Monte Carlo Simulation of the Computed Tomography Dose Index (CTDI) Using GATE

Mkimel, M.; Baydaoui, R. El; Mesradi, M.R.; Tahiri, Zakaria; Talasmat, K.; Halimi, A.; Krim, M.; Saad, Elmadani; Hilali, Abderraouf

doi:10.1134/s1547477120060084

Cited by 3 publications

(4 citation statements)

References 18 publications

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“…At each measurement point, attenuation and equivalent filter thickness were then calculated. The equivalent source model was validated by comparing the simulated and measured CTDI vol of both 32 and 16 cm CTDI phantoms [5,6]. The simulated and measured value differences range from 0.81% to 1.85%.…”

Section: Source Model Simulationmentioning

confidence: 99%

“…Because these values refer only to the CT scanner dose output of an examination, dose length product is introduced to involve the scan length [4]. The basic CTDI involves the use of a pencil ionization chamber and a standard cylindrical acrylic (polymethyl methacrylate (PMMA)) phantom [5,6]. This method typically measures the dose index in standard phantoms (16 cm in diameter) to represent an adult head and a child's body, or 32 cm in diameter to represent an adult body [7].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Tahiri¹,

Benameur²,

Mkimel³

et al. 2023

J. Radiol. Prot.

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Computed tomography dose index (CTDI) is an unreliable dose estimate outside of the standard CTDI phantom diameters (16 and 32 cm). Size-specific dose estimate (SSDE) for head computed tomography (CT) examination was studied in the American Association of Physicists in Medicine Report 293 to provide SSDE coefficient factors based on water equivalent diameter as size metrics. However, it is limited to one protocol and for a fully irradiated organ. This study aimed to evaluate the dependency of normalized organ dose (ND) on water equivalent diameter as a size metric in three common protocols: routine head, paranasal sinus, and temporal bone. CTDIw measurements were performed for outlined protocols in the Siemens Emotion 16-slice-configuration scanner. Geant4 Application for Tomographic Emission Monte Carlo simulation platform, coupled with ten GSF patient models, was used to estimate organ doses. CT scanner system was modeled. Helical CT scans were simulated using constructor scan parameters and calculated scan lengths of each patient model. Organ doses provided by simulations were normalized to CTDIvol. The water equivalent diameters (D w) of patient models were obtained via relationships between D w and both effective diameter for a sample of patients’ data.NDs received by fully, partially, and non-directly irradiated organs were then reported as a function of D w. For fully irradiated organs, brain (R 2 > 0.92), eyes (R 2 > 0.88), and eye lens (R 2 > 0.89) correlate well with D w. For the rest of the results, a poor correlation was observed. For partially irradiated organs, the exception was scalp (R 2 = 0.93) in temporal bone CT. For non-directly irradiated organs, the exception was thyroid (R 2 > 0.90) and lungs (R 2 > 0.91) in routine head CT. ND correlates well in routine head CT than other protocols. For the most part, no relationship seems to exist between R 2 and scan percentage coverage. The results have revealed additional factors that may influence the ND and D w relationship, which explains the need for more studies in the future to investigate the effect of scan conditions and organ anatomy variation.

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Section: Source Model Simulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Tahiri¹,

Benameur²,

Mkimel³

et al. 2023

J. Radiol. Prot.

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“…The energy spectrum of the source was produced using the SRS78 application and then inserted into GATE versus General Particle Source (GPS). To validate the simulated CT geometry, a CTDI 100 data set was simulated for body and head CTDI phantoms with diameters of 32 and 16 cm, respectively [7].…”

