increase in the size of the tumor on control T2 MR images, consistent with radiation-induced edema. One patient had transient decrease in visual acuity from treatment-related edema. At the last follow-up, 3/16 patients with meningiomas (19%) and 2/10 with acoustic neuromas (20%) showed a decrease in tumor volume and improvement in hearing.

A 5-fraction stereotactic radiotherapy regime, as used in this study, seems to be effective for local control of benign skull base tumors in this early follow-up evaluation. Neurological function preservation is excellent with this short regime in the early post-treatment period, but long-term follow-up is crucial for validation.