Methodology for real-time tumor motion management for improvement of accuracy in stereotactic body radiotherapy

Abstract

Intrafractional motion of patients such as respiratory motion during radiation treatment is an important issue of image-guided radiotherapy (IGRT). Accuracy of treatment beam delivery degrades as motion range increases. For respiratory motion management during radiation treatment, three-dimensional (3D) real-time tumor position have to be tracked precisely first. Our purpose is real-time target position tracking during stereotactic body radiation therapy (SBRT) with existing linear accelerator system. For this purpose, we developed 3D motion trajectory reconstruction method using interdimensional correlation model (IDCM) between 3D real target position and projected target position on 2D images from gantry-mounted kV on-board imaging system (OBI). Accuracy of the trajectory reconstruction was evaluated by simulating cone-beam CT (CBCT) image scanning and SBRT treatment. Then we developed a robotic-based patient immobilization system and its control system which can utilize the tracked target motion data to reduce tumor motion range during radiation treatment. First, a small-sized prototype was established with an industrial miniature robot. Required parameters for control system operation such as coordinate transformation and calibration were measured and evaluated with the development of prototype system. After developing and assessment of the control system with the prototype device, feasibility test was conducted for real-sized patient immobilization system with large industrial robot and couch. The performance of both prototype and real-sized device was evaluated with a respiratory motion phantom. In conclusion, the proposed target positon estimation method and the developed motion compensation system are expected to improve accuracy of treatment delivery in SBRT.