(Saturday, 3/30/2019)
Room: Exhibit Hall
Purpose: To extend the application of a conical, scintillation-based detector for machine and patient-specific QA by assessing signal dependence on irradiation conditions and device acquisition parameters.
Methods: Extending the use of a scintillation detector typically used for targeting accuracy to QA applications featuring a broad range of energies, dose rates, and aperture sizes requires further characterization of the device regarding these variables. For this purpose, we used a conventional c-arm linac to irradiate the device with square fields of varying size (1x1cm-8x8cm), position, angle (45° increments), energy (6-15MV, FF and FFF), and dose rate (100-600MU/min). Vendor-provided software was used to analyze both the entrance and exit scintillation spots observed for each irradiation to determine the effect of these variables on the device response. The dependence of device response on acquisition settings such as frame rate was also analyzed
Results: Differences in scintillation intensity with varying incident gantry angles were small (0.8%) although larger systematic differences were observed based on longitudinal position of the device (1.1%). The relative signal from irradiations of varying field sizes appear to be correlated with dose output factors acquired during machine commissioning. The device exhibits a bilinear response with respect to dose rate and acquisition frame rate. The scintillation intensity was observed to vary considerably (18.7%) and preliminary data suggests the behavior of the entrance and exit scintillation spot signals may differ in their energy-dependence.
Conclusion: Our initial characterization of a conical, scintillation-based detector suggests the response may depend on irradiation and acquisition parameters such as field size, position, angle, energy, dose rate, and frame rate. Understanding the influence of these factors on the device is imperative for its application to a broader range of QA applications such as patient-specific QA for IMRT, SBRT, and SABR.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by Logos Systems Int'l.
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