S Stathakis*, C Kabat, M Naessig, Mays Cancer Center - MD Anderson Cancer Center, San Antonio, TX

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  S Stathakis

PO-GePV-T-343 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: The purpose of this study is to evaluate a new semiconductor detector for photon beam dosimetry. Especially consideration was given to the narrow field dosimetry.

Methods: The PTW MicrosiliconX diode is being evaluated for its application in measurements for beam data collection. An ELEKTA VersaHD linac and the PTW BEAMSCAN water tank were used for the measurements. We used 6MV, 10MV, 18MV, 6MV FFF and 10MV FFF energies for all measurements and field sizes ranging from 0.5x0.5cm2 to 30x30cm2. We measured profiles at 5,10, 20cm depths, percent depth dose curves, and output factors. The same measurements were collected for fields with the motorized wedge in place. Finally, all measurements were repeated using the SNC Edge detector and the PTW Photon Diode 61016P detector. The dose per pulse dependency was also checked for all detectors.

Results: The dose per pulse dependency was acceptable for all detectors. The MicrosiliconX and 61016P detector had the lowest and the SNC edge had the highest dose per pulse dependency. The SNC Edge is also the most aged detector amongst them. The dose per pulse was 0.29%, 0.31%, 1.15% for the MicroSiliconX, 61016P and SNC Edge detectors. There was less than a 2% difference in all output factors. PDDs and profiles had small differences between them. The SNC Edge detector showed higher PDD values past 15cm depths but that the difference was within 1-2%. The profile penumbras were very similar. The PTW detectors had less noise in the measurements of PDDs and profiles.

Conclusion: The new PTW MicrosiliconX detector was compared against established detectors for photon beam measurements. The detector performed similarly to the other ones and had less noise in the PDD and profile scans which in turn requires less data smoothing and less time for processing while obtaining reliable measurements.

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