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Fadhel MN, Grizzard K, Vergara D, Franco RP, Zhao A, Hoerner M. The use of pencil ionization chamber with temporal readout capabilities to measure CT beam full width half maximum. Med Phys 2024; 51:4687-4695. [PMID: 38758726 DOI: 10.1002/mp.17084] [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: 06/29/2023] [Revised: 02/07/2024] [Accepted: 04/02/2024] [Indexed: 05/19/2024] Open
Abstract
BACKGROUND Measurement of Computed Tomography (CT) beam width is required by accrediting and regulating bodies for routine physics evaluations due to its direct correlation to patient dose. Current methods for performing CT beam width measurement require special hardware, software, and/or consumable films. Today, most 100-mm pencil chambers with a digital interface used to evaluate Computed Tomography Dose Index (CTDIvol) have a sufficiently high sampling rate to reconstruct a high-resolution dose profile for any acquisition mode. PURPOSE The goal of this study is to measure the CT beam width from the sampled dose profile under a single helical acquisition with the 100-mm pencil chamber used for CTDIvol measurements. METHODS The dose profiles for different scanners were measured for helical scans with varying collimation settings using a 100-mm pencil chamber placed at the isocenter and co-moving with the patient table. The measured dose profiles from the 100-mm pencil chamber were corrected for table attenuation by extracting a periodic correction function (PCF) to eliminate table interference. The corrected dose profiles were then deconvolved with the response function of the chamber to compute the beam profile. The beam width was defined by the full width half maximum (FWHM) of the resulting beam profile. Reference dose profiles were also measured using Gafchromic film for comparison. RESULTS The beam widths, estimated using the innovative deconvolution method from the 100-mm pencil chamber, exhibit an average percentage difference of 1.6 ± 1.8 when compared with measurements obtained through Gafchromic film for beam width assessment. CONCLUSION The proposed approach to deconvolve the pencil chamber response demonstrates the potential of obtaining the CT beam width at high accuracy without the need of special hardware, software, or consumable films. This technique can improve workflow for routine performance evaluation of CT systems.
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Affiliation(s)
- Muhannad N Fadhel
- Department of Radiology, Northwestern University, Chicago, Illinois, USA
| | - Kevin Grizzard
- Department of Radiology, Yale New Haven Health, New Haven, Connecticut, USA
| | - Daniel Vergara
- Department of Radiology, University of Washington, Seattle, Washington, USA
| | | | - Anzi Zhao
- Department of Radiology, Northwestern University, Chicago, Illinois, USA
| | - Matthew Hoerner
- Department of Radiology, Yale New Haven Health, New Haven, Connecticut, USA
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Costa PR, Nersissian DY, Umisedo NK, Gonzales AHL, Fernández-Varea JM. A comprehensive Monte Carlo study of CT dose metrics proposed by the AAPM Reports 111 and 200. Med Phys 2021; 49:201-218. [PMID: 34800303 DOI: 10.1002/mp.15306] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2021] [Revised: 09/22/2021] [Accepted: 10/10/2021] [Indexed: 11/11/2022] Open
Abstract
PURPOSE A Monte Carlo (MC) modeling of single axial and helical CT scan modes has been developed to compute single and accumulated dose distributions. The radiation emission characteristics of an MDCT scanner has been modeled and used to evaluate the dose deposition in infinitely long head and body PMMA phantoms. The simulated accumulated dose distributions determined the approach to equilibrium function, H(L). From these H ( L ) curves, dose-related information was calculated for different head and body clinical protocols. METHODS The PENELOPE/penEasy package has been used to model the single axial and helical procedures and the radiation transport of photons and electrons in the phantoms. The bowtie filters, heel effect, focal-spot angle, and fan-beam geometry were incorporated. Head and body protocols with different pitch values were modeled for x-ray spectra corresponding to 80, 100, 120, and 140 kV. The analytical formulation for the single dose distributions and experimental measurements of single and accumulated dose distributions were employed to validate the MC results. The experimental dose distributions were measured with OSLDs and a thimble ion chamber inserted into PMMA phantoms. Also, the experimental values of the C T D I 100 along the center and peripheral axes of the CTDI phantom served to calibrate the simulated single and accumulated dose distributions. RESULTS The match of the simulated dose distributions with the reference data supports the correct modeling of the heel effect and the radiation transport in the phantom material reflected in the tails of the dose distributions. The validation of the x-ray source model was done comparing the CTDI ratios between simulated, measured and CTDosimetry data. The average difference of these ratios for head and body protocols between the simulated and measured data was in the range of 13-17% and between simulated and CTDosimetry data varied 10-13%. The distributions of simulated doses