Deriving the mean excitation energy map from dual-energy and proton computed tomography

Vilches-Freixas, Gloria; Quiñones, C. T.; Létang, Jean Michel; Rit, Simon

doi:10.1016/j.phro.2018.04.001

Cited by 4 publications

(3 citation statements)

References 32 publications

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“…These additional quantities can be obtained through tabulated conversion from another quantity (Kanematsu et al, 2012). Alternatively, scattering proton CT could be combined with energy-loss proton CT, or even with x-ray based CT (Vilches-Freixas et al, 2018), to provide complementary information to the TPS. The accuracy of such a combined direct measurement would have to be at least as good as the one associated with a modelbased conversion.…”

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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“…With the clinical availability of proton therapy, the requirements for CT-based density estimation changed enormously as stopping power determination and dose calculation depend strongly on the tissue composition [26] , [27] . Consequently, dual energy CT (DECT) was proposed as an alternative CT-technique for proton therapy planning [28] , [29] , [30] , [31] , [32] , [33] , [34] . Furthermore, time-resolved CT imaging, so-called 4D-CT, has been shown to inform about tumor and organ motion and thus provide valuable information to be integrated into RT planning and delivery [24] , [35] , [36] .…”

Section: Ct Imaging For Rtmentioning

confidence: 99%

Imaging science and development in modern high-precision radiotherapy

Thorwarth

Muren

2019

Physics and Imaging in Radiation Oncology

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“…There has however recently been a number of DECT papers presenting alternative DECT formulations, often to little benefit over existing methods, which is the topic of another article in this special issue [11] . While the survey of Taasti et al alludes to the competition between DECT and the pre-clinical concept of proton CT, where stopping power is measured directly to a high accuracy [12] , an innovative paper from Vilches-Freixas et al [13] proposes their combination as a novel means of directly imaging the mean excitation energy, or I-value, a non-negligible source of uncertainty in proton therapy [14] .…”

Section: Dual Energy Ct Imaging For Proton Therapymentioning

confidence: 99%