Monte Carlo simulations play a crucial role for in-vivo treatment monitoring based on PET and prompt gamma imaging in proton and carbon-ion therapies. The accuracy of the nuclear fragmentation models ...implemented in these codes might affect the quality of the treatment verification. In this paper, we investigate the nuclear models implemented in GATE Geant4 and FLUKA by comparing the angular and energy distributions of secondary particles exiting a homogeneous target of PMMA. Comparison results were restricted to fragmentation of 16O and 12C. Despite the very simple target and set-up, substantial discrepancies were observed between the two codes. For instance, the number of high energy (>1 MeV) prompt gammas exiting the target was about twice as large with GATE Geant4 than with FLUKA both for proton and carbon ion beams. Such differences were not observed for the predicted annihilation photon production yields, for which ratios of 1.09 and 1.20 were obtained between GATE and FLUKA for the proton beam and the carbon ion beam, respectively. For neutrons and protons, discrepancies from 14% (exiting protons-carbon ion beam) to 57% (exiting neutrons-proton beam) have been identified in production yields as well as in the energy spectra for neutrons.
A Compton camera is being developed for the purpose of ion-range monitoring during hadrontherapy via the detection of prompt-gamma rays. The system consists of a scintillating fiber beam tagging ...hodoscope, a stack of double sided silicon strip detectors (90 Â 90 Â 2 mm 3 , 2 Â 64 strips) as scatter detectors, as well as bismuth germanate (BGO) scintillation detectors (38 Â 35 Â 30 mm 3 , 100 blocks) as absorbers. The individual components will be described, together with the status of their characterization.
This paper presents a study of energy deposits induced by ionising particles in liquid water at the molecular scale. Particles track structures were generated using the Geant4-DNA processes of the ...Geant4 Monte-Carlo toolkit. These processes cover electrons (0.025
eV–1
MeV), protons (1
keV–100
MeV), hydrogen atoms (1
keV–100
MeV) and alpha particles (10
keV–40
MeV) including their different charge states. Electron ranges and lineal energies for protons were calculated in nanometric and micrometric volumes.
•Quantitative estimation of beta + emitters production rates with the GEANT4 simulation toolkit at 55, 65, 120 and 220 MeV.•Comparison of the 55 MeV simulated production rates to data from Dendooven ...et al.•Comparison of the simulated β+ activity profiles to those extracted from experimental data.•Study of 12N which, from the work of Dendooven et al., is known to be the main isotope for in-beam PET.
The purpose of this work is to evaluate the precision with which the GEANT4 toolkit simulates the production of β+ emitters relevant for in-beam and real-time PET in proton therapy.
An important evolution in proton therapy is the implementation of in-beam and real-time verification of the range of protons by measuring the correlation between the activity of β+ and dose deposition.
For that purpose, it is important that the simulation of the various β+ emitters be sufficiently realistic, in particular for the 12N short-lived emitter that is required for efficient in-beam and real-time monitoring.
The GEANT4 toolkit was used to simulate positron emitter production for a proton beam of 55 MeV in a cubic PMMA target and results are compared to experimental data.
The three β+ emitters with the highest production rates in the experimental data (11C, 15O and 12N) are also those with the highest production rate in the simulation. Production rates differ by 8% to 174%. For the 12N isotope, the β+ spatial distribution in the simulation shows major deviations from the data. The effect of the long range (of the order of 20 mm) of the β+ originating from 12N is also shown and discussed.
At first order, the GEANT4 simulation of the β+ activity presents significant deviations from the data. The need for precise cross-section measurements versus energy below 30 MeV is of first priority in order to evaluate the feasibility of in-beam and real-time PET.
•Clustered distributions of gold nanoparticles in a cell induce higher radiation effect than uniform distributions.•The distance between nanoparticles clusters and cellular substructures affects the ...enhancement ratio.•The radiation enhancement ratio depends on distant interactions like chemical species diffusion.
