Consistency in quality correction factors for ionization chamber dosimetry in scanned proton beam therapy

Sorriaux, Jefferson; Testa, M.; Paganetti, Harald; Bertrand, D.; Lee, John A.; Vynckier, Stefaan; Sterpin, Edmond

doi:10.1002/mp.12434

Cited by 14 publications

(11 citation statements)

References 38 publications

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“…Well‐designed Monte Carlo (MC) codes can calculate the response of ionization chambers accurately provided correct data on the detector construction materials and dimensions and on the radiological properties of the constituting materials are available. Gomà et al and Sorriaux et al have performed simulations of ionization chambers using PENH and Geant4, respectively. These calculations are very sensitive to transport algorithm parameters, such as step size, and boundary‐crossing artifacts .…”

Section: Introductionmentioning

confidence: 99%

The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

et al. 2018

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Purpose In all recent protocols for the reference dosimetry of clinical proton beams, ionization chamber perturbation factors are assumed to be unity. In this work, such factors were computed using the FLUKA Monte Carlo code for three ionization chamber types, with particular attention to the influence of nuclear interactions. Methods The accuracy of the transport algorithms implemented in FLUKA was first evaluated by performing a Fano cavity test. Ionization chamber perturbation factors were computed for the PTW‐34001 Roos® and the PTW‐34070 and PTW‐34073 Bragg peak® chambers for proton beams of 60–250 MeV using the same transport parameters that were needed to pass the Fano test. Results FLUKA was found to pass the Fano test within 0.15%. Ionization chamber simulation results show that the presence of the air cavity and the wall results in dose perturbations of the order of 0.6% and 0.8%, respectively. The perturbation factors are shown to be energy dependent and nuclear interactions must be taken into account for accurate calculation of the ionization chamber's response. Conclusion Ionization chamber perturbations can amount to 1% in high‐energy proton beams and therefore need to be considered in dosimetry procedures.

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Section: Introductionmentioning

confidence: 99%

The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

et al. 2018

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“…Monte Carlo simulation was used to obtain the 3D voxelized proton dose and LET distributions at the sites of the animal irradiation with a fast multi-core Monte Carlo package MCsquare ( 49 , 50 ). This software simulates the dose and dose-weighted LET (LET D ), which was experimentally validated ( 48 , 51 – 53 ). The mouse CT DICOM images were modified to include the double-scattering animal proton FLASH platform ( 8 ).…”

Section: Methodsmentioning

confidence: 99%

A phenomenological model of proton FLASH oxygen depletion effects depending on tissue vasculature and oxygen supply

Zou

Kim²,

Diffenderfer³

et al. 2022

Front. Oncol.

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IntroductionRadiation-induced oxygen depletion in tissue is assumed as a contributor to the FLASH sparing effects. In this study, we simulated the heterogeneous oxygen depletion in the tissue surrounding the vessels and calculated the proton FLASH effective-dose-modifying factor (FEDMF), which could be used for biology-based treatment planning.MethodsThe dose and dose-weighted linear energy transfer (LET) of a small animal proton irradiator was simulated with Monte Carlo simulation. We deployed a parabolic partial differential equation to account for the generalized radiation oxygen depletion, tissue oxygen diffusion, and metabolic processes to investigate oxygen distribution in 1D, 2D, and 3D solution space. Dose and dose rates, particle LET, vasculature spacing, and blood oxygen supplies were considered. Using a similar framework for the hypoxic reduction factor (HRF) developed previously, the FEDMF was derived as the ratio of the cumulative normoxic-equivalent dose (CNED) between CONV and UHDR deliveries.ResultsDynamic equilibrium between oxygen diffusion and tissue metabolism can result in tissue hypoxia. The hypoxic region displayed enhanced radio-resistance and resulted in lower CNED under UHDR deliveries. In 1D solution, comparing 15 Gy proton dose delivered at CONV 0.5 and UHDR 125 Gy/s, 61.5% of the tissue exhibited ≥20% FEDMF at 175 μm vasculature spacing and 18.9 μM boundary condition. This percentage reduced to 34.5% and 0% for 8 and 2 Gy deliveries, respectively. Similar trends were observed in the 3D solution space. The FLASH versus CONV differential effect remained at larger vasculature spacings. A higher FLASH dose rate showed an increased region with ≥20% FEDMF. A higher LET near the proton Bragg peak region did not appear to alter the FLASH effect.ConclusionWe developed 1D, 2D, and 3D oxygen depletion simulation process to obtain the dynamic HRF and derive the proton FEDMF related to the dose delivery parameters and the local tissue vasculature information. The phenomenological model can be used to simulate or predict FLASH effects based on tissue vasculature and oxygen concentration data obtained from other experiments.

