Auto-segmentation of head and neck cancer (HNC) primary gross tumor volume (GTVt) is a necessary but challenging process for radiotherapy treatment planning and radiomics studies. The HEad and neCK TumOR Segmentation Challenge (HECKTOR) 2021 comprises two major tasks: auto-segmentation of GTVt in FDG-PET/CT images and the prediction of patient outcomes. In this paper, we focus on the segmentation part by proposing two PET normalization methods to mitigate impacts from intensity variances between PET scans for deep learning-based GTVt auto-segmentation. We also compared the performance of three popular hybrid loss functions. An ensemble of our proposed models achieved an average Dice Similarity Coefficient (DSC) of 0.779 and median 95% Hausdorff Distance (HD95) of 3.15 mm on the test set. Team: Aarhus_Oslo.