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Rodriguez-Granillo GA, Cirio J, Vila JF, Langzam E, Ivanc T, Fontana L, Descalzo A, Rubilar B, Lylyk P. Noncontrast Myocardial Characterization in Acute Myocardial Infarction Using Electron Density Imaging. J Thorac Imaging 2024; 39:173-177. [PMID: 37884390 DOI: 10.1097/rti.0000000000000749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2023]
Abstract
PURPOSE Spectral computed tomography (CT) enables improved tissue characterization, although virtually all research has focused on contrast-enhanced examinations. We hypothesized that changes in myocardial tissue related to acute myocardial infarction (AMI) might potentially be identified without the need for contrast administration using electron density (ED) imaging. PATIENTS AND METHODS This retrospective observational study involved a small series (n = 15) of patients admitted to our institution with a first AMI without signs of hemodynamic instability and identification of a culprit vessel with invasive coronary angiography during the same admission, who also underwent a noncontrast, low-dose chest CT using a dual-layer spectral CT scanner. Images were assessed in search of dark areas with low density on ED imaging, and the mean percentage ED relative to water (%EDW) was calculated. RESULTS Using a qualitative approach, ED assessment enabled the identification of 11/15 (73%) affected coronary territories, with a sensitivity of 73% (95% CI: 45; 92%) and a specificity of 87% (95% CI: 69; 96%). AMI segments showed significantly lower ED values than the remote myocardium (103.8 ± 0.8 vs 104.3 ± 0.6 %EDW, P < 0.0001), and a threshold below 103.9 %EDW had a sensitivity of 66% and specificity of 79% for the identification of AMI. In a control group of patients without a history of cardiovascular disease, none had areas with focal reduction of ED following the shape of the myocardial wall. CONCLUSIONS In our preliminary series, ED imaging showed the potential to enable the identification of myocardial tissue changes related to AMI without iodinated contrast requirement.
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Affiliation(s)
| | | | | | - Eran Langzam
- Philips Healthcare, CT Clinical Science, Buenos Aires, Argentina
| | - Thomas Ivanc
- Philips Healthcare, CT Clinical Science, Buenos Aires, Argentina
| | | | | | | | - Pedro Lylyk
- Department of Interventional Neuroradiology, Instituto Medico ENERI, Clinica La Sagrada Familia
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Tegtmeier RC, Ferris WS, Chen R, Miller JR, Bayouth JE, Culberson WS. Evaluating on-board kVCT- and MVCT-based dose calculation accuracy using a thorax phantom for helical tomotherapy treatments. Biomed Phys Eng Express 2023; 9. [PMID: 36745904 DOI: 10.1088/2057-1976/acb93f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2022] [Accepted: 02/06/2023] [Indexed: 02/08/2023]
Abstract
Purpose.To evaluate the impact of CT number calibration and imaging parameter selection on dose calculation accuracy relative to the CT planning process in thoracic treatments for on-board helical CT imaging systems used in helical tomotherapy.Methods and Materials.Direct CT number calibrations were performed with appropriate protocols for each imaging system using an electron density phantom. Large volume and SBRT treatment plans were simulated and optimized for planning CT scans of an anthropomorphic thorax phantom and transferred to registered kVCT and MVCT scans of the phantom as appropriate. Relevant DVH metrics and dose-difference maps were used to evaluate and compare dose calculation accuracy relative to the planning CT based on a variation in imaging parameters applied for the on-board systems.Results.For helical kVCT scans of the thorax phantom, median differences in DVH parameters for the large volume treatment plan were less than ±1% with dose to the target volume either over- or underestimated depending on the imaging parameters utilized for CT number calibration and thorax phantom acquisition. For the lung SBRT plan calculated on helical kVCT scans, median dose differences were up to -2.7% with a more noticeable dependence on parameter selection. For MVCT scans, median dose differences for the large volume plan were within +2% with dose to the target overestimated regardless of the imaging protocol.Conclusion.Accurate dose calculations (median errors of <±1%) using a thorax phantom simulating realistic patient geometry and scatter conditions can be achieved with images acquired with a helical kVCT system on a helical tomotherapy unit. This accuracy is considerably improved relative to that achieved with the MV-based approach. In a clinical setting, careful consideration should be made when selecting appropriate kVCT imaging parameters for this process as dose calculation accuracy was observed to vary with both parameter selection and treatment type.
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Affiliation(s)
- Riley C Tegtmeier
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53705, United States of America
| | - William S Ferris
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53705, United States of America
| | - Ruiming Chen
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53705, United States of America
| | - Jessica R Miller
- Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53792, United States of America
| | - John E Bayouth
- Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53792, United States of America
| | - Wesley S Culberson
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, WI 53705, United States of America
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Vergalasova I, McKenna M, Yue NJ, Reyhan M. Impact of computed tomography (CT) reconstruction kernels on radiotherapy dose calculation. J Appl Clin Med Phys 2020; 21:178-186. [PMID: 32889789 PMCID: PMC7497921 DOI: 10.1002/acm2.12994] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 06/27/2020] [Accepted: 07/11/2020] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To quantitatively evaluate the effect of computed tomography (CT) reconstruction kernels on various dose calculation algorithms with heterogeneity correction. METHODS The gammex electron density (ED) Phantom was scanned with the Siemens PET/CT Biograph20 mCT and reconstructed with twelve different kernel options. Hounsfield unit (HU) vs electron density (ED) curves were generated to compare absolute differences. Scans were repeated under head and pelvis protocols and reconstructed per H40s (head) and B40s (pelvis) kernels. In addition, raw data from a full-body patient scan were also reconstructed using the four B kernels. Per reconstruction, photon (3D and VMAT), electron (18 and 20 MeV) and proton (single field) treatment plans were generated using Varian Eclipse dose calculation algorithms. Photon and electron plans were also simulated to pass through cortical bone vs liver plugs of the phantom for kernel comparison. Treatment field monitor units (MU) and isodose volumes were compared across all scenarios. RESULTS The twelve kernels resulted in minor differences in HU, except at the extreme ends of the density curve with a maximum absolute difference of 55.2 HU. The head and pelvis scans of the phantom resulted in absolute HU differences of up to 49.1 HU for cortical bone and 45.1 HU for lung 300, which is a relative difference of 4.1% and 6.2%, respectively. MU comparisons across photon and proton calculation algorithms for the patient and phantom scans were within 1-2 MU, with a maximum difference of 5.4 MU found for the 20 MeV electron plan. The 20MeV electron plan also displayed maximum differences in isodose volumes of 20.4 cc for V90%. CONCLUSION Clinically insignificant differences were found among the various kernel generated plans for photon and proton plans calculated on patient and phantom scan data. However, differences in isodose volumes found for higher energy electron plans amongst the kernels may have clinical implications for prescribing dose to an isodose level.
