• Michael Bayne, Rodney J Hicks, Sarah Everitt, Natalie Fimmell, David Ball, John Reynolds, Eddie Lau, Alex Pitman, Robert Ware, and Michael MacManus.
• Dorset Cancer Centre, Poole Hospital, Poole, Dorset, UK.
• Int. J. Radiat. Oncol. Biol. Phys. 2010 Jul 15; 77 (4): 1151-7.

PurposePositron emission tomography/computed tomography (PET/CT) is increasingly used for delineating gross tumor volume (GTV) in non-small-cell lung cancer (NSCLC). The methodology for contouring tumor margins remains controversial. We developed a rigorous visual protocol for contouring GTV that uses all available clinical information and studied its reproducibility in patients from a prospective PET/CT planning trial.Methods And MaterialsPlanning PET/CT scans from 6 consecutive patients were selected. Six "observers" (two radiation oncologists, two nuclear medicine physicians, and two radiologists) contoured GTVs for each patient using a predefined protocol and subsequently recontoured 2 patients. For the estimated GTVs and axial distances, least-squares means for each observer and for each case were calculated and compared, using the F test and pairwise t-tests. In five cases, tumor margins were also autocontoured using standardized uptake value (SUV) cutoffs of 2.5 and 3.5 and 40% SUV(max).ResultsThe magnitude of variation between observers was small relative to the mean (coefficient of variation [CV] = 3%), and the total variation (intraclass correlation coefficient [ICC] = 3%). For estimation of superior/inferior (SI), left/right (LR), and anterior/posterior (AP) borders of the GTV, differences between observers were also small (AP, CV = 2%, ICC = 0.4%; LR, CV = 6%, ICC = 2%; SI, CV 4%, ICC = 2%). GTVs autocontoured generated using SUV 2.5, 3.5, and 40% SUV(max) differed widely in each case. An SUV contour of 2.5 was most closely correlated with the mean GTV defined by the human observers.ConclusionsObserver variation contributed little to total variation in the GTV and axial distances. A visual contouring protocol gave reproducible results for contouring GTV in NSCLC.Copyright 2010 Elsevier Inc. All rights reserved.

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