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 (SUV_max) on FDG-PET imaging. The length of tumors on PET scan were measured and recorded as Length_vis, Length_2.5, and Length₄₀, respectively, and compared with the length of gross tumor in the resected specimen (Length_gross). All PET data were reviewed again postoperatively, and the GTV was delineated using various percentages of SUV_max. The optimal-threshold SUV was generated when the length of PET matched the Length_gross. Results: The mean (±SD) Length_gross was 5.48 ± 1.98 cm. The mean Length_vis, Length_2.5, and Length₄₀ were 5.18 ± 1.93 cm, 5.49 ± 1.79 cm, and 4.34 ± 1.54 cm, respectively. The mean Length_vis (p = 0.123) and Length_2.5 (p = 0.957) were not significantly different from Length_gross, and Length_2.5 seems more approximate to Length_gross. The mean Length₄₀ was significantly shorter than Length_gross (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 SUV_max and Length_gross, respectively. Conclusions: The optimal PET method to estimate the length of gross tumor varies with tumor length and SUV_max; an SUV cutoff of 2.5 provided the closest estimation in this study.