Grad-MTSeg: Mitigating Multi-Task Gradient Conflicts via Hierarchical Gradient Optimization for NPC Radiotherapy Delineation

The precise delineation of nasopharyngeal carcinoma (NPC) is a critical prerequisite for radiation therapy, but manual methods are inefficient and inconsistent. Current automated segmentation techniques are challenged by the complexity of multi-modal inputs and multi-target outputs, including Organs at Risk (OARs), Gross Tumor Volume of the Primary Tumor (GTVp), Gross Tumor Volume of the Nodal Metastases (GTVn), clinical target volume prescribed with 70 Gy (CTV70), and clinical target volume prescribed with 63 Gy (CTV63). This process is frequently hindered by gradient conflicts during multitask optimization. To resolve these issues, we propose Grad-MTSeg, a novel deep learning framework. Our approach introduces two core innovations: Unidirectional Anatomic Guidance (UAG) to leverage CT structural priors for improved MRI-based segmentation, and Hierarchical Gradient Optimization (HGO) to alleviate destructive gradient interference among tasks. Our framework improves segmentation accuracy for relevant NPC tasks by effectively resolving conflicts across OARs, GTVs, and CTVs. Validation on three external datasets confirms that Grad-MTSeg provides an efficient and precise solution for complex multimodal segmentation, advancing the automation of NPC radiotherapy planning.