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Stereotactic body radiotherapy (SBRT) is a treatment option for early-stage lung cancer. The purpose of this study was to analyse the differences in failure patterns after SBRT for primary lung cancer according to the T stage, after accurately re-examining the initial 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). Before restaging, 35 tumours in contact with the pleura were initially diagnosed as T2 with visceral pleural invasion. Local failure, regional node metastasis, and distant metastasis were confirmed from clinical charts.

The 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. There were no significant differences in dosimetric parameters for PTV among the T1, T2, and T3 groups. The volume of PTV was significantly smaller in T1 tumours than in T2 and T3 tumours (p < 0.001 and = 0.003, respectively). However, no significant differences were observed in the volume of PTV between T2 and T3 tumours (p = 0.967).
Thirty-seven patients developed recurrences. The median progression free survival (PFS) was 38.1 months. The 1-, 3-, and 5-year PFS rates were 61.0%, 50.6%, and 34.6%, respectively. In the T1, T2, and T3 groups, the recurrence rates were 12% (8/69), 50% (18/36), and 73% (11/15), respectively. In addition, the 3-year PFS rates were 61.0%, 40.5%, and 22.9% for clinical stages T1, T2, and T3, respectively (p=0.001).
In T1 tumours, three and five patients experienced local failure and regional nodal metastasis, respectively. In T2 tumours, oligo-metastasis and locoregional failures alone were observed in 28% (5/18) and 44% (8/18) of the patients with recurrences, respectively. In T3 tumours with chest wall invasion, recurrences were noted in 77% (10/13) of tumours.
Forty-five of the 120 patients died during the follow-up period. The median overall survival (OS) was 53.8 months. The 1-, 3-, and 5-year OS rates were 88.1%, 60.8%, and 38.6%, respectively. The 3-year OS rates were 65.0%, 60.3%, and 47.5% in clinical T1, T2, and T3, respectively (p=0.213).

Clinical T stage was significantly associated with PFS and the incidence of recurrence after SBRT for lung cancer. There were differences in the failure patterns according to the clinical T stage. Pleural dissemination was a common failure pattern in the T3 group. In addition, 4D-CT might provide significant information for assessing chest wall invasion associated with unfavourable PFS.