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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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Tanki N, Katsuda T, Gotanda R, Gotanda T, Imai S, Kawaji Y, Noguchi A, Kuwano T, Fujita H, Takeda Y. THE CONCEPT OF X-RAY CT DOSE EVALUATION METHOD USING RADIOCHROMIC FILM AND FILM-FOLDING PHANTOM. RADIATION PROTECTION DOSIMETRY 2021; 193:96-104. [PMID: 33786601 DOI: 10.1093/rpd/ncab033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 11/22/2020] [Accepted: 02/15/2021] [Indexed: 06/12/2023]
Abstract
In this paper, we propose a novel radiochromic film (RCF)-based computed tomography (CT) dosimetry method, which is different from the method based on CT dose index. RCF dosimetry using Gafchromic QA2 films was performed using two lengths of film-folding phantoms. The phantom was exposed to X-ray CT through a single scan, while the RCF was sandwiched between the phantoms. We analysed the dose profile curve in two directions to investigate the dose distribution. We observed a difference in the dose distribution as the phantom size changed. Our results contradict with the results of previous studies such as Monte Carlo simulation or direct measurement. The ability to visually evaluate 2D dose distributions is an advantage of RCF dosimetry over other methods. This research investigated the ability of 2D X-ray CT dose evaluation using RCF and film-folding phantom.
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Affiliation(s)
- Nobuyoshi Tanki
- Department of Radiological Technology, Graduate School of Health Sciences, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
- Brain Activity Imaging Center, ATR-Promotions Inc., 2-2-2 Hikaridai, Sorakugun Seika-cho, Kyoto 619-0288, Japan
| | - Toshizo Katsuda
- Department of Medical Radiation Sciences, Shizuoka College of Medicalcare Science, 2000 Hiraguchi, Hamakita-ku, Hamamatsu, 434-0041 Shizuoka, Japan
| | - Rumi Gotanda
- Department of Radiological Technology, Faculty of Health Science and Technology, Kawasaki University of Medical Welfare, 288 Matsushima, Kurashiki, 701-0193 Okayama, Japan
| | - Tatsuhiro Gotanda
- Department of Radiological Technology, Faculty of Health Science and Technology, Kawasaki University of Medical Welfare, 288 Matsushima, Kurashiki, 701-0193 Okayama, Japan
| | - Shinya Imai
- Department of Radiological Science, Faculty of Health Science, Morinomiya University of Medical Sciences, 1-26-16 Nankou-kita, Suminoe-ku, 559-8611 Osaka, Japan
| | - Yasuyuki Kawaji
- Department of Radiological Science, Faculty of Health Sciences, Junshin Gakuen University, 1-1-1 Chikushioka, Minami-ku, 815-8510 Fukuoka, Japan
| | - Atsushi Noguchi
- Aoi Hospital, Medical Incorporated Association Seishokai, 6-14-2 Aramaki, Itami, 664-0001 Hyogo, Japan
| | - Tadao Kuwano
- Osaka Center for Cancer and Cardiovasucular Disease Prevention, 1-6-107 Morinomiya, Joutou-ku, 536-8588 Osaka, Japan
| | - Hideki Fujita
- Department of Radiation Oncology, Osaka Saiseikai Nakatsu Hospital, 2-10-39 Shibata, Kita-ku 530-0012 Osaka, Japan
| | - Yoshihiro Takeda
- Department of Radiological Technology, Graduate School of Health Sciences, Okayama University, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
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Rawashdeh M, Saade C, Zaitoun M, Abdelrahman M, Brennan P, Alewaidat H, McEntee MF. Establishment of diagnostic reference levels in cardiac computed tomography. J Appl Clin Med Phys 2019; 20:181-186. [PMID: 31469229 PMCID: PMC6807208 DOI: 10.1002/acm2.12711] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2019] [Revised: 08/03/2019] [Accepted: 08/07/2019] [Indexed: 11/14/2022] Open
Abstract
The aim of this study was to determine diagnostic reference levels (DRLs) for cardiac computed tomography (CCT) in Jordan. Volume computed tomography dose index (CTDIvol) and dose–length product (DLP) were collected from 228 CCTs performed at seven Jordanian hospitals specialized in cardiac CT. DRLs for cardiac CT were defined at the 75th percentile of CTDIvol and DLP. CTDIvol and DLP were collected from 30 successive cardiac CT in each center except for one center (18 scans). The 75th percentile of the CTDIvol and the DLP of the centers calculated from mixed retrospective and prospective gated modes were 47.74 milligray (mGy) and 1035 mGy/cm, respectively. This study demonstrated wide dose variations among the surveyed hospitals for cardiac CT scans; there was a 5.1‐fold difference between the highest and lowest median DLP with a range of 223.2–1146.7 mGy/cm. Differences were associated with variations in the mAs and kVp. This study confirmed large variability in CTDIvol and DLP for cardiac CT scans; variation was associated with acquisition protocols and highlights the need for dose optimization. DRLs are proposed for CCT; there remains substantial potential for optimization of cardiac CT examinations for adults in Jordan.
