Estimating surface radiation dose from multidetector CT: cylindrical phantoms, anthropomorphic phantoms, and Monte Carlo simulations

DeMarco, John J.; Cody, Dianna D.; Stevens, David B.; McCollough, Cynthia H.; O’Daniel, J; McNitt‐Gray, M

doi:10.1117/12.595933

Cited by 3 publications

(4 citation statements)

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“…Jarry et al [11] reported a difference between simulations and measurements equal to or less than 8.4% across all measurements and simulations, whereas DeMarco et al [12] reported 3.5% difference over all conditions for a CTDI body phantom and significant variation for the anthropomorphic phantom.…”

Section: Discussionmentioning

confidence: 96%

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Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Deak¹,

Straten²,

Shrimpton³

et al. 2007

Eur Radiol

191

138

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Estimating the dose delivered to the patient in X-ray computed tomography (CT) examinations is not a trivial task. Monte Carlo (MC) methods appear to be the method of choice to assess the 3D dose distribution. The purpose of this work was to extend an existing MC-based tool to account for arbitrary scanners and scan protocols such as multi-slice CT (MSCT) scanners and to validate the tool in homogeneous and heterogeneous phantoms. The tool was validated by measurements on MSCT scanners for different scan protocols under known conditions. Quantitative CT Dose Index (CTDI) measurements were performed in cylindrical CTDI phantoms and in anthropomorphic thorax phantoms of various sizes; dose profiles were measured with thermoluminescent dosimeters (TLD) in the CTDI phantoms and compared with the computed dose profiles. The in-plane dose distributions were simulated and compared with TLD measurements in an Alderson-Rando phantom. The calculated dose values were generally within 10% of measurements for all phantoms and all investigated conditions. Three-dimensional dose distributions can be accurately calculated with the MC tool for arbitrary scanners and protocols including tube current modulation schemes. The use of the tool has meanwhile also been extended to further scanners and to flat-detector CT.

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Section: Discussionmentioning

confidence: 96%

“…All of them are difficult to adapt to the specific conditions found in CT and suffer from a lack of flexibility. All these reasons motivated us and other groups [9][10][11][12][13] to develop MC-based tools for dose simulation purposes related to photon transport in diagnostic radiology applications, especially for CT procedures.…”

Section: Introductionmentioning

confidence: 99%

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Deak¹,

Straten²,

Shrimpton³

et al. 2007

Eur Radiol

191

138

View full text Add to dashboard Cite

show abstract

“…The voxelized phantom was created using an approach developed previously. 14,17 In this approach, spinal cord, spinal disk, and soft tissues are consolidated into one equivalent material. At the level of the chest, the lateral width of the phantom is 32 cm, and the anterior-posterior ͑AP͒ thickness of the phantom is 22 cm.…”

Section: Iib Phantomsmentioning

confidence: 99%

“…As part of their model verification, physical measurements were made using a collection of 20 MOSFET detectors placed nearly contiguously on the surface of the thorax of the anthropomorphic phantom. In a separate effort, DeMarco et al 14 used Monte Carlo simulation methods applied to cylindrical and physical anthropomorphic phantoms, where a film dosimeter was placed on the surface of CTDI phantoms to observe and measure the magnitude of the surface dose variation in MDCT. Both studies found that the larger cone angles from MDCT systems yield greater beam divergence and resulted in surface dose variations, with the peak value twice as high as the valley; these variations were observed for both helical and contiguous axial scans.…”

Section: Introductionmentioning

confidence: 99%

Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms

Zhang

Savandi²,

DeMarco

et al. 2009

Medical Physics

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The larger coverage afforded by wider z-axis beams in multidetector CT ͑MDCT͒ creates larger cone angles and greater beam divergence, which results in substantial surface dose variation for helical and contiguous axial scans. This study evaluates the variation of absorbed radiation dose in both cylindrical and anthropomorphic phantoms when performing helical or contiguous axial scans. The approach used here was to perform Monte Carlo simulations of a 64 slice MDCT. Simulations were performed with different radiation profiles ͑simulated beam widths͒ for a given collimation setting ͑nominal beam width͒ and for different pitch values and tube start angles. The magnitude of variation at the surface was evaluated under four different conditions: ͑a͒ a homogeneous CTDI phantom with different combinations of pitch and simulated beam widths, ͑b͒ a heterogeneous anthropomorphic phantom with one measured beam collimation and various pitch values, ͑c͒ a homogeneous CTDI phantom with fixed beam collimation and pitch, but with different tube start angles, and ͑d͒ pitch values that should minimize variations of surface dose-evaluated for both homogeneous and heterogeneous phantoms. For the CTDI phantom simulations, peripheral dose patterns showed variation with percent ripple as high as 65% when pitch is 1.5 and simulated beam width is equal to the nominal collimation. For the anterior surface dose on an anthropomorphic phantom, the percent ripple was as high as 40% when the pitch is 1.5 and simulated beam width is equal to the measured beam width. Low pitch values were shown to cause beam overlaps which created new peaks. Different x-ray tube start angles create shifts of the peripheral dose profiles. The start angle simulations showed that for a given table position, the surface dose could vary dramatically with minimum values that were 40% of the peak when all conditions are held constant except for the start angle. The last group of simulations showed that an "ideal" pitch value can be determined which reduces surface dose variations, but this pitch value must take into account the measured beam width. These results reveal the complexity of estimating surface dose and demonstrate a range of dose variability at surface positions for both homogeneous cylindrical and heterogeneous anthropomorphic phantoms. These findings have potential implications for small-sized dosimeter measurements in phantoms, such as with TLDs or small Farmer chambers.

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Effective dose estimation for U.S. Army soldiers undergoing multiple computed tomography scans

Prins¹

2011

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Estimating surface radiation dose from multidetector CT: cylindrical phantoms, anthropomorphic phantoms, and Monte Carlo simulations

Cited by 3 publications

References 0 publications

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Validation of a Monte Carlo tool for patient-specific dose simulations in multi-slice computed tomography

Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms

Effective dose estimation for U.S. Army soldiers undergoing multiple computed tomography scans

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