Accuracy of Monte Carlo simulations compared to <i>in‐vivo</i> MDCT dosimetry

Bostani, Maryam; Mueller, Jonathon W.; McMillan, Kyle; Cody, Dianna D.; Cagnon, Chris H.; DeMarco, John J.; McNitt‐Gray, Michael F.

doi:10.1118/1.4906178

Cited by 12 publications

(19 citation statements)

References 44 publications

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“…The density variations for the six different material designations are based on the CT scanner calibration curve and the linear relationship between mass density and electron density. This number of bins has been shown to be sufficient for CT dosimetry and has been validated in previous studies . Individual organs were not segmented for these patient models, but brain parenchyma tissue was semiautomatically contoured and explicitly identified.…”

Section: Methodsmentioning

confidence: 99%

“…This number of bins has been shown to be sufficient for CT dosimetry and has been validated in previous studies. 12,13 Individual organs were not segmented for these patient models, but brain parenchyma tissue was semiautomatically contoured and explicitly identified. The MCNPX model characteristics for all voxelized models used in this study are summarized in Table I.…”

Section: A Patient Modelsmentioning

confidence: 99%

“…All CT dose simulations for this investigation were conducted using a modified version of the radiation transport software package MCNPX (Monte Carlo N-Particle eXtended version 2.7.a). 13,15,16 Specifically, the source code was modified to model a MDCT scanner geometry and x-ray source trajectory. All simulations were conducted in photon transport mode with a 1 keV low-energy cutoff.…”

Section: D Monte Carlo Simulationsmentioning

confidence: 99%

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Estimating a size‐specific dose for helical head CT examinations using Monte Carlo simulation methods

et al. 2018

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Purpose Size‐specific dose estimates (SSDE) conversion factors have been determined by AAPM Report 204 to adjust CTDIvol to account for patient size but were limited to body CT examinations. The purpose of this work was to determine conversion factors that could be used for an SSDE for helical, head CT examinations for patients of different sizes. Methods Validated Monte Carlo (MC) simulation methods were used to estimate dose to the center of the scan volume from a routine, helical head examination for a group of patient models representing a range of ages and sizes. Ten GSF/ICRP voxelized phantom models and five pediatric voxelized patient models created from CT image data were used in this study. CT scans were simulated using a Siemens multidetector row CT equivalent source model. Scan parameters were taken from the AAPM Routine Head protocols for a fixed tube current (FTC), helical protocol, and scan lengths were adapted to the anatomy of each patient model. MC simulations were performed using mesh tallies to produce voxelized dose distributions for the entire scan volume of each model. Three tally regions were investigated: (1) a small 0.6 cc volume at the center of the scan volume, (2) 0.8–1.0 cm axial slab at the center of the scan volume, and (3) the entire scan volume. Mean dose to brain parenchyma for all three regions was calculated. Mean bone dose and a mass‐weighted average dose, consisting of brain parenchyma and bone, were also calculated for the slab in the central plane and the entire scan volume. All dose measures were then normalized by CTDIvol for the 16 cm phantom (CTDIvol,16). Conversion factors were determined by calculating the relationship between normalized doses and water equivalent diameter (Dw). Results CTDIvol,16‐normalized mean brain parenchyma dose values within the 0.6 cc volume, 0.8–1.0 cm central axial slab, and the entire scan volume, when parameterized by Dw, had an exponential relationship with a coefficient of determination (R2) of 0.86, 0.84, and 0.88, respectively. There was no statistically significant difference between the conversion factors resulting from these three different tally regions. Exponential relationships between CTDIvol,16‐normalized mean bone doses had R2 values of 0.83 and 0.87 for the central slab and for the entire scan volume, respectively. CTDIvol,16‐normalized mass‐weighted average doses had R2 values of 0.39 and 0.51 for the central slab and for the entire scan volume, respectively. Conclusions Conversion factors that describe the exponential relationship between CTDIvol,16‐normalized mean brain dose and a size metric (Dw) for helical head CT examinations have been reported for two different interpretations of the center of the scan volume. These dose descriptors have been extended to describe the dose to bone in the center of the scan volume as well as a mass‐weighted average dose to brain and bone. These may be used, when combined with other efforts, to develop an SSDE dose coefficients for routine, helical head CT examinations.

