POSTOPERATIVE RADIATION-THERAPY FOR MALIGNANT-TUMORS OF MINOR SALIVARY-GLANDS - OUTCOME AND PATTERNS OF FAILURE

Background. In the treatment of major salivary gland cancers, the addi tion of adjuvant postoperative radiation therapy for-patients with hig h risk features has been shown to reduce the incidence of local failur e. This retrospective study was done to determine the effectiveness of this approach for minor salivary gland cancers to document patterns o f failure, and to define prognostic variables for treatment outcome. M ethods. Between 1961 and 1990, 160 patients received postoperative rad iation at the University of Texas M.D. Anderson Cancer Center (UTMDACC ) after gross total removal of their tumors. These operations ranged f rom excisional biopsies to craniofacial resections with orbital exente rations depending on the original site and size of the tumor. The prim ary tumor site was in the oral cavity-oropharynx in 111 patients and i n the nasal cavity or paranasal sinuses in 46 patients; The most preva lent histologic type was adenoid cystic carcinoma (71%), Microscopic p ositive margins were present in 64 (40%) patients. Half of the patient s had pathologic evidence of perineural invasion. Radiation therapy te chniques varied, depending on the site and extent of disease and the e ra of treatment. Doses ranged from 50 to 75 Gy (median, 60 Gy; mean 59 .2 Gy). Follow-up for surviving patients ranged from 24 to 270 months (median, 110 months). Results. Fifty-seven (36%) patients experienced disease relapse. Nineteen (12%) patients had a local recurrence: 6 wit hin 5 years of treatment, 8 between 5 and 10 years, and 5 after 10 yea rs. Regional failures occurred in 3 of 13 patients with initially node -positive disease but were uncommon (less than 5%) in patients with no de-negative disease; regardless of elective neck treatments. Distant m etastases developed in 43 patients, mostly (79%) within 5 years of tre atment, Actuarial overall survival rates at 5, 10, and 15 years were 8 1%, 65%, and 43%, respectively. Complications occurred in 51 patients and were of three predominate types: bearing loss (26 patients), ocula r injury (15 patients), and bone exposure/necrosis (12 patients). Impr oved techniques, including better immobilization, customized beam Shap ing, and treating multiple fields per day, have substantially reduced the risk of serious complications during the past decade. Conclusions. Postoperative radiation therapy is effective in preventing local recu rrence in most patients with minor salivary gland rumors after gross t otal excision. When local failure occurs, it tends to be a late event. For most patients, the authors recommend a postoperative dose of 60 G y in 30 fractions to the operative bed; if there is named nerve invasi on, the path of the nerve is treated electively to its ganglion.