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Plyku D, Ghaly M, Li Y, Brown JL, O'Reilly S, Khamwan K, Goodkind AB, Sexton-Stallone B, Cao X, Zurakowski D, Fahey FH, Treves ST, Bolch WE, Frey EC, Sgouros G. Renal 99mTc-DMSA pharmacokinetics in pediatric patients. EJNMMI Phys 2021; 8:53. [PMID: 34283316 PMCID: PMC8292521 DOI: 10.1186/s40658-021-00401-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 07/05/2021] [Indexed: 11/10/2022] Open
Abstract
Abstract 99mTc-DMSA is one of the most commonly used pediatric nuclear medicine imaging agents. Nevertheless, there are no pharmacokinetic (PK) models for 99mTc-DMSA in children, and currently available pediatric dose estimates for 99mTc-DMSA use pediatric S values with PK data derived from adults. Furthermore, the adult PK data were collected in the mid-70’s using quantification techniques and instrumentation available at the time. Using pediatric imaging data for DMSA, we have obtained kinetic parameters for DMSA that differ from those applicable to adults. Methods We obtained patient data from a retrospective re-evaluation of clinically collected pediatric SPECT images of 99mTc-DMSA in 54 pediatric patients from Boston’s Children Hospital (BCH), ranging in age from 1 to 16 years old. These were supplemented by prospective data from twenty-three pediatric patients (age range: 4 months to 6 years old). Results In pediatric patients, the plateau phase in fractional kidney uptake occurs at a fractional uptake value closer to 0.3 than the value of 0.5 reported by the International Commission on Radiological Protection (ICRP) for adult patients. This leads to a 27% lower time-integrated activity coefficient in pediatric patients than in adults. Over the age range examined, no age dependency in uptake fraction at the clinical imaging time was observed. Female pediatric patients had a 17% higher fractional kidney uptake at the clinical imaging time than males (P < 0.001). Conclusions Pediatric 99mTc-DMSA kinetics differ from those reported for adults and should be considered in pediatric patient dosimetry. Alternatively, the differences obtained in this study could reflect improved quantification methods and the need to re-examine DMSA kinetics in adults. Supplementary Information The online version contains supplementary material available at 10.1186/s40658-021-00401-7.
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Affiliation(s)
- Donika Plyku
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Michael Ghaly
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Ye Li
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Justin L Brown
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, USA
| | - Shannon O'Reilly
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, USA
| | - Kitiwat Khamwan
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.,Department of Radiology, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand
| | - Alison B Goodkind
- Division of Nuclear Medicine and Molecular Imaging, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Briana Sexton-Stallone
- Division of Nuclear Medicine and Molecular Imaging, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Xinhua Cao
- Division of Nuclear Medicine and Molecular Imaging, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - David Zurakowski
- Departments of Anesthesiology and Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Frederic H Fahey
- Division of Nuclear Medicine and Molecular Imaging, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - S Ted Treves
- Division of Nuclear Medicine and Molecular imaging, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Wesley E Bolch
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, USA
| | - Eric C Frey
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - George Sgouros
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
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Schwarz BC, Godwin WJ, Wayson MB, Dewji SA, Jokisch DW, Lee C, Bolch WE. Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal electron sources. Phys Med Biol 2021; 66:035005. [PMID: 33142278 DOI: 10.1088/1361-6560/abc709] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In both the International Commission on Radiological Protection (ICRP) and Medical Internal Radiation Dose (MIRD) schemata of internal dosimetry, the S-value is defined as the absorbed dose to a target organ per nuclear decay of the radionuclide in a source organ. Its computation requires data on the energies and yields of all radiation emissions from radionuclide decay, the mass of the target organ, and the value of the absorbed fraction-the fraction of particle energy emitted in the source organ that