Title: Dose reduction improves hearing preservation rates after intracanalicular acoustic tumor radiosurgery.

Authors: Niranjan A, Lunsford LD, Flickinger JC, Maitz A, Kondziolka D
Location: Department of Neurological Surgery, University of Pittsburgh, Pennsylvania 15213, USA.

Source: Neurosurgery 1999 Oct;45(4):753-62; discussion 762-5


OBJECTIVE: To assess the potential for long-term serviceable hearing preservation in intracanalicular acoustic tumor patientswho underwent stereotactic radiosurgery.

METHODS: Between August 1987 and December 1997, 29 patients withintracanalicular acoustic tumors underwent stereotactic radiosurgery at our center using the Leksell gamma knife (ElektaInstruments, Inc., Atlanta, GA). Fifteen assessable patients had serviceable preradiosurgery hearing (pure tone average, < or =50 dB; speech discrimination score, > or = 50%). We retrospectively analyzed our hearing results and compared hearingpreservation in patients who received a minimal tumor dose of 14 Gy or less versus those who received more than 14 Gy to thetumor margin.

RESULTS: No perioperative patient morbidity or mortality was observed. Serviceable hearing was preserved in11 (73%) of 15 assessable patients (actuarial rate, 65%). Long-term follow-up demonstrated serviceable hearing preservationin 10 (100%) of 10 patients who received marginal tumor doses of 14 Gy or less but in only one of five patients who receivedmore than 14 Gy. Preradiosurgery Gardner-Robertson class was preserved in 49%, and testable hearing was present in 68%of patients who had any testable hearing at presentation. Five patients demonstrated improvement in hearing (three hadserviceable and two had nonserviceable hearing before radiosurgery). No patient developed a facial or trigeminal neuropathy. Seven of 13 patients with preoperative tinnitus continued to experience tinnitus in follow-up. Episodic vertigo continued in 3 ofthe 11 patients who presented with vertigo.

CONCLUSION: Gamma knife radiosurgery (using conformal dose planning,small-beam geometry, and < or = 14 Gy to the margin) prevents tumor growth and achieves excellent hearing preservation rates.

Inez's note: The important point concerns dose reduction: Dose reduction improves hearing preservation rates after intracanalicular acoustic tumor radiosurgery.

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