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Affiliation(s)
- Mohammad Rawashdeh
- Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid, Jordan
| | - Charbel Saade
- Department of Diagnostic Radiology, American University of Beirut Medical Center, Beirut, Lebanon
| | - Maha Zaitoun
- Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid, Jordan
| | - Mostafa Abdelrahman
- Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid, Jordan
| | - Patrick Brennan
- Faculty of Health Sciences, Medical Image Optimization and Perception Group (MIOPeG), and the Brain and Mind Centre, The University of Sydney, Sydney, NSW, Australia
| | - Haytham Alewaidat
- Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid, Jordan
| | - Mark F McEntee
- Discipline of Diagnostic Radiography, UG 12 Aras Watson, Brookfield Health Sciences, University College Cork, College Road, Cork, Ireland
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Paschoal C, Ferreira F, Souza D, Santos L. Comparison of dose measurements in CT using a photodiode and a small ion chamber. RADIAT MEAS 2016. [DOI: 10.1016/j.radmeas.2016.05.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Weir VJ. A model of CT dose profiles in Banach space; with applications to CT dosimetry. Phys Med Biol 2016; 61:5020-38. [DOI: 10.1088/0031-9155/61/13/5020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abuhaimed A, Martin CJ, Sankaralingam M, Gentle DJ. A Monte Carlo investigation of cumulative dose measurements for cone beam computed tomography (CBCT) dosimetry. Phys Med Biol 2015; 60:1519-42. [PMID: 25615012 DOI: 10.1088/0031-9155/60/4/1519] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Many studies have shown that the computed tomography dose index (CTDI100) which is considered as a main dose descriptor for CT dosimetry fails to provide a realistic reflection of the dose involved in cone beam computed tomography (CBCT) scans. Several practical approaches have been proposed to overcome drawbacks of the CTDI100. One of these is the cumulative dose concept. The purpose of this study was to investigate four different approaches based on the cumulative dose concept: the cumulative dose (1) f(0,150) and (2) f(0,∞) with a small ionization chamber 20 mm long, and the cumulative dose (3) f100(150) and (4) f100(∞) with a standard 100 mm pencil ionization chamber. The study also aimed to investigate the influence of using the 20 and 100 mm chambers and the standard and the infinitely long phantoms on cumulative dose measurements. Monte Carlo EGSnrc/BEAMnrc and EGSnrc/DOSXYZnrc codes were used to simulate a kV imaging system integrated with a TrueBeam linear accelerator and to calculate doses within cylindrical head and body PMMA phantoms with diameters of 16 cm and 32 cm, respectively, and lengths of 150, 600, 900 mm. f(0,150) and f100(150) approaches were studied within the standard PMMA phantoms (150 mm), while the other approaches f(0,∞) and f100(∞) were within infinitely long head (600 mm) and body (900 mm) phantoms. CTDI∞ values were used as a standard to compare the dose values for the approaches studied at the centre and periphery of the phantoms and for the weighted values. Four scanning protocols and beams of width 20-300 mm were used. It has been shown that the f(0,∞) approach gave the highest dose values which were comparable to CTDI∞ values for wide beams. The differences between the weighted dose values obtained with the 20 and 100 mm chambers were significant for the beam widths <120 mm, but these differences declined with increasing beam widths to be within 4%. The weighted dose values calculated within the infinitely long phantoms with both the chambers for the beam widths ≤140 were within 3% of those within the standard phantoms, but the differences rose to be within 15% at wider beams. By comparing the approaches studied in this investigation with other methodologies taking into account the efficiency of the approach as a dose descriptor and the simplicity of the implementation in the clinical environment, the f(0,150) method may be the best for CBCT dosimetry combined with the use of correction factors.
