Conventionally Fractionated Stereotactic Radiotherapy for Vestibular Schwannoma: Long-Term Outcome and Cranial Nerve Function
Diana Stripp, MD
University of Pennsylvania Cancer Center
Last Modified: November 8, 2001
Presenter: Chan, A
Presenter's Affiliation: Massachusetts Gerneral Hospital, Boston, MA
Type of Session: Scientific
BackgroundVestibular schwannoma/acoutic neuroma comprises 8% of all primary brain tumors.
It?s location ? closely associated with brain stem and cranial nerve, creates great challenge for treatment.
Surgical outcome has shown good results with tumor < 2cm. However, for tumor >2cm, cranial nerve damage could be permenant.
1945, 1st fractionated radiotherapy (RT) was done at UCSF. 1987, 1st large study on fractionated RT.
Methods48 patients (1993-2000) with vestibular schwannoma were treated with linac accelerator-based stereotactic radiotherapy at the Massachusetts General Hospital or Brigham and Women?s Hospital.
6 patients with neurofibromatosis type II, and 5 patients had intracanicular tumors only.
39 patients were treated with primary radiotherapy and 9 patients were treated after primary surgical resection for persistent (n = 1) or recurrent (n = 8) disease.
Six patients had pre-existing facial paresis at the time of radiation (House-Brackmann class 2 in 1, class 4 in 1, class 5 in 3, and class 6 in 1).
The median tumor volume was 3.1 cc (range: 0.17 cc - 21.07 cc). The median dose was 54 Gy in 1.8 Gy per fraction prescribed to 95% of the isodose.
Computerized tomography/magnetic resonance images were used for target definition. Conformal treatment plans were generated using one isocenter and three to six non-coplanar arcs. Follow-up duration ranged from 12 to 77 months.
ResultsThe overall local control rate (stabilization or regression of tumor) was 94%.
Post-radiation surgical intervention was performed in 3 patients (6%); two underwent microsurgical resection at 39 and 44 months for progressive enlargement of tumors, and one underwent shunt placement for persistent hydrocephalus and progressive disease at 6 months.
The rate of hearing preservation (maintenance of the pre-treatment Gardner-Robertson hearing function class or no subjective decline of hearing) was 83%.
All patients with pre-treatment useful hearing (Gardner-Robertson class 1 - 2) maintained useful hearing after radiation.
Pre-treatment normal facial and trigeminal nerve function was preserved in all cases.
One patient with an intracanicular tumor and a pre-treatment House-Brackmann class 2 facial dysfunction developed permanent class 5 facial weakness during the first week of radiation. Mild trigeminal toxicity was observed in one patient at 18 months after radiation.
There were no other complications or second cancer
Stereotactic radiotherapy using a conventionally fractionated schedule results in local control rate comparable with that reported for gamma knife radiosurgery and microsurgery resection, but with a high rate of hearing preservation and a very low rate of trigeminal and facial neuropathy
Clinical/Scientific ImplicationsImproved rate of hearing preservation and low rate of trigeminal and facial neuropathy provides a very attractive therapeutic scheme for treatment of vestibular schwannoma, if feasible with individual clinics.
Long term follow up is needed to evaluation late recurrence