This paper presents a Monte-Carlo study focusing on the effects of gold nanoparticles on the energy deposition patterns produced by incident photons in the close vicinity of the mitochondrial network modeled as a tube. Spherical shaped gold nanoparticles of 30 nm diameter were placed in a micrometric (10 × 10 × 10 μm3) water phantom containing a tube of 300 nm diameter and 5 μm length. The tube represented a mitochondrial fragment and nanoparticles were distributed in the water phantom outside the tube. Photons of 120 keV were simulated using the Geant4 Livermore processes and the Geant4-DNA electron processes to account for secondary electrons collisions. The Livermore processes took into account the Auger cascade inside the gold material. A data mining algorithm was then used to analyze the energy deposition clusters inside the water phantom and the tube. A comparison was made between the results obtained for a uniform distribution of nanoparticles and a vesicle distribution model. The results including energy deposition clusters are also compared to dose enhancement ratios.
The commissioning of an ion beam for hadrontherapy requires the evaluation of the biologically weighted effective dose that results from the microdosimetric properties of the therapy beam. The ...spectra of the energy imparted at cellular and sub-cellular scales are fundamental to the determination of the biological effect of the beam. These magnitudes are related to the microdosimetric distributions of the ion beam at different points along the beam path. This work is dedicated to the measurement of microdosimetric spectra at several depths in the central axis of a 12C beam with an energy of 94.98 AMeV using a novel 3D ultrathin silicon diode detector. Data is compared with Monte Carlo calculations providing an excellent agreement (deviations are less than 2% for the most probable lineal energy value) up to the Bragg peak. The results show the feasibility to determine with high precision the lineal energy transfer spectrum of a hadrontherapy beam with these silicon devices.
In hadrontherapy in order to fully take advantage of the assets of the ion irradiation, the position of the Bragg peak has to be monitored accurately. Here, we investigate a monitoring method relying ...on the detection in real time of the prompt γ emitted quasi instantaneously during the nuclear fragmentation processes. Our detection system combines a beam hodoscope and a double scattering Compton camera. The prompt-γ emission points are reconstructed by intersecting the ion trajectories given by the hodoscope and the Compton cones reconstructed with the camera. We propose here to study in terms of point spread function and efficiency the theoretical feasibility of the emission points reconstruction with our set-up in the case of a photon point source in air. First we analyze the nature of all the interactions which are likely to produce an energy deposit in the three detectors of the camera. It is underlined that upper energy thresholds in both scatter detectors are required in order to select mainly Compton events (one Compton interaction in each scatter detector and one interaction in the absorber detector). Then, we study the influence of various parameters such as the photon energy and the inter-detector distances on the Compton camera response. These studies are carried out by means of Geant4 simulations. We use a source with a spectrum corresponding to the prompt-γ spectrum emitted during the carbon ion irradiation of a water phantom. In the current configuration, the spatial resolution of the Compton camera is about 6 mm (Full Width at Half Maximum) and the detection efficiency 10 -5 . Finally, provided the detection efficiency is increased, the clinical applicability of our system is considered.
Light and heavy ions particle therapy, mainly by means of protons and carbon ions, represents an advantageous treatment modality for deep-seated and/or radioresistant tumours. An in-beam quality ...assurance principle is based on the detection of secondary particles induced by nuclear fragmentations between projectile and target nuclei. Three different strategies are currently under investigation: prompt γ rays imaging, proton interaction vertex imaging and in-beam positron emission tomography. Geant4 simulations have been performed first in order to assess the accuracy of some hadronic models to reproduce experimental data. Two different kinds of data have been considered: β+-emitting isotopes and prompt γ-ray production rates. On the one hand simulations reproduce experimental β+ emitting isotopes production rates to an accuracy of 24%. Moreover simulated β+ emitting nuclei production rate as a function of depth reproduce well the peak-to-plateau ratio of experimental data. On the other hand by tuning the tolerance factor of the photon evaporation model available in Geant4, we reduce significantly prompt γ-ray production rates until a very good agreement is reached with experimental data. Then we have estimated the total amount of induced annihilation photons and prompt γ rays for a simple treatment plan of ∼1 physical Gy in a homogenous equivalent soft tissue tumour (6 cm depth, 4 cm radius and 2 cm wide). The average annihilation photons emitted during a 45 s irradiation in a 4 π solid angle are ∼2 × 106 annihilation photon pairs and 108 single prompt γ whose energy ranges from a few keV to 10 MeV.
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