In the last several years, a number of groups have used fractionated radiation therapy to treat patients with acoustic neuromas. This technique developed when several centers who used linear accelerator irradiation technology were not satisfied with the results or accuracy of their device after single fraction irradiation (radiosurgery).

Fractionated Radiosurgery for Acoustic Tumors Chart

In order to decrease the cranial nerve morbidities they were observing, they began to deliver radiation over multiple sessions (fractionation). The goal of this approach is to weaken the effect of each radiation administration and try to maintain brain or nerve function. Correspondingly this also weakens the effect of the radiation on the tumor target.

There is little data on this approach in the peer reviewed literature that includes diligent outcomes and follow-up. Williams et al reported 80 patients who had fractionated stereotactic radiotherapy (39). Median follow-up after radiotherapy was 2.9 years. Seventy patients received 25 Gy in 5 fractions and 10 received 30 Gy in 10 fractions. The treatment was delivered using CT targeting which is limited in evaluating the intracanalicular portion of the tumor. Only 19 of 80 patients had Gardner Robertson grade 1 or 2 hearing at the time of treatment. Hearing levels were preserved in 82% (actuarial data). Two patients had transient trigeminal neuropathies and no patient had a significant facial neuropathy.

In a separate oral report, Lederman et al provided results from the Staten Island group at the 2001 meeting of the International Stereotactic Radiosurgery Society. They provided no treatment planning images, no cranial nerve outcome data using the accepted grading systems, and they did not define "hearing preservation". They did describe that hearing was preserved at a rate "above" 90%, but the quality of hearing was not reported.

In a more comprehensive report, Andrews et al reported 69 patients who had gamma knife radiosurgery and 56 patients who had linear accelerator based radiotherapy (38). Tumor control rates were high (97%) in early follow-up and cranial nerve morbidities were low in both groups. With their technique, they found a higher rate of early hearing preservation after radiotherapy, but both treatments had median follow-up times of less than 10 months. Their rate of hearing preservation after radiosurgery (33%) was lower than reported by others. The main drawback of this report is the lack of randomization. Patients were allocated to either treatment according to "strong physician preferences".

Optimally, appropriate doses of radiation should be delivered precisely to the tumor and the regional brain structures should be spared of radiation. This is not the case with fractionated techniques where larger volumes of regional tissue are irradiated.

We believe that any advantage in fractionation in limiting toxicity only makes sense if the target volume contains normal brain or nerve. Sophisticated stereotactic radiosurgical instruments allow regional brain or nerve to be spared through frame-based, single-session, image guidance. We do not believe that fractionation provides any useful advantage over radiosurgical techniques that have been in use for the last 10 years.

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