The potential of photon-counting CT for quantitative contrast-enhanced imaging in radiotherapy

Simard, Mikaël; Lapointe, Andréanne; Lalonde, Arthur; Bahig, Houda; Bouchard, Hugo

doi:10.1088/1361-6560/ab1af1

Cited by 16 publications

(49 citation statements)

References 35 publications

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“…For instance, the presented MAP framework cannot be used for contrast-enhanced imaging, although adaptations are possible. 18 The MAP framework might also not be adapted if characterizing tissues with an unconventional composition that differs from those in the tabulated tissue data used to generate the prior. Furthermore, small anatomical features of odd properties might be smoothened out with this framework.…”

Section: Discussionmentioning

confidence: 99%

“…Other models aim at estimating elemental compositions within a voxel as input for Monte Carlo simulations. 10,17,18 B€ ar et al 3 investigated the influence of image noise on the proton range uncertainty within a theoretical scope. They simulated SECT and DECT images of a humanoid phantom with different levels of image noise and analyzed the influence of noise on the beam range.…”

Section: Introductionmentioning

confidence: 99%

“…

Z_{med}

is then used to estimate the I ‐value of the respective material, 2,7 which is used together with

ρ_{e}

to calculate the SPR according to Bethe’s formula. Other models aim at estimating elemental compositions within a voxel as input for Monte Carlo simulations 10,17,18 …”

Section: Introductionmentioning

confidence: 99%

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Electron density and effective atomic number estimation in a maximum a posteriori framework for dual‐energy computed tomography

et al. 2020

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The stoichiometric calibration method for dual-energy CT (DECT) proposed by Bourque et al. (Phys Med Biol. 59:2059; 2014), which provides estimators of the electron density and the effective atomic number, is adapted to a maximum a posteriori (MAP) framework to increase the model's robustness to noise and biases in CT data, specifically for human tissues. Robust physical parameter estimation from noisy DECT scans is required to maximize the precision of quantities used for radiotherapy treatment planning such as the proton stopping power (SPR). Methods: Estimation of electron density and effective atomic number is performed by constraining their variation to the natural range of values expected for human tissues, while maximizing attenuation data fidelity. The MAP framework is first compared against the original method using theoretical CT numbers with Gaussian noise. The quantitative accuracy of the MAP framework is then validated experimentally on the Gammex 467 phantom. Then, using two clinical datasets, the advantages of the approach are experimentally evaluated, qualitatively, and quantitatively. Results: The theoretical study shows that the root-mean-square error on the electron density, the effective atomic number and the SPR are, respectively, reduced from 2.3 to 1.5, 5.7 to 3.2 and 2.8 to 1.7% with the adapted framework, when analyzing soft tissues and bone together. The experimental validation study shows that the standard deviation in Gammex inserts can be reduced, on average, by factors of 1.4 (electron density), 2.7 (effective atomic number), and 1.9 (SPR), while the quantitative accuracy of the three physical parameters is preserved, on average. Evaluation on clinical datasets show apparent noise reduction in maps of all estimated physical quantities, and suggests that the MAP framework has increased robustness to beam hardening and photon starvation artifacts. Mean values for the electron density, the effective atomic number, and the SPR averaged in four uniform regions of interest (brain, muscle, adipose, and cranium), respectively, differ by 0.7, 1.8, and 0.9% between both frameworks. The standard deviation in the same regions of interest is also reduced, on average, by factors of 1.8, 6.6, and 3.2 with the MAP framework. Differences in mean value and standard deviations are statistically significant. Conclusion: Theoretical and experimental results suggest that the MAP framework produces more accurate and precise estimates of the electron density and SPR. Thus, the present approach limits the propagation of noise in DECT attenuation data to radiotherapy-related parameters maps such as the SPR and the electron density. Using a MAP framework with DECT for radiotherapy treatment planning can help maximizing the precision of dose calculation. The method also provides more precise estimates of the effective atomic number. The MAP methodology is presented in a general way such that it can be adapted to any DECT image-based tissue characterization method.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron density and effective atomic number estimation in a maximum a posteriori framework for dual‐energy computed tomography

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“…The RMS errors on the VNC electron densities of the Kidney1 tissue inserts were relatively higher than the reported RMS errors for soft tissues. 21 The main reasons for this were discussed in Appendix C2.…”

Section: Discussionmentioning

confidence: 99%

“…Using the Bayesian eigentissue decomposition (Bayesian ETD) method, the radiotherapy-related parameters of the virtual non-contrast (VNC) tissue electron density and iodine contrast agent fraction were also quantitatively estimated for contrast-enhanced spectral CT of the proposed OBI. 21 The VNC tissue electron density can be used for radiation dose calculation, and the contrast agent uptake is related to functional/molecular changes within tumors. 22 The details of the method and the phantom experiment were described in Appendix A5.…”

Section: E Energy-resolved Spectral Ctmentioning

confidence: 99%

A Monte Carlo study to investigate the feasibility of an on‐board SPECT/spectral‐CT/CBCT imager for medical linear accelerator

