Influence of FDG-PET on computed tomography-based radiotherapy planning for locally recurrent nasopharyngeal carcinoma.

Abstract

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. 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 GTV PET/CT and GTV CT, respectively. Corresponding planning target volumes (PTV) were generated for the GTV CT (PTV(CT)) and GTV PET/CT (PTV PET/CT). Three-dimensional conformal radiotherapy plans were separately created for PTV CT and PTV PET/CT. To assess the potential geographic miss of the PET/CT-based disease in CT-based treatment planning, the size and location of the GTV PET/CT, PTV(PET/CT), and PTV(CT) were analyzed, and the three-dimensional conformal radiotherapy plans created using the PTV CT were evaluated with the GTV PET/CT and PTV PET/CT information. 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 GTV PET/CT and PTV PET/CT by the PTV CT occurred in 7 (18%) and 20 (51%) patients, respectively. This resulted in <95% of the GTV(PET/CT) and PTV PET/CT receiving >or=95% of the prescribed dose in 4 (10%) and 13 (33%) patients, respectively. 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.