Section: Ct Scannermentioning

confidence: 99%

Fetal organ dose assessment during pelvic CT examination using Monte Carlo/GATE simulation and pregnancy voxelized phantom Katja

et al. 2022

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In certain situations where there is a risk of fetal-pelvis disproportion (risk that the baby will not be able to pass through the pelvis), pelvic scan examination may be prescribed to the mother at the end of pregnancy. This examination assesses the dimensions of the pelvis by measuring various bone diameters. It also provides details information about pelvis morphology. Patients are routinely worried about the risk of unwanted effects on the fetus from radiation exposure. Accepting the possibility of adverse effects from fetal exposure and the inability to measure directly in vivo [1]. Medical physicists have developed several techniques to determine the amount of radiation that reaches the fetus. Physicians need to understand these methods and how the numbers they produce relate to possible biological effects on the fetus. In this study A 16 helical multi-slice CT scanner was simulated. Full technical specifications were obtained from the constructor and simulated in GATE to produce single x-ray beams. Katja voxelized patient phantom, pregnant in 24 weeks, was scanned with pelvis protocol. The code was used to estimate the absorbed and effective doses in the important organs of the fetus as a consequence of the scanning parameters. The purpose of this study was to use patient voxelized phantom Katja to assessed fetal organ dose, effective dose and evaluate the risk related to radiation due to pelvis CT examination using Monte Carlo/Gate platform. Fetal effective doses were 4.8, 6.3 and 8.2 mSv for 80, 110 and 130 kV respectively. Fetal dose in heart, eye lens, brain was 1.61, 1.6 and 0.8 mGy for 80 kV. Since the dose to the fetus from a pelvic scan is lower than 50 mGy, when exposed to a single scan teratogenic effects on the fetus are not significant concern [2].

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“…There are a few challenges to achieve that goal: (1) Physical measurements are limited by the dosimetry equipment accuracy and again limited availability of axial scan modes for certain protocols; (2) No analytical approach is available for helical acquisitions due to the complex geometry and almost infinitely long scatter tail [10][11][12] ; (3) Monte Carlo simulations will take prohibitively long to achieve high resolution results with sufficient accuracy for all possible helical scan models. [13][14][15][16][17][18] In this study, we propose a hybrid approach by combining Monte Carlo simulation with analytical simulation to overcome these challenges, with the goal to provide a comprehensive and intuitive picture of 3D dose distributions for both axial and helical CT acquisitions, based upon which a quantitative comparison between the two dose metrics can be performed.…”

Section: Introductionmentioning

confidence: 99%

Visualization and comparison of CT dose distribution between axial and helical acquisitions

Yang

Xin-hua

et al. 2023

Medical Physics

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BackgroundIt is challenging to assess the accuracy of volume CT Dose Index (CTDIvol) when the axial scan modes corresponding to a helical scan protocol are not available. An alternative approach was proposed to directly measure using helical acquisitions and relatively small differences (< 20%) from CTDIvol were observed.PurposeTo visually demonstrate the 3D dose distribution for both axial and helical CT acquisitions and quantitively compare and CTDIvol.Methods3D dose distribution within the standard CTDI phantoms (16 and 32 cm diameter) from a single CT projection, Dp(x,y,z) was first generated using Monte Carlo simulation (GEANT4) with 9×108 photons per combination of tube voltage (80–140 kV), collimation width (1–8 cm), and z‐axis location of the central ray of the x‐ray beam, with a spatial resolution of 1 mm3. These dose distributions from one single projection were analytically ensembled to simulate 3D dose volumes DA(x,y,z) and DH(x,y,z) for axial and helical scans, respectively, with different helical pitches (0.3–2) and scan lengths (100–150 mm). 2D planar dose distributions were obtained by integrating the inside 100 mm of the dose volumes. CTDIvol and were calculated using the planar dose data at corresponding pencil chamber locations and the percentage differences (PD) were reported.ResultsHigh spatial resolution 3D CT dose volumes were generated and visualized. PDs between and CTDIvol had strong dependency on scan length and peripheral chamber locations, with subtle dependency on collimation width and pitch. PDs were mostly within the range of ± 3% for a scan length of 150 mm with four peripheral chamber locations.ConclusionsWith a scan length covering the entire phantom length, directly measured from helical scans can serve as an alternative to CTDIvol only if all four peripheral locations were measured.

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Monte Carlo Simulation of the Computed Tomography Dose Index (CTDI) Using GATE

Cited by 3 publications

References 18 publications

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Fetal organ dose assessment during pelvic CT examination using Monte Carlo/GATE simulation and pregnancy voxelized phantom Katja

Visualization and comparison of CT dose distribution between axial and helical acquisitions

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