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Affiliation(s)
- Irina Vergalasova
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers University, New Brunswick, NJ, USA
| | - Michael McKenna
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers University, New Brunswick, NJ, USA
| | - Ning Jeff Yue
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers University, New Brunswick, NJ, USA
| | - Meral Reyhan
- Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, Rutgers University, New Brunswick, NJ, USA
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Dosimetric evaluation of two phases of respiratory movement using a lung equivalent material for radiotherapy treatment planning. JOURNAL OF RADIOTHERAPY IN PRACTICE 2020. [DOI: 10.1017/s1460396919000505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractBackground/aim:Radiation dosimetry requires special phantoms which are comparable with organs and tissues of a human body. The lung is one of the organs with a low density. Therefore, it is important to create and use lung equivalent phantoms in dosimetric controls. The aim of this study was to investigate the importance of using lung equivalent phantoms for different respiratory phases during measurements with both computed tomography (CT) and linear accelerator.Materials and methods:The maximum lung inhalation phantom (LIP) and lung exhalation phantom (LEP) were created for two respiratory phases. The Hounsfield Unit (HU) values based on the selected slice thickness and CT tube voltages were investigated, as well as the difference between energy and algorithms used in the treatment planning system.Results:It was found that the change in HU values according to slice thickness were more significant in measurements for respiratory phases. The dose difference between LEP and LIP at a point which is located 1 cm below the surface of the phantoms was found as 1·0% for 6 megavolt (MV) and 2·8% for 18 MV. The highest difference between the two algorithms was found to be 7·22% for 6 MV and 10·93% for 18 MV for LIP phantom.Conclusion:It can be said that the LIP and LEP phantoms prepared in accordance with respiratory phases can be a simple and inexpensive method to investigate any difference in dosimetry during respiratory phases. Also, measured and calculated dose values are in good agreement when thinner slice thickness was chosen.
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Effects of image distortion and Hounsfield unit variations on radiation treatment plans: An extended field-of-view reconstruction in a large bore CT scanner. Sci Rep 2020; 10:473. [PMID: 31949301 PMCID: PMC6965617 DOI: 10.1038/s41598-020-57422-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 12/11/2019] [Indexed: 11/20/2022] Open
Abstract
This study aimed to evaluate the effect of image distortion and Hounsfield unit (HU) variation due to the extended field-of-view (eFOV) of the large-bore (LB) computed tomography (CT) on dose distribution. Both home-made inhomogeneity and breast phantoms were scanned at the geometric center position and four different offset positions. We also performed dose optimizations based on different breast phantom CT sets for evaluating the effects of image artifacts on the intensity-modulated radiation techniques. The volume changes were 0.0% to 0.5% in the air, −0.5% to 3.0% in the water, and 4.0% to 5.0% in the high-density material of the inhomogeneity phantom. Both phantoms scanning results indicate that more distortions occurred in the eFOV area due to the biased scanning center. The gamma index differences ranged from 0.87% to 4.87% for the FIF plan and from 0.52% to 6.26% for the VMAT plan. This resulted in decrease of the minimum (7.3–13.1%), maximum (−0.8–2.2%), and mean doses (−0.2–4.4%). We recommend that it should be evaluated whether the applied CT would have an appropriate eFOV range for clinical radiation treatment planning for patients.
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Ota S. [16. Commissioning of a Computed Tomography Simulator: A Single-institution Experience]. Nihon Hoshasen Gijutsu Gakkai Zasshi 2020; 76:413-422. [PMID: 32307369 DOI: 10.6009/jjrt.2020_jsrt_76.4.413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Affiliation(s)
- Seiichi Ota
- Radiotherapy Unit, Division of Radiological Technology, University Hospital, Kyoto Prefectural University of Medicine
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Afifi MB, Abdelrazek A, Deiab NA, Abd El-Hafez AI, El-Farrash AH. The effects of CT x-ray tube voltage and current variations on the relative electron density (RED) and CT number conversion curves. JOURNAL OF RADIATION RESEARCH AND APPLIED SCIENCES 2019. [DOI: 10.1080/16878507.2019.1693176] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Mohamed Bahaaeldin Afifi
- Radiological Science and Medical Imaging Department, Faculty of Applied Medical Sciences, Prince Sattam bin Abulaziz University (PSAU), Al-Kharj, Kingdom of Saudi Arabia
- Medical Physics Department, Minia Oncology Center, Ministry of Health and Population, Al-Minia, Egypt
| | - A. Abdelrazek
- Physics Department, Faculty of Science, Mansoura University, Al-Mansoura, Egypt
| | - Nashaat Ahmed Deiab
- Radiotherapy and Nuclear Medicine Department, National Cancer Institute (NCI), Cairo University, Cairo, Egypt
| | - A. I. Abd El-Hafez
- Ionizing Radiation Metrology Laboratory (IRML), National Institute of Standard (NIS), Giza, Egypt
| | - A. H. El-Farrash
- Physics Department, Faculty of Science, Mansoura University, Al-Mansoura, Egypt
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Hasani M, Farhood B, Ghorbani M, Naderi H, Saadatmand S, Karimkhani Zandi S, Knaup C. Effect of computed tomography number-relative electron density conversion curve on the calculation of radiotherapy dose and evaluation of Monaco radiotherapy treatment planning system. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2019; 42:489-502. [PMID: 30848440 DOI: 10.1007/s13246-019-00745-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2018] [Accepted: 02/27/2019] [Indexed: 11/24/2022]
Abstract
The accuracy of a computed tomography (CT)-relative electron density (RED) curve may have an indirect impact on the accuracy of dose calculation by a treatment planning system (TPS). This effect has not been previously quantified for input of different CT-RED curves from different CT-scan units in the Monaco TPS. This study aims to evaluate the effect of CT-RED curve on the dose calculation by the Monaco radiotherapy TPS. Four CT images of the CIRS phantom were obtained by different CT scanners. The accuracy of the dose calculation in the three algorithms of the Monaco TPS (Monte Carlo, collapse cone, and pencil beam) is also evaluated based on TECDOC 1583. The CT-RED curves from the CT scanners were transferred to the Monaco TPS to audit the different algorithms of the TPS. The dose values were measured with an ionization chamber in the CIRS phantom. Then, the dose values were calculated by the Monaco algorithms in the corresponding points. For the Monaco TPS and based on TECDOC 1583, the accuracy of the dose calculation in all the three algorithms is within the agreement criteria for most of the points evaluated. For low dose regions, the differences between the calculated and measured dose values are higher than the agreement criteria in a number of points. For the majority of the points, the algorithms underestimate the calculated dose values. It was also found that the use of different CT-RED curves can lead to minor discrepancies in the dose calculation by the Monaco TPS, especially in low dose regions. However, it appears that these differences are not clinically significant in most of the cases.