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Affiliation(s)
- Abdullah Abuhaimed
- Radiotherapy Physics, Department of Clinical Physics and Bioengineering, Beatson West of Scotland Cancer Centre, Glasgow, UK. Department of Clinical Physics, University of Glasgow, Glasgow, UK. Department of Applied Physics, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia
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Zhang D, Li X, Gao Y, Xu XG, Liu B. A method to acquire CT organ dose map using OSL dosimeters and ATOM anthropomorphic phantoms. Med Phys 2014; 40:081918. [PMID: 23927332 DOI: 10.1118/1.4816299] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
PURPOSE To present the design and procedure of an experimental method for acquiring densely sampled organ dose map for CT applications, based on optically stimulated luminescence (OSL) dosimeters "nanoDots" and standard ATOM anthropomorphic phantoms; and to provide the results of applying the method--a dose data set with good statistics for the comparison with Monte Carlo simulation result in the future. METHODS A standard ATOM phantom has densely located holes (in 3×3 cm or 1.5×1.5 cm grids), which are too small (5 mm in diameter) to host many types of dosimeters, including the nanoDots. The authors modified the conventional way in which nanoDots are used, by removing the OSL disks from the holders before inserting them inside a standard ATOM phantom for dose measurements. The authors solved three technical difficulties introduced by this modification: (1) energy dependent dose calibration for raw OSL readings; (2) influence of the brief background exposure of OSL disks to dimmed room light; (3) correct pairing between the dose readings and measurement locations. The authors acquired 100 dose measurements at various positions in the phantom, which was scanned using a clinical chest protocol with both angular and z-axis tube current modulations. RESULTS Dose calibration was performed according to the beam qualities inside the phantom as determined from an established Monte Carlo model of the scanner. The influence of the brief exposure to dimmed room light was evaluated and deemed negligible. Pairing between the OSL readings and measurement locations was ensured by the experimental design. The organ doses measured for a routine adult chest scan protocol ranged from 9.4 to 18.8 mGy, depending on the composition, location, and surrounding anatomy of the organs. The dose distribution across different slices of the phantom strongly depended on the z-axis mA modulation. In the same slice, doses to the soft tissues other than the spinal cord demonstrated relatively small variations, with the maximum COV around 11.4%. This might be attributed to the angular mA modulation, the placement of the dosimeters, the chest cavity of the scanned region, and the size of the phantom. Doses to the spinal cord were consistently lower than those to other soft tissues. CONCLUSIONS The method is suited for acquiring densely sampled organ dose maps, and can be used for studying dose distributions relevant to subject size, organ location, and clinical CT protocols.
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Affiliation(s)
- Da Zhang
- Division of Diagnostic Imaging Physics and Webster Center for Advanced Research and Education in Radiation, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Li X, Zhang D, Liu B. Monte Carlo assessment of CT dose equilibration in PMMA and water cylinders with diameters from 6 to 55 cm. Med Phys 2013; 40:031903. [PMID: 23464318 DOI: 10.1118/1.4790470] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE In multidetector CT, the dose integral DIL of single scan dose profile over the integration interval (-L/2, L/2) can predict the accumulated dose DL(0) at the center of the scan range (-L/2, L/2) for a helical scan of pitch = 1. Both DIL and DL(0) increase with L until the limiting levels (DI∞ and Deq) are reached. The DL(0) equilibration is related to the DIL equilibration. The aim of this study was to evaluate the DIL∕DI∞ growth curve, and its variations with factors such as phantom diameter, phantom axis (center or periphery), material (PMMA or water), tube voltage, and bowtie filter (head or body). METHODS A Geant4-based Monte Carlo program was used to simulate single axial scans on a clinical CT scanner, and to compute axial dose profiles in the cylinders of 90 cm in length, and 6-50 cm (PMMA) and 6-55 cm (water) in diameters. DIL∕DI∞ ratios were calculated over a range of integration lengths, and were fitted to a mathematical model: f(L) = 1 - α × exp[ - (L/d)(n)], where α, d, and n were fitting parameters. The minimum length required for DIL to approach within 2% of DI∞ was referred to as the equilibrium length Leq. It could be directly derived from data, and was also calculated from the fits. RESULTS The Leq results of the above two approaches were consistent (deviation: 1.4% on average, and 3.6% maximum). When the other conditions (such as tube voltage, bowtie filter, and phantom material) were the same, DI∞ increased with the reduced phantom diameters. The center/periphery DI∞ ratio was greater than 1 for small phantoms, and increased with larger phantoms until their diameters were above about 16 cm. Dose to water was substantially higher than that to PMMA, especially at the centers of large phantoms. As phantom diameter increased, α, n, and Leq increased on the central axis, and initially increased and then saturated [α ≈ 0.555 (PMMA and water), n ≈ 0.81 (PMMA) and 0.80 (water), and Leq ≈ 29 cm (PMMA) and 30 cm (water)] on the peripheral axis. Bowtie filter and tube voltage affected dose, but had small effects on α, n, and Leq. Leq was almost constant on the central or peripheral phantom axis for beam widths from 0.1 to 40 mm. CONCLUSIONS The mathematical model can represent the DIL∕DI∞ curve from a single axial CT scan. Generally, n ≠ 1. The equilibrium dose, α, n, and Leq exhibit strong dependencies on phantom diameter and location in the phantom. On the other hand, α, n, and Leq have relatively weak dependencies on material (PMMA or water), tube voltage (80-140 kVp), and bowtie filter, and Leq is also insensitive to beam width (≤4 cm). A weak dependency of the DIL∕DI∞ curve on CT scanner using 80-140 kVp and beam width up to 4 cm is consistent with the results of this study and previous publications. The dose equilibration data provided in this paper can be useful for CT dose evaluation. A framework is presented for assessing dose at any point in infinitely long PMMA and water cylinders undergoing multidetector CT examinations.
