Abstract
Accurate organ segmentation is essential for clinical tasks such as radiotherapy planning and disease monitoring. Recent foundation models like MedSAM achieve strong results using point or bounding‑box prompts but still require manual interaction. We propose DescriptorMedSAM, a lightweight extension of MedSAM that incorporates structured text prompts, ranging from simple organ names to combined shape and location descriptors to enable click‑free segmentation. DescriptorMedSAM employs a CLIP text encoder to convert radiology‑style descriptors into dense embeddings, which are fused with visual tokens via a cross‑attention block and a multi-scale feature extractor. We designed four descriptor types: Name (N), Name + Shape (NS), Name + Location (NL), and Name + Shape + Location (NSL), and evaluated them on the FLARE 2022 dataset under zero‑shot and few‑shot settings, where organs unseen during training must be segmented with minimal additional data. NSL prompts achieved the highest performance, with a Dice score of 0.9405 under full supervision, a 76.31% zero‑shot retention ratio, and a 97.02% retention ratio after fine‑tuning with only 50 labeled slices per unseen organ. Adding shape and location cues consistently improved segmentation accuracy, especially for small or morphologically complex structures. We demonstrate that structured language prompts can effectively replace spatial interactions, delivering strong zero‑shot performance and rapid few‑shot adaptation. By quantifying the role of descriptor, this work lays the groundwork for scalable, prompt‑aware segmentation models that generalize across diverse anatomical targets with minimal annotation effort.