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MO‐F‐WAB‐03: Trajectory Imaging: Exploring Options of Kilovoltage Digital Tomosynthesis During Intensity Modulated Radiation Therapy
Author(s) -
Zhang P,
Hunt M,
Pham H,
Mageras G
Publication year - 2013
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4815292
Subject(s) - multileaf collimator , imaging phantom , fiducial marker , tomosynthesis , collimator , image guided radiation therapy , nuclear medicine , linear particle accelerator , physics , rotation (mathematics) , truebeam , cone beam computed tomography , computer science , medical imaging , beam (structure) , optics , computer vision , artificial intelligence , medicine , computed tomography , radiology , mammography , cancer , breast cancer
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. Part of the research is sponsored by Varian Medical System.