18F-FDG-PET/CT Plus MR-Based Treatment Planning For Definitive Radiotherapy Present Complementary Superiority In Head And Neck Squamous Cell Carcinoma

Abstract

Standard anatomical imaging used to delineate target volumes can be enriched by the tumor biology information gained with 18F-fluorodeoxy-D-glucose positron emission tomography (FDG-PET/CT) in head and neck squamous cell carcinoma (HNSCC) receiving radiotherapy. However, little is known about the role of FDG-PET/CT in addition to standard MR-based planning in patient clinical outcomes. The aim of this study is to compare target volumes on PET/CT images with standard MR-based planning volumes, as well as outcome analysis in both settings. 154 patients with histologically confirmed locally advanced HNSCC receiving IMRT was enrolled in this study from 2015 to 2019 in department of radiation oncology of Xijing hospital. FDG-PET/CT plus MR-based target volume delineation was applied in 76 patients (81 primary lesions), and MR-based target volume delineation was applied in 78 patients (85 primary lesions). In FDG-PET/CT plus MR group, all lesions including gross target volume (GTV) of primary lesions and positive lymph node before treatment were evaluated using FDG-PET/CT and MR respectively, the treatment plan modification refer to two images. The median follow-up was 36 months. Multivariate Cox regression analysis was performed to identify radiotherapy outcome. MR and FDG-PET/CT-imaging based volume delineation were performed by one experienced attending radiation oncologist and one nuclear medicine physician. The patients’ characteristics were well balanced between the two groups, including age, gender, smoking status, tumor location, tumor TNM stage etc. In FDG-PET/CT plus MR group, among the 81 primary GTV volume, 16.0% (13/81) GTV identified by FDG-PET/CT images failed to cover the lesions shown on MR images, which led to GTV volume modification. Similarly, several abnormal hypermetabolism in tumor marginal region were absent in primary GTV volume from MR images, led to 6.2% (5/81) GTV modification by FDG-PET/CT images. However, 86 positive lymph node were identified by MR, which were significantly less than 118 lymph nodes identified by FDG-PET/CT (P<0.01), and 33.1% (39/118) lymphatic GTV from MR was modified according to FDG-PET/CT imaging, only 7.6 (9/118) lymphatic GTV from FDG-PET/CT was modified according to MR imaging. Patients with FDG-PET/CT plus MR-based target volume definition had a significantly increased 3-year local regional (89.4% νs. 82.3%, HR: 0.63, 95% CI: 0.4-0.93, P = 0.023), overall survival (76.3% νs. 69.5%, HR: 0.72, 95% CI: 0.51-0.95, P = 0.031) and distant control (93.5% νs. 84.6%, HR: 0.65, 95% CI: 0.48-0.96, P = 0.037) compared to patients with MR-based target volume definition alone. FDG-PET/CT plus MR-based tumor volume delineation significantly improved local regional control, overall survival and distant control compared to patients with MR-based target volume definition alone in HNSCC. The combination of 18F-FDG-PET/CT and MRI was essential in the target delineation for HNSCC.