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Affiliation(s)
- Xinhua Li
- Division of Diagnostic Imaging Physics, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA
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Oliveira BB, Mourão AP, Silva TAD. Estimativa dos valores de MSAD em procedimentos de tomografia computadorizada utilizando filmes radiocrômicos. Radiol Bras 2013. [DOI: 10.1590/s0100-39842013000200013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
OBJETIVO: Verificar a viabilidade de filmes radiocrômicos como um dosímetro alternativo para estimativa da dose média em cortes múltiplos a partir dos perfis de kerma. MATERIAIS E MÉTODOS: Os filmes foram distribuídos em cilindros posicionados no centro e nas regiões periféricas de um objeto simulador padrão de abdome utilizado para dosimetria em tomografia computadorizada. RESULTADOS: Os valores de dose média em cortes múltiplos calculados foram 13,6 ± 0,7, 13,5 ± 0,7 e 18,7 ± 1,0 mGy para os valores de passo (pitch) de 0,75, 1,00 e 1,50, respectivamente. CONCLUSÃO: Apesar de os resultados mostrarem valores menores que o nível de referência de radiodiagnóstico de 25 mGy estabelecido pela legislação brasileira para exames de abdome, eles sugerem que há espaço para otimização dos procedimentos e uma revisão do valor para o nível de referência de radiodiagnóstico brasileiro.
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Liao YL, Kao HC, Chuang KS, Chen CP, Tsai HY. CT dose estimation using Gafchromic XR-CT film: Models comparison. RADIAT MEAS 2011. [DOI: 10.1016/j.radmeas.2011.08.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Martin CJ, Gentle DJ, Sookpeng S, Loveland J. Application of Gafchromic film in the study of dosimetry methods in CT phantoms. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2011; 31:389-409. [PMID: 22089894 DOI: 10.1088/0952-4746/31/4/001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Gafchromic film has been used for measurement of computed tomography (CT) dose distributions within phantoms. The film was calibrated in the beam from a superficial therapy unit and the accuracy confirmed by comparison with measurements with a 20 mm long ionisation chamber. The results have been used to investigate approaches to CT dosimetry. Dose profiles were recorded within standard CT head and body phantoms and scatter tail data fitted to exponential functions and extrapolated to predict dose levels in longer phantoms. The data have been used to simulate both CT dose index (CTDI) measurements with ionisation chambers of differing length and measurements of cumulative doses with a 20 mm chamber for scans of varying length. The results show that the length of a pencil ionisation chamber is the most significant factor affecting measurements of weighted CTDI (CTDI(w)) and a 100 mm chamber would record 50-61% of the dose measured with a 450 mm one. The cumulative dose measured at the centre of a 150 mm long body phantom records over 70% of the equilibrium dose from a helical scan of a longer phantom. For routine CT dosimetry tests, the determination of correction factors could allow measurements with a 100 mm chamber to be used to derive the CTDI that would be recorded with a longer chamber, and cumulative doses measured with a 20 mm chamber in shorter phantoms to be used to calculate equilibrium doses for helical scans.
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Affiliation(s)
- C J Martin
- Health Physics, Gartnavel Royal Hospital, Glasgow, G12 0XH, UK.
