Gamma Knife Stereotactic Radiosurgical Boost for Patients Treated Primarily with Neutron Radiotherapy for Salivary Gland Neoplasms

<i>Object:</i> To determine the feasibility of utilizing a Gamma Knife stereotactic boost for patients at high risk of local recurrence from minor salivary gland tumors invading the base of skull. <i>Methods:</i> Eight patients with minor salivary gland tumors invading the base of skull were treated with primary neutron radiotherapy followed by a Gamma Knife radiosurgical boost to the base of skull. Patients had the following characteristics: (1) primary site of disease: paranasal sinuses (n = 3), nasopharynx (n = 3), hard palate (n = 1), pterygopalatine fossa (n = 1); (2) median age 59 years (range 37–80); (3) interval from completion of neutron radiotherapy to Gamma Knife boost 4 weeks (range 2–8 weeks); (4) median stereotactic dose delivered 10 Gy (prescribed to 50% isodose line, range 8–12 Gy), and (5) median number of isocenters treated 16 (range 14–21). Dosimetry from the neutron radiotherapy was used to determine both the volume boosted and the dose utilized. The median follow-up interval from the time of Gamma Knife treatment was 21.5 months (range 16–23 months). <i>Results:</i> All patients tolerated the procedure well. Acute side effects were minimal and included 1 patient with a delayed fatigue reaction at 2 months, 1 patient with vertigo of limited duration, and a third patient with prolonged nausea requiring steroid use. All patients were placed on a tapering dose of steroids after the procedure. One patient suffered a local relapse, with a 2-year actuarial disease-free survival rate of 80%. <i>Conclusions:</i> Gamma Knife radiosurgical boost following primary neutron radiotherapy for patients with a high risk of local failure is feasible and well tolerated acutely. Careful attention must be given to the previously treated regions in regard to volume treated and dose delivered. Further follow-up will be necessary to determine the long-term effectiveness and complications of such a boost in these high-risk patients.