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Pakravan D, Babapour Mofrad F, Deevband MR, Ghorbani M, Pouraliakbar H. Organ dose in cardiac dual-energy computed tomography: a Monte Carlo study. Phys Eng Sci Med 2022; 45:157-166. [PMID: 35015205 DOI: 10.1007/s13246-021-01098-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 12/30/2021] [Indexed: 11/25/2022]
Abstract
Dual-energy computed tomography (DECT) has appeared as a novel approach with the aim of evaluating artery-related diseases. With the advent of DECT, concerns have been raised about the induction of diseases such as cancer due to high radiation exposure of patients. Therefore, the dose received by patients in DECT should be considered. The parameter most commonly used for patient dosimetry is the effective dose (ED). The purpose of this study is to model and validate a DECT scanner by a developed MCNP Monte Carlo code and to calculate the organ doses, the ED, and the conversion factor (k-factor) used in determining ED in the cardiac imaging protocol. To validate the DECT scanner simulation, a standard dosimetry body phantom was modeled in two radiation modes of single energy CT and DECT. The results of simulated CT dose index (CTDI) were compared with those of ImPACT or measurement data. Then dosimetry phantom was replaced by the male and female ORNL phantoms and the organ doses were calculated. The organ doses were also calculated by ImPACT dose software. In the initial validation stage, the minimum and maximum observed relative differences between results of MNCP simulation and measured were 2.77% and 5.79% for the central CTDI and 1.91% and 5.83% for the averaged peripheral CTDI, respectively. The mean ED of simulation and the ImPACT were 3.23 and 5.55 mSv/100 mAs, and the mean k-factor was 0.016 and 0.032 mSv mGy-1 cm-1 in the male and female phantoms, respectively. The k-factor obtained for males is close to the currently used k-factor, but the k-factor for females is almost twice.
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Affiliation(s)
- Delaram Pakravan
- Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Farshid Babapour Mofrad
- Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
| | - Mohammad Reza Deevband
- Biomedical Engineering and Medical Physics Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mahdi Ghorbani
- Biomedical Engineering and Medical Physics Department, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Hamidreza Pouraliakbar
- Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
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Pakravan D, Babapour Mofrad F, Deevband MR, Ghorbani M, Pouraliakbar H. A Monte Carlo Platform for Characterization of X-Ray Radiation Dose in CT Imaging. J Biomed Phys Eng 2021; 11:271-280. [PMID: 34189115 PMCID: PMC8236108 DOI: 10.31661/jbpe.v0i0.2012-1254] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2020] [Accepted: 02/20/2020] [Indexed: 11/16/2022]
Abstract
Background Computed tomography (CT) is currently known as a versatile imaging tool in the clinic used for almost all types of cancers. The major issue of CT is the health risk, belonging to X-ray radiation exposure. Concerning this, Monte Carlo (MC) simulation is recognized as a key computational technique for estimating and optimizing radiation dose. CT simulation with MCNP/MCNPX MC code has an inherent problem due to the lack of a fan-beam shaped source model. This limitation increases the run time and highly decreases the number of photons passing the body or phantom. Recently, a beta version of MCNP code called MCNP-FBSM (Fan-Beam Source Model) has been developed to pave the simulation way of CT imaging procedure, removing the need of the collimator. This is a new code, which needs to be validated in all aspects. Objective In this work, we aimed to develop and validate an efficient computational platform based on modified MCNP-FBSM for CT dosimetry purposes. Material and Methods In this experimental study, a setup is carried out to measure CTDI100 in air and standard dosimetry phantoms. The accuracy of the developed MC CT simulator results has been widely benchmarked through comparison with our measured data, UK's National Health Service's reports (known as ImPACT), manufacturer's data, and other published results. Results The minimum and maximum observed mean differences of our simulation results and other above-mentioned data were the 1.5%, and 9.79%, respectively. Conclusion The developed FBSM MC computational platform is a beneficial tool for CT dosimetry.