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Gomà C, Ruiz A, Jornet N, Latorre A, Pallerol RM, Carrasco P, Eudaldo T, Ribas M. Radiation dose assessment in a 320-detector-row CT scanner used in cardiac imaging. Med Phys 2011; 38:1473-80. [DOI: 10.1118/1.3558020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Yukihara EG, Ruan C, Gasparian PBR, Clouse WJ, Kalavagunta C, Ahmad S. An optically stimulated luminescence system to measure dose profiles in x-ray computed tomography. Phys Med Biol 2009; 54:6337-52. [DOI: 10.1088/0031-9155/54/20/020] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Huda W, Nickoloff EL, Boone JM. Overview of patient dosimetry in diagnostic radiology in the USA for the past 50 years. Med Phys 2009; 35:5713-28. [PMID: 19175129 DOI: 10.1118/1.3013604] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
This review covers the role of medical physics in addressing issues directly related to patient dosimetry in radiography, fluoroscopy, mammography, and CT. The sections on radiography and fluoroscopy radiation doses review the changes that have occurred during the last 50 to 60 years. A number of technological improvements have contributed to both a significant reduction in patient and staff radiation doses and improvements to the image quality during this period of time. There has been a transition from film-screen radiography with hand dip film processing to electronic digital imaging utilizing CR and DR. Similarly, fluoroscopy has progressed by directly viewing image intensifiers in darkened rooms to modern flat panel image receptor systems utilizing pulsed radiation, automated variable filtration, and digitally processed images. Mammography is one of the most highly optimized imaging procedures performed, because it is a repetitive screening procedure that results in annual radiation exposure. Mammography is also the only imaging procedure in the United States in which the radiation dose is regulated by the federal government. Consequently, many medical physicists have studied the dosimetry associated with screen-film and digital mammography. In this review, a brief history of mammography dose assessment by medical physicists is discussed. CT was introduced into clinical practice in the early 1970s, and has grown into one of the most important modalities available for diagnostic imaging. CT dose quantities and measurement techniques are described, and values of radiation dose for different types of scanner are presented. Organ and effective doses to adult patients are surveyed from the earliest single slice scanners, to the latest versions that include up to two x-ray tubes and can incorporate as many as 256 detector channels. An overview is provided of doses received by pediatric patients undergoing CT examinations, as well as methods, and results, of studies performed to assess the radiation absorbed by the conceptus of pregnant patients.
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Affiliation(s)
- Walter Huda
- Department of Radiology, Medical University of South Carolina, Charleston, South Carolina 29425-3230, USA.
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Hill B, Venning AJ, Baldock C. Polymer gel dosimetry on a multislice computed tomography scanner: effect of changing parameters on CTDI. Phys Med 2008; 24:149-58. [PMID: 18289906 DOI: 10.1016/j.ejmp.2007.11.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 11/20/2007] [Accepted: 11/22/2007] [Indexed: 11/15/2022] Open
Abstract
Polymer gel dosimetry undertaken on a multislice CT scanner provides an alternative method to conventional dosimetry measurements. Polymer gel dosimeters were used to measure CT radiation doses and compared to TLD and ionization chamber measurements in different diameter phantoms. CTDI was investigated for each of these phantoms for a range of mAs (100-400 mAs), tube voltage (100-135 kV) and nominal slice width (2-32 mm). Linear fits of the CTDI values for mAs show for the smallest phantom diameter an increase in CTDI of 60% for both TLD and polymer gel dosimeters. A similar increase in CTDI of 50% at 100 kVp and 100% for 135 kVp was also noted. It was also shown that slice width variation measured with either polymer gel or TLD was greatest with the smallest slice widths. In summary, it was found that polymer gels can be used as an alternative dosimeter to TLD for the determination of SWDP and subsequent CTDI calculations.
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Affiliation(s)
- B Hill
- Medical Physics, The Canberra Hospital, ACT Health, Woden, Canberra, ACT 2606, Australia.
