Room: Karl Dean Ballroom B1
Purpose: This work aims to develop a robotic ultrasound tomography (UST) system for image-guided prone breast stereotactic body radiotherapy (SBRT). This system will improve soft tissue contrast compared to x-ray imaging, with sufficient spatial resolution for image guidance.
Methods: The prototype is designed to be portable and fit beneath a prone breast board on the couch of a clinical linear accelerator. The system consists of a 3D printed water tank, ultrasound transducer holder and base. Tank rotations are accomplished using a rotation stage and bearing embedded in the base. Vertical motion of the transducer is performed using a vertical stepper and linear bearings that connect the transducer holder to the tank. A 0.5 mm thick silicone membrane separates the transducer and water. Acquisition of the image volume is analogous to that of early generation fan-beam CT, in which only a single plane is acquired for each rotation. Currently, images are acquired every degree. Each plane is reconstructed using a super-compounding technique. Preliminary experiments investigate spatial resolution, geometric and positioning accuracy of the system. This was done using silicone and gelatin/agar and line phantoms.
Results: Initial results show that the system has a limiting resolution of approximately 1.6 mm on the axis of rotation. This is partial due to the 0.32 mm pixel spacing utilized. Measurements show a geometric accuracy of approximately 1-2 mm and a positional accuracy of 1 mm between objects.
Conclusion: Exploratory results demonstrate that UST is promising image guidance technology for prone breast SBRT. Ongoing work continues to investigate spatial resolution of the system and methods to reduce artifacts. Future work aims to characterize soft tissue contrast, hidden target tests and alignment to treatment isocenter.