DESIGN AND CONSTRUCTION OF A RESPIRATORY MOTION PHANTOM FOR TESTING THE TARGETING ACCURACY OF THE CYBERKNIFE SYSTEM WITH THE SYNCHRONY® RESPIRATORY TRACKING SYSTEM

Abstract

Tumor moving due to respiration during the radiation treatment process is diffi cult to manage. Without management for respiratory motion, the critical organs may receive a high radiation dose with decreasing target dose. Synchrony® respiratory tracking of the Cyberknife system provides the unique possibility to do real-time patient and tumor motion tracking. An in-house respiratory motion phantom was designed and constructed for testing the targeting accuracy of the Synchrony® system. To simulate target and skin respiratory motions, an in-house respiratory motion phantom (17 × 45 × 15 cm3) made of acrylic was created. Inside the phantom, there were two parts; the mechanical part is composed of a cam and a slash cut pipe driven by a gear motor with 12 VDC to move the tumor and skin motion platform. The electrical part consists of AC to DC switching connected to an adjustable voltage regulator for supplying the gear motor. The amplitude and respiratory rate of the phantom were calibrated and evaluated using the Varian Real-Time Position Management (RPM) system. Then the phantom was used to test the targeting accuracy of the Synchrony® system by varying the amplitude of skin motion, respiratory rate, and tumor motion distance. The phantom can be moved along the superior-inferior (SI) directions (tumor motion) with the distances of 15, 25, and 35 mm and moved along the anterior-posterior (AP) direction (skin motion) from 0 to 15 mm. The respiratory rates can be varied from 0 to 30 cycles/min. The maximum standard deviation of amplitude and the respiratory rate in the phantom were 0.22 mm and 0.089 sec/cycle, respectively. The targeting error of the Synchrony® system is less than 1.0 mm. The skin motion amplitude, respiratory rate, and tumor distance do not affect the targeting accuracy of the system.