A Prospective Study to Determine Inter-observer Variability of Gross Tumor Volume with [18F] Fludeoxyglucose-PET/CT Compared to CT Alone in Stage III Non-Small Cell Lung Cancer Using Three-Dimensional Analysis

Abstract

Purpose: This study determined the interobserver variability of Gross Tumor Volume (GTV) with [18F] Fludeoxyglucose (FDG)-PET/CT compared to CT alone in Stage III Non-Small Cell Lung Cancer (NSCLC) using 3D analysis. Materials and Methods: Twenty-nine patients underwent simultaneous co-registered CT and FDG-PET/CT for radiotherapy planning. GTV for lung tumor and mediastinal lymphadenopathy contoured by three different radiation oncologists was compared for changes in volume and position. Interobserver variability was determined with vector displacement and Dice Similarity Coefficient (DSC). Concordance for the number of lymph nodes was determined. Results: Mean GTV for lung tumor with FDG-PET/CT and CT alone was 62.0 cm3 and 74.64 cm3, (p=0.0005) with 17% reduction in GTV by FDG-PET/CT. Mean GTV for mediastinal lymphadenopathy was 15.72 cm3 and 19.02 cm3 (p=0.084) with 17% reduction in GTV. Mean vector displacement of lung tumor was 2.0 mm with FDG-PET/CT versus 7.1 mm with CT alone (p = 0.0016) with 3.6 fold reduction in interobserver variability. Mean vector displacement of mediastinal lymphadenopathy was 1.53 mm with FDG-PET versus 10.2 mm for CT alone (p= 0.0005) with 6.7 fold reduction in interobserver variability. Median DSC for the primary GTV was 0.87 for FDG-PET/CT and 0.74 for CT alone. Median DSC for nodal GTV was 0.79 and 0.59 respectively. All physicians agreed on the number of lymph nodes on CT alone in 15/29 vs. 27/29 patients on PET/CT. Only two of the three physicians agreed on the number of lymph nodes contoured for CT alone in 12/29 versus only 2/29 patients for FDG-PET/CT (p=0.0018). Conclusion: FDG-PET/CT compared to CT alone is more precise, reduces mean lung tumor and mediastinal nodal GTV and interobserver variability. There was greater agreement for the number of lymph nodes contoured on FDG-PET/CT compared to CT alone.