AATSN: Anatomy Aware Tumor Segmentation Network for PET-CT volumes and images using a lightweight fusion-attention mechanism.

Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) provides metabolic information, while Computed Tomography (CT) provides the anatomical context of the tumors. Combined PET-CT segmentation helps in computer-assisted tumor diagnosis, staging, and treatment planning. Current state-of-the-art models mainly rely on early or late fusion techniques. These methods, however, rarely learn PET-CT complementary features and cannot efficiently co-relate anatomical and metabolic features. These drawbacks can be removed by intermediate fusion; however, it produces inaccurate segmentations in the case of heterogeneous textures in the modalities. Furthermore, it requires massive computation. In this work, we propose AATSN (Anatomy Aware Tumor Segmentation Network), which extracts anatomical CT features, and then intermediately fuses with PET features through a fusion-attention mechanism. Our anatomy-aware fusion-attention mechanism fuses the selective useful CT and PET features instead of fusing the full features set. Thus this not only improves the network performance but also requires lesser resources. Furthermore, our model is scalable to 2D images and 3D volumes. The proposed model is rigorously trained, tested, evaluated, and compared to the state-of-the-art through several ablation studies on the largest available datasets. We have achieved a 0.8104 dice score and 2.11 median HD95 score in a 3D setup, while 0.6756 dice score in a 2D setup. We demonstrate that AATSN achieves a significant performance gain while being lightweight at the same time compared to the state-of-the-art methods. The implications of AATSN include improved tumor delineation for diagnosis, analysis, and radiotherapy treatment.