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Affiliation(s)
- Delaram Pakravan
- PhD Candidate, Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Farshid Babapour Mofrad
- PhD, Department of Medical Radiation Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Mohammad Reza Deevband
- PhD, Department of Biomedical Engineering and Medical Physics, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Mahdi Ghorbani
- PhD, Department of Biomedical Engineering and Medical Physics, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - Hamidreza Pouraliakbar
- PhD, Rajaie Cardiovascular Medical and Research Center, Iran University of Medical Sciences, Tehran, Iran
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Radiation Dose Reduction for Computed Tomography Localizer Radiography Using an Ag Additional Filter. J Comput Assist Tomogr 2021; 45:84-92. [PMID: 33475316 DOI: 10.1097/rct.0000000000001026] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE This study aimed to assess the potential of an Ag additional filter attached to the bow tie filter of a computed tomography (CT) scanner to reduce the radiation dose in CT localizer radiography. METHODS Radiation doses in CT localizer radiography with Cu and Ag additional filters were evaluated based on dose measurements and Monte Carlo simulations. Image quality evaluations of an adult torso phantom were performed, and the automatic exposure control performance was evaluated in terms of the water-equivalent thickness estimated from CT localizer radiographs. RESULTS With the Ag additional filter, effective doses were approximately 72% to 75% lower than those with the Cu additional filter. The image quality and water-equivalent thickness with the Ag additional filter were similar to those with the Cu additional filter. CONCLUSIONS The Ag additional filter helped significantly reduce radiation doses in CT localizer radiography while maintaining image quality and performance.
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Yamauchi-Kawaura C, Fujii K, Yamauchi M, Yamamoto S, Kozuka M, Ohzawa N, Suga N, Ito N. SHAPE ESTIMATION OF BOWTIE FILTERS BASED ON THE LUMINESCENCE FROM POLYETHYLENE TEREPHTHALATE RESIN BY X-RAY IRRADIATION. RADIATION PROTECTION DOSIMETRY 2019; 185:432-439. [PMID: 30916354 DOI: 10.1093/rpd/ncz031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 01/27/2019] [Accepted: 02/28/2019] [Indexed: 06/09/2023]
Abstract
In this study, we devised a novel method estimating the bowtie filter shapes by imaging luminescence from a polyethylene terephthalate (PET) resin with X-ray irradiation in a computed tomography (CT) scanner. The luminescence distribution of the PET resin corresponding to the thickness of bowtie filter was imaged using a charge-coupled device camera. On the assumption that the material of bowtie filter is aluminium (Al), the shape of bowtie filters was estimated from the correlation between Al attenuation curves and the angular-dependent luminance attenuation profiles according to the thickness of bowtie filters. Dose simulations based on the estimated bowtie filter shapes were performed using head and body PMMA phantoms with 16 and 32 cm in diameter. The simulated values of head and body weighted CT dose index (CTDIw) based on bowtie filter shape by the luminescence imaging method agreed within ~9% with the measured values by a dosemeter.
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Affiliation(s)
- C Yamauchi-Kawaura
- Department of Radiological Sciences, Graduate School of Medicine, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - K Fujii
- Department of Radiological Sciences, Graduate School of Medicine, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - M Yamauchi
- Division of Radiology, Aichi Medical University Hospital, Nagakute, Aichi 480-1195, Japan
| | - S Yamamoto
- Department of Radiological Sciences, Graduate School of Medicine, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - M Kozuka
- Department of Radiological Technology, School of Health Sciences, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - N Ohzawa
- Department of Radiological Technology, School of Health Sciences, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - N Suga
- Department of Radiological Technology, School of Health Sciences, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
| | - N Ito
- Department of Radiological Technology, School of Health Sciences, Nagoya University, 1-1-20 Daikominami, Higashi-ku, Nagoya 461-8673, Japan
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Scarboro SB, Cody D, Stingo FC, Alvarez P, Followill D, Court L, Zhang D, McNitt‐Gray M, Kry SF. Calibration strategies for use of the nanoDot OSLD in CT applications. J Appl Clin Med Phys 2019; 20:331-339. [PMID: 30426664 PMCID: PMC6333198 DOI: 10.1002/acm2.12491] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 09/26/2018] [Accepted: 10/06/2018] [Indexed: 11/06/2022] Open
Abstract
Aluminum oxide based optically stimulated luminescent dosimeters (OSLD) have been recognized as a useful dosimeter for measuring CT dose, particularly for patient dose measurements. Despite the increasing use of this dosimeter, appropriate dosimeter calibration techniques have not been established in the literature; while the manufacturer offers a calibration procedure, it is known to have relatively large uncertainties. The purpose of this work was to evaluate two clinical approaches for calibrating these dosimeters for CT applications, and to determine the uncertainty associated with measurements using these techniques. Three unique calibration procedures were used to calculate dose for a range of CT conditions using a commercially available OSLD and reader. The three calibration procedures included calibration (a) using the vendor-provided method, (b) relative to a 120 kVp CT spectrum in air, and (c) relative to a megavoltage beam (implemented with 60 Co). The dose measured using each of these approaches was compared to dose measured using a calibrated farmer-type ion chamber. Finally, the uncertainty in the dose measured using each approach was determined. For the CT and megavoltage calibration methods, the dose measured using the OSLD nanoDot was within 5% of the dose measured using an ion chamber for a wide range of different CT scan parameters (80-140 kVp, and with measurements at a range of positions). When calibrated using the vendor-recommended protocol, the OSLD measured doses were on average 15.5% lower than ion chamber doses. Two clinical calibration techniques have been evaluated and are presented in this work as alternatives to the vendor-provided calibration approach. These techniques provide high precision for OSLD-based measurements in a CT environment.