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Affiliation(s)
- Mohsen Hasani
- Department of Radiotherapy Physics, Cancer Research Centre, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
| | - Bagher Farhood
- Department of Medical Physics and Radiology, Faculty of Paramedical Sciences, Kashan University of Medical Sciences, Kashan, Iran.
| | - Mahdi Ghorbani
- Cancer Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
| | - Hamideh Naderi
- Department of Radiotherapy Physics, Cancer Institute, Qom University of Medical Sciences, Qom, Iran
| | - Sepideh Saadatmand
- Department of Radiotherapy Physics, Cancer Institute, Qom University of Medical Sciences, Qom, Iran
| | - Saeed Karimkhani Zandi
- Department of Radiotherapy Physics, Cancer Institute, Qom University of Medical Sciences, Qom, Iran
| | - Courtney Knaup
- Comprehensive Cancer Centers of Nevada, Las Vegas, NV, USA
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Fang R, Mazur T, Mutic S, Khan R. The impact of mass density variations on an electron Monte Carlo algorithm for radiotherapy dose calculations. PHYSICS & IMAGING IN RADIATION ONCOLOGY 2018; 8:1-7. [PMID: 33458409 PMCID: PMC7807677 DOI: 10.1016/j.phro.2018.10.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 10/19/2018] [Accepted: 10/23/2018] [Indexed: 01/21/2023]
Abstract
Background and Purpose A key step in electron Monte Carlo dose calculation requires converting Computed Tomography (CT) numbers from a tomographic acquisition to a mass density. This study investigates the dosimetric consequences of perturbations applied to a calibration table between CT number and mass density. Materials and Methods A literature search was performed to define lower and upper bounds for physically reasonable perturbations to a reference CT number to mass density calibration table. Electron beam dose was calculated for ten patients using these variations and the results were compared to clinical plans originally derived with a reference calibration table. Dose differences both globally and in the Planning Target Volume (PTV) were assessed using dose- and volume-based metrics and 3- dimensional gamma analysis for each patient. Results Small but statistically significant differences were observed between perturbations and reference data for certain metrics including volume of the 50% prescription isodose. Upper and lower variations in CT number to mass density calibration yielded mean values of V50% that were 4.4% larger and 2.1% smaller than reference values respectively. Gamma analysis using 3%/3mm criteria indicated >99% passing rate for the PTV for all patients. Global gamma analysis for some patients showed larger discrepancies possibly due to large electron path lengths through inhomogeneities. Conclusions In most patients, physically reasonable perturbations in CT number to mass density curves will not induce clinically significant impact on calculated target dose distributions. Strong dependence of electron transport on voxel material may produce dose speckle throughout the volume. Care should be taken in evaluating critical structures at depths beyond the target volume in highly heterogeneous regions.
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Affiliation(s)
- Raymond Fang
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - Thomas Mazur
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - Sasa Mutic
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
| | - Rao Khan
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA
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Kaplan LP, Elstrøm UV, Møller DS, Hoffmann L. Cone beam CT based dose calculation in the thorax region. PHYSICS & IMAGING IN RADIATION ONCOLOGY 2018; 7:45-50. [PMID: 33458404 PMCID: PMC7807659 DOI: 10.1016/j.phro.2018.09.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Revised: 09/13/2018] [Accepted: 09/20/2018] [Indexed: 11/15/2022]
Abstract
Background and purpose The limited image quality in Cone Beam CT (CBCT) stemming primarily from scattered radiation hinders accurate CBCT based dose calculation in radiotherapy. We investigated the use of a stoichiometric calibration for dose calculation on CBCT images of lung cancer patients. Materials and methods CBCT calibrations were performed with thorax scan protocols, using a phantom with approximately the diameter of an average human thorax and a central cavity simulating the thoracic cavity. Thus scatter conditions resembling those in clinical thorax CBCT scans were simulated. A published stoichiometric parametrization was used. A treatment plan was simulated on CBCT and CT scans of an anthropomorphic phantom, the dose distributions were calculated, and clinically relevant DVH parameters were compared. Twelve lung cancer patients had surveillance CT scans (s-CT) taken twice during their treatment course in addition to daily setup CBCTs. Dose calculations were performed on the s-CTs and the corresponding CBCTs taken on the same day, and DVH parameters were compared. Results Eighty percent of CBCT DVH parameters found for the phantom were within ±1% of CT doses, and 98% were within ±3%. For patients, the median CT/CBCT dose difference was within ±2%, and 98% of DVH parameters were within ±4%. Minimum dose to the tumor was underestimated (median 1.9%) on CBCT, while maximum doses to most organs at risk were slightly overestimated. Conclusion Direct dose calculations on CBCTs of lung cancer patients were feasible within ∼4% accuracy using a simple calibration method, which is easily implemented in a clinical setting.
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Affiliation(s)
- Laura Patricia Kaplan
- Department of Medical Physics, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus, Denmark.,Institute of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus, Denmark
| | - Ulrik Vindelev Elstrøm
- Department of Medical Physics, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus, Denmark
| | - Ditte Sloth Møller
- Department of Medical Physics, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus, Denmark
| | - Lone Hoffmann
- Department of Medical Physics, Aarhus University Hospital, Nørrebrogade 44, 8000 Aarhus, Denmark
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Accuracy of electron density, effective atomic number, and iodine concentration determination with a dual-layer dual-energy computed tomography system. Med Phys 2018; 45:2486-2497. [DOI: 10.1002/mp.12903] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Revised: 01/26/2018] [Accepted: 03/09/2018] [Indexed: 01/30/2023] Open
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Du Plessis FCP. On the prediction of X-ray dose deviations and the influence of CT scan protocols. POLISH JOURNAL OF MEDICAL PHYSICS AND ENGINEERING 2017. [DOI: 10.1515/pjmpe-2017-0009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
Patients undergoing computerized tomography (CT) scans for tumor localization and treatment planning are frequently scanned using pre-set customized exposure protocols for optimal imaging of different anatomical sites. The question arises if these scanning protocols will produce a deviation in the Hounsfield number for a given tissue that can afterwards be used to predict the resulting dose calculation deviation due to this. The question is also if the deviation in the Hounsfield number of a tissue is large enough to affect dose calculation clinically significant.
A study was devised in which a RMI phantom was scanned with five different scanning protocols and two CT beam energies at 120 and 135 kV. To assess the effect of insert configuration, Hounsfield number measurements were repeated for high density RMI inserts in the center and outer rings in the phantom. For each material insert the standard deviation of the Hounsfield number was calculated. To assist in dose prediction a series of DOSXYZnrc Monte Carlo calculations were carried out for beam qualities between 6 and 16 MV for a range of Hounsfield numbers calculated for bone and water. This provided information on how the depth dose varied as a function of Hounsfield number variation. Lastly, a series of treatment plans were setup for absorbed dose calculation using the RMI insert electron densities vs Hounsfield relations measured above. The absorbed dose of corresponding plans with the largest Hounsfield number variation were subtracted to find the dose discrepancies.
It was found that the dose discrepancies in tissue types could be indicated by the deviation of the Hounsfield number due to different scanning protocols. The calculated dose difference were in all cases within 3%.
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Affiliation(s)
- Freek CP Du Plessis
- Department of Medical Physics , University of the Free State , P.O. Box 339, Bloemfontein, 9300 , South Africa
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Davis AT, Palmer AL, Nisbet A. Can CT scan protocols used for radiotherapy treatment planning be adjusted to optimize image quality and patient dose? A systematic review. Br J Radiol 2017; 90:20160406. [PMID: 28452568 PMCID: PMC5603945 DOI: 10.1259/bjr.20160406] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Revised: 03/16/2017] [Accepted: 04/24/2017] [Indexed: 01/27/2023] Open
Abstract
This article reviews publications related to the use of CT scans for radiotherapy treatment planning, specifically the impact of scan protocol changes on CT number and treatment planning dosimetry and on CT image quality. A search on PubMed and EMBASE and a subsequent review of references yielded 53 relevant articles. CT scan parameters significantly affect image quality. Some will also affect Hounsfield unit (HU) values, though this is not comprehensively reported on. Changes in tube kilovoltage and, on some scanners, field of view and reconstruction algorithms have been found to produce notable HU changes. The degree of HU change which can be tolerated without changing planning dose by >1% depends on the body region and size, planning algorithms, treatment beam energy and type of plan. A change in soft-tissue HU value has a greater impact than changes in HU for bone and air. The use of anthropomorphic phantoms is recommended when assessing HU changes. There is limited published work on CT scan protocol optimization in radiotherapy. Publications suggest that HU tolerances of ±20 HU for soft tissue and of ±50 HU for the lung and bone would restrict dose changes in the treatment plan to <1%. Literature related to the use of CT images in radiotherapy planning has been reviewed to establish the acceptable level of HU change and the impact on image quality of scan protocol adjustment. Conclusions have been presented and further work identified.
