A comparative study of target volumes based on ¹⁸F-FDG PET-CT and ten phases of 4DCT for primary thoracic squamous esophageal cancer

Abstract

PurposeTo investigate the correlations in target volumes based on 18F-FDG PET/CT and four-dimensional CT (4DCT) to detect the feasibility of implementing PET in determining gross target volumes (GTV) for tumor motion for primary thoracic esophageal cancer (EC).MethodsThirty-three patients with EC sequentially underwent contrast-enhanced 3DCT, 4DCT, and 18F-FDG PET-CT thoracic simulation. The internal gross target volume (IGTV)10 was obtained by combining the GTV from ten phases of 4DCT. The GTVs based on PET/CT images were defined by setting of different standardized uptake value thresholds and visual contouring. The difference in volume ratio, conformity index (CI), and degree of inclusion (DI) between IGTV10 and GTVPET was compared.ResultsThe images from 20 patients were suitable for further analysis. The optimal volume ratio of 0.95±0.32, 1.06±0.50, 1.07±0.49 was at standardized uptake value (SUV)2.5, SUV20%, or manual contouring. The mean CIs were from 0.33 to 0.54. The best CIs were at SUV2.0 (0.51±0.11), SUV2.5 (0.53±0.13), SUV20% (0.53±0.12), and manual contouring (0.54±0.14). The mean DIs of GTVPET in IGTV10 were from 0.60 to 0.90, and the mean DIs of IGTV10 in GTVPET ranged from 0.35 to 0.78. A negative correlation was found between the mean CI and different SUV (P=0.000).ConclusionNone of the PET-based contours had both close spatial and volumetric approximation to the 4DCT IGTV10. Further evaluation and optimization of PET as a tool for target identification are required.

Comparison of gross target volumes based on four‐dimensional CT, positron emission tomography‐computed tomography, and magnetic resonance imaging in thoracic esophageal cancer

“…Moreover the median volume variability between the GTV MRI and GTV PET2.5 and between the GTV MRI and GTV CT was statistically significant, while there was no significant difference between GTV PET2.5 and GTV CT , which were accorded with results reported in other literatures 20,21 . Guo et al's analysis 8 demonstrated that GTV PET2.5 resembled better with IGTV 10 , which included GTVs contoured on ten phase of 4DCT. It revealed a trend that 3D PET image included some individualized information derived from respiratory motion.…”

“…Furthermore, the SUV value of PET‐CT selected in delineating GTV may be so low as to including normal periesophageal tissue, which would reduce the accurate in target delineation inevitably. Finally, it should be noted that, the inconsistency of breathing pattern during the acquisition of T 2 W‐MRI and PET‐CT might affect the position and shape of the tumor to some extent 8,12 . As mentioned earlier, the size of GTV derived from MRI was significantly less than that from PET‐CT.…”

“…Motion derived from respiration and heart beating adds to the challenges to precise delineation of target volumes on 3DCT. The artifacts caused by respiratory motion can be reduced by the implementation of four‐dimensional CT (4DCT) techniques, and the most stable sequence for the end‐expiration (EE) phase of 4DCT scans were frequently selected for target delineation 6‐8 . However, delineation on 4DCT only is challenging, mainlly in poorly differentiating tumor from nomal tissue at the mediastinal tumor borders.…”

“…Especially, on T 2 weighted (T 2 W) turbo spin echo (TSE) sequence, MRI can well show the contour of the tumor based on the thickening of the wall and the signal change of this lesion, 4 suggesting that the use of MRI could be more accurate than CT to delineate GTVs of esophagus. Previously, it has been shown that the use of 4DCT combined with PET could improve the exact of target region 8 . As the wide application of MRI simulation, the value of MRI image in target volume delineation during multimodality imaging has been focused on, especially, the correlation in GTVs contouring for esophageal tumors between some particular sequence of MRI with PET‐CT and 4DCT imaging.…”