The role of radiotherapy in the treatment of malignant salivary gland tumors

Abstract

We analyzed the role of primary and postoperative low linear energy transfer radiotherapy in 538 patients treated for salivary gland cancer in centers of the Dutch Head and Neck Oncology Cooperative Group, in search for prognostic factors and dose response. The tumor was located in the parotid gland in 59%, submandibular gland in 14%, oral cavity in 23%, and elsewhere in 5%. In 386 of 498 patients surgery was combined with radiotherapy, with a median dose of 62 Gy. Median delay between surgery and radiotherapy was 6 weeks. In the postoperative radiotherapy group, adverse prognostic factors prevailed. Elective radiotherapy to the neck was given in 40%, with a median dose of 50 Gy. Primary radiotherapy (n = 40) was given for unresectable disease or M(1), with a dose range of 28-74 Gy. Postoperative radiotherapy improved 10-year local control significantly compared with surgery alone in T(3-4) tumors (84% vs. 18%), in patients with close (95% vs. 55%) and incomplete resection (82% vs. 44%), in bone invasion (86% vs. 54%), and perineural invasion (88% vs. 60%). Local control was not correlated with interval between surgery and radiotherapy. No dose-response relationship was shown. Postoperative radiotherapy significantly improved regional control in the pN(+) neck (86% vs. 62% for surgery alone). A rating scale for different sites, T stage, and histologic type may be applied to calculate the risk of disease in the neck at presentation, and so indicate the need for elective neck treatment. A marginal dose-response was seen, in favor of a dose > or =46 Gy. A clear dose-response relationship was shown for patients treated with primary radiotherapy. Five-year local control was 50% with a dose of 66-70 Gy. Postoperative radiotherapy with a dose of at least 60 Gy is indicated for patients with T(3-4) tumors, incomplete or close resection, bone invasion, perineural invasion, and pN(+). In unresectable tumors, a dose of at least 66 Gy is advisable.