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Treating ANs with GK
news from Pittsburgh

The June 1998 Issue of  Another Perspective (the newsletter of IRSA, the International Radiosurgery Support Assoc.) has an overview of the latest refinements and improvements in Gamma Knife treatments, by radiosurgeons from Pittsburgh (Kondziolka, Lundsford, Flickinger).

There is a section on ANs which presents some very interesting statistics:

We have managed 475 patients with ANs as an alternative to microsurgical resection... The most recent review of patients with ANs with at least 5 years follow-up (162 patients managed between 1987 and 1992) found that the clinical control rate (no requirement for surgical intervention) for the group was 98 percent...

Since 1987, there have been significant modifications in the technique of acoustic tumor radiosurgery including a change from CT to MRI based planning, improved computer workstations,  the use of more isocenters of radiation and a reduction in the radiation dose. Since the institution of these techniques beginning in 1991, there has been a significant reduction in the morbidity of radiosurgery. Currently, both the risk for a delayed, mild facial or trigeminal nerve deficit is below 3 percent.

That article has some very good news for NF2 patients.  It lists NF2 as one of the 5 criteria for preferring the Gamma Knife treatment over surgery:

[GK is] an alternative to miscrosurgical resection due to one or more of the following criteria: ... NF2 ..."

There is another section specifically on Trigeminal Neuralgia which presents very encouraging news as well.

Most recently and in more detail, in The New England Journal of Medicine (Nov. 12, 1998), the Pittsburgh radiosurgeons have reported on "Long-Term Outcomes after Radiosurgery for Acoustic Neuroma" for the 162 patients treated between 1987 and 1992.

The rate of tumor control (no surgery required) was 98%. One hundred tumors (62%) became smaller, 53 (33%) remained unchanged in size, and 9 (6%) became slightly larger.

Of the 97 patients with at least 5 years of follow-up, imaging studies showed that 70 (72%) had a decrease in tumor volume after radiosurgery and 27 (28%) had no change in the size of their tumors. No increase in tumor volume was identified an any patient from year 4 to year 10 after treatment.

Tumor growth was identified in four patients three years after radiosurgery. These patients underwent resection, which was described by the operating surgeons as no different from that of a nonirradiated tumor in the cases of three patients, and as more difficult in one case.

Normal facial-nerve function was preserved in 122 of 155 patients (79%) who could be evaluated; and normal functioning of the trigeminal nerve was preserved in 119 of 162 patients (73%). In none of the patients with intracanalicular tumors did facial sensory dysfunction develop after radiosurgery. Beginning in 1991-92, with the introduction of refinements such as dosage reduction for the tumor margin, cranial-nerve morbidity decreased considerably, with a rate of facial-nerve and trigeminal- nerve side effects below 7% for extracanalicular tumors and below 2% for intracanalicular tumors.

No change in hearing ability was found in 43 of 85 patients (51%). Of the 32 patients who had useful hearing before radiosurgery, 15 (47%) maintained hearing within those levels. Some degree of hearing and sound recognition was preserved in 52 of 85 patients (61%).

Finally, the report notes that, beginning in 1991, radiosurgery at Pittsburgh has been offered to all patients with acoustic tumors regardless of age, surgical history, or symptoms.  However, radiosurgery is rarely used for patients with tumors over 3 cm in extracanalicular diameter, because the reduction in the dose of radiation necessary to minimize adverse effects on tissue decreases the efficacy of the procedure.

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Last Edited: Friday, November 01, 2002