H. Kim1, S. Kim2, and J. J. Sohn3; 1Varian Medical System, Palo Alto, CA, 2Virginia Commonwealth University Health System, Department of Radiation Oncology, Richmond, VA, 3University of Chicago, Chicago, IL
Purpose/Objective(s): Surface-guided radiation therapy (SGRT) has become an integral part of ensuring the precision and accuracy of advanced treatment techniques such as deep-inspiration breath-hold (DIBH) and stereotactic body radiation therapy (SBRT). While the American Association of Physicists in Medicine (AAPM) Task Group 302 (TG- 302) has provided guidelines for SGRT implementation and quality assurance (QA), it has noted limitations in the currently available phantoms. Existing commercial SGRT phantoms often focus on internal target motion, simulating organs such as the lungs, but do not replicate a deformable external surface motion with anthropomorphic topography, which is crucial for SGRT QA. Additionally, specific guidelines and recommendations for comprehensive periodic SGRT QA have yet to be presented. This study aims to develop a cost-effective, SGRT-dedicated phantom, the SGRT objective operational motion (SOOM) phantom, which simulates breathing topography for comprehensive QA and performance evaluation in SGRT. Materials/
Methods: A cardiopulmonary resuscitation phantom with dark skin was modified to represent an adult human torso with an abundant surface area for SGRT simulation. A linear actuator, controlled by a microcontroller, was installed inside the phantom to move at millimeter accuracy and simulate various clinically relevant breathing patterns with a time log, including regular breathing at various cycles per minute (CPM), irregular free breathing with random variations, and breath-hold scenarios. The phantom was tested with a commercially available SGRT system to assess its performance in accurately tracking surface motion and the subsequent accuracy of a simulated gated treatment. The SGRT gated treatment threshold was set to 3 mm, aiming for an end of exhalation treatment under a 12 CPM breathing pattern. Results: Utilizing the 4D feature of the CT, the accuracy of the CPM of the phantom was measured to be within 2.67%. Relative dosimetry was performed using an ion chamber attached underneath the phantom surface. The average result was found to agree with the expected results within 2.1%. Conclusion: The developed SGRT-dedicated phantom aims to serve as a role of an affordable and versatile clinical solution for comprehensive QA of SGRT systems, addressing the limitations of current commercially available phantoms and the guidelines outlined by AAPM TG-302. Skin color can be adjusted to test systems that experience challenges with darker skin. An abundant topography that can simulate realistic clinical scenarios, versatility of modification and calibration according to user needs via a microcontroller, and dosimetric capabilities highlight SOOM phantom as a comprehensive SGRT system QA phantom.
