arXiv subjects

Frank Van den Heuvel

Publications and source records attributed to Frank Van den Heuvel.

5 recordsLinked to original sources

arXiv2025

LET measurements and simulation modelling of the charged particle field for the Clatterbridge ocular proton therapy beamline

Proton therapy can achieve a highly targeted treatment by utilising the advantageous dosimetric characteristics of the Bragg Peak. Protons traversing through a material will deposit their maximum energy at the Bragg Peak through ionisation and other interactions, transferring minimal excess dose to surrounding tissue and organs. This rate of energy loss is also quantified by the linear energy transfer (LET), which is indicative of radiation quality and radiobiological effects. However it is a challenging physical quantity to measure, as characterisation of radiation fields and the impact of LET on treatment requires advanced tools and technology. The MiniPIX-Timepix is a miniaturised, hybrid semiconductor pixel detector capable of high resolution spectrometric tracking, enabling wide-range detection of the deposited energy, position and direction of single particles. Experimental measurements were performed at a clinical facility, the Clatterbridge Cancer Centre which houses a 60 MeV ocular proton therapy beamline. A realistic end-to-end model of the facility was developed in the Monte Carlo code TOPAS (TOol for PArticle Simulation) and was used to simulate the experimental conditions. The detector was held at 45$^{\circ}$ and 60$^{\circ}$ perpendicular to the beam, and placed downstream of various thickness Polymethyl methacrylate (PMMA) blocks to acquire data along the dose deposition depth. Empirical cluster data providing track length and the energy deposition distributions were used to obtain the LET spectra. The determined values for the LET in silicon and dose averaged LET across the BP show general agreement with simulated results, supporting the applicability of the TOPAS CCC model. This work explores the capability of the MiniPIX detector to measure physical quantities to resolve the LET, and discusses experimental considerations and further possibilities.

physics.med-ph↗

arXiv2016

Using Stable Distributions to Characterize Proton Pencil Beams

Purpose: To introduce and evaluate the use of stable distributions as a means of describing the behavior of charged particle pencil beams in a medium, with specific emphasis on proton beam scanning (PBS). Methods: The proton pencil beams of a clinically commissioned proton treatment facility are replicated in a Monte Carlo simulation system (FLUKA). For each available energy the beam deposition in water medium is characterized by the dose deposition. Using an alpha--stable distribution methodology each beam with a nominal energy $E$ is characterized by the lateral spread at depth $z$: $S(z;α,γ,E)$ and a total energy deposition $I_D(z)$. The beams are then described as a function of the variation of the parameters at depth. Finally, an implementation in a freely available open source dose calculation suite (matRad, DKFZ, Heidelberg, Germany) is proposed. Results: Quantitatively, the fit of the stable distributions, compared to those implemented in standard treatment planning systems, are equivalent. The efficiency of the representation is better (2 compared to 3 and more parameters needed). The meta--parametrization (i.e. the description of the dose deposition by only providing the fitted parameters) allows for interpolation of non--measured data. In the case of the clinical data used in this paper, it was possible to only commission 1 out of 5 nominal energies to obtain a viable data set. Conclusions: Alpha--stable distributions are intrinsically suited to describe charged particle pencil beams in a medium and can be easily implemented in existing treatment planning systems. The use of alpha-distributions can easily be extended to other particles.

physics.med-ph↗

arXiv2014

A closed parameterization of DNA-damage by charged particles as a function of energy - A geometrical approach

Purpose: To present a closed formalism calculating charged particle radiation damage induced in DNA. The formalism is valid for all types of charged particles and due to its closed nature is suited to provide fast conversion of dose to DNA-damage. Methods: The induction of double strand breaks in DNA--strings residing in irradiated cells is quantified using a single particle model. This leads to a proposal to use the cumulative Cauchy distribution to express the mix of high and low LET type damage probability generated by a single particle. A microscopic phenomenological Monte Carlo code is used to fit the parameters of the model as a function of kinetic energy related to the damage to a DNA molecule embedded in a cell. The model is applied for four particles: electrons, protons, alpha--particles, and carbon ions. A geometric interpretation of this observation using the impact ionization mean free path as a quantifier, allows extension of the model to very low energies. Results: The mathematical expression describes the model adequately using a chi--square test ($χ^2/NDF < 1$). This applies to all particle types with an almost perfect fit for protons, while the other particles seem to result in some discrepancies at very low energies. The implementation calculating a strict version of the RBE based on complex damage alone is corroborated by experimental data from the measured RBE. The geometric interpretation generates a unique dimensionless parameter $k$ for each type of charged particle. In addition, it predicts a distribution of DNA damage which is different from the current models.

physics.med-ph↗

arXiv2011

Companding technique for high dynamic range measurements using gafchromic films

We propose a methodology to perform dose measurements using gafchromic films which can span several decades of dose levels. The technique is based on a rescaling approach using different films irradiated at different dose levels. This is combined with a registration protocol correcting positioning and scaling factors for each film.

physics.med-ph↗

arXiv2011

Gafchromic film dosimetry: calibration methodology and error analysis

Purpose : To relate the physical transmittance parameters of the water equivalent Gafchromic EBT 2 Film with the delivered dose in a transparent absolute calibration protocol. The protocol should be easy to understand, easy to perform, and should be able to predict the residual dose error. Conclussions : The gafchromic EBT2 Films are properly calibrated with an accessible robust calibration protocol. The protocol largely deals with the uniformity problems of the Film. The proposed method allowed to relate the dose with the red channel transmittance using only T0, T_inf, and a dose scaling factor. Based on the local and global uniformity the red channel dose errors could be predicted to be smaller than 5%.

physics.med-ph↗