# X-Ragent

The chest X-ray agent X-Ragent splits "should I seek evidence" from "is this measurement usable": the policy invokes region zoom, anatomical parsing and knowledge lookup only when needed, while quantitative measurements such as the cardiothoracic ratio enter reasoning only through an independent validity gate. Training runs in two stages, agentic supervised fine-tuning on 7,715 structured diagnostic trajectories followed by GRPO with an accuracy-gated reward that applies process terms only to correct trajectories. On the fully held-out ChestAgentBench, accuracy rises from 63.1% for the strongest baseline to 71.7%, with gains across all seven interpretation capabilities.

The chest X-ray agent X-Ragent splits "should I seek evidence" from "is this measurement usable": the policy invokes region zoom, anatomical parsing and knowledge lookup only when needed, while quantitative measurements such as the cardiothoracic ratio enter reasoning only through an independent validity gate. Training runs in two stages, agentic supervised fine-tuning on 7,715 structured diagnostic trajectories followed by GRPO with an accuracy-gated reward that applies process terms only to correct trajectories. On the fully held-out ChestAgentBench, accuracy rises from 63.1% for the strongest baseline to 71.7%, with gains across all seven interpretation capabilities.