Definitive carbon ion radiotherapy for tracheobronchial adenoid cystic carcinoma: a preliminary report

Tracheobronchial adenoid cystic carcinoma (TACC) is a rare tumour. About one-third of patients miss their chance of surgery or complete resection as it is mostly detected in the advanced stage; hence, photon radiotherapy (RT) is used. However, the outcomes of photon RT remain unsatisfactory. Carbon ion radiotherapy (CIRT) is thought to improve the therapeutic gain ratio; however, the outcomes of CIRT in TACC are unclear. Therefore, we aimed to assess the effects and toxicities of CIRT in patients with TACC.The inclusion criteria were as follows: 1) age 18-80 years; 2) Eastern Cooperative Oncology Group Performance Status 0-2; 3) histologically confirmed TACC; 4) stage III-IV disease; 5) visible primary tumour; and 6) no previous RT history. The planned prescription doses of CIRT were 66-72.6 GyE/22-23 fractions. The rates of overall survival (OS), local control (LC), and progression-free survival (PFS) were calculated using the Kaplan-Meier method. Treatment-induced toxicities and tumour response were scored according to the Common Terminology Criteria for Adverse Events and Response Evaluation Criteria in Solid Tumors, respectively.Eighteen patients with a median age of 48 (range 30-73) years were enrolled. The median follow-up time was 20.7 (range 5.8-44.1) months. The overall response rate was 88.2%. Five patients developed lung metastasis after 12.2-41.0 months and one of them experienced local recurrence at 31.9 months after CIRT. The rates of 2-year OS, LC, and PFS were 100, 100, and 61.4%, respectively. Except for one patient who experienced grade 4 tracheal stenosis, which was relieved after stent implantation, no other ≥3 grade toxicities were observed.CIRT might be safe and effective in the management of TACC based on a short observation period. Further studies with more cases and longer observation are warranted.