Efficacy and safety of stereotactic body radiotherapy using CyberKnife in Stage I primary lung tumor

Background: CyberKnife® (CK) is a new, advanced radiotherapy technique. This study aimed to evaluate its efficacy and toxicity in Japanese patients with early-stage primary lung tumor who were medically unfit and inoperable. Methods: This retrospective study investigated patients who received CK treatment for medically inoperable Stage І primary lung tumor at the Japanese Red Cross Medical Center between June 2011 and September 2016. Each patient received a total of 36-48 Gy (median, 43 Gy) administered by CK in 4-5 fractions. Results: Totally, 40 patients (T1a, n = 19; T1b, n = 15; T2a, n = 6) were included. Their median age was 86 (range, 56-95) years. Tracking required the use of fiducial markers in 28 patients and the Xsight Spine Tracking System in 12. The median follow-up was 14.5 (range, 1-51) months. Local recurrence occurred in seven (17.5%) patients. The local progression-free survival rates at 1 and 2 years were 83.9% and 74.0%, respectively. Distant recurrence occurred in regional lymph nodes (n = 5), the lung outside the radiation field (n = 3), and the bone (n = 1). Seven patients died. Overall survival rates at 1 and 2 years were 93.6% and 73.1%, respectively. Radiation pneumonitis was identified in 28 (70%) patients (Grade 1, n = 25; Grade 2, n = 2; Grade 5, n = 1). Conclusions: CK showed good local control with limited toxicity and could be an alternative treatment modality in medically inoperable patients with Stage І primary lung tumor.