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Affiliation(s)
- Anne T Davis
- Department of Physics, Faculty of Engineering and Physical Science, University of Surrey, Guildford, UK
- Department of Medical Physics, Portsmouth Hospitals NHS Trust, Portsmouth, UK
| | - Antony L Palmer
- Department of Physics, Faculty of Engineering and Physical Science, University of Surrey, Guildford, UK
- Department of Medical Physics, Portsmouth Hospitals NHS Trust, Portsmouth, UK
| | - Andrew Nisbet
- Department of Physics, Faculty of Engineering and Physical Science, University of Surrey, Guildford, UK
- Department of Medical Physics, Royal Surrey County Hospital NHS Foundation Trust, Guildford, UK
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Yohannes I, Prasetio H, Kallis K, Bert C. Dosimetric accuracy of the cone-beam CT-based treatment planning of the Vero system: a phantom study. J Appl Clin Med Phys 2016; 17:106-113. [PMID: 27455496 PMCID: PMC5690058 DOI: 10.1120/jacmp.v17i4.6194] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 02/25/2016] [Accepted: 02/23/2016] [Indexed: 11/23/2022] Open
Abstract
We report an investigation on the accuracy of dose calculation based on the cone‐beam computed tomography (CBCT) images of the nonbowtie filter kV imaging system of the Vero linear accelerator. Different sets of materials and tube voltages were employed to generate the Hounsfield unit lookup tables (HLUTs) for both CBCT and fan‐beam CT (FBCT) systems. The HLUTs were then implemented for the dose calculation in a treatment planning system (TPS). Dosimetric evaluation was carried out on an in‐house‐developed cube phantom that consists of water‐equivalent slabs and inhomogeneity inserts. Two independent dosimeters positioned in the cube phantom were used in this study for point‐dose and two‐dimensional (2D) dose distribution measurements. The differences of HLUTs from various materials and tube voltages in both CT systems resulted in differences in dose calculation accuracy. We found that the higher the tube voltage used to obtain CT images, the better the point‐dose calculation and the gamma passing rate of the 2D dose distribution agree to the values determined in the TPS. Moreover, the insert materials that are not tissue‐equivalent led to higher dose‐calculation inaccuracy. There were negligible differences in dosimetric evaluation between the CBCT‐ and FBCT‐based treatment planning if the HLUTs were generated using the tissue‐equivalent materials. In this study, the CBCT images of the Vero system from a complex inhomogeneity phantom can be applied for the TPS dose calculation if the system is calibrated using tissue‐equivalent materials scanned at high tube voltage (i.e., 120 kV). PACS number(s): 87.55.de, 87.56.Fc, 87.57.qp
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Das IJ, Cheng CW, Cao M, Johnstone PAS. Computed tomography imaging parameters for inhomogeneity correction in radiation treatment planning. J Med Phys 2016; 41:3-11. [PMID: 27051164 PMCID: PMC4795414 DOI: 10.4103/0971-6203.177277] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Modern treatment planning systems provide accurate dosimetry in heterogeneous media (such as a patient' body) with the help of tissue characterization based on computed tomography (CT) number. However, CT number depends on the type of scanner, tube voltage, field of view (FOV), reconstruction algorithm including artifact reduction and processing filters. The impact of these parameters on CT to electron density (ED) conversion had been subject of investigation for treatment planning in various clinical situations. This is usually performed with a tissue characterization phantom with various density plugs acquired with different tube voltages (kilovoltage peak), FOV reconstruction and different scanners to generate CT number to ED tables. This article provides an overview of inhomogeneity correction in the context of CT scanning and a new evaluation tool, difference volume dose-volume histogram (DVH), dV-DVH. It has been concluded that scanner and CT parameters are important for tissue characterizations, but changes in ED are minimal and only pronounced for higher density materials. For lungs, changes in CT number are minimal among scanners and CT parameters. Dosimetric differences for lung and prostate cases are usually insignificant (<2%) in three-dimensional conformal radiation therapy and < 5% for intensity-modulated radiation therapy (IMRT) with CT parameters. It could be concluded that CT number variability is dependent on acquisition parameters, but its dosimetric impact is pronounced only in high-density media and possibly in IMRT. In view of such small dosimetric changes in low-density medium, the acquisition of additional CT data for financially difficult clinics and countries may not be warranted.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Chee-Wai Cheng
- Department of Radiation Oncology, University Hospitals Case Medical Center, Cleveland, OH 44255, USA
| | - Minsong Cao
- Department of Radiation Oncology, University of California- Los Angeles School of Medicine, CA 90095, USA
| | - Peter A S Johnstone
- Department of Radiation Oncology, Moffitt Cancer Center, Tampa, FL 33612, USA
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Watson PGF, Mainegra-Hing E, Tomic N, Seuntjens J. Implementation of an efficient Monte Carlo calculation for CBCT scatter correction: phantom study. J Appl Clin Med Phys 2015. [PMID: 26219003 PMCID: PMC5690008 DOI: 10.1120/jacmp.v16i4.5393] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Cone-beam computed tomography (CBCT) images suffer from poor image quality, in a large part due to contamination from scattered X-rays. In this work, a Monte Carlo (MC)-based iterative scatter correction algorithm was implemented on measured phantom data acquired from a clinical on-board CBCT scanner. An efficient EGSnrc user code (egs_cbct) was used to transport photons through an uncorrected CBCT scan of a Catphan 600 phantom. From the simulation output, the contribution from primary and scattered photons was estimated in each projection image. From these estimates, an iterative scatter correction was performed on the raw CBCT projection data. The results of the scatter correction were compared with the default vendor reconstruction. The scatter correction was found to reduce the error in CT number for selected regions of interest, while improving contrast-to-noise ratio (CNR) by 18%. These results demonstrate the performance of the proposed scatter correction algorithm in improving image quality for clinical CBCT images.
