Feasibility of carbon-ion radiotherapy for re-irradiation of locoregionally recurrent, metastatic, or secondary lung tumors.

Intrathoracic recurrence after carbon-ion radiotherapy for primary or metastatic lung tumors remains a major cause of cancer-related deaths. However, treatment options are limited. Herein, we report on the toxicity and efficacy of re-irradiation with carbon-ion radiotherapy for locoregionally recurrent, metastatic, or secondary lung tumors. Data of 95 patients with prior intrathoracic carbon-ion radiotherapy who were treated with re-irradiation with carbon-ion radiotherapy at our institution between 2006 and 2016 were retrospectively analyzed. Seventy-three patients (76.8%) had primary lung tumors and 22 patients (23.2%) had metastatic lung tumors. The median dose of initial carbon-ion radiotherapy was 52.8 Gy (relative biological effectiveness) and the median dose of re-irradiation was 66.0 Gy (relative biological effectiveness). None of the patients received concurrent chemotherapy. The median follow-up period after re-irradiation was 18 months. In terms of grade ≥3 toxicities, one patient experienced each of the following: grade 5 bronchopleural fistula, grade 4 radiation pneumonitis, grade 3 chest pain, and grade 3 radiation pneumonitis. The 2-year local control and overall survival rates were 54.0% and 61.9%, respectively. In conclusion, re-irradiation with carbon-ion radiotherapy was associated with relatively low toxicity and moderate efficacy. Re-irradiation with carbon-ion radiotherapy might be an effective treatment option for patients with locoregionally recurrent, metastatic, or secondary lung tumors.