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Trajectory Imaging: Exploring Options of Kilovoltage Digital Tomosynthesis During Intensity Modulated Radiation Therapy

P Zhang

P Zhang*, M Hunt, H Pham, G Mageras, Memorial Sloan Kettering Cancer Center, New York, NY

MO-F-WAB-3 Monday 4:30PM - 6:00PM Room: Wabash Ballroom

Purpose: To integrate novel kilovoltage (kV) digital tomosynthesis (DTS) sequences into intensity modulated radiation therapy (IMRT) to determine 3D fiducial positions for intrafractional motion monitoring.

Method: In one method, we converted a static gantry IMRT beam into a series of arcs in which dose index and multileaf collimator positions for all control points were kept intact, but gantry angles were modified to oscillate +/-3° around the original angle. kV projections were acquired continuously throughout delivery and reconstructed to provide a series of 6° arc DTS images which were used to evaluate in-plane positions of gold fiducials embedded in an anthropomorphic phantom. To obtain out-of-plane positions via triangulation, a 20° gantry rotation with beam held-off was inserted during delivery to produce a pair of 6° DTS images separated by 14°. In a second method, the gantry remained stationary, but both kV source and detector moved over a 15° longitudinal arc via pitch and translational adjustment of the robotic arms. Evaluation of localization accuracy in phantom during simulated intrafractional motion used programmed couch translations from customized scripts. In-house software was used to reconstruct DTS images, register them to reference DTS images and calculate 3D fiducial positions.

Result: No significant dose difference (<0.5%) was found between the original and converted IMRT beams. For a typical hypofractionated spine treatment, 200 single DTS (6° arc) and 10 paired DTS (20° arc) were acquired for each IMRT beam, providing in-plane (IP) and out-of-plane (OP) monitoring every 1.5 and 30 seconds, respectively. Mean (standard deviation) error in predicted position was -0.3(0.2)mm, -0.1(0.1)mm IP, and 0.2(0.4)mm OP with rotational gantry, -0.1(0.1)mm, 0.7(0.3)mm IP and 1.9(1.1)mm OP with translational source/detector.

Conclusion: Acquiring 3D fiducial positions from kV-DTS during IMRT delivery is technically feasible. Enabling movement of kV-source and detector during delivery could further reduce imaging time overhead.

Funding Support, Disclosures, and Conflict of Interest: Part of the research is sponsored by Varian Medical System.

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