The role of ¹⁸F-FDG PET in minimizing variability in gross tumor volume delineation of soft tissue sarcomas.

Abstract

Accurate gross tumor volume (GTV) delineation is a critical step in radiation therapy treatment planning. However, it is reader dependent and thus susceptible to intra- and inter-reader variability. GTV delineation of soft tissue sarcoma (STS) often relies on CT and MR images. This study investigates the potential role of ¹⁸F-FDG PET in reducing intra- and inter-reader variability thereby improving reproducibility of GTV delineation in STS, without incurring additional costs or radiation exposure. Three readers performed independent GTV delineation of 61 patients with STS using first CT and MR followed by CT, MR, and ¹⁸F-FDG PET images. Each reader performed a total of six delineation trials, three trials per imaging modality group. Dice Similarity Coefficient (DSC) score and Hausdorff distance (HD) were used to assess both intra- and inter-reader variability using generated simultaneous truth and performance level estimation (STAPLE) GTVs as ground truth. Statistical analysis was performed using a Wilcoxon signed-ranked test. There was a statistically significant decrease in both intra- and inter-reader variability in GTV delineation using CT, MR ¹⁸F-FDG PET images vs. CT and MR images. This was translated by an increase in the DSC score and a decrease in the HD for GTVs drawn from CT, MR and ¹⁸F-FDG PET images vs. GTVs drawn from CT and MR for all readers and across all three trials. Incorporation of ¹⁸F-FDG PET into CT and MR images decreased intra- and inter-reader variability and subsequently increased reproducibility of GTV delineation in STS.