Robotic Volumetric Ultrasound and Dual-Modality Ultrasound–Protoacoustic Imaging for Proton Therapy Monitoring
Abstract
Purpose
Accurate radiotherapy delivery requires precise knowledge of soft-tissue anatomy at the time of treatment, particularly for abdominal targets affected by respiration, peristalsis, and inter-fractional anatomical changes. Current clinical systems provide limited volumetric soft-tissue imaging immediately prior to irradiation and lack real-time verification of dose deposition. While ultrasound offers real-time, radiation-free imaging, its clinical adoption during radiotherapy is limited by operator dependence. This work introduces an autonomous robotic ultrasound platform enabling volumetric pre-treatment imaging for patient alignment and dual-modality ultrasound–protoacoustic imaging for real-time anatomical and dose monitoring during proton therapy.
Methods
A human torso phantom was irradiated at the bladder site using a clinical proton beam with the gantry at 180°, placing the Bragg peak 7.6 cm below the surface. A bladder pseudo-tumor treatment plan was generated from a planning CT. Prior to irradiation, autonomous 3D volumetric ultrasound imaging was performed using a 6-DOF robotic arm. Patient-specific scan trajectories were derived from CT, and scan execution was guided by an RGB-D camera providing surface point clouds, while closed-loop force feedback ensured stable probe contact. B-mode ultrasound was acquired using a 64-element linear transducer (1–5 MHz) and synchronized with real-time optical tracking to enable 3D volumetric reconstruction. During proton delivery, the same transducer simultaneously recorded real-time 2D B-mode ultrasound and protoacoustic signals generated by proton dose absorption. Protoacoustic data were reconstructed using universal back-projection to localize the Bragg peak and co-registered with the ultrasound anatomy.
Results
High-precision 3D ultrasound volumes of a human torso phantom demonstrated clear delineation of abdominal organ boundaries with good agreement to CT. Protoacoustic imaging successfully reconstructed and co-registered the Bragg peak location within the ultrasound anatomy in real time.
Conclusion
This platform enables volumetric pre-treatment ultrasound for inter-fractional motion management and real-time intra-fractional monitoring of anatomy and proton dose deposition, advancing closed-loop adaptive proton therapy.