Volume-based Parameters Measured by Using FDG PET/CT in Patients with Stage I NSCLC Treated with Stereotactic Body Radiation Therapy: Prognostic Value

Abstract

To evaluate the prognostic importance and predictive performance of volume-based parameters of fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) in patients with stage I non-small cell lung cancer (NSCLC) after stereotactic body radiation therapy (SBRT). This study had institutional review board approval. All patients gave written informed consent for SBRT as well as for future anonymous use of clinical data. Data in 88 patients with stage I NSCLC (68 patients with T1N0M0 disease and 20 with T2aN0M0 disease) who had undergone FDG PET/CT and then SBRT were retrospectively evaluated. Seventy-seven tumors were histopathologically proved (48 adenocarcinomas, 24 squamous cell carcinomas, and five unspecified non-small cell carcinomas), and the remaining 11 tumors were diagnosed clinically without histopathologic diagnosis. Maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were analyzed. The MTV of the primary tumor was calculated as all voxels with an SUV of 2.5 or greater within the isocontour line, while TLG was calculated as MTV multiplied by the average SUV, by using fixed thresholds of either 50% (TLG50) or 60% (TLG60) of the maximum intratumoral FDG activity. The prognostic importance of PET parameters and other clinicopathologic variables (age, sex, tumor size, tumor location [peripheral or central], and biologically effective dose) was assessed by using Cox proportional hazards regression analysis of overall survival (OS) and disease-free survival (DFS) for both univariate and multiple-variable analyses. The median follow-up period was 33 months. At 3 years, OS and DFS were 70.0% and 49.7%, respectively. In the univariate analyses, SUVmax (P = .001), MTV (P = .002), TLG50 (P = .001), and TLG60 (P < .001) were found to be significantly associated with DFS. In multiple variable analysis, these parameters were also significantly associated with DFS (P = .011 for SUVmax, P = .010 for MTV, P = .004 for TLG50, and P = .005 for TLG60). Only volumetric parameters (MTV, TLG50, and TLG60) were significant indicators of DFS in patients with tumors larger than 3 cm. SUVmax, MTV, and TLG at FDG PET/CT have a prognostic role for patients with NSCLC treated with SBRT. When tumors are larger than 3 cm, only MTV and TLG are predictive of DFS.