- •Daily QA is of utmost importance in particle therapy due to the workflow complexity.
- •The Sphinx Compact can fasten the daily QA procedures in particle therapy.
- •Quenching effect is an issue for the Sphinx Compact, 3D measurements are discouraged.
- •The Sphinx Compact can be a useful and time-saving tool for constancy checks.
To fully characterize the flat panel detector of the new Sphinx Compact device with scanned proton and carbon ion beams.
Materials and methods
The Sphinx Compact is designed for daily QA in particle therapy. We tested its repeatability and dose rate dependence as well as its proportionality with an increasing number of particles and potential quenching effect. Potential radiation damage was evaluated. Finally, we compared the spot characterization (position and profile FWHM) with our radiochromic EBT3 film baseline.
The detector showed a repeatability of 1.7% and 0.9% for single spots of protons and carbon ions, respectively, while for small scanned fields it was inferior to 0.2% for both particles. The response was independent from the dose rate (difference from nominal value < 1.5%). We observed an under-response due to quenching effect for both particles, mostly for carbon ions. No radiation damage effects were observed after two months of weekly use and approximately 1350 Gy delivered to the detector. Good agreement was found between the Sphinx and EBT3 films for the spot position (central-axis deviation within 1 mm). The spot size measured with the Sphinx was larger compared to films. For protons, the average and maximum differences over different energies were 0.4 mm (3%) and 1 mm (7%); for carbon ions they were 0.2 mm (4%) and 0.4 mm (6%).
Despite the quenching effect the Sphinx Compact fulfills the requirements needed for constancy checks and could represent a time-saving tool for daily QA in scanned particle beams.
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Published online: March 08, 2023
Accepted: February 27, 2023
Received in revised form: February 21, 2023
Received: August 17, 2022
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.