and those measured with the thimble ion chamber are compatible within 3%. In this study, it was demonstrated that the efficiencies of the C T D I 100 measurements in head phantoms with nT = 20 mm and 120 kV are 80.6% and 87.8% at central and peripheral axes, respectively. In the body phantoms with n T = 40 mm and 120 kV, the efficiencies are 56.5% and 86.2% at central and peripheral axes, respectively. In general terms, the clinical parameters such as pitch, beam intensity, and voltage affect the Deq values with the increase of the pitch decreasing the Deq and the beam intensity and the voltage increasing its value. The H(L) function does not change with the pitch values, but depends on the phantom axis (central or peripheral). CONCLUSIONS The computation of the pitch-equilibrium dose product, D ̂ eq , evidenced the limitations of the C T D I 100 method to determine the dose delivered by a CT scanner. Therefore, quantities derived from the C T D I 100 propagate this limitation. The developed MC model shows excellent compatibility with both measurements and literature quantities defined by AAPM Reports 111 and 200. These results demonstrate the robustness and versatility of the proposed modeling method.
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Affiliation(s)
- Paulo R Costa
- Institute of Physics, University of São Paulo, São Paulo, SP, Brazil
| | | | - Nancy K Umisedo
- Institute of Physics, University of São Paulo, São Paulo, SP, Brazil
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Hernandez AM, Shin DW, Abbey CK, Seibert JA, Akino N, Goto T, Vaishnav JY, Boedeker KL, Boone JM. Validation of synthesized normal‐resolution image data generated from high‐resolution acquisitions on a commercial CT scanner. Med Phys 2020; 47:4775-4785. [DOI: 10.1002/mp.14395] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 06/08/2020] [Accepted: 06/29/2020] [Indexed: 12/19/2022] Open
Affiliation(s)
| | | | - Craig K. Abbey
- Department of Psychological & Brain Sciences University of California Santa Barbara Santa Barbara CA USA
| | - J. Anthony Seibert
- Department of Radiology University of California Davis Sacramento CA USA
| | | | | | | | | | - John M. Boone
- Department of Radiology University of California Davis Sacramento CA USA
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Al‐Senan R. A method to estimate transmission profiles of bow‐tie filters using rotating tube measurements. Med Phys 2018; 45:4964-4976. [DOI: 10.1002/mp.13203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Revised: 09/03/2018] [Accepted: 09/09/2018] [Indexed: 01/20/2023] Open
Affiliation(s)
- Rani Al‐Senan
- Department of Radiology Columbia University Medical Center 177 Ft Washington Ave. New York NY 10032 USA
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Muryn JS, Morgan AG, Liptak CL, Dong FF, Segars WP, Primak AN, Li X. Analysis of uncertainties in Monte Carlo simulated organ and effective dose in chest CT: scanner- and scan-related factors. Phys Med Biol 2017; 62:3175-3203. [DOI: 10.1088/1361-6560/aa60d7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Yang K, Li X, George Xu X, Liu B. Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration. Med Phys 2017; 44:57-70. [PMID: 28102951 DOI: 10.1002/mp.12024] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 11/03/2016] [Accepted: 11/12/2016] [Indexed: 01/28/2023] Open
Abstract
PURPOSE To accurately measure the beam filter profiles from a variety of CT scanner models and to provide reference data for Monte Carlo simulations of CT scanners. METHODS This study proposed a new method to measure CT beam filter profiles using a linear-array x-ray detector (X-Scan 0.8f3-512; Detection Technology Inc., Espoo, Finland) under gantry rotation mode. A robust geometrical calibration approach was developed to determine key geometrical parameters by considering the x-ray focal spot location relative to the linear-array detector and the gantry's angular increment at each acquisition point. CT beam intensity profiles were synthesized from continuously measured data during a 10° gantry rotation range with calibrated detector response and system geometry information. Relative transmission profiles of nineteen sets of beam filters were then derived for nine different CT scanner models from three different manufacturers. Equivalent aluminum thickness profiles of these beam filters were determined by analytical calculation using the Spektr Matlab software package to match the measured transmission profiles. Three experiments were performed to validate the accuracy of the geometrical calibration, detector response modeling, and the derived equivalent aluminum thickness profiles. RESULTS The beam intensity profiles measured from gantry rotation mode showed very good agreement with those measured with gantry stationary mode, with a maximal difference of 3%. The equivalent aluminum thickness determined by this proposed method agreed well with what was measured by an ion chamber, with a mean difference of 0.4%. The determined HVL profiles matched well with data from a previous study (max difference of 4.7%). CONCLUSIONS An accurate and robust method to directly measure profiles from a broad list of beam filters and CT scanner models was developed, implemented, and validated. Useful reference data was provided for future research on CT system modeling.
