RT Journal Article
T1 Charge collection efficiency, underlying recombination mechanisms, and the role of electrode distance of vented ionization chambers under ultra-high dose-per-pulse conditions
A1 Kranzer, Rafael
A1 Schüller, Andreas
A1 Gómez Rodríguez, Faustino
A1 Weidner, Jan
A1 Paz Martín, José
A1 Looe, Hui Khee
A1 Poppe, Björn
K1 Dosimetry
K1 FLASH radiotherapy
K1 ionization chamber
K1 Ultra-high dose per pulse
AB Purpose: Investigating and understanding of the underlying mechanisms affecting the charge collection efficiency (CCE) of vented ionization chambers under ultra-high dose rate pulsed electron radiation. This is an important step towards real-time dosimetry with ionization chambers in FLASH radiotherapy. Methods: Parallel-plate ionization chambers (PPIC) with three different electrode distances were build and investigated with electron beams with ultra-high dose-per-pulse (DPP) up to 5.4 Gy. The measurements were compared with simulations. The experimental determination of the CCE was done by comparison against the reference dose based on alanine dosimetry. The numerical solution of a system of partial differential equations taking into account charge creations by the radiation, their transport and reaction in an applied electric field was used for the simulations of the CCE and the underlying effects. Results: A good agreement between the experimental results and the simulated CCE could be achieved. The recombination losses found under ultra-high DPP could be attributed to a temporal and spatial charge carrier imbalance and the associated electric field distortion. With ultra-thin electrode distances down to 0.25 mm and a suitable chamber voltage, a CCE greater than 99 % could be achieved under the ultra-high DPP conditions investigated. Conclusions: Well-guarded ultra-thin PPIC are suited for real-time dosimetry under ultra-high DPP conditions. This allows dosimetry also for FLASH RT according to common codes of practice, traceable to primary standards. The numerical approach used allows the determination of appropriate correction factors beyond the DPP ranges where established theories are applicable to account for remaining recombination losses.
PB Associazione Italiana di Fisica Medica
SN 1120-1797
YR 2022
FD 2022-12
LK http://hdl.handle.net/10347/32065
UL http://hdl.handle.net/10347/32065
LA eng
NO Physica Medica Volume 104, Pages 10 - 17 December 2022
DS Minerva
RD 25 abr 2026