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Liu L, Antonuk LE, El-Mohri Y, Zhao Q, Jiang H. Optimization of the design of thick, segmented scintillators for megavoltage cone-beam CT using a novel, hybrid modeling technique. Med Phys 2015; 41:061916. [PMID: 24877827 DOI: 10.1118/1.4875724] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Active matrix flat-panel imagers (AMFPIs) incorporating thick, segmented scintillators have demonstrated order-of-magnitude improvements in detective quantum efficiency (DQE) at radiotherapy energies compared to systems based on conventional phosphor screens. Such improved DQE values facilitate megavoltage cone-beam CT (MV CBCT) imaging at clinically practical doses. However, the MV CBCT performance of such AMFPIs is highly dependent on the design parameters of the scintillators. In this paper, optimization of the design of segmented scintillators was explored using a hybrid modeling technique which encompasses both radiation and optical effects. METHODS Imaging performance in terms of the contrast-to-noise ratio (CNR) and spatial resolution of various hypothetical scintillator designs was examined through a hybrid technique involving Monte Carlo simulation of radiation transport in combination with simulation of optical gain distributions and optical point spread functions. The optical simulations employed optical parameters extracted from a best fit to measurement results reported in a previous investigation of a 1.13 cm thick, 1016 μm pitch prototype BGO segmented scintillator. All hypothetical designs employed BGO material with a thickness and element-to-element pitch ranging from 0.5 to 6 cm and from 0.508 to 1.524 mm, respectively. In the CNR study, for each design, full tomographic scans of a contrast phantom incorporating various soft-tissue inserts were simulated at a total dose of 4 cGy. RESULTS Theoretical values for contrast, noise, and CNR were found to be in close agreement with empirical results from the BGO prototype, strongly supporting the validity of the modeling technique. CNR and spatial resolution for the various scintillator designs demonstrate complex behavior as scintillator thickness and element pitch are varied--with a clear trade-off between these two imaging metrics up to a thickness of ~3 cm. Based on these results, an optimization map indicating the regions of design that provide a balance between these metrics was obtained. The map shows that, for a given set of optical parameters, scintillator thickness and pixel pitch can be judiciously chosen to maximize performance without resorting to thicker, more costly scintillators. CONCLUSIONS Modeling radiation and optical effects in thick, segmented scintillators through use of a hybrid technique can provide a practical way to gain insight as to how to optimize the performance of such devices in radiotherapy imaging. Assisted by such modeling, the development of practical designs should greatly facilitate low-dose, soft tissue visualization employing MV CBCT imaging in external beam radiotherapy.
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Affiliation(s)
- Langechuan Liu
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Larry E Antonuk
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Youcef El-Mohri
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Qihua Zhao
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
| | - Hao Jiang
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109
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Chaikh A, Giraud JY, Balosso J. Effect of the modification of CT scanner calibration curves on dose using density correction methods for chest cancer. Ing Rech Biomed 2014. [DOI: 10.1016/j.irbm.2014.06.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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The dependence of computed tomography number to relative electron density conversion on phantom geometry and its impact on planned dose. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2014; 37:385-91. [DOI: 10.1007/s13246-014-0272-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Accepted: 04/10/2014] [Indexed: 10/25/2022]
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Bourque AE, Carrier JF, Bouchard H. A stoichiometric calibration method for dual energy computed tomography. Phys Med Biol 2014; 59:2059-88. [DOI: 10.1088/0031-9155/59/8/2059] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Kry SF, Alvarez P, Molineu A, Amador C, Galvin J, Followill DS. Algorithms used in heterogeneous dose calculations show systematic differences as measured with the Radiological Physics Center's anthropomorphic thorax phantom used for RTOG credentialing. Int J Radiat Oncol Biol Phys 2013; 85:e95-100. [PMID: 23237006 DOI: 10.1016/j.ijrobp.2012.08.039] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2012] [Revised: 08/24/2012] [Accepted: 08/29/2012] [Indexed: 12/01/2022]
Abstract
PURPOSE To determine the impact of treatment planning algorithm on the accuracy of heterogeneous dose calculations in the Radiological Physics Center (RPC) thorax phantom. METHODS AND MATERIALS We retrospectively analyzed the results of 304 irradiations of the RPC thorax phantom at 221 different institutions as part of credentialing for Radiation Therapy Oncology Group clinical trials; the irradiations were all done using 6-MV beams. Treatment plans included those for intensity-modulated radiation therapy (IMRT) as well as 3-dimensional conformal therapy (3D-CRT). Heterogeneous plans were developed using Monte Carlo (MC), convolution/superposition (CS), and the anisotropic analytic algorithm (AAA), as well as pencil beam (PB) algorithms. For each plan and delivery, the absolute dose measured in the center of a lung target was compared to the calculated dose, as was the planar dose in 3 orthogonal planes. The difference between measured and calculated dose was examined as a function of planning algorithm as well as use of IMRT. RESULTS PB algorithms overestimated the dose delivered to the center of the target by 4.9% on average. Surprisingly, CS algorithms and AAA also showed a systematic overestimation of the dose to the center of the target, by 3.7% on average. In contrast, the MC algorithm dose calculations agreed with measurement within 0.6% on average. There was no difference observed between IMRT and 3D CRT calculation accuracy. CONCLUSION Unexpectedly, advanced treatment planning systems (those using CS and AAA algorithms) overestimated the dose that was delivered to the lung target. This issue requires attention in terms of heterogeneity calculations and potentially in terms of clinical practice.
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Affiliation(s)
- Stephen F Kry
- Radiological Physics Center, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
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Son SH, Kang YN, Ryu MR. The effect of metallic implants on radiation therapy in spinal tumor patients with metallic spinal implants. Med Dosim 2012; 37:98-107. [DOI: 10.1016/j.meddos.2011.01.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2010] [Revised: 01/13/2011] [Accepted: 12/08/2010] [Indexed: 11/24/2022]
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Nobah A, Moftah B, Tomic N, Devic S. Influence of electron density spatial distribution and X-ray beam quality during CT simulation on dose calculation accuracy. J Appl Clin Med Phys 2011; 12:3432. [PMID: 21844854 PMCID: PMC5718643 DOI: 10.1120/jacmp.v12i3.3432] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 01/13/2011] [Accepted: 02/06/2011] [Indexed: 11/29/2022] Open
Abstract
Impact of the various kVp settings used during computed tomography (CT) simulation that provides data for heterogeneity corrected dose distribution calculations in patients undergoing external beam radiotherapy with either high‐energy photon or electron beams have been investigated. The change of the Hounsfield Unit (HU) values due to the influence of kVp settings and geometrical distribution of various tissue substitute materials has also been studied. The impact of various kVp settings and electron density (ED) distribution on the accuracy of dose calculation in high‐energy photon beams was found to be well within 2%. In the case of dose distributions obtained with a commercially available Monte Carlo dose calculation algorithm for electron beams, differences of more than 10% were observed for different geometrical setups and kVp settings. Dose differences for the electron beams are relatively small at shallow depths but increase with depth around lower isodose values. PACS numbers: 87.57.Q‐, 87.55.D‐
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Affiliation(s)
- Ahmad Nobah
- Biomedical Physics Department, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.
