Analysis of IGRT QA Image Accuracy Over One Year
S Roy1*, B Sarkar2, A Pradhan3, (1) Manipal Hospital Dwarka & GLA University Mathura, Delhi, DELHI, IN, (2) Apollo Gleneagles Cancer Hospital Kolkata, Kolkata, WB, IN, (3) Centre for Cosmology, Astrophysics and Space Science, GLA University, Mathura, UP, IN
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Purpose: Image guided radiotherapy quality assurance was performed as per TG-142 based protocol. The purpose of this study was to analyse IGRT QA data obtained over a period of one year and confirm the correctness of the image-guided radiation treatment setup relative to the radiation isocenter.
Methods: This test used a cube (Isocube) consisting of an 8 mm dia. tungsten sphere at the center of a 5 cm3 phantom. We placed the phantom on linac treatment table with a central tungsten sphere that was placed at the isocenter. Placement of the cube was done using a fixed laser isocenter on the treatment couch. Four Gantry angles (0°, 90°, 180°, 270°) with 2x2 cm2 field size were chosen for planar imaging isocenter accuracy check for both kilo Voltage (kV) and Mega Voltage (MV) imaging using EPID panel. The acquired planar image with the tungsten ball was matched with the reference DRR image available from the Treatment planning system. The tungsten sphere in the reference CT image was aligned with a high-resolution cone-beam CT image in case of CBCT matching.
Results: Variation from planning isocenter to the imaging centre for MV at different gantry angles are as 0.43±0.44 mm, 0.43±0.52 mm, 0.42±0.27 mm, and 0.36±0.11 mm for MV (Gantry=0°), MV(Gantry=90°), MV(Gantry=180°) and MV(Gantry=270°) respectively. For kV imaging portals, the deviation was 0.36±0.14 mm, 0.37±0.13 mm, 0.39±0.13 mm, and 0.32±0.14 mm for Gantry 0°,90°,180°, and 270° respectively. CBCT imaging showed a variation of 0.34±0.12 mm from the planning isocenter.
Conclusion: Overall, CBCT has better accuracy compared to planer images. Apart from the MV portal at G=270, all MV imaging showed lesser accuracy compared to planar kV or CBCT. Performing this test on a regular basis can identify trends in IGRT positioning and prevent inaccuracy.
Keywords
Quality Assurance, Image-guided Therapy
Taxonomy
IM/TH- Formal Quality Management Tools: Sensitivity and statistical process control analyses
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