Neutron radiotherapy in adenoidcystic carcinoma: preliminary experience at the Münster neutron facility

In adenoidcystic carcinoma macroscopic residual disease after surgery, inoperable and recurrent tumors are characterized by relapse rates up to 70% if treated according to conventional treatment strategies including photon radiotherapy. By neutron therapy a tumor control rate of 70% has been reported. At the d,T-generator (14 MeV) in Münster nine patients with adenoidcystic carcinoma of the salivary glands in locally advanced stage have been treated since 1/86. A combined modality schedule (30 Gy photon/5 to 10 Gy neutrons) used in the beginning has been replaced by a definitive neutron therapy (15 Gy) with single fractions of 1.0 to 1.3 Gy in five to six weeks. Treatment planning included CT/MRI as well as computer assisted dose calculations based on a specific software for neutron therapy. The volume reduction by neutron radiotherapy was 82% for advanced disease. Continuous remission was achieved in seven of nine patients in a short follow-up period of medium 15 months (from six to 28 months). The two recurrences occurred at the field edge. Based on this preliminary experience and on a survey of the literature the main issues for neutron therapy in salivary glands tumors in particular adenoidcystic carcinomas are discussed: histology, stage, tumor size, location, surgery, treatment planning and delivery, dose, and side effects. A long term evaluation of neutron therapy within a controlled clinical multicenter trial is proposed.