Radiation Dose to Patients From Cardiac Diagnostic Imaging
2007; Lippincott Williams & Wilkins; Volume: 116; Issue: 11 Linguagem: Inglês
10.1161/circulationaha.107.688101
ISSN1524-4539
AutoresAndrew J. Einstein, K Moser, Randall C. Thompson, Manuel D. Cerqueira, Milena J. Henzlova,
Tópico(s)Advanced X-ray and CT Imaging
ResumoHomeCirculationVol. 116, No. 11Radiation Dose to Patients From Cardiac Diagnostic Imaging Free AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplemental MaterialFree AccessReview ArticlePDF/EPUBRadiation Dose to Patients From Cardiac Diagnostic Imaging Andrew J. Einstein, Kevin W. Moser, Randall C. Thompson, Manuel D. Cerqueira and Milena J. Henzlova Andrew J. EinsteinAndrew J. Einstein From the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY (A.J.E.); Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa (K.W.M.); Cardiovascular Consultants, PC, and Mid America Heart Institute, Kansas City, Mo (R.C.T.); Cleveland Clinic, Cleveland, Ohio (M.D.C.); and Mount Sinai Medical Center, New York, NY (M.J.H.). , Kevin W. MoserKevin W. Moser From the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY (A.J.E.); Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa (K.W.M.); Cardiovascular Consultants, PC, and Mid America Heart Institute, Kansas City, Mo (R.C.T.); Cleveland Clinic, Cleveland, Ohio (M.D.C.); and Mount Sinai Medical Center, New York, NY (M.J.H.). , Randall C. ThompsonRandall C. Thompson From the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY (A.J.E.); Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa (K.W.M.); Cardiovascular Consultants, PC, and Mid America Heart Institute, Kansas City, Mo (R.C.T.); Cleveland Clinic, Cleveland, Ohio (M.D.C.); and Mount Sinai Medical Center, New York, NY (M.J.H.). , Manuel D. CerqueiraManuel D. Cerqueira From the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY (A.J.E.); Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa (K.W.M.); Cardiovascular Consultants, PC, and Mid America Heart Institute, Kansas City, Mo (R.C.T.); Cleveland Clinic, Cleveland, Ohio (M.D.C.); and Mount Sinai Medical Center, New York, NY (M.J.H.). and Milena J. HenzlovaMilena J. Henzlova From the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University College of Physicians and Surgeons, New York, NY (A.J.E.); Penn State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pa (K.W.M.); Cardiovascular Consultants, PC, and Mid America Heart Institute, Kansas City, Mo (R.C.T.); Cleveland Clinic, Cleveland, Ohio (M.D.C.); and Mount Sinai Medical Center, New York, NY (M.J.H.). Originally published11 Sep 2007https://doi.org/10.1161/CIRCULATIONAHA.107.688101Circulation. 2007;116:1290–1305The volume of cardiac diagnostic procedures involving the use of ionizing radiation has increased rapidly in recent years. Whereas in 1990, fewer than 3 million nuclear cardiology studies were performed in the United States, by 2002 this figure more than tripled to 9.9 million.1 Cardiac computed tomographic (CT) volume doubled between 2002 and 2003, to 485 000 cases,2 and has continued to grow since then. The volume of procedures performed in cardiac catheterization labs increased from 2.45 million in 1993 to 3.85 million in 2002.3The powerful diagnostic and risk-stratification data provided by these procedures play a central role in clinical cardiology and have contributed to the decrease in morbidity and mortality from coronary heart disease. Nevertheless, performance of any diagnostic test requires a careful assessment of the risks and benefits of the test and optimization of protocols to minimize risks to patients, staff members, and the public. Procedures that utilize ionizing radiation should be performed in accordance with the As Low As Reasonably Achievable (ALARA) philosophy. Thus, physicians ordering and performing cardiac imaging should be very familiar with the dosage of radiation from cardiac diagnostic tests and ways in which dose can be minimized. In this report we discuss the measurement of radiation and the dosimetry of commonly performed cardiac diagnostic imaging tests, including nuclear scintigraphy, CT for calcium scoring and coronary angiography (CTCA), and conventional coronary angiography (CCA). For each modality, we address the terminology and methodology used to quantify radiation received by patients, doses to patients with typical protocols, and dose-reduction techniques.General Terminology Used in Quantifying RadiationBiological effects of ionizing radiation can be classified as deterministic or stochastic. Deterministic effects such as skin injuries and cataract formation occur predictably when dose exceeds a certain threshold, whereas stochastic effects such as cancer incidence and germ cell mutations occur with a probability that increases with dose.Numerous quantities and units are used to measure radiation, some of which are summarized in Table I in the online-only Data Supplement.4 Some ambiguity exists in the terminology used in the literature, confounded by multiple sets of units and changing nomenclature between guidelines. This nomenclature includes both general terms to describe quantities of radiation and specific terminology applicable to particular types of radiation sources or imaging modalities.Organizations Setting General TerminologyThe currently used general terminology is a product of the effort of multiple international organizations, notably the International Commission on Radiation Units and Measurements (ICRU), International Commission on Radiological Protection (ICRP), and Conférence Générale des Poids et Mesures (CGPM; General Conference on Weights and Measures). The ICRU, initially known as the International X-ray Unit Committee, was founded in 1925 by the International Congress of Radiology. Its principal objective is to develop international recommendations on quantities and units of radiation, on procedures for the measurement and application of these quantities, and on physical data required for the application of these procedures. The ICRU is composed of a chair and 13 commission members who are all physicists or physicians, assisted by 20 report committees addressing specific topics; to date, 76 reports have been issued. The ICRP, founded in 1928 as the International X-ray and Radium Protection Committee, is a daughter organization of the International Society of Radiology, although its work now focuses on all aspects of protection from ionizing radiation, not limited to