is deposited in the target organ. The specific absorbed fraction (SAF) is given as the ratio of the absorbed fraction and the target mass. Historically, in the early development of both schemata, computational simplifications were made to the absorbed fraction in considering both organ self-dose ([Formula: see text]) and organ cross-dose ([Formula: see text]). In particular, the value of the absorbed fraction was set to unity for all 'non-penetrating' particle emissions (electrons and alpha particles) such that they contributed only to organ self-dose. As radiation transport codes for charged particles became more widely available, it became increasingly possible to abandon this distinction and to explicitly consider the transport of internally emitted electrons in a manner analogous to that for photons. In this present study, we report on an extensive series of electron SAFs computed in a revised series of the UF/NCI pediatric phantoms. A total of 28 electron energies-0-10 MeV-along a logarithmic energy grid are provided in electronic annexes, where 0 keV is associated with limiting values of the SAF. Electron SAFs were computed independently for collisional energy losses (SAFCEL) and radiation energy losses (SAFREL) to the target organ. A methodology was employed in which values of SAFREL were compiled by first assembling organ-specific and electron energy-specific bremsstrahlung x-ray spectra, and then using these x-ray spectra to re-weight a previously established monoenergetic database of photon SAFs for all phantoms and source-target combinations. Age-dependent trends in the electron SAF were demonstrated for the majority of the source-target organ pairs, and were consistent to values given for the ICRP adult phantoms. In selected cases, however, anticipated age-dependent trends were not seen, and were attributed to anatomical differences in relative organ positioning at specific phantom ages. Both the electron SAFs of this study, and the photon SAFs from our companion study, are presently being used by ICRP Committee 2 in its upcoming pediatric extension to ICRP Publication 133.
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Affiliation(s)
- Bryan C Schwarz
- Department of Radiology, University of Florida, Gainesville, FL 32611, United States of America
| | - William J Godwin
- Department of Radiation Oncology, Medical University of South Carolina, Charleston, SC 29407, United States of America
| | - Michael B Wayson
- Baylor Scott & White Health, Dallas, TX 76051, United States of America
| | - Shaheen A Dewji
- Department of Nuclear Engineering, Texas A&M University, College Station, TX 77843, United States of America
| | - Derek W Jokisch
- Department of Physics and Engineering, Francis Marion University, Florence, SC 29502, United States of America.,Center for Radiation Protection Knowledge, Oak Ridge National Laboratory, Oak Ridge, TN 37830, United States of America
| | - Choonsik Lee
- Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD 20850, United States of America
| | - Wesley E Bolch
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, United States of America
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Abadi E, Segars WP, Tsui BMW, Kinahan PE, Bottenus N, Frangi AF, Maidment A, Lo J, Samei E. Virtual clinical trials in medical imaging: a review. J Med Imaging (Bellingham) 2020; 7:042805. [PMID: 32313817 PMCID: PMC7148435 DOI: 10.1117/1.jmi.7.4.042805] [Citation(s) in RCA: 57] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 03/23/2020] [Indexed: 12/13/2022] Open
Abstract
The accelerating complexity and variety of medical imaging devices and methods have outpaced the ability to evaluate and optimize their design and clinical use. This is a significant and increasing challenge for both scientific investigations and clinical applications. Evaluations would ideally be done using clinical imaging trials. These experiments, however, are often not practical due to ethical limitations, expense, time requirements, or lack of ground truth. Virtual clinical trials (VCTs) (also known as in silico imaging trials or virtual imaging trials) offer an alternative means to efficiently evaluate medical imaging technologies virtually. They do so by simulating the patients, imaging systems, and interpreters. The field of VCTs has been constantly advanced over the past decades in multiple areas. We summarize the major developments and current status of the field of VCTs in medical imaging. We review the core components of a VCT: computational phantoms, simulators of different imaging modalities, and interpretation models. We also highlight some of the applications of VCTs across various imaging modalities.
