Using 18F-Fluorodeoxyglucose Positron Emission Tomography to Estimate the Length of Gross Tumor in Patients With Squamous Cell Carcinoma of the Esophagus

Purpose: To determine the optimal method of using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) to estimate gross tumor length in esophageal carcinoma. Methods and Materials: Thirty-six patients with esophageal squamous cell carcinoma treated with radical surgery were enrolled. Gross tumor volumes (GTVs) were delineated using three different methods: visual interpretation, standardized uptake value (SUV) 2.5, and 40% of maximum standard uptake value (SUVmax) on FDG-PET imaging. The length of tumors on PET scan were measured and recorded as Lengthvis, Length2.5, and Length40, respectively, and compared with the length of gross tumor in the resected specimen (Lengthgross). All PET data were reviewed again postoperatively, and the GTV was delineated using various percentages of SUVmax. The optimal-threshold SUV was generated when the length of PET matched the Lengthgross. Results: The mean (±SD) Lengthgross was 5.48 ± 1.98 cm. The mean Lengthvis, Length2.5, and Length40 were 5.18 ± 1.93 cm, 5.49 ± 1.79 cm, and 4.34 ± 1.54 cm, respectively. The mean Lengthvis (p = 0.123) and Length2.5 (p = 0.957) were not significantly different from Lengthgross, and Length2.5 seems more approximate to Lengthgross. The mean Length40 was significantly shorter than Lengthgross (p < 0.001). The mean optimal threshold was 23.81% ± 11.29% for all tumors, and it was 19.78% ± 8.59%, 30.92% ± 12.28% for tumors ≥5 cm, and <5 cm, respectively (p = 0.009). The correlation coefficients of the optimal threshold were -0.802 and -0.561 with SUVmax and Lengthgross, respectively. Conclusions: The optimal PET method to estimate the length of gross tumor varies with tumor length and SUVmax; an SUV cutoff of 2.5 provided the closest estimation in this study