-
Ridge-filter crosstalk in conformal proton FLASH planning: dependence on beamlet pitch and iterative mitigation
Authors:
Zongsheng Hu,
Yuting Li,
Henry Meyer,
Xiaochun Wang,
Susan L. McGovern,
Emil Scheueler,
Radhe Mohan,
Uwe Titt
Abstract:
Objective: Patient-specific ridge filters (PSRFs) can enable conformal single-energy proton FLASH delivery without energy switching. However, converting optimized spot-based dose distributions into physically adjacent ridge-filter structures may introduce inter-beamlet modulation errors not captured by conventional isolated-spot optimization. This study characterized ridge-filter (RF) crosstalk, e…
▽ More
Objective: Patient-specific ridge filters (PSRFs) can enable conformal single-energy proton FLASH delivery without energy switching. However, converting optimized spot-based dose distributions into physically adjacent ridge-filter structures may introduce inter-beamlet modulation errors not captured by conventional isolated-spot optimization. This study characterized ridge-filter (RF) crosstalk, evaluated its dependence on the beam-width-to-pitch relationship, and developed an iterative mitigation strategy. Approach: A Monte Carlo dose influence matrix was generated for monoenergetic proton beamlets passing through RFs of varying thickness. A baseline spot-weighted IMPT plan was optimized to meet dose constraints and converted into PSRF geometries. PSRF dose distributions were calculated by explicitly modeling the PSRF in the scanned beam path. RF crosstalk was quantified by comparing PSRF and baseline IMPT plans. Lateral beamlet spacings of 8, 10, 12, and 15 mm were evaluated using gamma analysis, DVH metrics, and mean relative dose difference. An iterative re-optimization method was tested in water-phantom and patient CT geometries. Results: RF crosstalk produced hot and cold spots, reducing agreement between PSRF and baseline IMPT plans. For the same spot size and target geometry, crosstalk increased as beamlet spacing decreased. Iterative re-optimization substantially reduced dose discrepancies, lowering the mean relative dose difference in the target from 8.9% to 3.4% in water and from 3.7% to 1.8% in CT. Significance: RF crosstalk is an important source of dose inconsistency in ridge-filter-based conformal proton FLASH planning. Its dependence on the beam-width-to-pitch relationship and mitigation through iterative re-optimization provide a practical framework for improving the accuracy and robustness of patient-specific single-energy proton FLASH delivery.
△ Less
Submitted 25 June, 2026;
originally announced June 2026.
-
Beam modelling of Hitachi PROBEAT proton therapy system for a GPU-based Fast Monte Carlo dose engine
Authors:
Qianxia Wang,
Poenisch Falk,
Yao Zhao,
Xueming Bai,
Roelf Slopsema,
Kirk Jon Luca,
Thomas J Whitaker,
Yun Hu,
Uwe Titt,
Radhe Mohan,
Pablo Yepes
Abstract:
Background: An in-house dose engine independent of clinic TPS is not only a reliable tool for patient QA verification. More importantly, it plays vital role in cutting-edge research due to its flexibility in implementing new functions. In this study, we upgraded our existing beam model with using double-Gaussian distributions for both spatial and opening angle distributions of particles to obtain…
▽ More
Background: An in-house dose engine independent of clinic TPS is not only a reliable tool for patient QA verification. More importantly, it plays vital role in cutting-edge research due to its flexibility in implementing new functions. In this study, we upgraded our existing beam model with using double-Gaussian distributions for both spatial and opening angle distributions of particles to obtain more accurate phase space files. It is expected to potentially improve the performance of this independent dose engine in both clinic and research at the expanded MD Anderson proton center.
△ Less
Submitted 10 June, 2026;
originally announced June 2026.