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Dixon RL, Ballard AC. Experimental validation of a versatile system of CT dosimetry using a conventional ion chamber: beyond CTDI100. Med Phys 2007; 34:3399-413. [PMID: 17879802 DOI: 10.1118/1.2757084] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
This article is an experimental demonstration and authentication of a new method of computed tomography dosimetry [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003)], which utilizes a short, conventional ion chamber rather than a pencil chamber, and which is more versatile than the latter. The value of CTDI100 correctly predicts the accumulated dose only for a total scan length L equal to 100 mm and underestimates the limiting equilibrium dose approached for longer, clinically relevant body scan lengths [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003); K. D. Nakonechny, B. G. Fallone, and S. Rathee, Med. Phys. 32, 98-109 (2005); S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, Med. Phys. 32, 1061-1069 (2005); R. L. Dixon, M. T. Munley, and E. Bayram, Med. Phys. 32, 3712-3728 (2005); R. L. Dixon, Med. Phys. 33, 3973-3976 (2006)]. Dixon [Med. Phys. 30, 1272-1280 (2003)] originally proposed an alternative using a short ion chamber and a helical scan acquisition to collect the same integral for any scan length L (and not limited 100 mm). The primary purpose of this work is to demonstrate experimentally the implementation, robustness, and versatility of this small ion chamber method in measuring the accumulated dose in the body phantom for any desired scan length L (up to the available phantom length) including the limiting equilibrium dose (symbolically CTDIinfinity), and validation of the method against the pencil chamber methodology. Additionally, a simple and robust method for independently verifying the active length of a pencil chamber is described. The results of measurements made in a 400 mm long, 32 cm diameter polymethylmethacrylate body phantom using a small Farmer-type ion chamber and two pencil chambers of lengths l=100 and 150 mm confirm that the two methodologies provide the same dose values at the corresponding scan lengths L=l. The measured equilibrium doses obtained for GE MDCT scanners at 120 kVp are CTDIinfinity = 1.75 CTDI100 on the central axis and 1.22 CTDI100 on the peripheral axes, illustrating a nontrivial shortfall of CTDI100 in that regard and in good agreement with comparable data [S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, Med. Phys. 32, 1061-1069 (2005); J. M. Boone, Med. Phys. 34, 1364-1371 (2007)].
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Affiliation(s)
- Robert L Dixon
- Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157-1088, USA.
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Ngaile JE, Msaki P, Kazema R. Towards establishment of the national reference dose levels from computed tomography examinations in Tanzania. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2006; 26:213-25. [PMID: 16738417 DOI: 10.1088/0952-4746/26/2/006] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Without the knowledge of reference dose levels (RDLs) from computed tomography (CT) examinations, the optimal dose to patients undergoing CT examinations cannot be realised. The aim of this study was therefore to assess the radiation dose levels from CT examinations according to reference dose quantities proposed by the European Commission (EC) guidelines. The dosimetric quantities proposed in the EC for CT are weighted CT dose index (CTDI(w)) for a single slice and dose-length product (DLP) for a complete examination. The RDLs from five common CT examinations were obtained from eight hospitals. The RDLs in terms of CTDI(w) and DLP were estimated from measurements of CTDI in standard phantoms using typical exposure parameters. Mean values of CTDI(w) for head and lumbar spine had a range of 25-77 and 18-47 mGy, respectively, while those for chest, abdomen and pelvis had a range of about 11-25 mGy, respectively. Mean values of DLP for head, chest and abdomen had a range of 610-1684, 496-992 and 717-1428 mGy cm, respectively, while those for lumbar spine and pelvis had a range of 200-382 and 526-1302 mGy cm, respectively. Wide variations of mean CTDI(w) and DLP values among hospitals observed for similar CT examinations were mainly attributed to the variations of CT scanning protocols and scanner types. The mean CTDI(w) values per examination for almost all hospitals were below proposed RDLs, while the mean DLP values per examination were almost all above the proposed RDLs for all except one hospital. These were mainly influenced by the large scan length used in Tanzanian hospitals. In order to achieve the required level of dose for establishment of the national RDLs, it was concluded that further investigation of optimization of scanning protocols is needed.
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Affiliation(s)
- J E Ngaile
- Department of Physics, University of Dar es Salaam, PO Box 35063, Dar es Salaam, Tanzania.
