Gradient-based delineation of the primary GTV on FLT PET in squamous cell cancer of the thoracic esophagus and impact on radiotherapy planning

BACKGROUND: To validate a gradient-based segmentation method for gross tumor volume(GTV) delineation on (8)F-fluorothymidine (FLT)positron emission tomography (PET)/ computer tomography (CT) in esophageal squamous cell cancer through pathologic specimen, in comparison with standardized uptake values (SUV) threshold-based methods and CT. The corresponding impact of this GTV delineation method on treatment planning was evaluated. METHODS AND MATERIALS: Ten patients with esophageal squamous cell cancer were enrolled. Before radical surgery, all patients underwent FLT-PET/CT. GTVs were delineated by using four methods. GTV(GRAD), GTV(1.4) and GTV(30%max) were segmented on FLT PET using a gradient-based method, a fixed threshold of 1.4 SUV and 30% of SUV(max), respectively. GTV(CT) was based on CT data alone. The maximum longitudinal tumor length of each segmented GTV was compared with the measured tumor length of the pathologic gross tumor length (L(Path)). GTV(GRAD), GTV(1.4) and GTV(30%max) were compared with GTV(CT) by overlap index. Two radiotherapy plannings (plan(GRAD)) and (plan(CT)) were designed for each patient based on GTV(GRAD) and GTV(CT). The dose-volume parameters for target volume and normal tissues, CI and HI of plan(GRAD) and plan(CT) were compared. RESULTS: The mean ± standard deviation of L(Path) was 6.47 ± 2.70 cm. The mean ± standard deviation of L(GRAD),L(1.4), L(30%max) and L(CT) were 6.22 ± 2.61, 6.23 ± 2.80, 5.95 ± 2.50,7.17 ± 2.28 cm, respectively. The Pearson correlation coefficients between L(Path) and each segmentation method were 0.989, 0.920, 0.920 and 0.862, respectively. The overlap indices of GTV(GRAD), GTV(1.4), GTV(30%max) when compared with GTV(CT) were 0.75 ± 0.12, 0.71 ± 0.12, 0.57 ± 0.10, respectively. The V(5), V(10), V(20), V(30) and mean dose of total-lung,V(30) and mean dose of heart of plan(GRAD) were significantly lower than plan(CT). CONCLUSIONS: The gradient-based method provided the closest estimation of target length. The radiotherapy plannings based on the gradient-based segmentation method reduced the irradiated volume of lung, heart in comparison to CT.