-
Optimization of FLASH Proton Beams Using a Track-Repeating Algorithm
Authors:
Qianxia Wang,
Uwe Titt,
Radhe Mohan,
Fada Guan,
Yao Zhao,
Ming Yang,
Pablo Yepes
Abstract:
Methods: A phase space file in a plane at 202 mm downstream of the beam exit window is generated through tuning parameters to match FDC results with measured or MCNPX Monte Carlo-simulated integrated depth-dose distribution (IDD) and lateral dose profiles. To spread out the Bragg peak, widen the beam and reduce the penumbra, a ridge filter (RF), a high-Z material scatterer and a collimator with co…
▽ More
Methods: A phase space file in a plane at 202 mm downstream of the beam exit window is generated through tuning parameters to match FDC results with measured or MCNPX Monte Carlo-simulated integrated depth-dose distribution (IDD) and lateral dose profiles. To spread out the Bragg peak, widen the beam and reduce the penumbra, a ridge filter (RF), a high-Z material scatterer and a collimator with compensator are inserted in the beam path and their shapes and sizes have been optimized. The FDC calculations are validated by comparing Geant4 Monte Carlo simulations. In addition, a set of algorithms to automatically choose the optimum dimensions of the beam shaping elements is developed and tested using the same beams. At the last part, dose rates for optimized beams were estimated by scaling their dose distributions to that of their original beams. Results: The optimized 86.4 MeV beam had an 8.5 mm wide spread-out Bragg peak (SOBP) (proximal 90% to distal 90% of the maximum dose), 14.5 mm, 12.0 mm and 11.0 lateral widths with dose above 50%, 80% and 90% respectively and a 2.5 mm penumbra from 80% to 20% in the lateral profile for the energy. The 159.5 MeV beam had a SOBP of 39.0 mm and the lateral widths with dose above 50%, 80% and 90% of 20.5 mm, 15.0 and 12.5 mm when the source to surface distance (SSD) was 550 mm. Wider lateral widths was obtained with increased SSD. The FDC calculations had passing rates higher than 96% using 3mm/3% as the gamma-index criterion comparing with Geant4 simulations for both energies. The set of automatic algorithms can choose the proper dimensions for the high-density scatterer, RF, collimator and compensator efficiently. And the optimized 159.5 MeV beam with different SDDs had entrance dose rate higher than 40 Gy/s if the entrance dose rate of the original beam was 150 Gy/s.
△ Less
Submitted 30 November, 2021;
originally announced December 2021.
-
Development and application of an optical TPC for charged particle track structure imaging in microdosimetry
Authors:
U. Titt,
V. Dangendorf,
B. Grosswendt,
H. Schuhmacher
Abstract:
An imaging system for measuring the track structure of charged particles in a low-pressure gas is presented. We describe the experimental method and compare experimental results with first results of a simulation of the chamber response.
An imaging system for measuring the track structure of charged particles in a low-pressure gas is presented. We describe the experimental method and compare experimental results with first results of a simulation of the chamber response.
△ Less
Submitted 27 October, 2004;
originally announced October 2004.
-
Imaging of microscopic features of charged-particle tracks in a low-pressure gas
Authors:
V. Dangendorf,
H. Schuhmacher,
U. Titt,
K. Tittelmeier
Abstract:
An imaging system for measuring the spatial distribtion of charged particle tracks in a low-pressure gas is presented. The method is based on an optically read out time projection chamber. Results of experiments with fast heavy ions are shown.
An imaging system for measuring the spatial distribtion of charged particle tracks in a low-pressure gas is presented. The method is based on an optically read out time projection chamber. Results of experiments with fast heavy ions are shown.
△ Less
Submitted 27 October, 2004;
originally announced October 2004.
-
Digital imaging of charged particle track structures with a low-pressure optical time projection chamber
Authors:
U. Titt,
V. Dangendorf,
H. Schuhmacher
Abstract:
We describe first results obtained with a track structure imaging system for measuring the ionisation topology of charged particles in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Images of ionisation tracks of electrons, protons, and heavier ions are presented and analysed.
We describe first results obtained with a track structure imaging system for measuring the ionisation topology of charged particles in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Images of ionisation tracks of electrons, protons, and heavier ions are presented and analysed.
△ Less
Submitted 27 October, 2004;
originally announced October 2004.
-
A time projection chamber with optical readout for charged particle track structure imaging
Authors:
U. Titt,
A. Breskin,
R. Chechik,
V. Dangendorf,
H. Schmidt-Boecking,
H. Schuhmacher
Abstract:
We report about a nuclear track imaging system which is designed to study in detail the ionization topology of charged particle tracks in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Ionization electrons produced by energetic charged particles are three-dimensionally imaged by recording light from electron aval…
▽ More
We report about a nuclear track imaging system which is designed to study in detail the ionization topology of charged particle tracks in a low-pressure gas. The detection method is based on a time projection chamber (TPC) filled with low-pressure triethylamine (TEA). Ionization electrons produced by energetic charged particles are three-dimensionally imaged by recording light from electron avalanches with an intensified CCD system. The detector permits to inves-tigate the spatial ionization distributions of particle tracks in gas, of equivalent length and resolution in tissue of 4 mm and 40 nm (RMS), respectively. We explain the relevance of this technique for dosimetry, describe the experimental method and the basic operation parameters. First results of the chamber response to protons and alpha particles are presented.
△ Less
Submitted 27 October, 2004;
originally announced October 2004.