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“…Machine deliverable files were generated with 2 MU with single energy from 100 to 226.2 MeV at 10 MeV intervals at 2 cm depth. The k Q of the proton beam for the Advanced Markus chamber can be derived using Monte Carlo simulation regardless of the spot time structure 53,54 . We used the interpolated k Q values at energies from table 5 in Gomà et al 53 .…”

Section: Methodsmentioning

confidence: 99%

“…The k Q of the proton beam for the Advanced Markus chamber can be derived using Monte Carlo simulation regardless of the spot time structure. 53,54 We used the interpolated k Q values at energies from table 5 in Gomà et al 53 In this table, k Q was calculated as 0.997, 1.003, 1.002, and 1.006 for 100, 150, 200, and 250 MeV protons using water and graphite mean excitation energies of 78 and 81.1 eV and energy ratio Wair,Q/Wair,Q0 of 1.014 for creating an ion pair at beam qualities Q and Q 0 . The calibration coefficients at different energies were obtained as the ratio of the DAP w from the Markus chamber at the reference depth to the IC64-6 monitor chamber reading from the single spot beamlet.…”

Section: D Transmission Chamber Calibration With a Calibrated Ionization Chambermentioning

confidence: 99%

Characterization of a high‐resolution 2D transmission ion chamber for independent validation of proton pencil beam scanning of conventional and FLASH dose delivery

et al. 2021

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Introduction: Ultra-high dose rate (FLASH) radiotherapy has become a popular research topic with the potential to reduce normal tissue toxicities without losing the benefit of tumor control. The development of FLASH proton pencil beam scanning (PBS) delivery requires accurate dosimetry despite high beam currents with correspondingly high ionization densities in the monitoring chamber. In this study, we characterized a newly designed high-resolution position sensing transmission ionization chamber with a purpose-built multichannel electrometer for both conventional and FLASH dose rate proton radiotherapy. Methods: The dosimetry and positioning accuracies of the ion chamber were fully characterized with a clinical scanning beam. On the FLASH proton beamline, the cyclotron output current reached up to 350 nA with a maximum energy of 226.2 MeV, with 210 AE 3 nA nozzle pencil beam current. The ion recombination effect was characterized under various bias voltages up to 1000 V and different beam intensities. The charge collected by the transmission ion chamber was compared with the measurements from a Faraday cup. Results: Cross-calibrated with an Advanced Markus chamber (PTW, Freiburg, Germany) in a uniform PBS proton beam field at clinical beam setting, the ion chamber calibration was 38.0 and 36.7 GyEÁmm 2 /nC at 100 and 226.2 MeV, respectively. The ion recombination effect increased with larger cyclotron current at lower bias voltage while remaining ≤0.5 AE 0.5% with ≥200 V of bias voltage. Above 200 V, the normalized ion chamber readings demonstrated good linearity with the mass stopping power in air for both clinical and FLASH beam intensities. The spot positioning accuracy was measured to be 0.10 AE 0.08 mm in two orthogonal directions. Conclusion:We characterized a transmission ion chamber system under both conventional and FLASH beam current densities and demonstrated its suitability for use as a proton pencil beam dose and spot position delivery monitor under FLASH dose rate conditions.

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Consistency in quality correction factors for ionization chamber dosimetry in scanned proton beam therapy

Cited by 14 publications

References 38 publications

The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

The influence of nuclear interactions on ionization chamber perturbation factors in proton beams: FLUKA simulations supported by a Fano test

A phenomenological model of proton FLASH oxygen depletion effects depending on tissue vasculature and oxygen supply

Characterization of a high‐resolution 2D transmission ion chamber for independent validation of proton pencil beam scanning of conventional and FLASH dose delivery

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