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Dixon RL, Munley MT, Bayram E. An improved analytical model for CT dose simulation with a new look at the theory of CT dose. Med Phys 2006; 32:3712-28. [PMID: 16475771 DOI: 10.1118/1.2122507] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Gagne [Med. Phys. 16, 29-37 (1989)] has previously described a model for predicting the sensitivity and dose profiles in the slice-width (z) direction for CT scanners. The model, developed prior to the advent of multidetector CT scanners, is still widely used; however, it does not account for the effect of anode tilt on the penumbra or include the heel effect, both of which are increasingly important for the wider beams (up to 40 mm) of contemporary, multidetector scanners. Additionally, it applied only on (or near) the axis of rotation, and did not incorporate the photon energy spectrum. The improved model described herein transcends all of the aforementioned limitations of the Gagne model, including extension to the peripheral phantom axes. Comparison of simulated and measured dose data provides experimental validation of the model, including verification of the superior match to the penumbra provided by the tilted-anode model, as well as the observable effects on the cumulative dose distribution. The initial motivation for the model was to simulate the quasiperiodic dose distribution on the peripheral, phantom axes resulting from a helical scan series in order to facilitate the implementation of an improved method of CT dose measurement utilizing a short ion chamber, as proposed by Dixon [Med. Phys. 30, 1272-1280 (2003)]. A more detailed set of guidelines for implementing such measurements is also presented in this paper. In addition, some fundamental principles governing CT dose which have not previously been clearly enunciated follow from the model, and a fundamental (energy-based) quantity dubbed "CTDI-aperture" is introduced.
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Affiliation(s)
- Robert L Dixon
- Department of Radiology, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157-1088, USA.
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Maia AF, Caldas LVE. A simple method for evaluation of half-value layer variation in CT equipment. Phys Med Biol 2006; 51:1595-601. [PMID: 16510965 DOI: 10.1088/0031-9155/51/6/016] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Tandem systems, each formed by a pencil ionization chamber with and without a specific covering, were developed and tested in standard radiation beams. These systems were designed to be used in computed tomography radiation beams, where the half-value layer (HVL) determination is not an easy task. The behaviour of the tandem systems in diagnostic radiology showed the possibility of their use to confirm HVL values previously determined by the conventional HVL measurement method in quality control programmes. These systems also have other advantages: low cost, easy application and quick measurement procedure.
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Affiliation(s)
- Ana F Maia
- Instituto de Pesquisas Energéticas e Nucleares, Comissão Nacional de Energia Nuclear, Av. Prof. Lineu Prestes, 2242, CEP 05422-970 São Paulo, Brazil.
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Hill B, Venning AJ, Baldock C. A preliminary study of the novel application of normoxic polymer gel dosimeters for the measurement of CTDI on diagnostic x-ray CT scanners. Med Phys 2005; 32:1589-97. [PMID: 16013718 DOI: 10.1118/1.1925181] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Computer tomography dose index (CTDI) is a measurement undertaken during acceptance testing and subsequent quality assurance measurements of diagnostic x-ray CT scanners for the determination of patient dose. Normoxic polymer gel dosimeters have been used for the first time to measure dose and subsequently CTDI during acceptance testing of a CT scanner and compared with the conventional ionization chamber measurement for a range of imaging protocols. The normoxic polymer gel dosimeter was additionally used to simultaneously determine slice-width dose profiles and CTDI in the transaxial plane, the measurements of which are usually determined with thermoluminescent dosimetry or film. The resulting CTDI for all slice widths calculated from the normoxic polymer gel dosimeter were within corresponding ionization chamber CTDI values. Slice-width dose-profiles full-width half-maximum values from the normoxic polymer gel dosimeter were compared to the slice sensitivity profiles and were within the tolerances of the manufacturer. Normoxic polymer gel dosimeters have been shown to be a useful device for determining CTDI and dose distributions for CT equipment, and provide additional information not possible with just the use of an ionization chamber.
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Affiliation(s)
- Brendan Hill
- Medical Physics Section, Biomedical Engineering Services, The Canberra Hospital, POB 11 Woden ACT 2606, Australia.
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Muhogora WE, Nyanda AM, Ngoye WM, Shao D. Radiation doses to patients during selected CT procedures at four hospitals in Tanzania. Eur J Radiol 2005; 57:461-7. [PMID: 16165335 DOI: 10.1016/j.ejrad.2005.08.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2005] [Revised: 07/27/2005] [Accepted: 08/10/2005] [Indexed: 12/21/2022]
Abstract
The dose characteristics of CT scanners from local scanning protocols were investigated on the basis of questionnaire information provided by four hospitals conducting CT procedures in Tanzania. The information included scanner model, scanner manufacturer, number of most frequent CT examinations and the employed scanning parameters to previously diagnosed patients. For each scan technique, patient doses were estimated in terms of computerized tomography dose index, dose length product and effective dose using the software developed by the ImPACT scan group in conjunction with the NRPB conversion coefficients data. The results show that the mean CTDI_w,100, DLP and effective dose ranged from 8.5 +/- 2.8 to 79.3 +/- 23.7mGy, 145 +/- 5 to 1400 +/- 812.5 mGy cm and 3 +/- 2.3 to 15.7 +/- 10.4 mSv, respectively. On average, the observed CT doses are however roughly higher than the reported literature data such as 30 to 60 mGy, 570 to 1050 mGy cm and 2.4 to 11.7 mSv recommended by European Commission for similar CT examinations. The higher dose levels, which are possibly associated with significant risks, justify extensive similar studies at the national level in order to unify different approaches towards optimisation of CT examinations. In pursue of this noble objective, the need to train the radiology personnel, establish and using protocols and continuously monitor the performance of CT equipment to control patient CT doses is of utmost importance.
