arXiv subjects

Lucas Burigo

Publications and source records attributed to Lucas Burigo.

7 recordsLinked to original sources

arXiv2024

Ionization detail parameters and cluster dose: A mathematical model for selection of nanodosimetric quantities for use in treatment planning in charged particle radiotherapy

Objective: To propose a mathematical model for applying Ionization Detail (ID), the detailed spatial distribution of ionization along a particle track, to proton and ion beam radiotherapy treatment planning (RTP). Approach: Our model provides for selection of preferred ID parameters (I_p) for RTP, that associate closest to biological effects. Cluster dose is proposed to bridge the large gap between nanoscopic I_p and macroscopic RTP. Selection of I_p is demonstrated using published cell survival measurements for protons through argon, comparing results for nineteen Ip: N_k; k = 2,3,...,10, the number of ionizations in clusters of k or more per particle, and F_k; k = 1,2,...,10, the number of clusters of k or more per particle. We then describe application of the model to ID-based RTP and propose a path to clinical translation. Main results: The preferred I_p were N_4 and F_5 for aerobic cells, N_5 and F_7 for hypoxic cells. Signifcant differences were found in cell survival for beams having the same LET or the preferred N_k. Conversely, there was no signi?cant difference for F_5 for aerobic cells and F_7 for hypoxic cells, regardless of ion beam atomic number or energy. Further, cells irradiated with the same cluster dose for these I_p had the same cell survival. Based on these preliminary results and other compelling results in nanodosimetry, it is reasonable to assert that I_p exist that are more closely associated with biological effects than current LET-based approaches and microdosimetric RBE-based models used in particle RTP. However, more biological variables such as cell line and cycle phase, as well as ion beam pulse structure and rate still need investigation. Signifcance: Our model provides a practical means to select preferred I_p from radiobiological data, and to convert I_p to the macroscopic cluster dose for particle RTP.

physics.med-ph↗

arXiv2022

Multivariate error modeling and uncertainty quantification using importance (re-)weighting for Monte Carlo simulations in particle transport

Fast and accurate predictions of uncertainties in the computed dose are crucial for the determination of robust treatment plans in radiation therapy. This requires the solution of particle transport problems with uncertain parameters or initial conditions. Monte Carlo methods are often used to solve transport problems especially for applications which require high accuracy. In these cases, common non-intrusive solution strategies that involve repeated simulations of the problem at different points in the parameter space quickly become infeasible due to their long run-times. Intrusive methods however limit the usability in combination with proprietary simulation engines. In our previous paper [51], we demonstrated the application of a new non-intrusive uncertainty quantification approach for Monte Carlo simulations in proton dose calculations with normally distributed errors on realistic patient data. In this paper, we introduce a generalized formulation and focus on a more in-depth theoretical analysis of this method concerning bias, error and convergence of the estimates. The multivariate input model of the proposed approach further supports almost arbitrary error correlation models. We demonstrate how this framework can be used to model and efficiently quantify complex auto-correlated and time-dependent errors.

physics.med-ph↗

arXiv2021

Efficient uncertainty quantification for Monte Carlo dose calculations using importance (re-)weighting

The high precision and conformity of intensity-modulated particle therapy (IMPT) comes at the cost of susceptibility to treatment uncertainties in particle range and patient set-up. Dose uncertainty quantification and mitigation, which is usually based on sampled error scenarios, however becomes challenging when computing the dose with computationally expensive but accurate Monte Carlo (MC) simulations. This paper introduces an importance (re-)weighting method in MC history scoring to concurrently construct estimates for error scenarios, the expected dose and its variance from a single set of MC simulated particle histories. The approach relies on a multivariate Gaussian input and uncertainty model, which assigns probabilities to the initial phase space sample, enabling the use of different correlation models. Exploring and adapting bivariate emittance parametrizations for the beam shape, accuracy can be traded between that of the uncertainty or the nominal dose estimate. The method was implemented using the MC code TOPAS and tested for proton IMPT plan delivery in comparison to a reference scenario estimate. We achieve accurate results for set-up uncertainties ($γ_{3mm/3\%} \geq 99.99\%$) and expectedly lower but still sufficient agreement for range uncertainties, which are approximated with uncertainty over the energy distribution ($γ_{3 mm/3\%} \geq 99.50\%$ ($E[\boldsymbol{d}]$), $γ_{3mm/3\%} \geq 91.69\%$ ($σ(\boldsymbol{d})$) ). Initial experiments on a water phantom, a prostate and a liver case show that the re-weighting approach lowers the CPU time by more than an order of magnitude. Further, we show that uncertainty induced by interplay and other dynamic influences may be approximated using suitable error correlation models.

physics.med-ph↗

arXiv2019

Impact of new ICRU90 key data on stopping-power ratios and beam quality correction factors for carbon ion beams

