Purpose: To determine the optimal method of using (18)F-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 Length(40), 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 Length(40) 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 Length(40) 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.