Atmospheric pressure influence on the charge collection efficiency of air-vented ionization chambers in ultra-high dose per pulse electron beams for FLASH radiotherapy
Autor(in); Institution
Flores-Mancera, Miguel Angel; Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin Madison, WI, USA
Schüller, Andreas; 6.2, Dosimetrie für Strahlentherapie und Röntgendiagnostik, PTB-Braunschweig
Paz-Martin, Jose; Departamento de Física de Partículas, Universidade de Santiago de Compostela, Praza do Obradorio, Santiago de Compostela, A Coruña, SPAIN
Gago-Arias, Araceli; Departamento de Física de Partículas, Universidade de Santiago de Compostela, Praza do Obradorio, Santiago de Compostela, A Coruña, SPAIN
Culberson, Wesley; Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin Madison, WI, USA
Gomez, Faustino; Departamento de Física de Partículas, Universidade de Santiago de Compostela, Praza do Obradorio, Santiago de Compostela, A Coruña, SPAIN; Laboratorio de Radiofísica, Universidade de Santiago de Compostela, Estrada de San Lourenzo, Santiago de Compostela, A Coruña, SPAIN
Quelle/Jahr
Physics in Medicine & Biology: 71
(2026), 8, 1
- 17
This work studies the dependency of the charge collection efficiency (CCE) on the atmospheric pressure of commercial ionization chambers (ICs) using an ultra-high dose-per-pulse (DPP) electron beam and proves a theoretical model of this phenomenon.
Approach: A custom-made PMMA water phantom, water- and pressure-tight sealed, was connected to a vacuum/pressure pump to vary its inside pressure from 900 hPa to 1100 hPa. ICs were placed at different depths in water and irradiated with ultra-high DPP electron beams (20 MeV, 1.2 μs and 2.0 μs pulse duration). Chamber signals were air-density- and polarity-corrected as a function of DPP (0.1 Gy – 6.5 Gy) at different pressures. The actual DPP was determined and monitored using a calibrated PTW flashDiamond and a current transformer, respectively. Experimental CCEs were compared with numerical calculations, describing the charge transport inside ICs, including free electrons and electric field distortion.
Main results: The CCE decreased with increasing pressure (-6%/100 hPa and -8%/100 hPa for the Advanced Markus, and Roos IC, respectively) and followed “logistic functions” with DPP. The CCE0 at a given pressure P0 can be obtained from a CCE1 at different pressure P1 (scaling rule) as: CCE0(P0,DPP) = CCE1(P1,DPP*(P0/P1)^2). Our theoretical model predicted the relative variation of the CCE with pressure, with residuals <3%. The effect can be corrected using the scaling rule even at small changes in pressure (~35 hPa), which can cause a 2% deviation on the CCE, without adding significant CCE uncertainty (~0.1%) for a DPP up to 6.5 Gy per pulse. Significance: This work proposes a scaling rule to correct for recombination losses dependent on atmospheric pressure in ultra-high DPP electron beams. The proposed scaling rule provides a simple, low-uncertainty correction that can be applied to empirically predetermined CCE functions, improving the accuracy of commercial IC-based dosimetry in ultra-high DPP electron beams.
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Rechteinformation
CC BY 4.0 ; Creative Commons Attribution 4.0 License
Förderinformationen (1)
Förderername: European Commission (EC)
Förderer ID: 0000 0001 2242 8989
Förderer ID Typ: ISNI
Förderprogramm: EPM 2024
Titel der Förderung: 24NRM01: FLASH-DOSE
Förderungsnummer: 24NRM01
Zitierung
Flores-Mancera, M. A., Schüller, A., Paz-Martin, J., Gago-Arias, A., Culberson, W., & Gomez, F. (2026). Atmospheric pressure influence on the charge collection efficiency of air-vented ionization chambers in ultra-high dose per pulse electron beams for FLASH radiotherapy. Physics in Medicine & Biology, 71(8), 1–17. https://doi.org/10.1088/1361-6560/ae556b
