Definitive radiotherapy for unresected adenoid cystic carcinoma of the trachea.

Adenoid cystic carcinoma is a rare malignancy that usually originates in the salivary glands of the head and neck but has rarely been known to originate in the trachea. This histology has a predilection for perineural invasion and a tendency for both local and distant recurrences. While surgical resection is the mainstay of treatment of tracheal adenoid cystic carcinoma, tumor size, location, and patient comorbidities may preclude surgery, and the optimal nonsurgical management remains undefined. In the absence of locoregional lymph node metastases, we recommend highly conformal radiotherapy alone to a dose of 80 Gy. We report on two patients with unresectable disease who were treated with definitive radiotherapy: one using conventional photons and one treated with a combination of photon and proton beams. Both patients were treated to a dose of 80 Gy with acceptable toxicities and objective clinical and radiographic response. The patient treated with conventional photons has no evidence of recurrent disease at 5 years; the patient treated with protons has continued evidence of response without evidence of disease recurrence 11 months after treatment.