Background: Our aim was to examine the outcome of patients treated with a planned gamma knife boost after completion of neutron radiotherapy for salivary gland neoplasms involving the base of skull.

Methods: Thirty-four patients with salivary gland neoplasms involving the base of skull were treated from 2001 to 2005 at our institution. These results were compared with a similar historical group treated at our institution from 1984 to 2000. The patients had the following characteristics: median age: 54 years (range, 23-80); median follow-up period: 20.5 months (range, 4-55); women-to-men patient ratio: 1.1:1; histology: 29 adenoid cystic, 3 adenocarcinoma, 1 acinic cell, 1 mucoepidermoid; primary sites of disease: 6 nasopharyngeal, 14 paranasal sinuses, 4 parotid gland, 8 oral cavity, 1 lacrimal gland, and 1 auditory canal. All patients had gross residual disease at the time of treatment. The median neutron dose prescribed to isocenter was 19.2 nGy and the median dose to the effected temporal tip was 11.98 nGy. The median prescribed gamma knife dose was 12 Gy to the 50% isodose line. The median number of isocenters was 17. The median target volume treated was 12.4 cm3 (range, 1.9-28.9) with a median total volume treated of 18.3 cm3 (range, 5.9-53.9).

Results: The 24-month and 40-month Kaplan-Meier estimated local control was 82% versus 81% (24 months) and 82% versus 39% (40 months; p = .04) for the gamma knife treated group versus historical controls (n = 61). Two of the 4 failures in the gamma knife-treated group occurred outside the boosted area. Complications were no greater in the gamma knife-treated group than in those treated with neutron radiotherapy alone.

Conclusions: Patients with primary salivary gland neoplasms that involve the base of skull and are treated with neutron radiotherapy alone are at high risk of local recurrence. A gamma knife boost improves local control and adds little additional toxicity. These preliminary results suggest that all patients with salivary neoplasms and base of skull invasion should be considered for a gamma knife boost after primary treatment with neutron radiotherapy.