The Role of F-FDG PET in Minimizing Variability in Gross Tumor Volume Delineation of Soft Tissue Sarcomas

Background: 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.

Purpose: This study investigates the potential role of F-FDG PET in reducing intra- and inter-reader variability thereby improving reproducibility of GTV delineation in STS, without incurring additional costs or radiation exposure.

Materials And Methods: Three readers performed independent GTV delineation of 61 patients with STS using first CT and MR followed by CT, MR, and F-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.

Results: There was a statistically significant decrease in both intra- and inter-reader variability in GTV delineation using CT, MR F-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 F-FDG PET images vs. GTVs drawn from CT and MR for all readers and across all three trials.

Conclusion: Incorporation of F-FDG PET into CT and MR images decreased intra- and inter-reader variability and subsequently increased reproducibility of GTV delineation in STS.