CTs and MRIs were both acquired under radiotherapy immobilization protocols with patients in the treatment position.CT scans were acquired on one of four machine models (LightSpeed RT16, GE Medical Systems, Waukesha, WI, USA; Brilliance 64 or Brilliance Big Bore, Philips Healthcare, Cambridge, MA, USA; SOMATOM Definition Edge, Siemens, Washington D.C., USA) using x-ray tube currents between 208 – 434 mA at 120 kVp. All scans have slice thicknesses of either 2.5 or 3 mm, with 2.5 or 3 mm of space between slices. Sections are displayed in 512 x 512 pixel matrices and were reconstructed in diameters between 500 – 600 mm. MRI scans were acquired in one of two machine models (Discovery MR750, GE Medical Systems, Waukesha, WI, USA; Ingenia, Phili...