ESTRO 2023 - Abstract Book

S1462

Digital Posters

ESTRO 2023

The very compact design of the ZAP-X creates a challenge for measurements set-ups and acquisition of a consistent datasets. Our findings show good congruence of measurements methods and robust benchmarking against MC synthetic data. The combination of IC31021 DDC and of OFs measurements clearly indicate that the beam spectrum is shifted towards higher energies (with MC showing the max at 3,7MV). Furthermore, correction factors are not needed for OFs acquired with the PSD and that satisfactory (below 1%) results are reached with diamond detector.

PO-1741 Development of 2D pixel array ionization chamber system for Flash Proton beam

Y. Jang 1 , T. Yang 1 , S. Park 2 , J. Kim 1 , H. Jang 1 , K. Kim 1 , G. Kim 1 , S. Choi 1

1 Korea Institute of Radiological and Medical Sciences, Medical Physics Research Team, Seoul, Korea Republic of; 2 Korea University, Department of Accelerator Science, Sejong, Korea Republic of Purpose or Objective To accurately measure an ultra-high dose rate ion beam, a system for measuring a high dose rate in real time is important. But more important thing is to minimize the ion recombination effect due to the many ion charges that occur instantaneously in ionization chamber. The objective of this study is to conduct to find a condition to minimize ion recombination effect according to the electrode spacing and high voltage control of the pixel-type ionization chamber and monitoring the proton FLASH beam in real time. Materials and Methods The two-dimensional pixel-type ionization chamber used in this study is consists of 256 pixels, and the volume of each electrode is 4.0mm x 4.0mm x 35µm. The proton beam used in the experiment was 45 MeV/1~70nA and the detector was placed at SSD 100cm. We used DAQ board for data collection and the measured intensity values, beam position, and dispersion value during beam monitoring are displayed through Labview software in real time. To minimize the ion recombination effect, Boag’s theory was applied to calculate the collection efficiency. The ion-pair value was obtained through the PHITS monte Carlo simulation and the amount of charge generated in the electrodes was controlled by adjusting the gap between the electrodes of the detector to 2 ~ 5mm in the experiments. Results The ion recombination effect was less than 1% when the high voltage was 200, 900, and 1300 V or more at 2, 4, and 5 mm gaps, respectively. This result is consistent with the theoretical value obtained through PHITS simulation. The center position of the proton beam while irradiating the beam at 45MeV/10nA for 3 seconds was x=0.316 y=0.410 from the center of the ionization chamber, and the dispersion value was x=2.070 y=2.043. We converted the intensity value to Dose[Gy] by comparing the measured beam profile and irradiated film. As a results, even at a current of 10nA, the dose value at the center was 70 Gy/s or more confirming that the ultra-high dose rate ion beam. Conclusion In this study, we developed a monitoring system that can accurately measure ultra-high dose rate ion beams. In a 45MeV/70nA proton beam, a dose rate of 300Gy/s or more could be monitored in real time, and the condition of less than 1% ion recombination effect was obtained. Based on these results, we plan to conduct an experiment on the ultra-high dose rate electron beam condition and develop a 2D pixel arrary detector with high-resolution and large area. M. MARRALE 1 , M.C. D'Oca 1 , G. Milluzzo 2 , S. Capaccioli 3 , D. Del Sarto 4 , F. Di Martino 5 , G. Felici 6 , L. Masturzo 5 , M. Montefiori 7 , F. Paiar 4 , J. Pensavalle 7 , E. Sangregorio 8 , F. Romano 9 1 University of Palermo, Department of Physics and Chemistry "Emilio Segrè", Palermo, Italy; 2 National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy; 3 Centro Pisano ricerca e implementazione clinica Flash Radiotherapy , Presidio S. Chiara, Pisa, Italy; 4 Centro Pisano ricerca e implementazione clinica Flash Radiotherapy, Presidio S. Chiara, Pisa, Italy; 5 Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, Pisa, Italy; 6 SIT-Sordina, SIT-Sordina, Aprilia, Italy; 7 University of Pisa, Department of Physics, Pisa, Italy; 8 University of Pisa, Radiation Oncology Unit, Department of Translational Research, Pisa, Italy; 9 National Institute of Nuclear Physics (INFN), , Catania Division, Catania, Italy Purpose or Objective Significant dosimetric challenges should be dealt with ultra-high dose rate (UHDR) beams for FLASH radiotherapy. Reference dosimetry at UHDRS has not yet fully established and many efforts are made to develope alternative techniques and detectors, as ionization chambers suffer of ion recombination effects. Alanine passive dosimeters still represent a reliable reference for UHDR measurements, although dose determination is typically time consuming. This work aims at investigating the response of alanine pellets exposed to UHDR electron beams to comprehensively assess this dosimetric approach as a reference method for absolute dose measurements at UHDRs. Dose rate systematic investigations have been also carried out. Moreover, a multi-centre cross-comparison was performed, to check consistency of the measurements at the same irradiation conditions, using different alanine batches and independent readout systems. Materials and Methods Alanine pellets (produced by Gamma Service GmbH) were irradiated with ultra-high dose rate (UHDR) electron beams at 7 and 9 MeV using the SIT Sordina ElectronFLASH linac at conventional and UHDR regimes were used. Pulse structure is PO-1742 Characterization of alanine/EPR pellets for reference dosimetry of UHDR beams of FLASH radiotherapy