Adult abdomen–pelvis CT: Does equilibrium dose‐pitch product better account for the kVp dependence of organ dose than conventional CTDI?

Li, Xiang; Morgan, Ashraf G.; Liptak, Christopher L.; Muryn, John S.; Dong, Frank; Primak, Andrew N.; Segars, W. Paul

doi:10.1118/1.4932222

Cited by 4 publications

(4 citation statements)

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“…where nT denotes the nominal collimation of the beam. This approach to simulating and calculating CTDI 100 was also used in an earlier study, 12 which found good agreement between simulations and measurements. In addition to CTDI 100 at individual hole locations, the planar average CTDI 100 (i.e., an average over the cross-sectional area of the phantom), denoted as CTDI xsec , was also calculated using Eqs.…”

Section: Monte Carlo Simulations Of Ctdi 100 and Itsmentioning

confidence: 93%

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Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

et al. 2017

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The purpose of this study was to extend the concept of weighted CT dose index ([Formula: see text]) to the elliptical phantoms. Based on the published body dimension data, eight body aspect ratios were chosen between 1 (perfectly circular) and 1.72 (extremely elliptical). For each aspect ratio, two elliptical cylinders were created digitally to represent adult and pediatric bodies. Their cross-sectional areas were identical to the standard 32- and 16-cm CTDI phantoms. For each phantom, [Formula: see text] at center and periphery were simulated for tube voltages between 70 and 140 kVp using a validated Monte Carlo program. The simulations also provided the average dose over the cross-sectional area, [Formula: see text]. Values of [Formula: see text] and [Formula: see text] allowed linear systems of equations to be established, from which central and peripheral weighting coefficients were solved. Regardless of phantom shape, only two weighting coefficients were needed: [Formula: see text] for the central [Formula: see text] and [Formula: see text] for the average of the four peripheral [Formula: see text]'s. Over the full range of aspect ratios, [Formula: see text] increased linearly from 0.37 to 0.46, whereas [Formula: see text] decreased linearly from 0.63 to 0.54, allowing the concept of [Formula: see text] to be readily extended to the elliptical phantoms. When cross-sectional area (hence volume) was kept constant, all phantoms had the same [Formula: see text] regardless of shape.

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Section: Monte Carlo Simulations Of Ctdi 100 and Itsmentioning

confidence: 93%

“…hCTDI p i∕CTDI c also decreased with increasing kVp, consistent with the fact that a higher energy beam produces more uniform dose distribution. 12 3.2 Definition of CTDI w for Elliptical Phantoms Table 5 summarizes the solutions to Eq. (5) for various kVp and aspect ratios.…”

Section: Sample Values Of Ctdi 100 and Ctdi Xsecmentioning

confidence: 99%

Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

et al. 2017

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“…Monte Carlo calculation in the 10 cm air holes would be very time consuming in order to arrive at a statistical error of about 1-2%, because of the low density of air, which makes photon interactions less frequent, and, at the same time, because of the much greater electron range compared to PMMA. Applying a method already used by Boone (2007) and Li et al (2015b), photon interactions were simulated assuming the holes are filled with PMMA and the results were then transformed into air kerma using ratios between the mass-energy absorption coefficients (MEAC) of air and PMMA. Thereby, it is possible to do a calculation with 20 million source photons in about 15 minutes on a desktop computer with a Pentium CORE i7 processor achieving a statistical error of about 1%, also maintaining the above mentioned cut-off energies.…”