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Affiliation(s)
- Ehsan Abadi
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - William P. Segars
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - Benjamin M. W. Tsui
- Johns Hopkins University, Department of Radiology, Baltimore, Maryland, United States
| | - Paul E. Kinahan
- University of Washington, Department of Radiology, Seattle, Washington, United States
| | - Nick Bottenus
- Duke University, Department of Biomedical Engineering, Durham, North Carolina, United States
- University of Colorado Boulder, Department of Mechanical Engineering, Boulder, Colorado, United States
| | - Alejandro F. Frangi
- University of Leeds, School of Computing, Leeds, United Kingdom
- University of Leeds, School of Medicine, Leeds, United Kingdom
| | - Andrew Maidment
- University of Pennsylvania, Department of Radiology, Philadelphia, Pennsylvania, United States
| | - Joseph Lo
- Duke University, Department of Radiology, Durham, North Carolina, United States
| | - Ehsan Samei
- Duke University, Department of Radiology, Durham, North Carolina, United States
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Díaz Londoño G, García-Pareja S, Salvat F, Lallena AM. Simple variance reduction in Monte Carlo calculations of specific absorbed fractions: Russian roulette and splitting at the source organ. Biomed Phys Eng Express 2020; 6:035015. [PMID: 33438660 DOI: 10.1088/2057-1976/ab817f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE To investigate the capabilities of several variance reduction techniques in the calculation of specific absorbed fractions in cases where the source and the target organs are far away and/or the target organs have a small volume. METHODS The specific absorbed fractions have been calculated by using the Monte Carlo code PENELOPE and by assuming the thyroid gland as the source organ and the testicles, the urinary bladder, the uterus, and the ovaries as the target ones. A mathematical anthropomorphic phantom, similar to the MIRD-type phantoms, has been considered. Photons with initial energies of 50, 100 and 500 keV were emitted isotropically from the volume of the source organ. Simulations have been carried out by implementing the variance reduction techniques of splitting and Russian roulette at the source organ only and the interaction forcing at the target organs. The influence of the implementation details of those techniques have been investigated and optimal parameters have been determined. All simulations were run with a CPU time of 1.5 · 105 s. RESULTS Specific absorbed fractions with relative uncertainties well below 10% have been obtained in most cases, agreeing with those used as reference. The best value for the factor defining the application of the Russian roulette technique was r = 0.3. The best value for the splitting number was between s = 3 and s = 10, depending on the specific energies and target organs. CONCLUSIONS The proposed strategy provides an effective method for computing specific absorbed fractions for the most unfavorable situations, with a computing effort that is considerably reduced with respect to other methodologies.
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Affiliation(s)
- G Díaz Londoño
- Grupo de Investigación e Innovación Biomédica, Facultad de Ciencias Exactas y Aplicadas, Instituto Tecnológico Metropolitano, Calle 73 No. 76A-354, Vía al Volador, Medellín, Colombia
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Xie T, Park JS, Zhuo W, Zaidi H. Development of a nonhuman primate computational phantom for radiation dosimetry. Med Phys 2019; 47:736-744. [DOI: 10.1002/mp.13936] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 11/01/2019] [Accepted: 11/13/2019] [Indexed: 01/27/2023] Open
Affiliation(s)
- Tianwu Xie
- Institute of Radiation Medicine Fudan University 2094 Xietu Road Shanghai 200032China
- Department of Medical Imaging and Information Sciences Geneva University Hospital Geneva Switzerland
| | - Jin Seo Park
- Department of Anatomy Dongguk University School of Medicine Gyeongju Korea
| | - Weihai Zhuo
- Institute of Radiation Medicine Fudan University 2094 Xietu Road Shanghai 200032China
| | - Habib Zaidi
- Department of Medical Imaging and Information Sciences Geneva University Hospital Geneva Switzerland
- Geneva Neuroscience Center Geneva University Geneva Switzerland
- Department of Nuclear Medicine and Molecular Imaging University of Groningen University Medical Center Groningen Groningen Netherlands
- Department of Nuclear Medicine University of Southern Denmark DK‐500Odense Denmark
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Papadimitroulas P, Balomenos A, Kopsinis Y, Loudos G, Alexakos C, Karnabatidis D, Kagadis GC, Kostou T, Chatzipapas K, Visvikis D, Mountris KA, Jaouen V, Katsanos K, Diamantopoulos A, Apostolopoulos D. A Review on Personalized Pediatric Dosimetry Applications Using Advanced Computational Tools. IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 2019. [DOI: 10.1109/trpms.2018.2876562] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Khamwan K, O'Reilly SE, Plyku D, Goodkind A, Josefsson A, Cao X, Fahey FH, Treves ST, Bolch WE, Sgouros G. Re-evaluation of pediatric 18F-FDG dosimetry: Cristy-Eckerman versus UF/NCI hybrid computational phantoms. Phys Med Biol 2018; 63:165012. [PMID: 30022768 DOI: 10.1088/1361-6560/aad47a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Because of the concerns associated with radiation exposure at a young age, there is an increased interest in pediatric absorbed dose estimates