Comparison of 18F-FDG-PET/CT and CT Tumour Volume Delineation in Head and Neck Cancer Patients

Abstract

Introduction: Aim of the current study was to compare gross tumour volume delineation for radiation therapy planning by PET/CT and CT scan in head and neck tumour patients. Methods: 70 oncological patients with primary head and neck cancer were enrolled in the study. CT and 18F-FDGPET/ CT scans were performed within 3 weeks of enrolment in the planned irradiation position. For radiation therapy planning delineation of the target volumes was performed manually both in conventional topometric CT slides and in FDG-PET/CT images. Gross tumour target volume was calculated (GTVcm3) using both modalities. Numerical and geometrical (intersection divided union ratio) comparisons were assessed. Intraobserver, interobserver, and intermodality variation analyses were performed. Results: Intra- and interobserver agreement (intraclass correlation coefficients: 0.99 and 0.97) of tumour volume delineation with 18F-FDG-PET/CT was excellent. Radiotherapy target volume as assessed by FDG-PET/ CT differed in 98% (69/70) from target volumes calculated by the CT scans. According to the metabolic information, the target volume was larger in 12 cases (18%) and smaller in 58 cases (82%). Significant differences were found between CT and PET/CT based tumour volume (paired t-test, p<0.0001). Intersection divided union ratio showed low overlap (0.32). Conclusions: Tumour delineation for radiation therapy planning with PET/CT shows good reproducibility in patients with head and neck cancer. CT based morphologic information compared to PET/CT overestimates the tumour volume in larger lesions and may underestimate it in smaller target lesions. Differences are not only evident in tumour volume, but in geometry: Morphology of tumour volume and position.