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Updated: Aug 14, 2025
Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator
Published on: May 9, 2014
Ion recombination correction factors and detector comparison in a very-high dose rate proton scanning beam
A M M Leite1, M Cavallone2, M G Ronga2
1Institut Curie, PSL Research University, Université Paris-Saclay, CNRS UMR 3347, INSERM U1021, 91898 Orsay, France; Institut Curie, PSL Research University, Radiation Oncology Department, Proton Therapy Center, Centre Universitaire, 91898 Orsay, France.
Purpose:
Accurate dosimetry is paramount to study the FLASH biological effect since dose and dose rate are critical dosimetric parameters governing its underlying mechanisms. With the goal of assessing the suitability of standard clinical dosimeters in a very-high dose rate (VHDR) experimental setup, we evaluated the ion collection efficiency of several commercially available air-vented ionization chambers (IC) in conventional and VHDR proton irradiation conditions.
Methods:
A cyclotron at the Orsay Proton Therapy Center was used to deliver VHDR pencil beam scanning irradiation. Ion recombination correction factors (ks) were determined for several detectors (Advanced Markus, PPC05, Nano Razor, CC01) at the entrance of the plateau and at the Bragg peak, using the Niatel model, the Two-voltage method and Boag's analytical formula for continuous beams.
Results:
Mean dose rates ranged from 4 Gy/s to 385 Gy/s, and instantaneous dose rates up to 1000 Gy/s were obtained with the experimental set-up. Recombination correction factors below 2 % were obtained for all chambers, except for the Nano Razor, at VHDRs with variations among detectors, while ks values were significantly smaller (0.8 %) for conventional dose rates.
Conclusions:
While the collection efficiency of the probed ICs in scanned VHDR proton therapy is comparable to those in the conventional regime with recombination coefficiens smaller than 1 % for mean dose rates up to 177 Gy/s, the reduction in collection efficiency for higher dose rates cannot be ignored when measuring the absorbed dose in pre-clinical proton scanned FLASH experiments and clinical trials.