for imaging agents. Almost all reported pediatric absorbed dose estimates, however, have been determined using adult pharmacokinetic data with radionuclide S values that take into account the anatomical differences between adults and children based upon the older Cristy-Eckerman (C-E) stylized phantoms. In this work, we use pediatric model-derived pharmacokinetics to compare absorbed dose and effective dose estimates for 18F-FDG in pediatric patients using S values generated from two different geometries of computational phantoms. Time-integrated activity coefficients of 18F-FDG in brain, lungs, heart wall, kidneys and liver, retrospectively, calculated from 35 pediatric patients at the Boston's Children Hospital were used. The absorbed dose calculation was performed in accordance with the Medical Internal Radiation Dose method using S values generated from the University of Florida/National Cancer Institute (UF/NCI) hybrid phantoms, as well as those from C-E stylized computational phantoms. The effective dose was computed using tissue-weighting factors from ICRP Publication 60 and ICRP Publication 103 for the C-E and UF/NCI, respectively. Substantial differences in the absorbed dose estimates between UF/NCI hybrid pediatric phantoms and the C-E stylized phantoms were found for the lungs, ovaries, red bone marrow and urinary bladder wall. Large discrepancies in the calculated dose values were observed in the bone marrow; ranging between -26% to +199%. The effective doses computed by the UF/NCI hybrid phantom S values were slightly different than those seen using the C-E stylized phantoms with percent differences of -0.7%, 2.9% and 2.5% for a newborn, 1 year old and 5 year old, respectively. Differences in anatomical modeling features among computational phantoms used to perform Monte Carlo-based photon and electron transport simulations for 18F, and very likely for other radionuclides, impact internal organ dosimetry computations for pediatric nuclear medicine studies.
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Affiliation(s)
- Kitiwat Khamwan
- The Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, School of Medicine, Baltimore, MD, United States of America. Division of Nuclear Medicine, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand. Chulalongkorn University Biomedical Imaging Group, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
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Papadimitroulas P, Erwin WD, Iliadou V, Kostou T, Loudos G, Kagadis GC. A personalized, Monte Carlo-based method for internal dosimetric evaluation of radiopharmaceuticals in children. Med Phys 2018; 45:3939-3949. [PMID: 29920693 DOI: 10.1002/mp.13055] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Revised: 05/31/2018] [Accepted: 06/12/2018] [Indexed: 11/08/2022] Open
Abstract
PURPOSE Herein, we introduce a methodology for estimating the absorbed dose in organs at risk that is based on specified clinically derived radiopharmaceutical biodistributions and personalized anatomical characteristics. METHODS To evaluate the proposed methodology, we used realistic Monte Carlo (MC) simulations and computational pediatric models to calculate a parameter called in this work the "specific absorbed dose rate" (SADR). The SADR is a unique quantitative metric in that it is specific to a particular organ. It is defined as the absorbed dose rate in an organ when the biodistribution of radioactivity over the whole body is considered. Initially, we applied a validation procedure that calculated specific absorbed fractions (SAFs) from mono-energetic photon sources in the range of 10 keV-2 MeV and compared them with previously published data. We calculated the SADRs for five different radiopharmaceuticals (99m Tc-MDP, 123 I-mIBG, 131 I-MIBG, 131 I-NaI, and 153 Sm-EDTMP) based on their biodistributions at four or five different times; the biodistributions were derived from the clinical scintigraphic data of pediatric patients. We used six models representing male and female patients aged 5, 8, and 14 yr to investigate the absorbed dose variability due to anatomical variations. The GATE Monte Carlo toolkit was used to calculate absorbed doses per organ. Finally, we compared the SADR methodology to that of OLINDA/EXM 1.1 using rescaled masses according to the studied models. Four target organs were considered for calculating the absorbed doses. RESULTS The ratios of SAFs calculated with GATE simulations to those based on previously published data were between 0.9 and 2.2 when the liver was used as a source organ. Subsequently, we used GATE to calculate a dataset of SADRs for the six pediatric models. The SADRs for pediatric models whose total body weights ranged from 20 to 40 kg varied up to approximately 90%, whereas those for models of similar body masses varied less than 15%. Finally, we found absorbed dose discrepancies of approximately 10-150% between the SADR methodology and OLINDA for two different radiopharmaceuticals. Absorbed doses from SADRs and from individualized S-values in the same pediatric model differed approximately 1-50%. CONCLUSIONS Because pediatric radiopharmaceutical dosimetric estimates demonstrate large variation due to the patient's anatomical characteristics, personalized data should be considered. Using our SADR method in a larger population of phantoms and for a variety of radiopharmaceuticals could enhance the personalization of dosimetry in pediatric nuclear medicine. The proposed methodology provides the advantage of creating time-dependent organ dose rate curves.
