  Radiotherapy (RT) combined with cetuximab is the standard treatment for
patients with inoperable head and neck cancers. Segmentation of head and neck
(H&N) tumors is a prerequisite for radiotherapy planning but a time-consuming
process. In recent years, deep convolutional neural networks have become the de
facto standard for automated image segmentation. However, due to the expensive
computational cost associated with enlarging the field of view in DCNNs, their
ability to model long-range dependency is still limited, and this can result in
sub-optimal segmentation performance for objects with background context
spanning over long distances. On the other hand, Transformer models have
demonstrated excellent capabilities in capturing such long-range information in
several semantic segmentation tasks performed on medical images. Inspired by
the recent success of Vision Transformers and advances in multi-modal image
analysis, we propose a novel segmentation model, debuted, Cross-Modal Swin
Transformer (SwinCross), with cross-modal attention (CMA) module to incorporate
cross-modal feature extraction at multiple resolutions.To validate the
effectiveness of the proposed method, we performed experiments on the HECKTOR
2021 challenge dataset and compared it with the nnU-Net (the backbone of the
top-5 methods in HECKTOR 2021) and other state-of-the-art transformer-based
methods such as UNETR, and Swin UNETR. The proposed method is experimentally
shown to outperform these comparing methods thanks to the ability of the CMA
module to capture better inter-modality complimentary feature representations
between PET and CT, for the task of head-and-neck tumor segmentation.