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El-Mohri Y, Antonuk LE, Zhao Q, Choroszucha RB, Jiang H, Liu L. Low-dose megavoltage cone-beam CT imaging using thick, segmented scintillators. Phys Med Biol 2011; 56:1509-27. [PMID: 21325709 PMCID: PMC3062516 DOI: 10.1088/0031-9155/56/6/001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Megavoltage, cone-beam computed tomography (MV CBCT) employing an electronic portal imaging device (EPID) is a highly promising technique for providing soft-tissue visualization in image-guided radiotherapy. However, current EPIDs based on active matrix flat-panel imagers (AMFPIs), which are regarded as the gold standard for portal imaging and referred to as conventional MV AMFPIs, require high radiation doses to achieve this goal due to poor x-ray detection efficiency (∼2% at 6 MV). To overcome this limitation, the incorporation of thick, segmented, crystalline scintillators, as a replacement for the phosphor screens used in these AMFPIs, has been shown to significantly improve the detective quantum efficiency (DQE) performance, leading to improved image quality for projection imaging at low dose. Toward the realization of practical AMFPIs capable of low dose, soft-tissue visualization using MV CBCT imaging, two prototype AMFPIs incorporating segmented scintillators with ∼11 mm thick CsI:Tl and Bi(4)Ge(3)O(12) (BGO) crystals were evaluated. Each scintillator consists of 120 × 60 crystalline elements separated by reflective septal walls, with an element-to-element pitch of 1.016 mm. The prototypes were evaluated using a bench-top CBCT system, allowing the acquisition of 180 projection, 360° tomographic scans with a 6 MV radiotherapy photon beam. Reconstructed images of a spatial resolution phantom, as well as of a water-equivalent phantom, embedded with tissue equivalent objects having electron densities (relative to water) varying from ∼0.28 to ∼1.70, were obtained down to one beam pulse per projection image, corresponding to a scan dose of ∼4 cGy--a dose similar to that required for a single portal image obtained from a conventional MV AMFPI. By virtue of their significantly improved DQE, the prototypes provided low contrast visualization, allowing clear delineation of an object with an electron density difference of ∼2.76%. Results of contrast, noise and contrast-to-noise ratio are presented as a function of dose and compared to those from a conventional MV AMFPI.
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Affiliation(s)
- Youcef El-Mohri
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109, USA.
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Landry G, Reniers B, Murrer L, Lutgens L, Bloemen-Van Gurp E, Pignol JP, Keller B, Beaulieu L, Verhaegen F. Sensitivity of low energy brachytherapy Monte Carlo dose calculations to uncertainties in human tissue composition. Med Phys 2010; 37:5188-98. [DOI: 10.1118/1.3477161] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Wang Y, El-Mohri Y, Antonuk LE, Zhao Q. Monte Carlo investigations of the effect of beam divergence on thick, segmented crystalline scintillators for radiotherapy imaging. Phys Med Biol 2010; 55:3659-73. [PMID: 20526032 PMCID: PMC2909124 DOI: 10.1088/0031-9155/55/13/006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The use of thick, segmented scintillators in electronic portal imagers offers the potential for significant improvement in x-ray detection efficiency compared to conventional phosphor screens. Such improvement substantially increases the detective quantum efficiency (DQE), leading to the possibility of achieving soft-tissue visualization at clinically practical (i.e. low) doses using megavoltage (MV) cone-beam computed tomography. While these DQE increases are greatest at zero spatial frequency, they are diminished at higher frequencies as a result of degradation of spatial resolution due to lateral spreading of secondary radiation within the scintillator--an effect that is more pronounced for thicker scintillators. The extent of this spreading is even more accentuated for radiation impinging the scintillator at oblique angles of incidence due to beam divergence. In this paper, Monte Carlo simulations of radiation transport, performed to investigate and quantify the effects of beam divergence on the imaging performance of MV imagers based on two promising scintillators (BGO and CsI:Tl), are reported. In these studies, 10-40 mm thick scintillators, incorporating low-density polymer, or high-density tungsten septal walls, were examined for incident angles corresponding to that encountered at locations up to approximately 15 cm from the central beam axis (for an imager located 130 cm from a radiotherapy x-ray source). The simulations demonstrate progressively more severe spatial resolution degradation (quantified in terms of the effect on the modulation transfer function) as a function of increasing angle of incidence (as well as of the scintillator thickness). Since the noise power behavior was found to be largely independent of the incident angle, the dependence of the DQE on the incident angle is therefore primarily determined by the spatial resolution. The observed DQE degradation suggests that 10 mm thick scintillators are not strongly affected by beam divergence for detector areas up to approximately 30x30 cm2. For thicker scintillators, the area that is relatively unaffected is significantly reduced, requiring a focused scintillator geometry in order to preserve spatial resolution, and thus DQE.
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Affiliation(s)
- Yi Wang
- Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109, USA
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Computed tomography as a source of electron density information for radiation treatment planning. Strahlenther Onkol 2010; 186:327-33. [PMID: 20458451 DOI: 10.1007/s00066-010-2086-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Accepted: 03/05/2010] [Indexed: 10/19/2022]
Abstract
PURPOSE To evaluate the performance of computed tomography (CT) systems of various designs as a source of electron density (rho(el)) data for treatment planning of radiation therapy. MATERIAL AND METHODS Dependence of CT numbers on relative electron density of tissue-equivalent materials (HU-rho(el) relationship) was measured for several general-purpose CT systems (single-slice, multislice, wide-bore multislice), for radiotherapy simulators with a single-slice CT and kV CBCT (cone-beam CT) options, as well as for linear accelerators with kV and MV CBCT systems. Electron density phantoms of four sizes were used. Measurement data were compared with the standard HU-rhoel relationships predefined in two commercial treatment-planning systems (TPS). RESULTS The HU-rho(el) relationships obtained with all of the general-purpose CT scanners operating at voltages close to 120 kV were very similar to each other and close to those predefined in TPS. Some dependency of HU values on tube voltage was observed for bone- equivalent materials. For a given tube voltage, differences in results obtained for different phantoms were larger than those obtained for different CT scanners. For radiotherapy simulators and for kV CBCT systems, the information on rhoel was much less precise because of poor uniformity of images. For MV CBCT, the results were significantly different than for kV systems due to the differing energy spectrum of the beam. CONCLUSION The HU-rho(el) relationships predefined in TPS can be used for general-purpose CT systems operating at voltages close to 120 kV. For nontypical imaging systems (e.g., CBCT), the relationship can be significantly different and, therefore, it should always be measured and carefully analyzed before using CT data for treatment planning.
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Pesznyák C, Weisz C, Király R, Kiss B, Zelić S, Polgár I, Zaránd P. [Quality control of computed tomography scanners from the viewpoint of radiotherapy planning in Hungary]. Magy Onkol 2009; 53:247-51. [PMID: 19793688 DOI: 10.1556/monkol.53.2009.3.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The aim of this publication is to review the requirements necessary for using computed tomography (CT) for radiotherapy treatment planning. The equipments were tested with different CT phantoms. The authors made several measurements for checking the CT number, the quality and the mechanical parameters of CT tables. The CT numbers measured on the equipments of different manufacturers were in quite good agreement with the IAEA requirements. The geometric distortions of CT images are negligible, while the mechanical parameters of CT tables show considerable variety. A quality assurance - quality control protocol is recommended to implement in a safe workflow.
