Helium <scp>CT</scp>: Monte Carlo simulation results for an ideal source and detector with comparison to proton <scp>CT</scp>

Piersimoni, Pierluigi; Faddegon, Bruce A.; Ramos-Méndez, Jose; Schulte, R.; Volz, Lennart; Seco, Joao

doi:10.1002/mp.12942

Cited by 20 publications

(35 citation statements)

References 23 publications

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“…Helium or even heavier ions have been investigated as alternative particles for ion imaging (Parodi, 2014), with the former hypothesised to be optimal in terms of spatial resolution of the images (Collins-Fekete et al, 2016;Piersimoni et al, 2018). Studying these particles in the context of scattering proton CT in detail was beyond the scope of our work, but we share a few considerations here.…”

Section: Discussionmentioning

confidence: 99%

Scattering proton CT

et al. 2020

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Proton computed tomography (CT) is an imaging modality investigated mainly in the context of proton therapy as a complement to x-ray CT. It uses protons with high enough energy to fully traverse the imaged object. Common prototype systems measure each proton's position and direction upstream and downstream of the object as well as the energy loss which can be converted into the water equivalent thickness. A reconstruction algorithm then produces a map of the relative stopping power in the object. As an alternative to energy-loss proton CT, it has been proposed to reconstruct a map of the object's scattering power based on the protons' angular dispersion which can be estimated from the measured directions. As in energy-loss proton CT, reconstruction should best be performed considering the non-linear shape of proton trajectories due to multiple Coulomb scattering, but no algorithm to achieve this is so far available in the literature. In this work, we propose a filtered backprojection algorithm with distance-driven binning to account for the protons' most likely path. Furthermore, we present a systematic study of scattering proton CT in terms of inherent noise and spatial resolution and study the artefacts which arise from the physics of multiple Coulomb scattering. Our analysis is partly based on analytical models and partly on Monte Carlo simulations. Our results show that the proposed algorithm performs well in reconstructing relative scattering power maps, i.e. scattering power relative to that of water. Spatial resolution is improved by almost a factor of three compared to straight line projection and is comparable to energy-loss proton CT. Image noise, on the other hand, is inherently much higher. For example, in a water cylinder of 20 cm diameter, representative of a human head, noise in the central image pixel is about 40 times higher in scattering proton CT than in energy-loss proton CT. Relative scattering power in dense regions such as bone inserts is systematically underestimated by a few percent, depending on beam energy and phantom geometry.

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Section: Discussionmentioning

confidence: 99%

Scattering proton CT

et al. 2020

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“…This work presented a theoretical assessment using Monte Carlo simulations of the effect of magnetic fields on dose distributions from brachytherapy. The Monte Carlo method has proved its validity when an experimental measurement is difficult to perform, as in the assessment of theoretical predictions, development of prototyped technology, and analysis of uncertainties [6,8,36,37]. In these kinds of applications, well-controlled conditions and prior verification of the components involved (physics models and geometry models) must be ensured.…”

Section: Discussionmentioning

confidence: 99%

Monte Carlo simulation of the effect of magnetic fields on brachytherapy dose distributions in lung tissue material

et al. 2020

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The aim of this work was to use TOPAS Monte Carlo simulations to model the effect of magnetic fields on dose distributions in brachytherapy lung treatments, under ideal and clinical conditions. Idealistic studies were modeled consisting of either a monoenergetic electron source of 432 keV, or a polyenergetic electron source using the spectrum of secondary electrons produced by 192 Ir gamma-ray irradiation. The electron source was positioned in the center of a homogeneous, lung tissue phantom (ρ = 0.26 g/cm 3). Conversely, the clinical study was simulated using the VariSource VS2000 192 Ir source in a patient with a lung tumor. Three contoured volumes were considered: the tumor, the planning tumor volume (PTV), and the lung. In all studies, dose distributions were calculated in the presence or absence of a constant magnetic field of 3T. Also, TG-43 parameters were calculated for the VariSource and compared with published data from EGS-brachy (EGSnrc) and PENEL-OPE. The magnetic field affected the dose distributions in the idealistic studies. For the monoenergetic and poly-energetic studies, the radial distance of the 10% iso-dose line was reduced in the presence of the magnetic field by 64.9% and 24.6%, respectively. For the clinical study, the magnetic field caused differences of 10% on average in the patient dose distributions. Nevertheless, differences in dose-volume histograms were below 2%. Finally, for TG-43 parameters, the dose-rate constant from TOPAS differed by 0.09% ± 0.33% and 0.18% ± 0.33% with respect to EGS-brachy and PENELOPE, respectively. The geometry and anisotropy functions differed within 1.2% ± 1.1%, and within 0.0% ± 0.3%, respectively. The Lorentz forces inside a 3T magnetic resonance machine during 192 Ir brachytherapy treatment of the lung are not large enough to affect the tumor dose distributions significantly, as expected. Nevertheless, large local differences were found in the lung tissue. Applications of this effect are therefore limited by the fact that meaningful differences appeared only in regions containing air, which is not abundant inside the human.