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Affiliation(s)
| | - William D Erwin
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Vasiliki Iliadou
- Department of Medical Physics, School of Medicine, University of Patras, Rion, GR-26504, Greece
| | - Theodora Kostou
- R&D Department, BET Solutions, 116 Alexandras Ave., Athens, GR-11472, Greece
- Department of Medical Physics, School of Medicine, University of Patras, Rion, GR-26504, Greece
| | - George Loudos
- Department of Biomedical Engineering, University of West Attica, 28 Ag. Spyridonos Street, Egaleo, GR-12210, Greece
| | - George C Kagadis
- Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
- Department of Medical Physics, School of Medicine, University of Patras, Rion, GR-26504, Greece
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Wayson MB, Bolch WE. Individualized adjustments to reference phantom internal organ dosimetry-scaling factors given knowledge of patient external anatomy. Phys Med Biol 2018; 63:085007. [PMID: 29546846 DOI: 10.1088/1361-6560/aab72f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Internal radiation dose estimates for diagnostic nuclear medicine procedures are typically calculated for a reference individual. Resultantly, there is uncertainty when determining the organ doses to patients who are not at 50th percentile on either height or weight. This study aims to better personalize internal radiation dose estimates for individual patients by modifying the dose estimates calculated for reference individuals based on easily obtainable morphometric characteristics of the patient. Phantoms of different sitting heights and waist circumferences were constructed based on computational reference phantoms for the newborn, 10 year-old, and adult. Monoenergetic photons and electrons were then simulated separately at 15 energies. Photon and electron specific absorbed fractions (SAFs) were computed for the newly constructed non-reference phantoms and compared to SAFs previously generated for the age-matched reference phantoms. Differences in SAFs were correlated to changes in sitting height and waist circumference to develop scaling factors that could be applied to reference SAFs as morphometry corrections. A further set of arbitrary non-reference phantoms were then constructed and used in validation studies for the SAF scaling factors. Both photon and electron dose scaling methods were found to increase average accuracy when sitting height was used as the scaling parameter (~11%). Photon waist circumference-based scaling factors showed modest increases in average accuracy (~7%) for underweight individuals, but not for overweight individuals. Electron waist circumference-based scaling factors did not show increases in average accuracy. When sitting height and waist circumference scaling factors were combined, modest average gains in accuracy were observed for photons (~6%), but not for electrons. Both photon and electron absorbed doses are more reliably scaled using scaling factors computed in this study. They can be effectively scaled using sitting height alone as patient-specific morphometric parameter.
