Comparison of 18F-Fluorothymidine and 18F-Fluorodeoxyglucose PET/CT in Delineating Gross Tumor Volume by Optimal Threshold in Patients With Squamous Cell Carcinoma of Thoracic Esophagus

Purpose To determine the optimal method of using 18F-fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) simulation to delineate the gross tumor volume (GTV) in esophageal squamous cell carcinoma verified by pathologic examination and compare the results with those using 18F-fluorodeoxyglucose (FDG) PET/CT. Methods and Materials A total of 22 patients were enrolled and underwent both FLT and FDG PET/CT. The GTVs with biologic information were delineated using seven different methods in FLT PET/CT and three different methods in FDG PET/CT. The results were compared with the pathologic gross tumor length, and the optimal threshold was obtained. Next, we compared the simulation plans using the optimal threshold of FLT and FDG PET/CT. The radiation dose was prescribed as 60 Gy in 30 fractions with a precise radiotherapy technique. Results The mean ± standard deviation pathologic gross tumor length was 4.94 ± 2.21 cm. On FLT PET/CT, the length of the standardized uptake value 1.4 was 4.91 ± 2.43 cm. On FDG PET/CT, the length of the standardized uptake value 2.5 was 5.10 ± 2.18 cm, both of which seemed more approximate to the pathologic gross tumor length. The differences in the bilateral lung volume receiving ≥20 Gy, heart volume receiving ≥40 Gy, and the maximal dose received by spinal cord between FLT and FDG were not significant. However, the values for mean lung dose, bilateral lung volume receiving ≥5, ≥10, ≥30, ≥40, and ≥50 Gy, mean heart dose, and heart volume receiving ≥30 Gy using FLT PET/CT-based planning were significant lower than those using FDG PET/CT. Conclusion A standardized uptake value cutoff of 1.4 on FLT PET/CT and one of 2.5 on FDG PET/CT provided the closest estimation of GTV length. Finally, FLT PET/CT-based treatment planning provided potential benefits to the lungs and heart. To determine the optimal method of using 18F-fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) simulation to delineate the gross tumor volume (GTV) in esophageal squamous cell carcinoma verified by pathologic examination and compare the results with those using 18F-fluorodeoxyglucose (FDG) PET/CT. A total of 22 patients were enrolled and underwent both FLT and FDG PET/CT. The GTVs with biologic information were delineated using seven different methods in FLT PET/CT and three different methods in FDG PET/CT. The results were compared with the pathologic gross tumor length, and the optimal threshold was obtained. Next, we compared the simulation plans using the optimal threshold of FLT and FDG PET/CT. The radiation dose was prescribed as 60 Gy in 30 fractions with a precise radiotherapy technique. The mean ± standard deviation pathologic gross tumor length was 4.94 ± 2.21 cm. On FLT PET/CT, the length of the standardized uptake value 1.4 was 4.91 ± 2.43 cm. On FDG PET/CT, the length of the standardized uptake value 2.5 was 5.10 ± 2.18 cm, both of which seemed more approximate to the pathologic gross tumor length. The differences in the bilateral lung volume receiving ≥20 Gy, heart volume receiving ≥40 Gy, and the maximal dose received by spinal cord between FLT and FDG were not significant. However, the values for mean lung dose, bilateral lung volume receiving ≥5, ≥10, ≥30, ≥40, and ≥50 Gy, mean heart dose, and heart volume receiving ≥30 Gy using FLT PET/CT-based planning were significant lower than those using FDG PET/CT. A standardized uptake value cutoff of 1.4 on FLT PET/CT and one of 2.5 on FDG PET/CT provided the closest estimation of GTV length. Finally, FLT PET/CT-based treatment planning provided potential benefits to the lungs and heart.