Four-dimensional cone beam computed tomography for image-guided radiotherapy. Images acquired at the time of treatment delivery are sorted into temporal phases according to the time-dependent diaphragm position. Coronal (A), transaxial (B) and sagittal (C) views at 30 percent phase show the gross tumor volume (red contour), planning target volume (orange contour) and esophagus (green contour). The PTV was defined on the maximum intensity projection of a respiratory-gated simulation CT. While the PTV encompasses the motion of the lesion prior to treatment delivery, its definition may be enhanced through individual phase adaption as part of a motion-managed and PET/CT-guided radiotherapy regimen.