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Affiliation(s)
- Michael B Wayson
- Present address: Medical Physics and Radiation Safety, Baylor Scott and White Health, 3500 Gaston Avenue, Dallas, TX 75246, United States of America
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Belinato W, Santos WS, Perini AP, Neves LP, Caldas LV, Souza DN. Estimate of S-values for children due to six positron emitting radionuclides used in PET examinations. Radiat Phys Chem Oxf Engl 1993 2017. [DOI: 10.1016/j.radphyschem.2017.02.038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Geyer AM, Schwarz BC, O'Reilly SE, Hobbs RF, Sgouros G, Bolch WE. Depth-dependent concentrations of hematopoietic stem cells in the adult skeleton: Implications for active marrow dosimetry. Med Phys 2017; 44:747-761. [PMID: 28133749 DOI: 10.1002/mp.12056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 09/18/2016] [Accepted: 11/22/2016] [Indexed: 01/19/2023] Open
Abstract
PURPOSE The hematopoietically active (or red) bone marrow is the target tissue assigned in skeletal dosimetry models for assessment of stochastic effects (leukemia induction) as well as tissue reactions (marrow toxicity). Active marrow, however, is in reality a surrogate tissue region for specific cell populations, namely the hematopoietic stem and progenitor cells. Present models of active marrow dosimetry implicitly assume that these cells are uniformly localized throughout the marrow spaces of trabecular spongiosa. Data from Watchman et al. and Bourke et al., however, clearly indicate that there is a substantial spatial concentration gradient of these cells with the highest concentrations localized near the bone trabeculae surfaces. The purpose of the present study was thus to explore the dosimetric implications of these spatial gradients on active marrow dosimetry. METHODS Images of several bone sites from a 45-yr female were retagged to group active marrow voxels into 50 μm increments of marrow depth, after which electron and alpha-particle depth-dependent specific absorbed fractions were computed for four source tissues - active marrow, inactive marrow, bone trabeculae volumes, and bone trabeculae surfaces. Corresponding depth-dependent S values (dose to a target tissue per decay in a source tissue) were computed and further weighted by the relative target cell concentration. These depth-weighted radionuclide S values were systematically compared to the more traditional volume-averaged radionuclide S values of the MIRD schema for both individual bones of the skeleton and their skeletal-averaged quantities. RESULTS For both beta-emitters and alpha-emitters localized in the active and inactive marrow, depth-weighted S values were shown to differ from volume-averaged S values by only a few percent, as dose gradients across the marrow tissues are nonexistent. For bone volume and bone surface sources of alpha-emitters and lower energy beta-emitters, when marrow dose gradients are expected, explicit consideration of target cell spatial concentration gradients are shown to significantly impact marrow dosimetry. CONCLUSIONS For medical isotopes currently utilized for treatment of skeletal metastases, namely 153 Sm and 223 Ra, accounting for hematopoietic stem and progenitor cell concentration gradients resulted in maximum percent differences to reference skeletal-averaged S values of ~21% and 55%, respectively.
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Affiliation(s)
- Amy M Geyer
- J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611-6131, USA
| | - Bryan C Schwarz
- J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611-6131, USA
| | - Shannon E O'Reilly
- J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611-6131, USA
| | - Robert F Hobbs
- Department of Radiation Oncology, Johns Hopkins University School of Medicine, Baltimore, MD, 21231, USA
| | - George Sgouros
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, 21231, USA
| | - Wesley E Bolch
- J Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, 32611-6131, USA
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Patient-specific dosimetry using pretherapy [¹²⁴I]m-iodobenzylguanidine ([¹²⁴I]mIBG) dynamic PET/CT imaging before [¹³¹I]mIBG targeted radionuclide therapy for neuroblastoma. Mol Imaging Biol 2015; 17:284-94. [PMID: 25145966 DOI: 10.1007/s11307-014-0783-7] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
