ESTRO 2020 Abstract book

S749 ESTRO 2020

energy transfer (LET) for these beam energies. Only one axial projection was used to generate integrated depth dose curves (the same quenching correction would apply for all three cameras). We compared the light output to the dose calculated by the Monte Carlo simulation and applied Birks’ scintillation model to fit the measured light. Optical artefact corrections were used to correct for refraction at the air-scintillator interface, and image perspective resulting in sub-millimeter accuracy in calculating physical distances within the tank. However, these corrections did not account for the non-orthogonal integration of data off the central axis of the image. Therefore, we compared the light output to an integrated Monte Carlo dose and LET along the non-orthogonal path to use Birks’ quenching correction model. Results After accounting for the non-orthogonal integration of the data, the Monte Carlo assigned values of fluence-averaged LET for each pixel on the camera projection correlated well with the light output independent of the delivered proton beam energy. In particular, the correction reduced the dose error at the Bragg peak region from 15% to 3% for low energy proton beams. Overall, the doses at the Bragg peak region using the Birks' model were less than ±3% of the Monte Carlo dose after implementing the non- orthogonal path corrections. Conclusion We have improved the application of Birks’ model quenching corrections in 3D scintillators by numerically projecting the dose and LET 3D grid to camera projections. In our future work, we will obtain the light distribution in 3D from the three camera projections to simplify the application of quenching correction models in 3D scintillator detectors.

Figure1: Two UFSD strip sensors in a telescope for beam energy measurement. Results Both the detectors were tested first in laboratory and then with two different clinical proton beams. Beam flux, pile- up inefficiency, signal-to-noise ratio, accuracy of TOF and mean energy measurements were determined from the analysis of the collected data. Using correction methods, the pile-up effect was mitigated to lower than 2% in therapeutic fluxes. The difference between calculated and nominal energies at the isocenter, for various energies and distances between the two sensors, reading out only one channel per sensor, showed an uncertainty lower than 0.5 MeV. Conclusion This work demonstrates the feasibility of using the UFSD technology, combined with a dedicated read out electronic in the case of the counter prototype, as an option to control the beam flux and position in particle therapy. The preliminary results of the beam energy prototype indicate that the clinical requirements (accuracy in the range measurement within 1 mm) can be achieved. In the next future, multiple channels from each sensor will be read out, to improve the statistics, an optimized readout electronics will be developed, along with a high precision mechanical support. PO-1328 Ionization quenching correction for 3D scintillator detectors for spot scanning proton therapy F. Alsanea 1 , S. Beddar 1 1 U.T. M.D. Anderson Cancer Center, Radiation Physics, Houston- TX, USA Purpose or Objective The ionization quenching phenomenon in scintillators must be corrected to obtain accurate dosimetry in particle therapy. The purpose of this study was to develop a methodology for correcting camera projection measurements of a 3D scintillator detector exposed to The 3D scintillator detector consists of a liquid scintillator filled tank (20 cm x 20 cm x 20 cm) and three cameras. The scintillation light is collected by a three camera system, each consisting of an objective lens and a scientific complementary metal–oxide–semiconductor (sCMOS) camera. We have exposed our detector to four different proton beam energies produced by the synchrotron at M.D. Anderson Cancer Center Proton Therapy Center (85.6, 100.9, 144.9, and 161.6 MeV). We used Monte Carlo simulations to obtain the dose and linear proton pencil beams. Material and Methods