SU-E-J-157: Evaluation of Surface-Tracking and Respiratory Gating Capacities of a Novel Surface-Mapping System Using Deformable Image Registration

Abstract

Purpose: We have tested the capabilities of an innovative surface-mapping system that utilizes deformable image registration tools (C-RAD Catalyst). Its 3D positioning stability has been verified as well as its respiratory capabilities. Methods: The Catalyst daily QA phantom was used to test the stability of the system. A MatriXX ion-chamber array in a solid water phantom was mounted on a motion platform which can provide longitudinal 1D motion.The vertical-motion plate (respiratory plate) of the platform was used to mimic the chest movement in respiratory cycles. The respiratory plate was tracked by the Catalyst surface-mapping system. A static 10×10 field was first delivered to establish the baseline. Gated deliveries using different gating windows (from 10% to 90% duty cycle) were also performed and the results were recorded. A comparison between the Catalyst surface tracking signal and ABC data was performed for a breast cancer patient on-treatment. Results: Analysis of the experiment data indicates that the Catalyst is stable and reliable in detecting surface position and movement. With 50 numbers of phantom setups, the mean deviation of the shifts and rotations along all three directions was 0.6mm and 0.02 degrees, respectively. The gating capacity study suggested that respiratory gating using Catalyst system on an Elekta linac can be delivered safely and accurately. In fact, in gated beam delivery with the Catalyst system, dose distribution, dose profiles, gamma passing rates all show improvements as the gating window gets smaller. Gamma passing rates increase from 84.7% at non-gating to 95.6% at 10% gating window. The Catalyst system also correctly recognizes the respiratory pattern of a patient under our ABC gated treatment delivery. Conclusion: Based on a phantom study and clinical observations, we have found that Catalyst system is robust in surface tracking and positioning. It also can serve as a respiratory gating solution. Funded by Elekta