Results of fast neutron therapy of adenoid cystic carcinoma of the salivary glands

Introduction: Patients with adenoid cystic carcinoma (ACC) of the salivary glands in the head and neck region have been reported to benefit from neutron radiotherapy according to significant clinical experience. A prospective clinical trial on the efficacy and treatment related morbidity of fast neutron radiotherapy was performed between 1986 and 1995 at the (d+T) 14 MeV neutron generator in Munster. Material and Methods: 72 consecutive patients with ACC were treated with fast neutrons, 66 after surgery, 6 for primarily unresectable disease, 43/66 for macroscopic residual disease, 23/66 for unresectable recurrent disease. 45/72 tumors were localized in the minor, 27 in the major salivary glands. T-stage was in 13 pts T2, in 33 T3, in 26 T4; positive nodes were in 10 pts, M+ in 15 pts. Mean tumor volume was 89 cm(3). Neutron therapy was 15.03 Gy in 3 weeks with 1.67 Gy per fraction three times per week. Individual computer assisted treatment planning was performed based on CT and/or MRI, using bolus material if necessary. Target volume was the macroscopic tumor volume with a generous safety margin. Results: Complete response was achieved in 28 pts, partial response in 35 pts. Local control was observed in 73.4% after a mean observation period of 36 months. Overall and recurrence free survival was 85%/81% at two years, and 58%/53% at 5 years (Kaplan-Meier). In univariate analysis tumor volume (>100 cm(3)), distant metastases, histologic subtype (solid) and neutron dose (<15 Gy) turned out to be significant parameters for predicting outcome, in multivariate analysis tumor volume and histologic subtype remained the only significant parameters. Acute morbidity was grade III/IV (EORTC/RTOG) in 6% for skin (desquamation), in 4% for mucosa (ulceration), late morbidity (grade III/IV) in one patient with local temporal brain necrosis. Conclusion: According to this experience and taking into account the so far collected experience, fast neutron radiotherapy remains the treatment of choice for large and unresectable primary and recurrent ACC, and residual disease after surgery.