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Seet KYT, Barghi A, Yartsev S, Van Dyk J. The effects of field-of-view and patient size on CT numbers from cone-beam computed tomography. Phys Med Biol 2009; 54:6251-62. [DOI: 10.1088/0031-9155/54/20/014] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Guan H, Dong H. Dose calculation accuracy using cone-beam CT (CBCT) for pelvic adaptive radiotherapy. Phys Med Biol 2009; 54:6239-50. [DOI: 10.1088/0031-9155/54/20/013] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Papanikolaou N, Stathakis S. Dose-calculation algorithms in the context of inhomogeneity corrections for high energy photon beams. Med Phys 2009; 36:4765-75. [DOI: 10.1118/1.3213523] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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Lee L, Le QT, Xing L. Retrospective IMRT dose reconstruction based on cone-beam CT and MLC log-file. Int J Radiat Oncol Biol Phys 2008; 70:634-44. [PMID: 18207036 DOI: 10.1016/j.ijrobp.2007.09.054] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 09/27/2007] [Accepted: 09/28/2007] [Indexed: 11/24/2022]
Abstract
PURPOSE Head-and-neck (HN) cone-beam computed tomography (CBCT) can be exploited to probe the IMRT dose delivered to a patient taking into account the interfraction anatomic variation and any potential inaccuracy in the IMRT delivery. The aim of this work is to reconstruct the intensity-modulated radiation therapy dose delivered to an HN patient using the CBCT and multileaf collimator (MLC) log-files. METHODS AND MATERIALS A cylindrical CT phantom was used for calibrating the electron density and validating the procedures of the dose reconstruction. Five HN patients were chosen, and for each patient, CBCTs were performed on three separate fractions spaced every 2 weeks starting from the first fraction. The respective MLC log-files were retrieved and converted into fluence maps. The dose was then reconstructed on the corresponding CBCT with the regenerated fluence maps. The reconstructed dose distribution, dosimetric endpoints, and DVHs were compared with that of the treatment plan. RESULTS Phantom study showed that HN CBCT can be directly used for dose reconstruction. For most treatment sessions, the CBCT-based dose reconstructions yielded DVHs of the targets close (within 3%) to that of the original treatment plans. However, dosimetric changes (within 10%) due to anatomic variations caused by setup inaccuracy, organ deformation, tumour shrinkage, or weight loss (or a combination of these) were observed for the critical organs. CONCLUSIONS The methodology we established affords an objective dosimetric basis for the clinical decision on whether a replanning is necessary during the course of treatment and provides a valuable platform for adaptive therapy in future.
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Affiliation(s)
- Louis Lee
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305-5847, USA
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Wang Y, Antonuk LE, El-Mohri Y, Zhao Q, Sawant A, Du H. Monte Carlo investigations of megavoltage cone-beam CT using thick, segmented scintillating detectors for soft tissue visualization. Med Phys 2008; 35:145-58. [PMID: 18293571 PMCID: PMC2920060 DOI: 10.1118/1.2818957] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Megavoltage cone-beam computed tomography (MV CBCT) is a highly promising technique for providing volumetric patient position information in the radiation treatment room. Such information has the potential to greatly assist in registering the patient to the planned treatment position, helping to ensure accurate delivery of the high energy therapy beam to the tumor volume while sparing the surrounding normal tissues. Presently, CBCT systems using conventional MV active matrix flat-panel imagers (AMFPIs), which are commonly used in portal imaging, require a relatively large amount of dose to create images that are clinically useful. This is due to the fact that the phosphor screen detector employed in conventional MV AMFPIs utilizes only approximately 2% of the incident radiation (for a 6 MV x-ray spectrum). Fortunately, thick segmented scintillating detectors can overcome this limitation, and the first prototype imager has demonstrated highly promising performance for projection imaging at low doses. It is therefore of definite interest to examine the potential performance of such thick, segmented scintillating detectors for MV CBCT. In this study, Monte Carlo simulations of radiation energy deposition were used to examine reconstructed images of cylindrical CT contrast phantoms, embedded with tissue-equivalent objects. The phantoms were scanned at 6 MV using segmented detectors having various design parameters (i.e., detector thickness as well as scintillator and septal wall materials). Due to constraints imposed by the nature of this study, the size of the phantoms was limited to approximately 6 cm. For such phantoms, the simulation results suggest that a 40 mm thick, segmented CsI detector with low density septal walls can delineate electron density differences of approximately 2.3% and 1.3% at doses of 1.54 and 3.08 cGy, respectively. In addition, it was found that segmented detectors with greater thickness, higher density scintillator material, or lower density septal walls exhibit higher contrast-to-noise performance. Finally, the performance of various segmented detectors obtained at a relatively low dose (1.54 cGy) was compared with that of a phosphor screen similar to that employed in conventional MV AMFPIs. This comparison indicates that for a phosphor screen to achieve the same contrast-to-noise performance as the segmented detectors approximately 18 to 59 times more dose is required, depending on the configuration of the segmented detectors.
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Affiliation(s)
- Yi Wang
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109, USA.
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Yoo S, Yin FF. Dosimetric feasibility of cone-beam CT-based treatment planning compared to CT-based treatment planning. Int J Radiat Oncol Biol Phys 2006; 66:1553-61. [PMID: 17056197 DOI: 10.1016/j.ijrobp.2006.08.031] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 08/14/2006] [Accepted: 08/16/2006] [Indexed: 11/23/2022]
Abstract
PURPOSE Cone-beam computed tomography (CBCT) images are currently used for positioning verification. However, it is yet unknown whether CBCT could be used in dose calculation for replanning in adaptive radiation therapy. This study investigates the dosimetric feasibility of CBCT-based treatment planning. METHODS AND MATERIALS Hounsfield unit (HU) values and profiles of Catphan, homogeneous/inhomogeneous phantoms, and various tissue regions of patients in CBCT images were compared to those in CT. The dosimetric consequence of the HU variation was investigated by comparing CBCT-based treatment plans to conventional CT-based plans for both phantoms and patients. RESULTS The maximum HU difference between CBCT and CT of Catphan was 34 HU in the Teflon. The differences in other materials were less than 10 HU. The profiles for the homogeneous phantoms in CBCT displayed reduced HU values up to 150 HU in the peripheral regions compared to those in CT. The scatter and artifacts in CBCT became severe surrounding inhomogeneous tissues with reduced HU values up to 200 HU. The MU/cGy differences were less than 1% for most phantom cases. The isodose distributions between CBCT-based and CT-based plans agreed very well. However, the discrepancy was larger when CBCT was scanned without a bowtie filter than with bowtie filter. Also, up to 3% dosimetric error was observed in the plans for the inhomogeneous phantom. In the patient studies, the discrepancies of isodose lines between CT-based and CBCT-based plans, both 3D and IMRT, were less than 2 mm. Again, larger discrepancy occurred for the lung cancer patients. CONCLUSION This study demonstrated the feasibility of CBCT-based treatment planning. CBCT-based treatment plans were dosimetrically comparable to CT-based treatment plans. Dosimetric data in the inhomogeneous tissue regions should be carefully validated.
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Affiliation(s)
- Sua Yoo
- Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27710, USA.
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Kendall RL, Gifford KA, Kirsner SM. The impact of peak-kilovoltage settings on heterogeneity-corrected photon-beam treatment plans. Radiother Oncol 2006; 81:206-8. [PMID: 17069913 DOI: 10.1016/j.radonc.2006.10.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Revised: 10/03/2006] [Accepted: 10/04/2006] [Indexed: 11/20/2022]
Abstract
Differences were evaluated in external-beam treatment plan dose calculations that result from the use of different Hounsfield-unit to electron-density conversion curves with CT images acquired with various tube potentials. These differences were found to be clinically insignificant and it was concluded that the impact of CT tube potential on treatment planning is negligible.