The recent update of dosimetric key data by the `International Commission on Radiation Units and Measurements' impacts the computation of beam quality correction factors $k_Q$ via several changes, e.g. for the mean excitation energies, $I$, which enters the stopping power computation for water and air, the computation procedure itself, the average energy expended in the production of an ion pair in air, $W/e$, as well as chamber perturbation factors for Cobalt-60. An accurate assessment of water-to-air stopping-power ratio, $s_{\rm w,air}$, in reference conditions with new recommendation is necessary to update the dosimetry protocols for carbon ion beams. The new ICRU90 key data were considered for computation of $s_{\rm w,air}$ for carbon ion beams using Monte Carlo transport simulations for a number of reference conditions, namely monoenergetic carbon ion beams with range in water from 3 to 30\,cm and Spread-Out Bragg peaks (SOBPs) of different widths and depths in water. New recommendations for $s_{\rm w,air}$ are presented, namely 1.1247 for the reference condition of 1\,g\,cm$^{-2}$ depth for monoenergetic carbon ion beams and 1.1274 at the center of physically-optimized SOBPs. The recommendation of a constant value (1.126) represents the stopping-power ratio within a 0.3\,\% variation of $s_{\rm w,air}$ for the different reference conditions. The impact of these new $s_{\rm w,air}$ values and the updated key data on the $k_Q$ for carbon ion beams was evaluated in a second step. The changes agree very well with experimental data for the case of cylindrical ionization chambers, but larger discrepancies are observed for plate-parallel ionization chambers.

physics.med-ph↗

arXiv2014

Comparative study of RBE and cell survival fractions for $^{1}$H, $^{4}$He, $^{12}$C and $^{16}$O beams using Geant4 and Microdosimetric Kinetic model

Beams of $^{4}$He and $^{16}$O nuclei are considered for ion-beam cancer therapy as alternative options to protons and $^{12}$C nuclei. Spread-out Bragg peak (SOBP) distributions of physical dose and relative biological effectiveness for 10% survival are calculated by means of our Geant4-based Monte Carlo model for Heavy Ion Therapy (MCHIT) and the modified microdosimetric kinetic model. The depth distributions of cell survival fractions are calculated for $^{1}$H, $^{4}$He, $^{12}$C and $^{16}$O for tissues with normal (HSG cells), low and high radiosensitivity. In each case the cell survival fractions were compared separately for the target volume, behind and in front of it. In the case of normal radiosensitivity $^{4}$He and $^{12}$C better spare tissues in the entrance channel compared to protons and $^{16}$O. The cell survival fractions calculated, respectively, for the entrance channel and target volume are similar for $^{4}$He and $^{12}$C. When it is important to spare healthy tissues located after the distal edge of the SOBP plateau, $^{4}$He can be recommended due to reduced nuclear fragmentation of these projectiles. No definite advantages of $^{16}$O with respect to $^{12}$C were found, with the except of an enhanced impact of these heavier projectiles on radioresistant tumors.

physics.med-ph↗

arXiv2013

Microdosimetry spectra and RBE of H-1, He-4, Li-7 and C-12 nuclei in water studied with Geant4

A Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) is used to study radiation fields of H-1, He-4, Li-7 and C-12 beams with similar ranges (~160-180 mm) in water. Microdosimetry spectra are simulated for wall-less and walled Tissue Equivalent Proportional Counters (TEPCs) placed outside or inside a phantom, as in experiments performed, respectively, at NIRS, Japan and GSI, Germany. The impact of fragmentation reactions on microdosimetry spectra is investigated for He-4, Li-7 and C-12, and contributions from nuclear fragments of different charge are evaluated for various TEPC positions in the phantom. The microdosimetry spectra measured on the beam axis are well described by MCHIT, in particular, in the vicinity of the Bragg peak. However, the simulated spectra for the walled TEPC far from the beam axis are underestimated. Relative Biological Effectiveness (RBE) of the considered beams is estimated using a modified microdosimetric-kinetic model. Calculations show a similar rise of the RBE up to 2.2-2.9 close to the Bragg peak for helium, lithium and carbon beams compared to the modest values of 1-1.2 at the plateau region. Our results suggest that helium and lithium beams are also promising options for cancer therapy.

physics.med-ph↗

arXiv2013

Microdosimetry of radiation field from therapeutic C-12 beam in water: a study with Geant4 toolkit

We model the responses of Tissue-Equivalent Proportional Counters (TEPC) to radiation fields of therapeutic C-12 beams in a water phantom and to quasi-monoenergetic neutrons in a PMMA phantom. Simulations are performed with the Monte Carlo model for Heavy Ion Therapy (MCHIT) based on the Geant4 toolkit. The shapes of the calculated lineal energy spectra agree well with measurements in both cases. The influence of fragmentation reactions on the TEPC response to a narrow pencil-like beam with its width smaller than the TEPC diameter is investigated by Monte Carlo modeling. It is found that total lineal energy spectra are not very sensitive to the choice of the nuclear fragmentation model used. The calculated frequency-mean lineal energy y_f differs from the data on the axis of a therapeutic beam by less than 10% and by 10-20% at other TEPC positions. The validation of MCHIT with neutron beams gives us confidence in estimating the contributions to lineal energy spectra due to secondary neutrons produced in water by C-12 nuclei. As found, the neutron contribution at 10 cm distance from the beam axis amounts to ~ 50% close the entrance to the phantom and decreases to ~ 25% at the depth of the Bragg peak and beyond it. The presented results can help in evaluating biological out-of-field doses in carbon-ion therapy.

physics.med-ph↗