A new study has determined that when compared to large single treatments, multiple smaller radiosurgical treatments (fractionation) may result in greater preservation of normal function including hearing, facial strength and facial sensation in the treatment of acoustic neuromas. This technique, fractionated stereotactic radiotherapy (FSR) offers high control of the treated tumors while preserving normal function. The study, "Fractionated Stereotactic Radiotherapy for Acoustic Neuromas,"which was presented by Jeffery A. Williams, MD, during the 70th Annual Meeting of the American Association of Neurological Surgeons (AANS), on April 8, 2002.

Harvey Cushing Society, the American Association of Neurological Surgeons is a scientific and educational association with nearly 5,500 members worldwide. The AANS is dedicated to advancing the specialty of neurological surgery in order to provide the highest quality of neurosurgical care to the public. All active members of the AANS are certified by the American Board of Neurological Surgery.

Unlike stereotactic radiosurgery (SRS) treatments that provide single-doses of targeted radiation that may result in loss of facial function and loss of hearing, the FSR offers preservation of these important functions in the treatment of acoustic neuromas (benign tumors arising from or near the acoustic nerve). Similar to surgery, the risk for loss of cranial nerve functions following single shot radiosurgery (SRS) may be proportionate to the size of the treated tumor. However, the fractionation (separation into different portions) offers higher preservation of the normal tissue when compared to surgery or SRS and is the basis for the conventional radiotherapy of many brain tumors because it spares normal tissues and kills tumor tissues. The addition of the stereotactic, precise method for delivery of the fractionated treatments combine to deliver safe and effective treatment for the acoustic neuromas.

"Although surgery offers both immediacy and low rates of recurrence, the potential loss of facial and auditory cranial nerve functions during resection (removal) remains a challenge," said Jeffery A. Williams, MD, author of the study and AANS member. "Fractionated stereotactic radiotherapy or FSR, may preserve normal nerve function while controlling both small and large acoustic neuromas."

Over the past six years, 249 consecutive patients have received FSR for acoustic neuromas. The 125 consecutive patients comprising this study have had follow up greater than one year. The median age at the time of treatment was 54.

Four patients had initial surgery for the acoustic neuroma and had FSR for recurrence. Patient assessments were performed every three months after FSR for the first year, every six months for the second year, and annually thereafter.

Measurements of hearing after FSR procedures showed preservation. Based upon the results of these audiograms, hearing (19) was unchanged in 26 of 56 patents, showed increase in 20 patients and decrease (improvement in hearing) in 10 patients. None of the patients developed facial weakness. For cranial nervel function, two patients had temporary, moderate decrease in facial sensation.

For surgery, the risk for facial nerve dysfunction is proportionate to the size of the resected acoustic neuroma. For preservation of hearing, the researchers note that the size of the resected tumor correlates well with the outcome that candidates for post-surgical preservation of hearing are selected according to the preoperative size of the acoustic neuroma. For SRS, the risks to facial, trigeminal and auditory functions may be proportionate to size of the acoustic neuroma.

The study results suggest that for both large and small acoustic neuromas, the described schedules for the fractionated stereotactic radiotherapy may result in both control of the tumor and preservation of the normal cranial nerve functions. However, extensive follow up is required to determine the durability of both tumor control and preservation of normal cranial nerve function.