Use of single MRI and 18F-FDG PET-CT scans in both diagnosis and radiotherapy treatment planning in patients with head and neck cancer: advantage on target volume and critical organ delineation.

BACKGROUND The use of a single MRI and 18F-fluoro deoxyglucose positron emission tomography-CT (18F-FDG PET-CT) was evaluated, both in diagnostic procedure and radiotherapy planning, in patients with head and neck cancer. METHODS Thirty-five patients with nasopharyngeal and oropharyngeal tumors were studied. The MRI and 18F-FDG PET-CT were used for both diagnostic work-up and gross tumor volume and critical structure delineation. The interobserver variation (IOV) of volumes determined on MRI and CT by a radiotherapist and by a radiologist were compared as well as their impact on dose distribution. RESULTS The CT-MRI decreased the IOV of parotid glands in 12 of 35 and target volume in 15 of 35 patients. The use of 18F-FDG PET-CT changed the treatment design in 6 of 21 patients. CONCLUSIONS Diagnostic imaging performed in the treatment position can improve the accuracy of radiotherapy planning in case of intracranial tumor extension, heavy dental work, or contraindication for contrast-enhanced CT, but not in the absence of these conditions.