Room: Karl Dean Ballroom A1
Purpose: The respiratory gating system combined the TrueBeam and a new real-time tumor-tracking radiotherapy (RTRT) system, SyncTraX (Shimadzu Co., Japan) were installed in our institution. However, the quality assurance (QA) method of this system was not established. The purposes of this study were to develop the four-dimensional (4D) dynamic robotic phantom system and to apply it for the patient-specific QA of RTRT.
Methods: Three-dimensional (3D) printing technology was used to make individualized lung phantoms that closely mimicked the lung anatomy of actual patients using planning CT images. The 3D-printed lung phantom was designed to set the Gafchromic film and several nanodot dosimeters. The water-equivalent phantom (WEP) with 3D-printed lung phantom was set at the tip of the robotic arm. The log file recorded the 3D positions of lung tumor measured using SyncTraX was input to 4D dynamic robotic phantom and the WEP was driven in 3D respiratory motion. The RTRT was performed while driving the WEP. The tracking accuracy was calculated as the differences between actual and measured position. For absolute dose and dose distribution, the difference between planned and measured dose were calculated.
Results: The 4D dynamic robotic phantom accurately reproduced the 3D complicated tumor motion affected by the heart beat and hysteresis using a log file. The lung and tumor mass density of the 3D-printed lung phantom were 0.211 g/cmÂ³ and 0.944 g/cmÂ³ and good agreement with those of real tissues. As results of clinical application of this phantom, the differences between planned and measured absolute dose were â‰¤ 2 % at isocenter. The gamma pass rates of Î³3%/3 mm were â‰¥ 95%. The 3D root mean squared errors of tracking accuracy were â‰¤ 1 mm.
Conclusion: Developed 4D robotic phantom system has advanced the QA for RTRT and made it possible to perform the patient-specific QA.