Section: Quantities In Ct Dosimetrymentioning

confidence: 99%

Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry

et al. 2017

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The purpose of bowtie filters in CT scanners is to homogenize the x-ray intensity measured by the detectors in order to improve the image quality and at the same time to reduce the dose to the patient because of the preferential filtering near the periphery of the fan beam. For CT dosimetry, especially for Monte Carlo calculations of organ and tissue absorbed doses to patients, it is important to take the effect of bowtie filters into account. However, material composition and dimensions of these filters are proprietary. Consequently, a method for bowtie filter simulation independent of access to proprietary data and/or to a specific scanner would be of interest to many researchers involved in CT dosimetry. This study presents such a method based on the weighted computer tomography dose index, CTDI, defined in two cylindrical PMMA phantoms of 16 cm and 32 cm diameter. With an EGSnrc-based Monte Carlo (MC) code, ratios CTDI/CTDI were calculated for a specific CT scanner using PMMA bowtie filter models based on sigmoid Boltzmann functions combined with a scanner filter factor (SFF) which is modified during calculations until the calculated MC CTDI/CTDI matches ratios CTDI/CTDI, determined by measurements or found in publications for that specific scanner. Once the scanner-specific value for an SFF has been found, the bowtie filter algorithm can be used in any MC code to perform CT dosimetry for that specific scanner. The bowtie filter model proposed here was validated for CTDI/CTDI considering 11 different CT scanners and for CTDI, CTDI and their ratio considering 4 different CT scanners. Additionally, comparisons were made for lateral dose profiles free in air and using computational anthropomorphic phantoms. CTDI/CTDI determined with this new method agreed on average within 0.89% (max. 3.4%) and 1.64% (max. 4.5%) with corresponding data published by CTDosimetry (www.impactscan.org) for the CTDI HEAD and BODY phantoms, respectively. Comparison with results calculated using proprietary data for the PHILIPS Brilliance 64 scanner showed agreement on average within 2.5% (max. 5.8%) and with data measured for that scanner within 2.1% (max. 3.7%). Ratios of CTDI/CTDI, for this study and corresponding data published by CTDosimetry (www.impactscan.org) agree on average within about 11% (max. 28.6%). Lateral dose profiles calculated with the proposed bowtie filter and with proprietary data agreed within 2% (max. 5.9%), and both calculated data agreed within 5.4% (max. 11.2%) with measured results. Application of the proposed bowtie filter and of the exactly modelled filter to human phantom Monte Carlo calculations show agreement on the average within less than 5% (max. 7.9%) for organ and tissue absorbed doses.

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“…The relationships between the organ dose to CTDI vol ratio and tube voltage were investigated by Li et al in a Monte Carlo simulation study with three patient models undergoing abdomen-pelvis scans on a Siemens Somatom Definition Flash scanner operated at 70-140 kV. 18 The scan length was 43 cm for the normal-weight and the overweight models (effective diameters 23.1 and 27.9 cm), and 47 cm for the obese model (effective diameter 36.4 cm). The results of the doses to liver, spleen, stomach, pancreas, kidneys, colon, small intestine, bladder, and ovaries indicated that the organ dose to CTDI vol ratios increased with tube voltage.…”

Section: Introductionmentioning

confidence: 99%

A study of the midpoint dose to CTDI_vol ratio: Implications for CT dose evaluation

Yang

Liu

2016

Medical Physics

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Adult abdomen–pelvis CT: Does equilibrium dose‐pitch product better account for the kVp dependence of organ dose than conventional CTDI?

Abstract: In adult abdomen-pelvis CT, equilibrium dose-pitch product better accounts for the kVp dependence of organ dose than CTDI100.

Cited by 4 publications

References 35 publications

Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry

A study of the midpoint dose to CTDI_vol ratio: Implications for CT dose evaluation

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Adult abdomen–pelvis CT: Does equilibrium dose‐pitch product better account for the kVp dependence of organ dose than conventional CTDI?

Abstract: In adult abdomen-pelvis CT, equilibrium dose-pitch product better accounts for the kVp dependence of organ dose than CTDI100.

Cited by 4 publications

References 35 publications

Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

Extending the concept of weighted CT dose index to elliptical phantoms of various aspect ratios

Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry

A study of the midpoint dose to CTDIvol ratio: Implications for CT dose evaluation

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A study of the midpoint dose to CTDI_vol ratio: Implications for CT dose evaluation