PURPOSE Iodine-131-m-iodobenzylguanidine ([(131)I]mIBG)-targeted radionuclide therapy (TRT) is a standard treatment for recurrent or refractory neuroblastoma with response rates of 30-40 %. The aim of this study is to demonstrate patient-specific dosimetry using quantitative [(124)I]mIBG positron emission tomography/X-ray computed tomography (PET/CT) imaging with a GEometry ANd Tracking 4 (Geant4)-based Monte Carlo method for better treatment planning. PROCEDURES A Monte Carlo dosimetry method was developed using the Geant4 toolkit with voxelized anatomical geometry and source distribution as input. The presegmented hybrid computational human phantoms developed by the University of Florida and the National Cancer Institute (UF/NCI) were used as a surrogate to characterize the anatomy of a given patient. S values for I-131 were estimated by the phantoms coupled with Geant4 and compared with those estimated by OLINDA|EXM and MCNPX for the newborn model. To obtain patient-specific biodistribution of [(131)I]mIBG, a 10-year-old girl with relapsed neuroblastoma was imaged with [(124)I]mIBG PET/CT at four time points prior to the planned [(131)I]mIBG TRT. The organ- and tumor-absorbed doses of the clinical case were estimated with the Geant4 method using the modified UF/NCI 10-year-old phantom with tumors and the patient-specific residence time. RESULTS For the newborn model, the Geant4 S values were consistent with the MCNPX S values. The S value ratio of the Geant4 method to OLINDA|EXM ranged from 0.08 to 6.5 of all major organs. The [(131)I]mIBG residence time quantified from the pretherapy [(124)I]mIBG PET/CT imaging of the 10-year-old patient was mostly comparable to those previously reported. Organ-absorbed dose for the salivary glands was 98.0 Gy, heart wall 36.5 Gy, and liver 34.3 Gy, while tumor-absorbed dose ranged from 143.9 to 1,641.3 Gy in different sites. CONCLUSIONS Patient-specific dosimetry for [(131)I]mIBG TRT was accomplished using pretherapy [(124)I]mIBG PET/CT imaging and a Geant4-based Monte Carlo dosimetry method. The Geant4 method with quantitative pretherapy imaging can provide dose estimates to normal organs and tumors with more realistic simulation geometry, and thus may improve treatment planning for [(131)I]mIBG TRT.
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Xie T, Lee C, Bolch WE, Zaidi H. Assessment of radiation dose in nuclear cardiovascular imaging using realistic computational models. Med Phys 2015; 42:2955-66. [PMID: 26127049 PMCID: PMC5148206 DOI: 10.1118/1.4921364] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 04/24/2015] [Accepted: 05/08/2015] [Indexed: 12/26/2022] Open
Abstract
PURPOSE Nuclear cardiology plays an important role in clinical assessment and has enormous impact on the management of a variety of cardiovascular diseases. Pediatric patients at different age groups are exposed to a spectrum of radiation dose levels and associated cancer risks different from those of adults in diagnostic nuclear medicine procedures. Therefore, comprehensive radiation dosimetry evaluations for commonly used myocardial perfusion imaging (MPI) and viability radiotracers in target population (children and adults) at different age groups are highly desired. METHODS Using Monte Carlo calculations and biological effects of ionizing radiation VII model, we calculate the S-values for a number of radionuclides (Tl-201, Tc-99m, I-123, C-11, N-13, O-15, F-18, and Rb-82) and estimate the absorbed dose and effective dose for 12 MPI radiotracers in computational models including the newborn, 1-, 5-, 10-, 15-yr-old, and adult male and female computational phantoms. RESULTS For most organs, (201)Tl produces the highest absorbed dose whereas (82)Rb and (15)O-water produce the lowest absorbed dose. For the newborn baby and adult patient, the effective dose of (82)Rb is 48% and 77% lower than that of (99m)Tc-tetrofosmin (rest), respectively. CONCLUSIONS (82)Rb results in lower effective dose in adults compared to (99m)Tc-labeled tracers. However, this advantage is less apparent in children. The produced dosimetric databases for various radiotracers used in cardiovascular imaging, using new generation of computational models, can be used for risk-benefit assessment of a spectrum of patient population in clinical nuclear cardiology practice.
