A comparison of radiation dose measured in CT dosimetry phantoms with calculations using EGS4 and voxel-based computational models

Caon, Martin; Bibbo, Giovanni; Pattison, John E.

doi:10.1088/0031-9155/42/1/014

Cited by 42 publications

(31 citation statements)

References 17 publications

(15 reference statements)

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“…9,17,37 Instead, weighting factors were applied to angular sampling within a fan beam angle based on a lateral free-in-air dose profile measured by a pencil ion chamber. A 100 mm Radcal ® ion chamber model 10ϫ 5-10.3CT and an MDH model 1015 electrometer ͑Radcal Corp., Monrovia, CA͒ were used to measure the lateral dose profile while the x-ray tube was fixed at the 12 o'clock position under service mode.…”

Section: Iia Modeling Of X-ray Source In the Ct Scannermentioning

confidence: 99%

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Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

et al. 2011

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Purpose: To develop a computed tomography ͑CT͒ organ dose estimation method designed to readily provide organ doses in a reference adult male and female for different scan ranges to investigate the degree to which existing commercial programs can reasonably match organ doses defined in these more anatomically realistic adult hybrid phantoms Methods: The x-ray fan beam in the SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code MCNPX2.6. The simulated CT scanner model was validated through comparison with experimentally measured lateral free-in-air dose profiles and computed tomography dose index ͑CTDI͒ values. The reference adult male and female hybrid phantoms were coupled with the established CT scanner model following arm removal to simulate clinical head and other body region scans. A set of organ dose matrices were calculated for a series of consecutive axial scans ranging from the top of the head to the bottom of the phantoms with a beam thickness of 10 mm and the tube potentials of 80, 100, and 120 kVp. The organ doses for head, chest, and abdomen/pelvis examinations were calculated based on the organ dose matrices and compared to those obtained from two commercial programs, CT-EXPO and CTDOSIMETRY. Organ dose calculations were repeated for an adult stylized phantom by using the same simulation method used for the adult hybrid phantom. Results: Comparisons of both lateral free-in-air dose profiles and CTDI values through experimental measurement with the Monte Carlo simulations showed good agreement to within 9%. Organ doses for head, chest, and abdomen/pelvis scans reported in the commercial programs exceeded those from the Monte Carlo calculations in both the hybrid and stylized phantoms in this study, sometimes by orders of magnitude. Conclusions: The organ dose estimation method and dose matrices established in this study readily provides organ doses for a reference adult male and female for different CT scan ranges and technical parameters. Organ doses from existing commercial programs do not reasonably match organ doses calculated for the hybrid phantoms due to differences in phantom anatomy, as well as differences in organ dose scaling parameters. The organ dose matrices developed in this study will be extended to cover different technical parameters, CT scanner models, and various age groups.

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Section: Iia Modeling Of X-ray Source In the Ct Scannermentioning

confidence: 99%

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] The human body lying on a CT scanner table and helical fan beam x-ray generated from a CT scanner are fully simulated in the computer using the Monte Carlo method.…”

Section: Introductionmentioning

confidence: 99%

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

et al. 2011

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“…The number of initial particles was 10 8 for all phantom studies. Following a simplified approach from Caon et al (18) and Jones and Shrimpton, (19) only the weighted attenuation of the beam passing the filter materials is calculated, as scattering in the filter materials is negligible for the following dose calculations. Applying this technique to Monte Carlo CT codes has already been shown to be consistent (e.g., by Jarry et al (20) or Long et al (21) ).…”

Section: Methodsmentioning

confidence: 99%

Effect of ROI filtering in 3D cone‐beam rotational angiography on organ dose and effective dose in cerebral investigations

