Faraday cup for commissioning and quality assurance for proton pencil beam scanning beams at conventional and ultra-high dose rates

Winterhalter, Carla; Togno, Michele; Nesteruk, Konrad Pawel; Emert, Frank; Psoroulas, S.; Vidal, M.; Meer, D.; Weber, Damien Charles; Lomax, Anthony; Safai, Sairos

doi:10.1088/1361-6560/abfbf2

Cited by 15 publications

(39 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…During the animal experiments, the dose rate increases linearly with cyclotron output current ( 8 , 56 ), which was measured to be 213 ± 3 nA. A higher extracted current of 800 nA was recently reported on a hospital-based cyclotron ( 57 ). Our cyclotron has achieved similar extraction current previously ( 58 ) and was repeated recently, which produces 500 nA nozzle current.…”

Section: Methodsmentioning

confidence: 81%

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

Zou

Kim²,

Diffenderfer³

et al. 2022

Front. Oncol.

View full text Add to dashboard Cite

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.

show abstract

Section: Methodsmentioning

confidence: 81%

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

Zou

Kim²,

Diffenderfer³

et al. 2022

Front. Oncol.

View full text Add to dashboard Cite

show abstract

“…There are many studies describing the calibration of MU per number of protons, or gigaproton (Gp), for PBS systems. [1][2][3][4][5][6][7][8][9][10] These studies, however,use the pencil beam position on the nozzle axis.…”

Section: Introductionmentioning

confidence: 99%

“…The latter conversion is typically parameterized and calibrated with a Faraday cup. 10,17 Approximately,…”

Section: Introductionmentioning

confidence: 99%

“…The intensity of a proton pencil beam is more naturally expressed in terms of the number of protons in the beam and not its typical clinical representation in terms of MU. There are many studies describing the calibration of MU per number of protons, or gigaproton (Gp), for PBS systems 1–10 . These studies, however, use the pencil beam position on the nozzle axis.…”

Section: Introductionmentioning

confidence: 99%

“…Gp is proportional to MU Δ and MU Δ can be converted to Gp. The latter conversion is typically parameterized and calibrated with a Faraday cup 10,17 . Approximately,

\begin{equation}{N_{{\rm{Gp}}}} \propto \ {{{N_{{\rm{M}}{{\rm{U}}_\Delta }}}} \mathord{\left/ {\vphantom {{{N_{{\rm{M}}{{\rm{U}}_\Delta }}}} {{S_{{\rm{gas}}}}\left( E \right)}}} \right.

…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Pencil beam scanning dose calibration at reduced source‐to‐axis distance

et al. 2022

View full text Add to dashboard Cite

Background Pencil beam scanning (PBS) monitoring chambers use an ionization control signal, monitor units (MUs), or gigaprotons (Gp) to irradiate a pencil beam and normalize dose calculations. The nozzle deflects the beam from the nozzle axis by an angle subtended at the source‐to‐axis distance (τ) from the isocenter. If the angle is not correctly considered in calibrations or calculations, it can lead to systematic errors. Purpose Aspects to consider for machines of various τs are fourfold. First, for the machine, there is a pathlength change of proton tracks in the monitor chamber. Second, for measurements, a uniform‐square irradiation over a plane, with constant Gp per spot, does not deliver uniform dose in a measurement plane. Third, for Monte Carlo (MC) simulations, Gp (and not MU) is proportional to simulating a number of protons. Fourth, for pencil beam algorithms (PBA), MU or Gp may be used for pencil beam weight, but usage needs to be consistent. Another consideration is the beam shape change from circular to oval in the projection onto voxels. Methods Coordinate systems for PBS delivery are described. Results Users of intermediate‐τ machines, corresponding to the onset of 1% pathlength corrections within the scanned field size, must not assume that MUs are proportional to the number of particles in MC simulations, and the PBA may need pathlength corrections. For a field size of 24 × 24 cm2, intermediate‐τ machines correspond to 59 cm ≤ τ < 120 cm. For a field size of 40 × 40 cm2, intermediate‐τ machines correspond to 98 cm ≤ τ < 200 cm. Small‐τ machines correspond to τ < 59 and 98 cm at these field sizes, respectively, which require corrections in projecting the beam shape onto voxels. Conclusions Identifying corrections due to the pencil beam angle and their onset are important for reducing the outer diameter of proton therapy gantries. The use of Gp (or the number of protons) meterset standardizes data interchange and helps to reduce systematic errors due to the angle of the beam.

show abstract

Ultra‐high dose rate dosimetry: Challenges and opportunities for FLASH radiation therapy

et al. 2022

View full text Add to dashboard Cite

The clinical translation of FLASH radiotherapy (RT) requires challenges related to dosimetry and beam monitoring of ultra‐high dose rate (UHDR) beams to be addressed. Detectors currently in use suffer from saturation effects under UHDR regimes, requiring the introduction of correction factors. There is significant interest from the scientific community to identify the most reliable solutions and suitable experimental approaches for UHDR dosimetry. This interest is manifested through the increasing number of national and international projects recently proposed concerning UHDR dosimetry. Attaining the desired solutions and approaches requires further optimization of already established technologies as well as the investigation of novel radiation detection and dosimetry methods. New knowledge will also emerge to fill the gap in terms of validated protocols, assessing new dosimetric procedures and standardized methods. In this paper, we discuss the main challenges coming from the peculiar beam parameters characterizing UHDR beams for FLASH RT. These challenges vary considerably depending on the accelerator type and technique used to produce the relevant UHDR radiation environment. We also introduce some general considerations on how the different time structure in the production of the radiation beams, as well as the dose and dose‐rate per pulse, can affect the detector response. Finally, we discuss the requirements that must characterize any proposed dosimeters for use in UDHR radiation environments. A detailed status of the current technology is provided, with the aim of discussing the detector features and their performance characteristics and/or limitations in UHDR regimes. We report on further developments for established detectors and novel approaches currently under investigation with a view to predict future directions in terms of dosimetry approaches, practical procedures, and protocols. Due to several on‐going detector and dosimetry developments associated with UHDR radiation environment for FLASH RT it is not possible to provide a simple list of recommendations for the most suitable detectors for FLASH RT dosimetry. However, this article does provide the reader with a detailed description of the most up‐to‐date dosimetric approaches, and describes the behavior of the detectors operated under UHDR irradiation conditions and offers expert discussion on the current challenges which we believe are important and still need to be addressed in the clinical translation of FLASH RT.

show abstract

Faraday cup for commissioning and quality assurance for proton pencil beam scanning beams at conventional and ultra-high dose rates

Cited by 15 publications

References 21 publications

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

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

Pencil beam scanning dose calibration at reduced source‐to‐axis distance

Ultra‐high dose rate dosimetry: Challenges and opportunities for FLASH radiation therapy

Contact Info

Product

Resources

About