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Affiliation(s)
- Tianwu Xie
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva 4 CH-1211, Switzerland
| | - Choonsik Lee
- Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institute of Health, Bethesda, Maryland 20852
| | - Wesley E Bolch
- Departments of Nuclear & Radiological and Biomedical Engineering, University of Florida, Gainesville, Florida 32611
| | - Habib Zaidi
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva 4 CH-1211, Switzerland; Geneva Neuroscience Center, Geneva University, Geneva CH-1205, Switzerland; and Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen 9700 RB, Netherlands
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Díaz-Londoño G, García-Pareja S, Salvat F, Lallena AM. Monte Carlo calculation of specific absorbed fractions: variance reduction techniques. Phys Med Biol 2015; 60:2625-44. [DOI: 10.1088/0031-9155/60/7/2625] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Xie T, Bolch WE, Lee C, Zaidi H. Pediatric radiation dosimetry for positron-emitting radionuclides using anthropomorphic phantoms. Med Phys 2014; 40:102502. [PMID: 24089923 DOI: 10.1118/1.4819939] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Positron emission tomography (PET) plays an important role in the diagnosis, staging, treatment, and surveillance of clinically localized diseases. Combined PET/CT imaging exhibits significantly higher sensitivity, specificity, and accuracy than conventional imaging when it comes to detecting malignant tumors in children. However, the radiation dose from positron-emitting radionuclide to the pediatric population is a matter of concern since children are at a particularly high risk when exposed to ionizing radiation. METHODS The authors evaluate the absorbed fractions and specific absorbed fractions (SAFs) of monoenergy photons/electrons as well as S-values of 9 positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Rb-82, Y-86, and I-124) in 48 source regions for 10 anthropomorphic pediatric hybrid models, including the reference newborn, 1-, 5-, 10-, and 15-yr-old male and female models, using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code. RESULTS The self-absorbed SAFs and S-values for most organs were inversely related to the age and body weight, whereas the cross-dose terms presented less correlation with body weight. For most source/target organ pairs, Rb-82 and Y-86 produce the highest self-absorbed and cross-absorbed S-values, respectively, while Cu-64 produces the lowest S-values because of the low-energy and high-frequency of electron emissions. Most of the total self-absorbed S-values are contributed from nonpenetrating particles (electrons and positrons), which have a linear relationship with body weight. The dependence of self-absorbed S-values of the two annihilation photons varies to the reciprocal of 0.76 power of the mass, whereas the self-absorbed S-values of positrons vary according to the reciprocal mass. CONCLUSIONS The produced S-values for common positron-emitting radionuclides can be exploited for the assessment of radiation dose delivered to the pediatric population from various PET radiotracers used in clinical and research settings. The mass scaling method for positron-emitters can be used to derive patient-specific S-values from data of reference phantoms.
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Affiliation(s)
- Tianwu Xie
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, CH-1211 Geneva 4, Switzerland
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Zankl M, Schlattl H, Petoussi-Henss N, Hoeschen C. Electron specific absorbed fractions for the adult male and female ICRP/ICRU reference computational phantoms. Phys Med Biol 2012; 57:4501-26. [PMID: 22722546 DOI: 10.1088/0031-9155/57/14/4501] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The calculation of radiation dose from internally incorporated radionuclides is based on so-called absorbed fractions (AFs) and specific absorbed fractions (SAFs). SAFs for monoenergetic electrons were calculated for 63 source regions and 67 target regions using the new male and female adult reference computational phantoms adopted by the ICRP and ICRU and the Monte Carlo radiation transport programme package EGSnrc. The SAF values for electrons are opposed to the simplifying assumptions of ICRP Publication 30. The previously applied assumption of electrons being fully absorbed in the source organ itself is not always true at electron energies above approximately 300-500 keV. High-energy electrons have the ability to leave the source organ and, consequently, the electron SAFs for neighbouring organs can reach the same magnitude as those for photons for electron energies above 1 MeV. The reciprocity principle known for photons can be extended to electron SAFs as well, thus making cross-fire electron SAFs mass-independent. To quantify the impact of the improved electron dosimetry in comparison to the dosimetry using the simple assumptions of ICRP Publication 30, absorbed doses per administered activity of three radiopharmaceuticals were evaluated with and without explicit electron transport. The organ absorbed doses per administered activity for the two evaluation methods agree within 2%-3% for most organs for radionuclides with decay spectra having electron energies below a few hundred keV and within approximately 20% if higher electron energies are involved. An important exception is the urinary bladder wall, where the dose is overestimated by 60-150% using the simplified ICRP 30 approach for the radiopharmaceuticals of this study.
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Affiliation(s)
- Maria Zankl
- Helmholtz Zentrum München-German Research Center for Environmental Health, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany.
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