Monte Carlo assessment of computed tomography dose to tissue adjacent to the scanned volume

Boone, John M.; Cooper, Virgil N.; Nemzek, William R.; McGahan, John P.; Seibert, J. Anthony

doi:10.1118/1.1312809

Cited by 52 publications

(33 citation statements)

References 12 publications

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“…The previously validated SIERRA Monte Carlo code system [8][9][10][11] was modified to accommodate the measurement geometry required in this investigation. Figure 1 illustrates the simulated acquisition geometry utilized.…”

Section: Iia Monte Carlo Simulationsmentioning

confidence: 99%

Dose spread functions in computed tomography: A Monte Carlo study

Boone

2009

Medical Physics

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Purpose: Current CT dosimetry employing CTDI methodology has come under fire in recent years, partially in response to the increasing width of collimated x-ray fields in modern CT scanners. This study was conducted to provide a better understanding of the radiation dose distributions in CT. Methods: Monte Carlo simulations were used to evaluate radiation dose distributions along the z axis arising from CT imaging in cylindrical phantoms. Mathematical cylinders were simulated with compositions of water, polymethyl methacrylate ͑PMMA͒, and polyethylene. Cylinder diameters from 10 to 50 cm were studied. X-ray spectra typical of several CT manufacturers ͑80, 100, 120, and 140 kVp͒ were used. In addition to no bow tie filter, the head and body bow tie filters from modern General Electric and Siemens CT scanners were evaluated. Each cylinder was divided into three concentric regions of equal volume such that the energy deposited is proportional to dose for each region. Two additional dose assessment regions, central and edge locations 10 mm in diameter, were included for comparisons to CTDI 100 measurements. Dose spread functions ͑DSFs͒ were computed for a wide number of imaging parameters. Results: DSFs generally exhibit a biexponential falloff from the z = 0 position. For a very narrow primary beam input ͑ Ӷ 1 mm͒, DSFs demonstrated significant low amplitude long range scatter dose tails. For body imaging conditions ͑30 cm diameter in water͒, the DSF at the center showed ϳ160 mm at full width at tenth maximum ͑FWTM͒, while at the edge the FWTM was ϳ80 mm. Polyethylene phantoms exhibited wider DSFs than PMMA or water, as did higher tube voltages in any material. The FWTM were 80, 180, and 250 mm for 10, 30, and 50 cm phantom diameters, respectively, at the center in water at 120 kVp with a typical body bow tie filter. Scatter to primary dose ratios ͑SPRs͒ increased with phantom diameter from 4 at the center ͑1 cm diameter͒ for a 16 cm diameter cylinder to ϳ12.5 for a 32 cm diameter cylinder. The SPRs increased dramatically at the center of the phantom compared to the edge. For the three equal area regions, the edge to center SPRs for a 32 cm diameter phantom were ϳ1.8, 3.5, and 6.3, respectively. Conclusions: DSFs demonstrate low amplitude long ranging tails which reach considerable distances in cylindrical phantoms. The buildup that results from these long-ranged tails increases at the center of the field ͑at z =0͒ with increasing scan length. The DSF distributions lend a better understanding of the trends in CT dose deposition over a range of relevant imaging parameters. The DSFs as well as other related data are available to interested parties using EPAPS at

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Section: Iia Monte Carlo Simulationsmentioning

confidence: 99%

Dose spread functions in computed tomography: A Monte Carlo study

Boone

2009

Medical Physics

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“…It can be expected that dose distributions vary considerably for different FOV sizes. 17 In addition, the isocentre (i.e. the centre of the FOV) can be positioned centrally or peripherally in the patients head, affecting the dose distribution to all head and neck organs.…”

Section: Introductionmentioning

confidence: 99%

Dose distribution for dental cone beam CT and its implication for defining a dose index

Pauwels

Theodorakou²,

Walker³

et al. 2012

Dentomaxillofacial Radiology

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6 Listing of partners on www.sedentexct.euObjectives: To characterize the dose distribution for a range of cone beam CT (CBCT) units, investigating different field of view sizes, central and off-axis geometries, full or partial rotations of the X-ray tube and different clinically applied beam qualities. The implications of the dose distributions on the definition and practicality of a CBCT dose index were assessed. Methods: Dose measurements on CBCT devices were performed by scanning cylindrical head-size water and polymethyl methacrylate phantoms, using thermoluminescent dosemeters, a small-volume ion chamber and radiochromic films. Results: It was found that the dose distribution can be asymmetrical for dental CBCT exposures throughout a homogeneous phantom, owing to an asymmetrical positioning of the isocentre and/ or partial rotation of the X-ray source. Furthermore, the scatter tail along the z-axis was found to have a distinct shape, generally resulting in a strong drop (90%) in absorbed dose outside the primary beam. Conclusions: There is no optimal dose index available owing to the complicated exposure geometry of CBCT and the practical aspects of quality control measurements. Practical validation of different possible dose indices is needed, as well as the definition of conversion factors to patient dose.

