SU-F-T-518: Development and Characterization of a Gated Treatment System Implemented with An In-House Optical Tracking System and the Elekta Response Interface

Purpose: To report the development and characterization of the first in-house gating system implemented with an optical tracking system (OTS) and the Elekta Response™ interface. Methods: The Response™ connects a patient tracking system with a linac, enabling the tracking system to control radiation delivery. The developed system uses an in-house OTS to monitor patient breathing. The OTS consists of two infrared-based cameras, tracking markers affixed on patient. It achieves gated or breath-held (BH) treatment by calling beam ON/OFF functions in the Response™ dynamic-link library (DLL). A 4D motion phantom was used to evaluate its dosimetric and time delay characteristics. Two FF- and two FFF-IMRT beams were delivered in non-gated, BH and gated mode. The sinusoidal gating signal had a 6 sec period and 15 mm amplitude. The duty cycle included 10%, 20%, 30% and 50%. The BH signal was adapted from the sinusoidal wave by inserting 15 sec BHs. Each delivery was measured with a 2D diode array (MapCHECK™) and compared with the non-gated delivery using gamma analysis (3%). The beam ON/OFF time was captured using the service graphing utility of the linac. Results: The gated treatments were successfully delivered except the 10% duty cycle. The BH delivery had perfect agreement (100%) with non-gated delivery; the agreement of gated delivery decreased from 99% to 88% as duty cycle reduced from 50% to 20%. The beam on/off delay was on average 0.25/0.06 sec. The delivery time for the 50%, 30% and 20% duty cycle increased by 29%, 71% and 139%, respectively. No dosimetric or time delay difference was noticed between FF- and FFF-IMRT beams. Conclusion: The in-house gating system was successfully developed with dosimetric and time delay characteristics in line with published results for commercial systems. It will be an important platform for further research and clinical development of gated treatment.