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Section: Methodsmentioning

confidence: 99%

Section: A Patient Modelsmentioning

confidence: 99%

Section: D Monte Carlo Simulationsmentioning

confidence: 99%

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Estimating a size‐specific dose for helical head CT examinations using Monte Carlo simulation methods

et al. 2018

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“…It is believed that the number of dosimeters used per organ based on its axial and z‐extent justifies using averaged point doses to estimate the true organ dose. It should also be noted that previous work has shown minimal angular dependence for these particular OSL dosimeters when used for in‐phantom CT dosimetry, especially at deeper depths in tissue …”

Section: Methodsmentioning

confidence: 92%

Physical validation of a Monte Carlo‐based, phantom‐derived approach to computed tomography organ dosimetry under tube current modulation

et al. 2017

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“…In the case of TCM simulations, an additional text file with information on individual table location, tube angle, and tube current value throughout the scan was utilized in the simulation. Validation of this MC simulation package under a variety of conditions including TCM has been previously reported . This work used the computational and storage services of the Hoffman2 Shared Cluster provided by the UCLA Institute for Digital Research and Education's Research Technology Group.…”

Section: Methodsmentioning

confidence: 99%

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

et al. 2019

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Purpose The purpose of this work was to estimate scanner‐independent CTDIvol‐to‐fetal‐dose coefficients for tube current‐modulated (TCM) and fixed tube current (FTC) computed tomography (CT) examinations of pregnant patients of various gestational ages undergoing abdominal/pelvic CT examinations. Methods For 24 pregnant patients of gestational age from <5 to 36 weeks who underwent clinically indicated CT examinations, voxelized models of maternal and fetal (or embryo) anatomy were created from abdominal/pelvic image data. Absolute fetal dose (Dfetus) was estimated using Monte Carlo (MC) simulations of helical scans covering the abdomen and pelvis for TCM and FTC scans. Estimated TCM schemes were generated for each patient model using a validated method that accounts for patient attenuation and scanner output limits for one scanner model and were incorporated into MC simulations. FTC scans were also simulated for each patient model with multidetector row CT scanners from four manufacturers. Normalized fetal dose estimates, nDfetus, was obtained by dividing Dfetus from the MC simulations by CTDIvol. Patient size was described using water equivalent diameter (Dw) measured at the three‐dimensional geometric centroid of the fetus. Fetal depth (DEf) was measured from the anterior skin surface to the anterior part of the fetus. nDfetus and Dw were correlated using an exponential model to develop equations for fetal dose conversion coefficients for TCM and FTC abdominal/pelvic CT examinations. Additionally, bivariate linear regression was performed to analyze the correlation of nDfetus with Dw and fetal depth (DEf). For one scanner model, nDfetus from TCM was compared to FTC and the size‐specific dose estimate (SSDE) conversion coefficients (f‐factors) from American Association of Physicists in Medicine (AAPM) Report 204. nDfetus from FTC simulations was averaged across all scanners for each patient (nDfetus¯). nDitalicfetus¯ was then compared with SSDE f‐factors and correlated with Dw using an exponential model and with Dw and DEf using a bivariate linear model. Results For TCM, the coefficient of determination (R2) of nDfetus and Dw was observed to be 0.73 using an exponential model. Using the bivariate linear model with Dw and DEf, an R2 of 0.78 was observed. For the TCM technology modeled, TCM yielded nDfetus values that were on average 6% and 17% higher relative to FTC and SSDE f‐factors, respectively. For FTC, the R2 of nDitalicfetus¯ with respect to Dw was observed to be 0.64 using an exponential model. Using the bivariate linear model, an R2 of 0.75 was observed for nDitalicfetus¯ with respect to Dw and DEf. A mean difference of 0.4% was observed between nDitalicfetus¯ and SSDE f‐factors. Conclusion Good correlations were observed for nDfetus from TCM and FTC scans using either an exponential model with Dw or a bivariate linear model with both Dw and DEf. These results indicate that fetal dose from abdomen/pelvis CT examinations of pregnant patients of various gestational ages may be reasonably estimated with mod...

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Accuracy of Monte Carlo simulations compared to in‐vivo MDCT dosimetry

Cited by 12 publications

References 44 publications

Estimating a size‐specific dose for helical head CT examinations using Monte Carlo simulation methods

Estimating a size‐specific dose for helical head CT examinations using Monte Carlo simulation methods

Physical validation of a Monte Carlo‐based, phantom‐derived approach to computed tomography organ dosimetry under tube current modulation

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

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