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Affiliation(s)
- Sarah B. Scarboro
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
| | - Dianna Cody
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
| | - Francesco C. Stingo
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
| | - Paola Alvarez
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
| | - David Followill
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
| | - Laurence Court
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
| | - Di Zhang
- Biomedical Physics Graduate ProgramDavid Geffen School of Medicine at UCLALos AngelesCAUSA
- Present address:
Toshiba American Medical SystemsTustinCAUSA
| | - Michael McNitt‐Gray
- The Department of Radiological SciencesDavid Geffen School of Medicine at UCLALos AngelesCAUSA
| | - Stephen F. Kry
- The University of Texas MD Anderson Cancer CenterHoustonTXUSA
- Graduate School of Biomedical SciencesThe University of Texas Health Science Center HoustonHoustonTXUSA
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Muroga K, Fukuzawa A, Tsukioka H, Akizawa Y, Ichikawa K. [Effect of Tube Voltage on Contrast Enhancement and Contrast Medium Dose in Abdominal Contrast-enhanced Computed Tomography]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2018; 74:61-67. [PMID: 29353837 DOI: 10.6009/jjrt.2018_jsrt_74.1.61] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The purpose of this study was to investigate the effect of tube voltage on relationship between a patient's body weight and contrast enhancement in abdominal contrast-enhanced computed tomography (CT). Five phantoms with diameters ranging from 19.2 to 30.6 cm, including syringes filled with iodine solution diluted to different concentrations, were used to compare the effects at tube voltages of 80, 100, and 120 kVp. Furthermore, for clinical study, 300 patients who underwent abdominal contrast-enhanced CT examinations were enrolled and enhancements of aorta and hepatic parenchyma in arterial phase and equilibrium phase were compared at 80, 100, and 120 kVp using a contrast medium administration proportional to the body weight. The contrast enhancement was decreased with increase in phantom size because of the beam-hardening effect, and however, the decrease was less at low tube voltages of 80 and 100 kVp (lowest at 80 kVp), demonstrating the beam-hardening effect was reduced at low tube voltages. The enhancements of aorta and hepatic parenchyma indicated tended to increase in patients with a heavy body weight, and this trend was stronger at 80 and 100 kVp (80 kVp>100 kVp). Therefore, it was indicated that the problem of excessive contrast enhancement in patients with a high body weight was prominent at low tube voltages because the beam-hardening effect in patients with a heavy body weight was weaken by low tube voltages.
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Affiliation(s)
- Koji Muroga
- Department of Diagnostic Radiology, Nagano Red Cross Hospital.,Graduate School of Medical Science, Kanazawa University
| | - Akira Fukuzawa
- Department of Diagnostic Radiology, Nagano Red Cross Hospital
| | | | - Yuka Akizawa
- Department of Diagnostic Radiology, Nagano Red Cross Hospital
| | - Katsuhiro Ichikawa
- Institute of Medical, Pharmaceutical and Health Science, Kanazawa University
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Mathieu KB, McNitt-Gray MF, Cody DD. The impact of x-ray tube stabilization on localized radiation dose in axial CT scans: initial results in CTDI phantoms. Phys Med Biol 2016; 61:7363-7376. [PMID: 27694696 DOI: 10.1088/0031-9155/61/20/7363] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Rise, fall, and stabilization of the x-ray tube output occur immediately before and after data acquisition on some computed tomography (CT) scanners and are believed to contribute additional dose to anatomy facing the x-ray tube when it powers on or off. In this study, we characterized the dose penalty caused by additional radiation exposure during the rise, stabilization, and/or fall time (referred to as overscanning). A 32 cm CT dose-index (CTDI) phantom was scanned on three CT scanners: GE Healthcare LightSpeed VCT, GE Healthcare Discovery CT750 HD, and Siemens Somatom Definition Flash. Radiation exposure was detected for various x-ray tube start acquisition angles using a 10 cm pencil ionization chamber placed in the peripheral chamber hole at the phantom's 12 o'clock position. Scan rotation time, ionization chamber location, phantom diameter, and phantom centering were varied to quantify their effects on the dose penalty caused by overscanning. For 1 s single, axial rotations, CTDI at the 12 o'clock chamber position (CTDI100, 12:00) was 6.1%, 4.0%, and 4.4% higher when the start angle of the x-ray tube was aligned at the top of the gantry (12 o'clock) versus when the start angle was aligned at 9 o'clock for the Siemens Flash, GE CT750 HD, and GE VCT scanner, respectively. For the scanners' fastest rotation times (0.285 s for the Siemens and 0.4 s for both GE scanners), the dose penalties increased to 22.3%, 10.7%, and 10.5%, respectively, suggesting a trade-off between rotation speed and the dose penalty from overscanning. In general, overscanning was shown to have a greater radiation dose impact for larger diameter phantoms, shorter rotation times, and to peripheral phantom locations. Future research is necessary to determine an appropriate method for incorporating the localized dose penalty from overscanning into standard dose metrics, as well as to assess the impact on organ dose.
