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 <95% of the GTVPET/CT and PTVPET/CT receiving ≥95% of the prescribed dose in 4 (10%) and 13 (33%) patients, respectively. Conclusions: The addition of FDG-PET information might influence CT-based radiotherapy planning for locally recurrent nasopharyngeal carcinoma by altering the definition of the target volume, with the potential to avoid a geographic miss of true disease