The study population was composed of 6 head and neck cancer patients. These patients underwent a planning CT scan (CTplan) which was acquired prior to radiation, and a repeat CT scan (CTrep) which was acquired during the course of radiation. CTrep scans were performed 11 to 35 days (range) after the start of radiotherapy. The CT images were made with the patient in supine position on a multidetector-row spiral CT scanner (Somatom Sensation Open, 24 slice configuration; Siemens Medical Solutions, Erlangen, Germany). The acquisition parameters were: gantry un-angled, spiral mode, rotation time 0.5 s, 24 detector rows at 1.2 mm intervals, table speed 18.7 mm/rotation, reconstruction interval 2 mm at Kernel B30 and 120 kVp/195 mA. The matrix size was 512 × 512, with a pixel spacing of 0.97 × 0.97 × 2.0 mm in the x, y and z directions, respectively.
Five specialized head and neck radiation oncologists (R.S., A.N., H.B., O.C. and F.B.), all treating more than 50 head and neck patients per year, delineated five OARs on axial CT slices in all CT images. The radiation oncologist did not have clinical patient information additional to the CT scan. The OAR set included the spinal cord, the parotid and submandibular glands, the thyroid cartilage, and the glottic larynx. For one patient, the right parotid gland contained tumour infiltration and therefore the patient was excluded from analysis for this particular OAR beforehand. The total number of delineated structures was 410.
CTplan and CTrep were delineated under slightly different circumstances, since CTplan was made with contrast-enhancement (iodine containing contrast medium, intravenously applied) while CTrep was acquired without contrast enhancement. Furthermore, the CTplan scan was delineated from scratch and the CTrep scan was delineated using a template obtained from the delineated contours of the CTplan, which were propagated to CTrep after a rigid registration of CTrep to CTplan in each individual patient.
Five specialized head and neck radiation oncologists (R.S., A.N., H.B., O.C. and F.B.), all treating more than 50 head and neck patients per year, delineated five OARs on axial CT slices in all CT images. The radiation oncologist did not have clinical patient information additional to the CT scan. The OAR set included the spinal cord, the parotid and submandibular glands, the thyroid cartilage, and the glottic larynx. For one patient, the right parotid gland contained tumour infiltration and therefore the patient was excluded from analysis for this particular OAR beforehand. The total number of delineated structures was 410.
CTplan and CTrep were delineated under slightly different circumstances, since CTplan was made with contrast-enhancement (iodine containing contrast medium, intravenously applied) while CTrep was acquired without contrast enhancement. Furthermore, the CTplan scan was delineated from scratch and the CTrep scan was delineated using a template obtained from the delineated contours of the CTplan, which were propagated to CTrep after a rigid registration of CTrep to CTplan in each individual patient.
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