Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Liver Cancer Radiotherapy

Abstract

Background: Hybrid 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) has been increasingly incorporated into the practice of radiation oncologists since it contains both anatomical and biological data and may bring about personalized radiation plans for each patient. The objective of this study was to evaluate the feasibility of gross tumor volume (GTV) delineation from hybrid PET/MRI compared with that from current-practice MRI during radiotherapy planning in patients with liver cancer. Methods: Twelve patients (eighteen lesions) with liver cancer were enrolled in this study. We chose one of the most popular delineating methods—the visual method—in this study, and three physicians delineated the target volume of each lesion from MRI, PET, and hybrid PET/MRI images. The difference and correlation of GTV values obtained by MRI, PET and hybrid PET/MRI were subjected to statistical analysis. In addition, the Dice similarity coefficient (DSC) was calculated to assess the spatial overlap. GTV-MRI was set as a reference. Results: Most GTV-PET/MRI (83%) and 50% of GTV-PET were larger than the reference GTV-MRI. Statistical analysis revealed that GTV-PET/MRI (p=0.021) diverged statistically significantly from the reference GTV-MRI. In contrast, GTV-PET (p=0.266) was not significantly different from GTV-MRI. GTV-PET (r=0.991, p<0.001) and GTV-PET/MRI (r=0.997, p<0.001) were significantly related to GTV-MRI. The average DSC value between GTV-MRI and GTV-PET was 0.45 (range 0–0.90) and that between GTV-MRI and GTV-PET/MRI was 0.76 (range 0.43–0.90). Conclusions: With the database used, PET/MRI-based target volume delineation for liver cancer is feasible. The larger GTV-PET/MRI may allow adequate irradiation of the diseased tissue and improved treatment effect.