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The on-board flat-panel cone-beam computed tomography (CBCT) lacks molecular/functional information for current online image-guided radiation therapy (IGRT). It might not be adequate for adaptive radiation therapy (ART), particularly for biologically guided tumor delineation and targeting which might be shifted and/or distorted during the course of RT. A linear accelerator (Linac) gantry-mounted on-board imager (OBI) was proposed using a single photon counting detector (PCD) panel to achieve single photon emission computed tomography (SPECT), energy-resolved spectral CT, and conventional CBCT triple on-board imaging, which might facilitate online ART with an addition of volumetric molecular/functional imaging information. Methods: The system was designed and evaluated in the GATE Monte Carlo platform. The OBI system including a kV-beam source and a pixelated cadmium zinc telluride (CZT) detector panel mounted on a medical Linac orthogonally to the MV beam direction was designed to obtain online CBCT, spectral CT, and SPECT tri-modal imaging of patients in the treatment room. The spatial resolutions of the OBI system were determined by imaging simulated phantoms. The CBCT imaging was evaluated by a simulated contrast phantom. A PMMA phantom containing gadolinium was imaged to demonstrate quantitative imaging of spectral-CT/CBCT of the system. The capability of tri-modal imaging of the OBI was demonstrated using three different spectral CT imaging methods to differentiate gadolinium, gold, calcium within simulated PMMA and the SPECT to image radioactive 99m Tc distribution. The dual-isotope SPECT imaging of the system was also evaluated by imaging a phantom containing 99m Tc and 123 I. The radiotherapy-related parameters of iodine contrast fraction and virtual non-contrast (VNC) tissue electron density in the Kidney1 inserts of a simulated phantom were decomposed using the Bayesian eigentissue decomposition method for contrastenhanced CBCT/spectral-CT of the OBI in a single scan. Results: The spatial resolutions of CBCT and SPECT of the OBI were determined to be 15.1 lp/cm at 10% MTF and 4.8-12 mm for radii of rotation of 10-40 cm, respectively. In CBCT image of the contrast phantom, most of the soft-tissue inserts were visible with sufficient spatial structure details. As compared to the CBCT image of gadolinium, the spectral CT image provided higher image contrasts. Calcium, gadolinium, and gold were separated well by using the spectral CT material imaging methods. The reconstructed distribution of 99m Tc agreed with the spatial position within the phantom. The two isotopes were separated from each other in dual-isotope SPECT imaging of the OBI. The iodine fractions and the VNC electron densities were estimated in the iodine-enhanced Kidney1 tissue inserts with reasonable RMS errors. The main procedures of the tri-modal imaging guided online ART workflow were presented with new functional features included. Conclusions: Using a single photon counting CZT detector panel, an on-board SPECT, spectral CT, and CBCT tr...

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Quantitative imaging performance of MARS spectral photon‐counting CT for radiotherapy

Simard

Panta

Bell³

et al. 2020

Medical Physics

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Purpose To evaluate the quantitative imaging performance of a spectral photon‐counting computed tomography (SPCCT) scanner for radiotherapy applications. An experimental comparison of the quantitative performance of a Siemens dual‐energy CT (DECT) and a MARS SPCCT scanner is performed to estimate physical properties relevant to radiotherapy of human substitute materials and contrast agent solutions. In human substitute materials, the accuracy of quantities relevant to photon therapy, proton therapy, and Monte‐Carlo simulations, such as the electron density, proton stopping power, and elemental composition is evaluated. For contrast agent solutions, the accuracy of the contrast agent concentrations and the virtual non‐contrast (VNC) electron density is evaluated. Methods Human tissue substitute phantoms (Gammex 467 and 472) as well as diluted solutions of contrast agents (iodine and gadolinium based) are scanned with two commercial systems: a Siemens dual‐source CT (SOMATOM Definition Flash, Siemens Healthineers, Forchheim, Germany) and a MARS spectral photon‐counting micro‐CT (MARS V5.2, MARS Bioimaging Ltd., Christchurch, New Zealand). Material decomposition is performed in a maximum a posteriori framework with an optimized material basis tailored to characterize either human substitute materials or contrast agents in the context of experimental multi‐energy CT data. Results The root‐mean‐square error (RMSE) of the electron density calculated over all Gammex inserts is reduced from 1.09 to 0.89% when going from DECT to SPCCT. For the proton stopping power, the RMSE is reduced from 1.92 to 0.89%. Elemental mass fractions of hydrogen, carbon, nitrogen, oxygen, and calcium are more accurately estimated with the MARS scanner. The RMSE on the iodine‐based contrast agents concentration is reduced from 0.27 to 0.12 mg/mL with SPCCT, and the VNC electron density from 0.40 to 0.22%. Conclusion In the present phantom study, a MARS photon‐counting scanner provides superior accuracy compared to a Siemens SOMATOM Definition Flash DECT scanner to quantify physical parameters relevant to radiotherapy. This work experimentally demonstrates the benefits of using more energies to characterize human tissue equivalent materials. This highlights the potential of SPCCT for particle therapy, where more accurate tissue characterization is needed, as well as for Monte‐Carlo based planning, which requires accurate elemental mass fractions.

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The potential of photon-counting CT for quantitative contrast-enhanced imaging in radiotherapy

Cited by 16 publications

References 35 publications

Electron density and effective atomic number estimation in a maximum a posteriori framework for dual‐energy computed tomography

Electron density and effective atomic number estimation in a maximum a posteriori framework for dual‐energy computed tomography

A Monte Carlo study to investigate the feasibility of an on‐board SPECT/spectral‐CT/CBCT imager for medical linear accelerator

Quantitative imaging performance of MARS spectral photon‐counting CT for radiotherapy

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