Comparison of Tumor Volumes as Determined by Pathologic Examination and FDG-PET/CT Images of Non–Small-Cell Lung Cancer: A Pilot Study

Purpose To determine the cut-off standardized uptake value (SUV) on18 F fluoro-2-deoxy-glucose (FDG) positron emission tomography/computed tomography (FDG-PET/CT) images that generates the best volumetric match to pathologic gross tumor volume (GTVpath ) for non–small-cell lung cancer (NSCLC). Methods and Materials Fifteen patients with NSCLC who underwent FDG-PET/CT scans followed by lobectomy were enrolled. The surgical specimen was dissected into 5–7-μm sections at approximately 4-mm intervals and stained with hematoxylin and eosin. The tumor-containing area was outlined slice by slice and the GTVpath determined by summing over all the slices, taking into account the interslice thickness and fixation-induced volume reduction. The gross tumor volume from the PET images, GTVPET , was determined as a function of cut-off SUV. The optimal threshold or optimal absolute SUV was defined as the value at which the GTVPET was the same as the GTVpath. Results The fixation process induced a volumetric reduction to 82% ± 10% (range, 62–100%) of the original. The maximal SUV was 10.1 ± 3.6 (range, 4.2–18.7). The optimal threshold and absolute SUV were 31% ± 11% and 3.0 ± 1.6, respectively. The optimal threshold was inversely correlated with GTVpath and tumor diameter ( p < 0.05), but the optimal absolute SUV had no significant correlation with GTVpath or tumor diameter ( p > 0.05). Conclusion This study evaluated the use of GTVpath as a criterion for determining the optimal cut-off SUV for NSCLC target volume delineation. Confirmatory studies including more cases are being performed.