Original article: Impact of 18‐fluorodeoxyglucose positron emission tomography on computed tomography defined target volumes in radiation treatment planning of esophageal cancer: reduction in geographic misses with equal inter‐observer variability

Target volume definition in modern radiotherapy is based on planning computed tomography (CT). So far, 18‐fluorodeoxyglucose positron emission tomography (FDG‐PET) has not been included in planning modality in volume definition of esophageal cancer. This study evaluates fusion of FDG‐PET and CT in patients with esophageal cancer in terms of geographic misses and inter‐observer variability in volume definition. In 28 esophageal cancer patients, gross, clinical and planning tumor volumes (GTV; CTV; PTV) were defined on planning CT by three radiation oncologists. After software‐based emission tomography and computed tomography (PET/CT) fusion, tumor delineations were redefined by the same radiation‐oncologists. Concordance indexes (CCI's) for CT and PET/CT based GTV, CTV and PTV were calculated for each pair of observers. Incorporation of PET/CT modified tumor delineation in 17/28 subjects (61%) in cranial and/or caudal direction. Mean concordance indexes for CT‐based CTV and PTV were 72 (55–86)% and 77 (61–88)%, respectively, vs. 72 (47–99)% and 76 (54–87)% for PET/CT‐based CTV and PTV. Paired analyses showed no significant difference in CCI between CT and PET/CT. Combining FDG‐PET and CT may improve target volume definition with less geographic misses, but without significant effects on inter‐observer variability in esophageal cancer.