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Affiliation(s)
- Kelsey B Mathieu
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
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Minehiro K, Takata T, Hayashi H, Sakuda K, Nunome H, Kawashima H, Sanada S. [Phantom Study on Dose Reduction Using Iterative Reconstruction in Low-dose Computed Tomography for Lung Cancer Screening]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2015; 71:1201-1208. [PMID: 26685831 DOI: 10.6009/jjrt.2015_jsrt_71.12.1201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We investigated dose reduction ability of an iterative reconstruction technology for low-dose computed tomography (CT) for lung cancer screening. The Sinogram Affirmed Iterative Reconstruction (SAFIRE) provided in a multi slice CT system, Somatom Definition Flash (Siemens Healthcare) was used. An anthropomorphic chest phantom (N-1, Kyoto Kagaku) was scanned at volume CT dose index (CTDIvol) of 0.50-11.86 mGy with 120 kV. For noise (standard deviation) and contrast-to-noise ratio (CNR) measurements, CTP486 and CTP515 modules in the Catphan (The Phantom Laboratory) were scanned. Radiological technologists were participated in the perceptual comparison. SAFIRE reduced the SD values by approximately 50% compared with filter back projection (FBP). The estimated dose reduction rates by SAFIRE determined from the perceptual comparison was approximately 23%, while 75% dose reduction rate was expected from the SD value reduction of 50%.
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Sommerville M, Poirier Y, Tambasco M. A measurement-based X-ray source model characterization for CT dosimetry computations. J Appl Clin Med Phys 2015; 16:386-400. [PMID: 26699546 PMCID: PMC5691008 DOI: 10.1120/jacmp.v16i6.5231] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2014] [Revised: 07/31/2015] [Accepted: 07/28/2015] [Indexed: 11/23/2022] Open
Abstract
The purpose of this study was to show that the nominal peak tube voltage potential (kVp) and measured half-value layer (HVL) can be used to generate energy spectra and fluence profiles for characterizing a computed tomography (CT) X-ray source, and to validate the source model and an in-house kV X-ray dose computation algorithm (kVDoseCalc) for computing machine- and patient-specific CT dose. Spatial variation of the X-ray source spectra of a Philips Brilliance and a GE Optima Big Bore CT scanner were found by measuring the HVL along the direction of the internal bow-tie filter axes. Third-party software, Spektr, and the nominal kVp settings were used to generate the energy spectra. Beam fluence was calculated by dividing the integral product of the spectra and the in-air NIST mass-energy attenuation coefficients by in-air dose measurements along the filter axis. The authors found the optimal number of photons to seed in kVDoseCalc to achieve dose convergence. The Philips Brilliance beams were modeled for 90, 120, and 140 kVp tube settings. The GE Optima beams were modeled for 80, 100, 120, and 140 kVp tube settings. Relative doses measured using a Capintec Farmer-type ionization chamber (0.65 cc) placed in a cylindrical polymethyl methacrylate (PMMA) phantom and irradiated by the Philips Brilliance, were compared to those computed with kVDoseCalc. Relative doses in an anthropomorphic thorax phantom (E2E SBRT Phantom) irradiated by the GE Optima were measured using a (0.015 cc) PTW Freiburg ionization chamber and compared to computations from kVDoseCalc. The number of photons required to reduce the average statistical uncertainty in dose to < 0.3% was 2 × 105. The average percent difference between calculation and measurement over all 12 PMMA phantom positions was found to be 1.44%, 1.47%, and 1.41% for 90, 120, and 140 kVp, respectively. The maximum percent difference between calculation and measurement for all energies, measurement positions, and phantoms was less than 3.50%. Thirty-five out of a total of 36 simulation conditions were within the experimental uncertainties associated with measurement reproducibility and chamber volume effects for the PMMA phantom. The agreement between calculation and measurement was within experimental uncertainty for 19 out of 20 simulation conditions at five points of interest in the anthropomorphic thorax phantom for the four beam energies modeled. The source model and characterization technique based on HVL measurements and nominal kVp can be used to accurately compute CT dose. This accuracy provides experimental validation of kVDoseCalc for computing CT dose.
