Influence of FDG-PET on Computed Tomography-Based Radiotherapy Planning for Locally Recurrent Nasopharyngeal Carcinoma

Purpose Assuming F-18-fluoro-2-deoxy- d -glucose positron emission tomography (FDG-PET)/computed tomography (CT) to be more accurate in representing the true disease extent than CT alone, we prospectively designed this study to evaluate how the addition of FDG-PET influences CT-based radiotherapy planning for locally recurrent nasopharyngeal carcinoma. Patients and Methods All patients underwent FDG-PET/CT simulation scans. For each patient, the gross tumor volume (GTV) was separately delineated with or without the addition of PET information and defined as GTVPET/CT and GTVCT , respectively. Corresponding planning target volumes (PTV) were generated for the GTVCT (PTVCT ) and GTVPET/CT (PTVPET/CT ). Three-dimensional conformal radiotherapy plans were separately created for PTVCT and PTVPET/CT . To assess the potential geographic miss of the PET/CT-based disease in CT-based treatment planning, the size and location of the GTVPET/CT , PTVPET/CT , and PTVCT were analyzed, and the three-dimensional conformal radiotherapy plans created using the PTVCT were evaluated with the GTVPET/CT and PTVPET/CT information. Results A total of 43 patients were enrolled in this study. Distant metastasis was found in 4 patients with the addition of the PET information. The 39 patients without distant metastasis proceeded to three-dimensional conformal radiotherapy planning. Inadequate coverage of the GTVPET/CT and PTVPET/CT by the PTVCT occurred in 7 (18%) and 20 (51%) patients, respectively. This resulted in