(Saturday, 4/7/2018) 10:30 AM - 12:30 PM
Room: Marquis Ballroom 5-8
Purpose: Cherenkov light emission has been shown to correlate with ionizing radiation dose delivery in solid tissue. An important clinical application of this is the real-time verification of radiation treatment delivery in vivo. To determine the detectability of treatment field matching, we acquired Cherenkov images of photon and electron fields matched with known spacing.
Methods: Cherenkov light was captured using a PI-MAX4 intensified charge coupled device system. A Varian Trilogy linear accelerator was operated at 6MV or 12MeV and 400MU/min to deliver anterior-posterior beams to a 5cm thick block phantom at 100cm or 110cm SSD, respectively. Field overlap and gap distances of 0, 2, 5, and 10mm were delivered and evaluated. Before delivery the 10x10cm2 projected light field was imaged for pixel size calibration in subsequent acquisitions. Geometric perspective distortions were corrected using Moving Least Square transformation with landmark correspondence. Composite images were created by frame summation followed by background subtraction and evaluated using ImageJ and MATLAB software packages.
Results: Discrepancy between delivered field size and Cherenkov light edges was 2-5mm, with Cherenkov images systematically demonstrating a larger penumbra than the radiation field. Photon field gaps and overlaps of 2mm were easily detected, indicating the feasibility of detecting similar spacing in a clinical situation. Cherenkov images of 0mm gap photon fields appeared as a small field gap, but smaller than planned 2mm gap images. Cherenkov images of matched electron fields had larger penumbras compared with matched photon fields, with known gaps as large as 5mm appearing as overlaps.
Conclusion: This study indicates that Cherenkov imaging can be used to provide live detection of field matching error in a clinical scenario, with the most promising results demonstrated in photon-photon field matching. Electron-electron matched fields systematically overestimated the incidence of field overlap, but this can be corrected in future clinical scenarios.
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