Göpfert

Schmidt

Wulff

et al. 2015

J Applied Clin Med Phys

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The assessment of intracranial aneurysms is increasingly performed using three‐dimensional cone‐beam rotational angiography (3D CBRA). To reduce the dose to the patient during 3D CBRA procedures, filtered region‐of‐interest imaging (FROI) is presented in literature to be an effective technique as the dose in regions of low interest is reduced, while high image quality is preserved in the ROI. The purpose of this study was to quantify the benefit of FROI imaging during a typical 3D CBRA procedure in a patient's head region. A cone‐beam rotational angiography unit (Infinix) was modeled in GMctdospp, an EGSnrc‐based Monte Carlo software, which calculates patient dose distributions in rotational computed tomography. Kodak Lanex, a gadolinium compound, was chosen to be the ROI filter material. The adult female ICRP reference phantom was integrated in GMctdospp to calculate organ and effective doses in simulations of FROI‐CBRA examinations. During the Monte Carlo simulations, different parameters as the ROI filter thickness, the ROI opening size, the tube voltage, and the isocenter position were varied. The results showed that the reduction in dose clearly depends on these parameters. Comparing the reduction in organ dose in standard 3D CBRA and FROI‐CBRA, a maximum reduction of about 60%–80% could be achieved with a small sized ROI filter and about 40%–70% of the dose could be saved using a ROI filter with a large opening. Further we could show that dose reduction strongly depends on filter thickness, the location of the organ in the radiated area, and the position of the isocenter. As a consequence, dose reduction partially differs from theoretically calculated values by a factor up to 1.6. The effective dose could be reduced to a minimum of about 40%. Due to the fact that standard 3D CBRA is only used for the assessment of aneurysms at present and, thus, most of the patient dose originates from the aneurysm treatment (with 2D techniques) itself, the dose reduction effect of ROI filtering in 3D CBRA tends to be much smaller, if the patient dose of a whole aneurysm treatment procedure is considered.PACS numbers: 87.59.DJ, 87.55.kh

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“…6 The accuracy of Monte Carlo techniques in the area of CT dosimetry is well established. [7][8][9][10][11] More recently, Monte Carlo techniques have been used to simulate the dose from the kV imagers integrated into linear accelerators, such as the On-Board Imager (OBI) integrated into the Trilogy accelerator (Varian Medical Systems, Palo Alto, CA). [12][13][14][15] In order to generate an accurate Monte Carlo simulation of the OBI dose, detailed information about the x-ray spectrum, internal filtration, added bowtie filtration and beam geometry (i.e., focal spot to isocenter distance, cone angle, and collimation) is needed.…”

Section: Introductionmentioning

confidence: 99%

Development and validation of a measurement‐based source model for kilovoltage cone‐beam CT Monte Carlo dosimetry simulations

2013

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Purpose: The purpose of this study is to adapt an equivalent source model originally developed for conventional CT Monte Carlo dose quantification to the radiation oncology context and validate its application for evaluating concomitant dose incurred by a kilovoltage (kV) cone-beam CT (CBCT) system integrated into a linear accelerator. Methods: In order to properly characterize beams from the integrated kV CBCT system, the authors have adapted a previously developed equivalent source model consisting of an equivalent spectrum module that takes into account intrinsic filtration and an equivalent filter module characterizing the added bowtie filtration. An equivalent spectrum was generated for an 80, 100, and 125 kVp beam with beam energy characterized by half-value layer measurements. An equivalent filter description was generated from bowtie profile measurements for both the full-and half-bowtie. Equivalent source models for each combination of equivalent spectrum and filter were incorporated into the Monte Carlo software package MCNPX. Monte Carlo simulations were then validated against in-phantom measurements for both the radiographic and CBCT mode of operation of the kV CBCT system. Radiographic and CBCT imaging dose was measured for a variety of protocols at various locations within a body (32 cm in diameter) and head (16 cm in diameter) CTDI phantom. The in-phantom radiographic and CBCT dose was simulated at all measurement locations and converted to absolute dose using normalization factors calculated from air scan measurements and corresponding simulations. The simulated results were compared with the physical measurements and their discrepancies were assessed quantitatively. Results: Strong agreement was observed between in-phantom simulations and measurements. For the radiographic protocols, simulations uniformly underestimated measurements by 0.54%-5.14% (mean difference = −3.07%, SD = 1.60%). For the CBCT protocols, simulations uniformly underestimated measurements by 1.35%-5.31% (mean difference = −3.42%, SD = 1.09%). Conclusions: This work demonstrates the feasibility of using a measurement-based kV CBCT source model to facilitate dose calculations with Monte Carlo methods for both the radiographic and CBCT mode of operation. While this initial work validates simulations against measurements for simple geometries, future work will involve utilizing the source model to investigate kV CBCT dosimetry with more complex anthropomorphic phantoms and patient specific models.

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A comparison of radiation dose measured in CT dosimetry phantoms with calculations using EGS4 and voxel-based computational models

Cited by 42 publications

References 17 publications

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

Effect of ROI filtering in 3D cone‐beam rotational angiography on organ dose and effective dose in cerebral investigations

Development and validation of a measurement‐based source model for kilovoltage cone‐beam CT Monte Carlo dosimetry simulations

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