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Affiliation(s)
- W E Muhogora
- Tanzania Atomic Energy Commission, P.O. Box 743, Arusha, United Republic of Tanzania.
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Nakonechny KD, Fallone BG, Rathee S. Novel methods of measuring single scan dose profiles and cumulative dose in CT. Med Phys 2005; 32:98-109. [PMID: 15719960 DOI: 10.1118/1.1835571] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Computed tomography dose index (CTDI) is a conventional indicator of the patient dose in CT studies. It is measured as the integration of the longitudinal single scan dose profile (SSDP) by using a 100-mm-long pencil ionization chamber and a single axial scan. However, the assumption that most of the SSDP is contained within the chamber length may not be valid even for thin slices. We have measured the SSDPs for several slice widths on two CT scanners using a PTW diamond detector placed in a 300 mm x 200 mm x 300 mm water-equivalent plastic phantom. One SSDP was also measured using lithium fluoride (LiF) TLDs and an IC-10 small volume ion chamber, verifying the general shape of the SSDP measured using the diamond detector. Standard cylindrical PMMA CT phantoms (140 mm length) were also used to qualitatively study the effects of phantom shape, length, and composition on the measured SSDP. The SSDPs measured with the diamond detector in the water-equivalent phantom were numerically integrated to calculate the relative accumulated dose D(L)(0)calc at the center of various scan lengths L. D(L)(0)calc reached an equilibrium value for L > 300 mm, suggesting the need for phantoms longer than standard CT dose phantoms. We have also measured the absolute accumulated dose using an IC-10 small volume ion chamber, D(L)(0)SV, at three points in the phantom cross section for several beamwidths and scan lengths. For one CT system, these measurements were made in both axial and helical scanning modes. The absolute CTDI100, measured with a 102 mm active length pencil chamber, were within 4% of D(L)(0)SV measured with the small volume ion chamber for L approximately 100 mm suggesting that nonpencil chambers can be successfully used for CT dosimetry. For nominal beam widths ranging from 3 to 20 mm and for L approximately 250 mm, D(L)(0)SV values at the center of the water-equivalent phantom's elliptic cross section were approximately 25%-30% higher than the measured CTDI100. For small beamwidths, the difference in D(L)(0)SV for L approximately 250 mm and L approximately 14 x beamwidth (CTDI14nT) reached up to 50%. Peripheral point doses at 70 mm depth along the major axis of the phantom for L approximately 250 mm were up to 22% higher than for L approximately 100 mm. The differences between CTDI100 and D(L)(0)SV for L approximately 250 mm were in good agreement with the predictions made from the numerical integration of the measured SSDPs. Due to the considerable dose measured beyond the length of standard CT phantoms, CT dosimetry for longer body scan series should be performed in longer phantoms. Measurements could be made as we have shown, using a small volume chamber translating through the beam using multiple scans.
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Affiliation(s)
- K D Nakonechny
- Department of Medical Physics, Cross Cancer Institute, University of Alberta, Edmonton, Alberta T6G 1Z2, Canada
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Fenwick JD, Tomé WA, Kissick MW, Mackie TR. Modelling simple helically delivered dose distributions. Phys Med Biol 2005; 50:1505-17. [PMID: 15798340 DOI: 10.1088/0031-9155/50/7/013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
In a previous paper, we described quality assurance procedures for Hi-Art helical tomotherapy machines. Here, we develop further some ideas discussed briefly in that paper. Simple helically generated dose distributions are modelled, and relationships between these dose distributions and underlying characteristics of Hi-Art treatment systems are elucidated. In particular, we describe the dependence of dose levels along the central axis of a cylinder aligned coaxially with a Hi-Art machine on fan beam width, couch velocity and helical delivery lengths. The impact on these dose levels of angular variations in gantry speed or output per linear accelerator pulse is also explored.
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Affiliation(s)
- John D Fenwick
- Department of Human Oncology, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI 53792, USA.
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