Purpose: To investigate clinical feasibility and toxicity of combined photon and carbon ion radiotherapy in locally advanced adenoid cystic carcinomas (ACC) within a prospective Phase I/II trial.
Methods and materials: Between September 1998 and April 2002, 16 patients with histopathologically proven ACC and residual macroscopic tumor were treated with combined photon RT and a carbon ion boost to the macroscopic tumor. Median total tumor dose within the gross tumor volume (GTV) was 72 GyE. Photon radiation therapy (RT) consisted of fractionated stereotactic RT in 7 patients; 9 patients received stereotactic intensity-modulated RT. Carbon ion boost was delivered by intensity-controlled raster scanning at the heavy ion synchrotron (SIS) at the Heavy Ion Research Center (GSI) in Darmstadt.
Results: Median follow-up was 12 months. Three patients developed locoregional recurrences 9, 11, and 24 months after RT, respectively. Actuarial local control rates were 80.8% and 64.6% at 1 and 3 years, respectively. Overall survival rates were 100% and 83.3% at 1 and 3 years, respectively. Acute side effects greater than Common Toxicity Criteria (CTC) Grade 2 were observed in 2 patients; no patient developed late effects > CTC Grade 2.
Conclusions: Combined photon and carbon ion RT is feasible and effective in patients with locally advanced ACC. Acute and late toxicity is moderate with respect to the delivered tumor doses and in accordance with the radiobiologic modeling. A Phase III trial is designed.