Difference in failure patterns after stereotactic body radiotherapy for lung cancer according to clinical T stage based on 4D computed tomography

Stereotactic body radiotherapy (SBRT) is a treatment option for early-stage lung cancer. We aimed to examine the differences in failure patterns after SBRT according to the clinical T stage. A total of 120 patients with early-stage lung cancer (T1-3N0M0) who underwent SBRT were analysed. The clinical stage in patients whose tumours were in contact with the chest wall was confirmed using four-dimensional computed tomography (4D-CT). Local failure, regional node metastasis, and distant metastasis were confirmed from clinical charts. Median follow-up time was 27.5 months (range 7-122) after SBRT. Thirteen patients were restaged from clinical T2 with visceral pleural invasion to T3 with chest wall invasion using 4D-CT analysis. Thirty-seven patients developed recurrences. The median progression-free survival (PFS) and overall survival (OS) were 38.1 and 53.8 months, respectively. The 3-year PFS and OS rates were 50.7% and 60.3%, respectively. A significant difference was observed in PFS according to the clinical T stage (p = 0.001). No significant differences were observed in OS according to the clinical T stage (p = 0.213). The proportion of locoregional failures relative to distant metastasis decreased with progression from T1 to T3. The pleural dissemination rate was significantly higher in T3 tumours than in T1 and T2 tumours (p = 0.010). Clinical T stage is associated with PFS after SBRT for lung cancer. There were differences in the failure patterns according to T stage. 4D-CT might provide significant information for assessing chest wall invasion associated with unfavourable PFS.