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Quantitative Evaluation of Rigid and Non-Rigid Motion of Liver Tumors Using Stereo Imaging During SBRT

Q Xu

Q Xu1*, G Hanna1 , J Grimm2 , G Kubicek1 , N Pahlajani3 , S Asbell1 , J Fan4 , Y Chen1 , T LaCouture1 , (1) MD Anderson Cancer Center at Cooper, Mt Laurel, NJ, (2) Holy Redeemer, Meadowbrook, PA, (3) First Radiation and Oncology Group, Jacksonville, FL,(4) Virtua Fox Chase Cancer Center, Philadelphia, PA


SU-E-J-225 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To quantitatively evaluate rigid and nonrigid motion of liver tumors based on fiducial tracking in 3D by stereo imaging during CyberKnife SBRT.
Twenty-five liver patients previously treated with three-fractions of SBRT were retrospectively recruited in this study. During treatment, the 3D locations of fiducials were reported by the CyberKnife system after two orthogonal kV X-ray images were taken and further validated by geometry derivations. A total of 5004 pairs of X-ray images acquired during the course of treatment for all the patients, were analyzed. For rigid motion, the rotational angles and translational shifts by aligning 3D fiducial groups in different image pairs after least-square fitting were reported. For nonrigid motion, the relative interfractional tumor shape variations were reported and correlated to the sum of inter-fiducial distances. The individual fiducial displacements were also reported after rigid corrections and without angle corrections.
The relative tumor volume variation indicated by the inter-fiducial distances demonstrated an increasing trend in the second (101.6±3.4%) and third fraction (101.2±5.6%) among most patients. The cause could be possibly due to radiation-induced edema. For all the patients, the translational shift was 8.1±5.7 mm, with shifts in LR, AP and SI were 2.1±2.4 mm, 2.8±2.9 mm and 6.7±5.1 mm, respectively. The greatest translation shift occurred in SI, mainly due the breathing motion of diaphragm The rotational angles were 1.1±1.7°, 1.9±2.6° and 1.6±2.2°, in roll, pitch, and yaw, respectively. The 3D fiducial displacement with rigid corrections were 0.2±0.2 mm and increased to 0.6±0.3 mm without rotational corrections.
The fiducial locations in 3D can be precisely reconstructed from CyberKnife stereo imaging system during treatment. The fiducials provide close estimation of both rigid and nonrigid motion of .liver tumors. The reported data could be further utilized for tumor margin design and motion management in in conventional linac-based treatments.

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