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“…For example, if CTPA is performed because of suspected PE in the mother, the foetus is exposed to scatter radiation. In early pregnancy, the distance from the directly irradiated region to the embryo is at least 20 cm, and scatter radiation levels have been estimated to be no more than 1 % of the chest dose [90]. With the progression of pregnancy, foetal radiation exposure will increase because the growing foetus moves closer to the imaging volume.…”

Section: Foetal Radiation Exposurementioning

confidence: 99%

“…A population-based study of 1.8 million mother-child pairs in Ontario (Canada) did not reveal a significant increase in the risk of cancer in children of mothers who underwent CT or radionuclear imaging during pregnancy compared with children born to mothers with no exposure (adjusted hazard ratio 0.68; 95 % CI 0.25 -1.80), although small harmful eff ects could not be excluded [91]. Moreover, the overall risk of radiologic imaging seems to be small in comparison with the natural risks of pregnancy: 15 % risk of spontaneous miscarriage, 4 % risk of prematurity and growth retardation, 3 % risk of spontaneous birth defects, and 1 % risk of mental retardation [63,90].…”

Section: Foetal Radiation Exposurementioning

confidence: 99%

Diagnosis of pregnancy-associated venous thromboembolism - position paper of the Working Group in Women’s Health of the Society of Thrombosis and Haemostasis (GTH)

Linnemann¹,

Scholz

Rott

et al. 2016

Vasa

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EpidemiologyVTE is a leading cause of maternal morbidity in the developed world and, in the case of PE, of mortality as well [1]. While the relative risk of VTE is greatly increased during pregnancy compared with that in non-pregnant women, the absolute risk remains low: estimates of the incidence of pregnancy-associated VTE have varied from 1:500 to 1:1500 pregnancies [2 -7]. The risk of VTE is approximately 5-fold greater in pregnant women than in non-pregnant women.Approximately 80 % of pregnancy-associated VTEs are isolated DVTs, and approximately 20 % are PEs or both DVTs and PEs [5]. Although a systematic review reported weighted event rates for DVT of 21.9 %, 33.7 % and 47.6 % for the fi rst, second and third trimesters, respectively [6], a recent study suggested that the risk might in fact increase exponentially over the duration of the pregnancy [7], with 12.4 % of VTEs diagnosed in the fi rst trimester, 15.3 % in the second trimester and 72.3 % in the third trimester. This detailed risk assessment for each gestational week demonstrated a 21-fold increased risk for the last two weeks before delivery [7]. Summary: Pregnancy and the postpartum period are associated with an increased risk of venous thromboembolism (VTE). Over the past decade, new diagnostic algorithms have been established, combining clinical probability, laboratory testing and imaging studies for the diagnosis of deep vein thrombosis (DVT) and pulmonary embolism (PE) in the non-pregnant population. However, there is no such generally accepted algorithm for the diagnosis of pregnancy-associated VTE. Studies establishing clinical prediction rules have excluded pregnant women, and prediction scores currently in use have not been prospectively validated in pregnancy or during the postpartum period. D-dimers physiologically increase throughout pregnancy and peak at delivery, so a negative D-dimer test result, based on the reference values of non-pregnant subjects, becomes unlikely in the second and third trimesters. Imaging studies therefore play a major role in confi rming suspected DVT or PE in pregnant women. Major concerns have been raised against radiologic imaging because of foetal radiation exposure, and doubts about the diagnostic value of ultrasound techniques in attempting to exclude isolated iliac vein thrombosis grow stronger as pregnancy progresses. As members of the Working Group in Women's Health of the Society of Thrombosis and Haemostasis (GTH), we summarise evidence from the available literature and aim to establish a more uniform strategy for diagnosing pregnancy-associated VTE. Review Diagnosis of pregnancy-associated

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Monte Carlo assessment of computed tomography dose to tissue adjacent to the scanned volume

Cited by 52 publications

References 12 publications

Dose spread functions in computed tomography: A Monte Carlo study

Dose spread functions in computed tomography: A Monte Carlo study

Dose distribution for dental cone beam CT and its implication for defining a dose index

Diagnosis of pregnancy-associated venous thromboembolism - position paper of the Working Group in Women’s Health of the Society of Thrombosis and Haemostasis (GTH)

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