(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Transmission detectors are increasingly used in linac/treatment delivery Quality Assurance (QA) and Control (QC). We are developing a thin transmission detector array for real-time beam monitoring during radiotherapy treatments and linac QA/QC. The detector employs fast electron current detector technology which can withstand very high dose rates without saturation.
Methods: Our sensor is a multilayer structure with N basic elements composed of 3-electrodes: N x (Al-aerogel-Ta-aerogel-Al). 10µm-Ta and 16µm-Al thin-film electrodes are separated by low density nano-porous aerogel 125µm-thick. We performed radiation transport simulations to optimize the geometry and we fabricated several detector array prototypes to monitor beam profiles in X -/Y-directions with mm resolution, and to track MLC motion in real-time. Stacked and planar strip arrays have been prototyped and tested using TB Linac 6MV/6FFF. In the stacked geometry 5mm-wide 20cm-long strip electrodes were parallel to the beam, while in the planar geometry the electrodes were side by side.
Results: linearity to MU and MU/min was established and x-ray beam profiles were acquired with ~1 mm of spatial resolution. Beam attenuation by detector arrays is about 1-2% for 6MV/6FFF. The device can monitor each linac pulse or integrate over few pulses at each control point. MLC segments are monitored by acquisition of signal integrated along the x- and y-strips. From the raw x-/y-signals the beam output and MLC leaf positions are extracted for each control point using a custom MLC beam model.
Conclusions: The nano-porous aerogel strip arrays allow high spatial resolution measurements required for beam monitoring. The simplicity of operation of these arrays opens possibilities for novel ways to verify MLC leaf positions in real-time. This technology is suitable for monitoring of very high dose rate beams such those used in FLASH-RT.
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