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Ichikawa K, Kobayashi T, Sagawa M, Katagiri A, Uno Y, Nishioka R, Matsuyama J. A phantom study investigating the relationship between ground-glass opacity visibility and physical detectability index in low-dose chest computed tomography. J Appl Clin Med Phys 2015; 16:202–215. [PMID: 26218991 PMCID: PMC5690005 DOI: 10.1120/jacmp.v16i4.5001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 03/19/2015] [Accepted: 03/16/2015] [Indexed: 12/02/2022] Open
Abstract
In this study, the relationship between ground-glass opacity (GGO) visibility and physical detectability index in low-dose computed tomography (LDCT) for lung cancer screening was investigated. An anthropomorphic chest phantom that included synthetic GGOs with CT numbers of -630 Hounsfield units (HU; high attenuation GGO: HGGO) and -800 HU (low attenuation GGO: LGGO), and three phantoms for physical measurements were employed. The phantoms were scanned using 12 CT systems located in 11 screening centers in Japan. The slice thicknesses and CT dose indices (CTDI(vol)) varied over 1.0-5.0 mm and 0.85-3.30 mGy, respectively, and several reconstruction kernels were used. Physical detectability index values were calculated from measurements of resolution, noise, and slice thickness properties for all image sets. Five radiologists and one thoracic surgeon, blind to one another's observations, evaluated GGO visibility using a five-point scoring system. The physical detectability index correlated reasonably well with the GGO visibility (R² = 0.709, p < 0.01 for 6 mm HGGO and R² = 0.646, p < 0.01 for 10 mm LGGO), and was nearly proportional to the CTDI(vol). Consequently, the CTDI(vol) also correlated reasonably well with the GGO visibility (R² = 0.701, p < 0.01 for 6 mm HGGO and R² = 0.680, p < 0.01 for 10 mm LGGO). As a result, the CTDI(vol) was nearly dominant in the GGO visibility for image sets with different reconstruction kernels and slice thicknesses, used in this study.
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Bostani M, McMillan K, DeMarco JJ, Cagnon CH, McNitt-Gray MF. Validation of a Monte Carlo model used for simulating tube current modulation in computed tomography over a wide range of phantom conditions/challenges. Med Phys 2015; 41:112101. [PMID: 25370652 DOI: 10.1118/1.4887807] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Monte Carlo (MC) simulation methods have been widely used in patient dosimetry in computed tomography (CT), including estimating patient organ doses. However, most simulation methods have undergone a limited set of validations, often using homogeneous phantoms with simple geometries. As clinical scanning has become more complex and the use of tube current modulation (TCM) has become pervasive in the clinic, MC simulations should include these techniques in their methodologies and therefore should also be validated using a variety of phantoms with different shapes and material compositions to result in a variety of differently modulated tube current profiles. The purpose of this work is to perform the measurements and simulations to validate a Monte Carlo model under a variety of test conditions where fixed tube current (FTC) and TCM were used. METHODS A previously developed MC model for estimating dose from CT scans that models TCM, built using the platform of mcnpx, was used for CT dose quantification. In order to validate the suitability of this model to accurately simulate patient dose from FTC and TCM CT scan, measurements and simulations were compared over a wide range of conditions. Phantoms used for testing range from simple geometries with homogeneous composition (16 and 32 cm computed tomography dose index phantoms) to more complex phantoms including a rectangular homogeneous water equivalent phantom, an elliptical shaped phantom with three sections (where each section was a homogeneous, but different material), and a heterogeneous, complex geometry anthropomorphic phantom. Each phantom requires varying levels of x-, y- and z-modulation. Each phantom was scanned on a multidetector row CT (Sensation 64) scanner under the conditions of both FTC and TCM. Dose measurements were made at various surface and depth positions within each phantom. Simulations using each phantom were performed for FTC, detailed x-y-z TCM, and z-axis-only TCM to obtain dose estimates. This allowed direct comparisons between measured and simulated dose values under each condition of phantom, location, and scan to be made. RESULTS For FTC scans, the percent root mean square (RMS) difference between measurements and simulations was within 5% across all phantoms. For TCM scans, the percent RMS of the difference between measured and simulated