Is using a consolidation tumor ratio 0.5 as criterion feasible in daily practice? Evaluation of interobserver measurement variability of consolidation tumor ratio of lung cancer less than 3 cm in size

BACKGROUND: Consolidation tumor ratio (CTR) calculated as the ratio of the tumor consolidation diameter to the tumor maximum diameter on thin‐section computed tomography (CT) of lung cancer has been reported as an important prognostic factor. It has also been used for treatment decision‐making. This study aimed to investigate the interobserver variability of CTR measurements on preoperative CT and propose a clinically useful CTR‐based classification criterion. METHODS: We enrolled 119 patients who underwent surgery for suspected or diagnosed small‐sized lung cancer (≤3.0 cm in diameter). Nine doctors reviewed preoperative CT scans to measure CTR. Interobserver variability of CTR measurements was evaluated using the coefficient of variation (CV) and Fleiss' κ. The prognostic effect of the CTR‐based classification was assessed using the Kaplan–Meier method. RESULTS: Interobserver variability of CTR measurement was the highest for tumors with the lowest CTR (CTR = 0); it decreased as CTR increased and reached a plateaued level of low variability (CV <0.5) at CTR of 0.5. We proposed a three‐group classification based on the findings of CTR interobserver variability (CTR < 0.5, 0.5 ≤ CTR < 1, and CTR = 1). Interobserver agreement of the judgment of the CTR‐based classification was excellent (Fleiss' κ = 0.81). The classification significantly stratified patient prognosis (p < 0.001, 5‐year overall survival rates with CTR < 0.5, 0.5 ≤ CTR < 1, and CTR = 1 were 100, 88, and 73.8%, respectively). CONCLUSIONS: CTR 0.5 is a clinically relevant and helpful cutoff for treatment decision‐making in patients with early‐stage lung cancer based on high interobserver agreement and good prognostic stratification.