Prognostic impact of solid tumor component diameter in early-stage non-small cell lung carcinoma treated with intensity-modulated fractionated radiotherapy: a retrospective analysis impact of solid tumor component diameter in NSCLC treated with IMRT

Objective: To investigate the suitability of the new diameter-based subgroupings of the eighth edition Tumor Node Metastasis (TNM) classification system regarding radiotherapy treatment for early-stage non-small-cell lung cancer (NSCLC), we retrospectively re-analyzed the clinical data of patients treated with intensity-modulated radiotherapy using non-coplanar beams (ncIMRT) for Stage I NSCLC. Methods: Between March 2011 and March 2018, 92 patients with 94 tumors who were diagnosed with Stage I NSCLC according to the seventh edition TNM classification system were enrolled and underwent ncIMRT of 75 Gy in 30 fractions. Local control (LC), progression-free survival (PFS), and overall survival (OS) were retrospectively investigated according to the T-classification subdivisions of the eighth edition and maximal solid tumor component diameter. Results: The median follow-up period was 32.5 months. The median maximum tumor and solid tumor component diameters were 22 mm and 18 mm, respectively. 3-year LC, PFS, and OS rates were 84.1%, 69.4%, and 85.3%, respectively. The 3-year LC rates were 91.0 and 76.8% in the groups with tumor diameter <= 2 cm and >2 cm, corresponding to the T1c and T1b subdivisions of the eighth edition, respectively (p = 0.24). In the <= 2 cm and >2 cm solid tumor component groups, the 3 year LC rates were 93.6 and 63.2%, respectively, which were significantly different (p = 0.007). Conclusion: LC rates after radiotherapy in patients with Stage I NSCLC were correlated with solid tumor component diameter. High LC rates in patients with solid tumor components <2 cm in diameter were associated with high PFS and OS rates. Advances in knowledge: This study suggests that the eighth edition TNM classification system, which focuses on solid tumor components rather than tumor diameter, can be applied to radiotherapy.