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“…In recent years, along with protons, heavier ions (mostly helium or carbon) have been considered for imaging given their smaller deviation due to multiple Coulomb scattering. The expected effect of an improved spatial resolution was observed, once the ion fragmentation was taken into account [25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 90%

“…The phantom is made of an epoxy cylinder of 40 mm height, and 150 mm diameter, and contains eight cylindrical cavities of 12.2 mm diameter, six of which are filled with different plastic inserts, and 2 with air. For material and compositions please refer to Table I in Piersimoni et al [30]. RSP values for each material were calculated from MC simulations and are: 1.363 (Delrin), 1.179 (PMMA), 1.048 (Polystyrene), 1.003 (LDPE), 0.886 (PMP), 1.833 (Teflon), and 1.143 (Epoxy).…”

Section: Simulated Phantomsmentioning

confidence: 99%

“…The data were divided into 40 optimization blocks per iteration and the algorithm was stopped after eight iterations. The reconstruction parameters were kept the same as in previous studies [18,19,30,31] investigating the same phantoms with different detector designs, such that a direct comparison between different pCT systems is possible. Optimization of the parameter settings for the single-sided design was out of the scope of this work.…”

Section: Image Reconstructionmentioning

confidence: 99%

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A High-Granularity Digital Tracking Calorimeter Optimized for Proton CT

Alme¹,

Barnaföldi²,

Barthel³

et al. 2020

Front. Phys.

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A typical proton CT (pCT) detector comprises a tracking system, used to measure the proton position before and after the imaged object, and an energy/range detector to measure the residual proton range after crossing the object. The Bergen pCT collaboration was established to design and build a prototype pCT scanner with a high granularity digital tracking calorimeter used as both tracking and energy/range detector. In this work the conceptual design and the layout of the mechanical and electronics implementation, along with Monte Carlo simulations of the new pCT system are reported. The digital tracking calorimeter is a multilayer structure with a lateral aperture of 27 cm × 16.6 cm, made of 41 detector/absorber sandwich layers (calorimeter), with aluminum (3.5 mm) used both as absorber and carrier, and two additional layers used as tracking system (rear trackers) positioned downstream of the imaged object; no tracking upstream the object is included. The rear tracker's structure only differs from the calorimeter layers for the carrier made of ∼200 μm carbon fleece and carbon paper (carbon-epoxy sandwich), to minimize scattering. Each sensitive layer consists of 108 ALICE pixel detector (ALPIDE) chip sensors (developed for ALICE, CERN) bonded on a polyimide flex and subsequently bonded to a larger flexible printed circuit board. Beam tests tailored to the pCT operation have been performed using high-energetic (50-220 MeV/u) proton and ion beams at the

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Helium CT: Monte Carlo simulation results for an ideal source and detector with comparison to proton CT

Abstract: MC simulations were used to compare HeCT and pCT image reconstruction. HeCT images had similar or better RSP accuracy and higher spatial resolution compared to pCT. Further investigation of the potential of helium ion imaging is warranted.

Cited by 20 publications

References 23 publications

Scattering proton CT

Scattering proton CT

Monte Carlo simulation of the effect of magnetic fields on brachytherapy dose distributions in lung tissue material

A High-Granularity Digital Tracking Calorimeter Optimized for Proton CT

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