Adenoid cystic Carcinoma and Carbon ion Only irradiation (ACCO): Study protocol for a prospective, open, randomized, two-armed, phase II study.

Background Adenoid cystic carcinoma is a rare form of head and neck cancer with a slow, but aggressive growth pattern which remains a challenge for local tumor control. Based on phase II data, radiation treatment using partially high LET radiation results in a prolonged PFS and OS. There is a paucity of randomized clinical data examining the role of the use of high LET radiation only. Therefore, the purpose of this prospective clinical trial is to analyze local control rates in patients with node negative ACC treated with carbon ion radiotherapy alone compared to a combined modality approach. Methods This trial is conducted as a prospective, open-label, phase II, two-armed, investigator-initiated study comparing the local control rates in node negative ACCs of the head and neck treated either with sole carbon ion radiotherapy or a combination of carbon ions and photons. Secondary outcomes investigated are progression-free survival, overall survival, acute and late toxicity, and quality of life. A total of 314 patients will be randomly assigned to C12 treatment alone or bimodal treatment: Patients in the experimental group will receive a dose of 51 Gy (RBE) in 17 fractions and a boost of 15 Gy (RBE) in 5 fractions. Patients in the control group will receive 25 fractions photon IMRT 50Gy and a boost using 8 × 3 Gy (RBE) carbon ions. Local control will be assessed in regular follow up examinations until 5 years after the completion of treatment. Discussion The present trial aims to evaluate local control rates to compare sole carbon ion radiotherapy to bimodal radiotherapy with carbon ions and photons in patients with node negative ACCs of the head and neck region. Local control is selected as the primary endpoint due to its major clinical relevance because of slow but aggressive growth patterns. Trial registration The study was prospectively registered on 2nd January 2020: ClinicalTrials.gov, NCT04214366 . "Adenoid Cystic Carcinoma and Carbon Ion Only Irradiation (ACCO)". Study status Under recruitment, participant recruitment is not completed. Start of recruitment was January 2020. There are no results been published or submitted to any journal.