values when using detailed TCM and z-axis-only TCM simulations was 4.5% and 13.2%, respectively. For the anthropomorphic phantom, the difference between TCM measurements and detailed TCM and z-axis-only TCM simulations was 1.2% and 8.9%, respectively. For FTC measurements and simulations, the percent RMS of the difference was 5.0%. CONCLUSIONS This work demonstrated that the Monte Carlo model developed provided good agreement between measured and simulated values under both simple and complex geometries including an anthropomorphic phantom. This work also showed the increased dose differences for z-axis-only TCM simulations, where considerable modulation in the x-y plane was present due to the shape of the rectangular water phantom. Results from this investigation highlight details that need to be included in Monte Carlo simulations of TCM CT scans in order to yield accurate, clinically viable assessments of patient dosimetry.
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Affiliation(s)
- Maryam Bostani
- Departments of Biomedical Physics and Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024
| | - Kyle McMillan
- Departments of Biomedical Physics and Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024
| | - John J DeMarco
- Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, California 90095
| | - Chris H Cagnon
- Departments of Biomedical Physics and Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024
| | - Michael F McNitt-Gray
- Departments of Biomedical Physics and Radiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90024
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Kim S, Song H, Movsas B, Chetty IJ. Characteristics of x-ray beams in two commercial multidetector computed tomography simulators: Monte Carlo simulations. Med Phys 2011; 39:320-9. [DOI: 10.1118/1.3670377] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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13
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Mathieu KB, Kappadath SC, White RA, Atkinson EN, Cody DD. An empirical model of diagnostic x-ray attenuation under narrow-beam geometry. Med Phys 2011; 38:4546-55. [PMID: 21928626 DOI: 10.1118/1.3592933] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The purpose of this study was to develop and validate a mathematical model to describe narrow-beam attenuation of kilovoltage x-ray beams for the intended applications of half-value layer (HVL) and quarter-value layer (QVL) estimations, patient organ shielding, and computer modeling. METHODS An empirical model, which uses the Lambert W function and represents a generalized Lambert-Beer law, was developed. To validate this model, transmission of diagnostic energy x-ray beams was measured over a wide range of attenuator thicknesses [0.49-33.03 mm Al on a computed tomography (CT) scanner, 0.09-1.93 mm Al on two mammography systems, and 0.1-0.45 mm Cu and 0.49-14.87 mm Al using general radiography]. Exposure measurements were acquired under narrow-beam geometry using standard methods, including the appropriate ionization chamber, for each radiographic system. Nonlinear regression was used to find the best-fit curve of the proposed Lambert W model to each measured transmission versus attenuator thickness data set. In addition to validating the Lambert W model, we also assessed the performance of two-point Lambert W interpolation compared to traditional methods for estimating the HVL and QVL [i.e., semi-logarithmic (exponential) and linear interpolation]. RESULTS The Lambert W model was validated for modeling attenuation versus attenuator thickness with respect to the data collected in this study (R2 > 0.99). Furthermore, Lambert W interpolation was more accurate and less sensitive to the choice of interpolation points used to estimate the HVL and/or QVL than the traditional methods of semilogarithmic and linear interpolation. CONCLUSIONS The proposed Lambert W model accurately describes attenuation of both monoenergetic radiation and (kilovoltage) polyenergetic beams (under narrow-beam geometry).
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Affiliation(s)
- Kelsey B Mathieu
- Department of Bioengineering, Rice University, Houston, Texas 77005, USA.
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Goshima S, Kanematsu M, Nishibori H, Sakurai K, Miyazawa D, Watanabe H, Kondo H, Shiratori Y, Onozuka M, Moriyama N, Bae KT. CT of the Pancreas: Comparison of Anatomic Structure Depiction, Image Quality, and Radiation Exposure between 320-Detector Volumetric Images and 64-Detector Helical Images. Radiology 2011; 260:139-47. [DOI: 10.1148/radiol.11101459] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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