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Dosimetric Impact of Intra-Fraction Lung Tumor Rotation in Real-Time Tumor-Tracking Radiotherapy Using a Developed 6DoF Robotic Phantom System

T Shiinoki*, F Fujii, Y Yuasa, T Nonomura, K Fujimoto, T Sera, H Tanaka, Yamaguchi University


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: The respiratory gating system combined the TrueBeam and a real-time tumor-tracking radiotherapy (RTRT) system, SyncTraX (Shimadzu Co., Japan) were installed in our institution. The purposes of this study were to develop the six degree-of-freedom (6DoF) robotic phantom system and to evaluate the dosimetric impact of intra-fraction lung tumor rotation for RTRT.

Methods: The water-equivalent phantom (WEP) was set at the tip of the robotic arm. The log file recorded the 3D coordinates of the three fiducial markers implanted near lung tumor using SyncTraX were used to calculate the translation and rotation of lung tumor and the motion data was input to 6DoF robotic phantom. The WEP was driven in 6DoF respiratory translation and rotation. The RTRT was performed while driving the WEP. The accuracy of 6DoF robotic phantom was calculated as the differences between actual and measured position. To evaluate the dosimetric impact of intra-fraction rotation, the absolute dose distributions under RTRT and moving conditions were compared with those under static condition.

Results: For 15 patient respiratory translation and rotation, the accuracy of the translation and rotation of 6DoF robotic phantom were < 0.55 mm and < 0.85° in all directions. The ?3%/2 mm under translation moving conditions with/without RTRT were 97.6 ± 2.2 % /80.9 ± 18.1% and 96.8 ± 2.3%/80.0 ± 17.0% in coronal and sagittal plane, respectively. Those under rotation moving conditions with/without RTRT were 91.5 ± 6.5 %/72.8 ± 18.6% and 89.5 ± 8.1%/72.9 ± 15.7% in coronal and sagittal plane, respectively.

Conclusion: We have developed a 6DoF robotic phantom system to derive the translation and rotation lung tumor motion with high accuracy. The RTRT using an internal surrogate marker was effective to compensate the translation motion of lung tumor, but might be not enough to correct the rotation motion.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant number 18K07753.


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