Clinical outcome analysis of ultrasound-guided Stereotactic Body Radiotherapy (SBRT)

Prostate stereotactic body radiotherapy (SBRT) demands submillimetric geometric accuracy because of steep dose gradients and tight planning target volume (PTV) margins. Intrafraction prostate motion remains a key uncertainty, limiting the performance of conventional image-guided radiotherapy (IGRT) workflows that rely on intermittent verification. This work reviews and compares ultrasound-guided radiotherapy (USgRT) with established IGRT approaches, with emphasis on intrafraction motion management, achievable margin reduction, dosimetric consequences, and reported clinical outcomes. The literature supports real-time transperineal ultrasound (TPUS) as a non-ionizing modality capable of continuous target tracking, enabling PTV margins on the order of 2--3\,mm while preserving target coverage and reducing exposure of organs at risk, with associated reductions in treatment-related toxicity. Overall, the evidence points toward a shift from purely margin-based planning to real-time, motion-managed precision radiotherapy for prostate SBRT.