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Affiliation(s)
- Kai Yang
- Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA
| | - Xinhua Li
- Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA
| | - X George Xu
- Nuclear Engineering Program, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA
| | - Bob Liu
- Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114, USA
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Kramer R, Cassola VF, Andrade MEA, de Araújo MWC, Brenner DJ, Khoury HJ. Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry. Phys Med Biol 2017; 62:781-809. [PMID: 28072578 DOI: 10.1088/1361-6560/aa5343] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
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, CTDIw, defined in two cylindrical PMMA phantoms of 16 cm and 32 cm diameter. With an EGSnrc-based Monte Carlo (MC) code, ratios CTDIw/CTDI100,a 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 CTDIw/CTDI100,a matches ratios CTDIw/CTDI100,a, 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 CTDIw/CTDI100,a considering 11 different CT scanners and for CTDI100,c, CTDI100,p and their ratio considering 4 different CT scanners. Additionally, comparisons were made for lateral dose profiles free in air and using computational anthropomorphic phantoms. CTDIw/CTDI100,a 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 CTDI100,c/CTDI100, p 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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Affiliation(s)
- R Kramer
- Department of Nuclear Energy, Federal University of Pernambuco, Avenida Prof Luiz Freire, 1000, CEP 50740-540, Recife, Brazil
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Li X, Shi JQ, Zhang D, Singh S, Padole A, Otrakji A, Kalra MK, Xu XG, Liu B. A new technique to characterize CT scanner bow-tie filter attenuation and applications in human cadaver dosimetry simulations. Med Phys 2016; 42:6274-82. [PMID: 26520720 DOI: 10.1118/1.4932364] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
PURPOSE To present a noninvasive technique for directly measuring the CT bow-tie filter attenuation with a linear array x-ray detector. METHODS A scintillator based x-ray detector of 384 pixels, 307 mm active length, and fast data acquisition (model X-Scan 0.8c4-307, Detection Technology, FI-91100 Ii, Finland) was used to simultaneously detect radiation levels across a scan field-of-view. The sampling time was as short as 0.24 ms. To measure the body bow-tie attenuation on a GE Lightspeed Pro 16 CT scanner, the x-ray tube was parked at the 12 o'clock position, and the detector was centered in the scan field at the isocenter height. Two radiation exposures were made with and without the bow-tie in the beam path. Each readout signal was corrected for the detector background offset and signal-level related nonlinear gain, and the ratio of the two exposures gave the bow-tie attenuation. The results were used in the geant4 based simulations of the point doses measured using six thimble chambers placed in a human cadaver with abdomen/pelvis CT scans at 100 or 120 kV, helical pitch at 1.375, constant or variable tube current, and distinct x-ray tube starting angles. RESULTS Absolute attenuation was measured with the body bow-tie scanned at 80-140 kV. For 24 doses measured in six organs of the cadaver, the median or maximum difference between the simulation results and the measurements on the CT scanner was 8.9% or 25.9%, respectively. CONCLUSIONS The described method allows fast and accurate bow-tie filter characterization.
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Affiliation(s)
- Xinhua Li
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Jim Q Shi
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Da Zhang
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Sarabjeet Singh
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Atul Padole
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Alexi Otrakji
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - Mannudeep K Kalra
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
| | - X George Xu
- Nuclear Engineering Program, Rensselaer Polytechnic Institute, Troy, New York 12180
| | - Bob Liu
- Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114
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