(Wednesday, 8/1/2018) 10:15 AM - 12:15 PM
Room: Karl Dean Ballroom A1
Purpose: Investigate Cherenkov emission (CE) as a robust tool for in-water electron, photon, and small-field dosimetry through Monte Carlo and experiment using a detector prototype setup.
Methods: We previously described EGSnrc-based simulation of dose and CE-to-dose conversation factors, from which CE is calculated, and we performed preliminary theoretical and experimental studies with electrons. In addition, dose was measured with a CC13 ionization chamber and CE was detected at 90° to the beam with optics, fiber, and CCD spectrometer. Percent-depth dose (PDD) and CE (PDC) were simulated and measured for clinical 6, 12, and 20-MeV electron beams in previous work and for 6 and 10-MV photon beams in this work, at normal incidence on water, 100-cm SSD, and 10x10-cm² field. Uncertainties were evaluated based on the agreement between simulated and experimental PDD/PDC ratios, i.e., relative CE-to-dose conversion factors. PDC was measured with two plano-convex spherical lenses, with curved surfaces facing and adjacent apertures (to minimize axial aberrations), 4° field-of-view, and focus on beam axis. For the photon beams, dose (DOF) and CE (COF) output factors were also simulated and measured for 1-14-cm equivalent-square fields at 5-cm depth by normalizing to 10x10-cm². COF was measured with 0°/4-mm field-of-view by removing the lens furthest from the fiber.
Results: Preliminary standard uncertainties on relative CE-to-dose conversion factors (PDD/PDC), based on the agreement between simulations and experiments, were ≤1% for PDC>50% for electron beams in the previous study and for depths>1 cm for photon beams in this study. Deviations at other depths corresponded to known detector limitations. Simulated and measured DOF and COF were in agreement within uncertainty (at most ±7%, CI=90%, smallest field).
Conclusion: Based on the agreement between simulated and experimental conversion and output factors, we conclude that CE-based dosimetry is feasible and could be an interesting alternative to conventional probe-detector based dosimetry.
Keywords
Dosimetry, Optical Dosimetry, Small Fields
Taxonomy
TH- Radiation dose measurement devices: Development (new technology and techniques)
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