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STEREOTACTIC RADIOSURGERY FOR ACOUSTIC NEUROMA

- Introduction
- SRS Procedure and Results
- Follow-up
- SRS Team
- References

Introduction :
Acoustic Neuromas are slow growing tumors which form on CN VIII. They can cause progressive hearing loss, decreased balance, headaches, and rarely death. Management options include Surgical Resection and Stereotactic Radiosurgery (SRS). SRS can be delivered either via Gamma Knife or X-Knife (Linear Accelerator). The University of Pittsburgh recently reported an interesting single institution study comparison of 87 patients treated with SRS (n = 47) versus surgery (n = 40) [1]. Patients were comparable in regard to presenting symptoms and tumor size. The SRS patients were slightly older. The patients were compared with respect to 7 endpoints. SRS was superior in all 7, with 5 reaching statistical significance. The p-values are shown in the following table :

ACOUSTIC NEUROMAS
COMPARATIVE TREATMENT OUTCOME

GAMMA KNIFE SURGERY
Facial Nerve Function 0.004 -
Hearing Preservation 0.03 -
Morbidity 0.01 -
Post-Operative Function 0.07 -
Patient Satisfaction 0.10 -
Return to Independence 0.001 -
Hospital Cost 0.001 -

This single institution data is comparable to large multi-institution reviews as shown below :
ACOUSTIC NEUROMA
GAMMA KNIFE VS. MICROSURGERY

SRS [2,3] MICROSURGERY [4]

Acute CN VII palsy 2.3% 36.0%
Chronic CN VII palsy 0% 9.0%
Useful Hearing Preserved 58.0% 39.0%
Acute CN V Numbness, Tingling 5.8% 9.0%
Chronic CN V Numbness, Tingling 1.7% nr
CSF Leak 0% 9.2%
Hydrocephalus 0% 2.3%
Mortality 0% 1.1%
Hospitalization Days 0.5 10.5
ICU Days 0 2.4
Loss of Work Days 5 60

SRS Procedure :
SRS technique calls for placement of a frame or halo by a Neurosurgeon. The frame serves to hold the patient's head still during SRS. The frame also gives the Radiation Physicist a reference point to perform 3-Dimensional Computer Radiation Treatment Planning. The patient then undergoes MRI and CT Scanning, and a CT Cisternogram for identification of the treatment target. The images are then sent by fiberoptic link for 3-Dimensional Computer Radiation Treatment Planning. The target and radiation doses are then identified and agreed on by the Neurosurgeon and Radiation Oncologist.
Following completion of SRS treatment planning, the patient undergoes treatment on the Linear Accelerator (X-Knife). SRS treatment typically lasts for about 1 hour. The treatment is painless. Following completion of SRS treatment, the frame is removed and the patient sent to a Hospital Room for overnight observation. There is a slight risk of acute edema and seizures following SRS. So far, we have not seen these problems in any patient.

Follow-up :
Following SRS, Acoustic Neuromas usually shrink slowly. Therefore, we recommend an MRI at 6 months after SRS, and then annually.

SRS Team :
Our SRS Team includes Neurosurgeons, Radiologists, Radiation Oncologists, Physicists, Nurses, and Radiation Therapy Technologists. Our team has experience in more than 1,000 SRS cases with Gamma Knife, and more than 100 cases with X-Knife.

References :
1. Neurosurgery, 1995 ; 36 : 215
2. J Neurosurg, 2000 ; 92 : 745
3. Acta Neurochir, 1997 ; 139 : 942
4. Neurosurg, 1997 ; 40 : 11