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Affiliation(s)
- Robin L Kendall
- Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
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Wei J, Sandison GA, Hsi WC, Ringor M, Lu X. Dosimetric impact of a CT metal artefact suppression algorithm for proton, electron and photon therapies. Phys Med Biol 2006; 51:5183-97. [PMID: 17019032 DOI: 10.1088/0031-9155/51/20/007] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Accurate dose calculation is essential to precision radiation treatment planning and this accuracy depends upon anatomic and tissue electron density information. Modern treatment planning inhomogeneity corrections use x-ray CT images and calibrated scales of tissue CT number to electron density to provide this information. The presence of metal in the volume scanned by an x-ray CT scanner causes metal induced image artefacts that influence CT numbers and thereby introduce errors in the radiation dose distribution calculated. This paper investigates the dosimetric improvement achieved by a previously proposed x-ray CT metal artefact suppression technique when the suppressed images of a patient with bilateral hip prostheses are used in commercial treatment planning systems for proton, electron or photon therapies. For all these beam types, this clinical image and treatment planning study reveals that the target may be severely underdosed if a metal artefact-contaminated image is used for dose calculations instead of the artefact suppressed one. Of the three beam types studied, the metal artefact suppression is most important for proton therapy dose calculations, intermediate for electron therapy and least important for x-ray therapy but still significant. The study of a water phantom having a metal rod simulating a hip prosthesis indicates that CT numbers generated after image processing for metal artefact suppression are accurate and thus dose calculations based on the metal artefact suppressed images will be of high fidelity.
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Affiliation(s)
- Jikun Wei
- School of Health Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, USA
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Langen KM, Meeks SL, Poole DO, Wagner TH, Willoughby TR, Kupelian PA, Ruchala KJ, Haimerl J, Olivera GH. The use of megavoltage CT (MVCT) images for dose recomputations. Phys Med Biol 2005; 50:4259-76. [PMID: 16148392 DOI: 10.1088/0031-9155/50/18/002] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Megavoltage CT (MVCT) images of patients are acquired daily on a helical tomotherapy unit (TomoTherapy, Inc., Madison, WI). While these images are used primarily for patient alignment, they can also be used to recalculate the treatment plan for the patient anatomy of the day. The use of MVCT images for dose computations requires a reliable CT number to electron density calibration curve. In this work, we tested the stability of the MVCT numbers by determining the variation of this calibration with spatial arrangement of the phantom, time and MVCT acquisition parameters. The two calibration curves that represent the largest variations were applied to six clinical MVCT images for recalculations to test for dosimetric uncertainties. Among the six cases tested, the largest difference in any of the dosimetric endpoints was 3.1% but more typically the dosimetric endpoints varied by less than 2%. Using an average CT to electron density calibration and a thorax phantom, a series of end-to-end tests were run. Using a rigid phantom, recalculated dose volume histograms (DVHs) were compared with plan DVHs. Using a deformed phantom, recalculated point dose variations were compared with measurements. The MVCT field of view is limited and the image space outside this field of view can be filled in with information from the planning kVCT. This merging technique was tested for a rigid phantom. Finally, the influence of the MVCT slice thickness on the dose recalculation was investigated. The dosimetric differences observed in all phantom tests were within the range of dosimetric uncertainties observed due to variations in the calibration curve. The use of MVCT images allows the assessment of daily dose distributions with an accuracy that is similar to that of the initial kVCT dose calculation.
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Affiliation(s)
- K M Langen
- Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA.
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Abstract
An important step in Monte Carlo treatment planning (MCTP), which is commonly performed uncritically, is segmentation of the patient CT data into a voxel phantom for dose calculation. In addition to assigning mass densities to voxels, as is done in conventional TP, this entails assigning media. Mis-assignment of media can potentially lead to significant dose errors in MCTP. In this work, a test phantom with exact-known composition was used to study CT segmentation errors and to quantify subsequent MCTP inaccuracies. For our test cases, we observed dose errors in some regions of up to 10% for 6 and 15 MV photons, more than 30% for an 18 MeV electron beam and more than 40% for 250 kVp photons. It is concluded that a careful CT calibration with a suitable phantom is essential. Generic calibrations and the use of commercial CT phantoms have to be critically assessed.
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Affiliation(s)
- Frank Verhaegen
- Medical Physics Department, McGill University, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Québec H3G1A4, Canada
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Mosleh‐Shirazi MA, Hansen VN, Childs PJ, Warrington AP, Saran FH. Commissioning and implementation of a stereotactic conformal radiotherapy technique using a general-purpose planning system. J Appl Clin Med Phys 2004; 5:1-14. [PMID: 15753935 PMCID: PMC5723485 DOI: 10.1120/jacmp.v5i3.1948] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The purpose of this paper is to report on commissioning and clinical implementation of a customized system for pediatric stereotactic conformal radiotherapy (SCRT). The system is based on the Pinnacle treatment‐planning system and its interfaces with other equipment: (1) Beam models were optimized for our compact blocking system and a new LINAC. (2) Three CT‐to‐density conversion tables were evaluated, one using tabulated data for a commercial phantom, the second including additional points from the manufacturer's data for the inserts in an in‐house phantom, and the third using measured densities for the in‐house phantom materials combined with tabulated data for the commercial phantom. (3) Blocks were transferred to a computerized block cutter using in‐house software that extracted the block shape from the export file and custom‐fitted the additional necessary shapes. (4) In the absence of a DICOM RT Image link, a method based on screen data capture was used to export digitally reconstructed radiographs (DRRs) to two portal imaging systems for treatment verification. Lens shielding by multileaf collimation in the anterior‐posterior isocenter verification field was investigated. (1) Computed dose distributions using the beam models agreed with measurements well within published acceptability criteria. A difference of up to 1.0 mm was measured between the beam's eye views of aperture blocks and computed 50% isodose contours for a 2×2×2 mm dose calculation grid. (2) The third table, which included measured densities, improved the accuracy of the calculated isocenter dose by up to 0.5% in typical patient SCRT treatments and up to 1.0% in a phantom with 5‐cm diameter inhomogeneity inserts. (3) The block export and customization process was shown to introduce no additional uncertainty. A 1‐mm block production uncertainty was measured using film dosimetry on six blocks. (4) The DRR transfer method did not introduce uncertainty into the process. Verification field shielding reduced lens dose by 12 to 15 times. In conclusion, this customized system for planning and verification of pediatric SCRT provides a high level of precision as well as reasonable practical efficiency. PACS numbers: 87.53.Kn, 87.53.Ly, 87.53.Oq, 87.53.Tf, 87.53.Uv
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Affiliation(s)
- M. Amin Mosleh‐Shirazi
- Joint Department of PhysicsThe Institute of Cancer Research and The Royal Marsden NHS TrustSuttonSurreySM2 5PTUnited Kingdom
| | - Vibeke N. Hansen
- Joint Department of PhysicsThe Institute of Cancer Research and The Royal Marsden NHS TrustSuttonSurreySM2 5PTUnited Kingdom
| | - Peter J. Childs
- Joint Department of PhysicsThe Institute of Cancer Research and The Royal Marsden NHS TrustSuttonSurreySM2 5PTUnited Kingdom
| | - Alan P. Warrington
- Joint Department of PhysicsThe Institute of Cancer Research and The Royal Marsden NHS TrustSuttonSurreySM2 5PTUnited Kingdom
| | - Frank H. Saran
- Department of RadiotherapyThe Institute of Cancer Research and The Royal Marsden NHS TrustSuttonSurreySM2 5PTUnited Kingdom
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