medical applications. It is composed of a main commission, with a chair and 12 members with backgrounds in medicine, physical and biological science, engineering, and epidemiology, and 5 standing committees focusing on different aspects of radiological protection, supported by a scientific secretariat. Toward its goals, it has issued ≈100 reports authored by expert panels providing specific recommendations in 1 area of radiological protection, as well as periodically updated general recommendations, reflecting the state of knowledge on the biological effects of ionizing radiation. The CGPM is 1 of 3 linked organizations established by the Convention du Mètre, an international treaty signed in 1875 and now with 51 states as members, that have authority to conduct international activities in standardizing measurement. The CGPM established the Système International d'Unités (SI; International System of Units) in 1960 and now meets every 4 years to maintain and update it. Delegates to the CGPM are typically representatives of national standards or metrology institutes, although other related international organizations such as the International Atomic Energy Agency are represented as well. Although the CGPM has attempted to keep the SI as parsimonious as possible, special units have been introduced to quantify ionizing radiation to avoid its underestimation and thereby safeguard human health.5NomenclatureWhile the term exposure is used in a general sense to apply to an occurrence in which an individual is exposed to radiation, it also has a specific technical definition. Exposure equals the total charge of ions of 1 sign (positive or negative) produced per unit of dry air by a given amount of ionizing radiation. In SI units, exposure is measured in terms of coulombs (C) per kilogram. Exposure is also commonly measured in units of roentgens (R), where 1 R=2.58×10−4 C/kg. A related quantity is air kerma. Kerma, an acronym for "kinetic energy released in material,"6 is the sum of the kinetic energy of all of the charged particles liberated per unit mass of a material by an amount of ionizing radiation. When that material is air, the kerma is referred to as air kerma. Thus, whereas exposure measures electric charge produced in air per unit mass from an amount of ionizing radiation, air kerma measures its energy produced in air per unit mass. While often easy to measure, exposure and air kerma specifically measure ionization in air, not tissue, and thus do not directly quantify radiation's effect on humans. Absorbed dose is the mean energy imparted to the matter in a volume by ionizing radiation, divided by the mass of the matter in the volume. The SI unit of absorbed dose, introduced at the 15th CGPM in 1975, is the gray (Gy), which is a special name for joule per kilogram. The traditional unit is the rad, short for radiation absorbed dose, and equal to 0.01 Gy. These units are also used for air kerma.Although absorbed dose is a useful concept, the biological effect of a given absorbed dose varies depending on the type and quality of radiation emitted by the radionuclide or external radiation field. Current ICRP terminology uses a dimensionless radiation weighting factor (wR) to normalize for this effect, where the weighting factor ranges from 1 for photons (including x-rays and γ-rays) and electrons to 20 for α-particles. In cardiac imaging, the most common emissions are photons (nuclear cardiology), and external radiation is typically from x-rays (CT and CCA), and thus wR is usually 1. Equivalent dose (HT, which in most contexts has replaced the similar term dose equivalent) in a tissue or organ due to a radiation field is defined as the product of the absorbed dose and the radiation weighting factor. If the field is composed of types of radiation with different radiation weighting factors, then equivalent dose is determined by summing these products over the constituent radiations. Thus, equivalent dose differs from absorbed dose in that it reflects not only the energy imparted to matter by radiation but also the relative biological harm caused by the type of radiation. A special SI unit, the sievert (Sv), was adopted at the 16th CGPM in 1979 to avoid possible confusion between absorbed dose and dose equivalent and the resultant underestimation of dose equivalent.5 The sievert is also a special name for joule per kilogram, used for doses that have been weighted to reflect the type of radiation. The traditional unit for equivalent dose is the rem, short for roentgen equivalent man, and equal to 0.01 Sv. These relationships are illustrated in Figure 1. Download figureDownload PowerPointFigure 1. Top, Relationship between units of organ absorbed dose, using a log scale. Bottom, Relationship between units of effective dose, with effective doses of some representative radiation sources. CFR indicates Code of Federal Regulations; RERF, Radiation Effects Research Foundation; LD50, lethal dose to 50% of individuals; and wR, radiation weighting factor (=1 for x-rays and γ-rays). Chest x-ray dose of 0.02 mSv per European Commission.7In addition to the absorbed dose and type of radiation, the probability of stochastic effects varies depending on the organ or tissue irradiated. A second weighting factor, the dimensionless tissue weighting factor (wT), is used to normalize for this effect. Equivalent dose multiplied by wT is termed weighted equivalent dose, properly measured in sieverts or rem. The sum of weighted equivalent dose over all organs or tissues in an individual is termed the effective dose (E), that is, equationDownload figurewhere DT, typically measured in units of mGy, represents the mean absorbed dose in tissue T from all radiations, and DT,R represents the mean absorbed dose in tissue T from radiation R. The older and more cumbersome term effective dose equivalent, supplanted by effective dose,4 is still found in some current literature. Thus, weighted equivalent dose to a particular tissue corresponds to the contribution to E of the radiation absorbed by that tissue. Tissue-weighting factors are chosen to sum to 1 so that a uniform equivalent dose over the whole body results in an E equal to that equivalent dose, and therefore the equivalent dose to a particular organ corresponds to the E of a hypothetical scan in which each organ receives the same dose as does the particular organ.The ICRP has offered recommended tissue weighting factors in 2 reports, their Publication 268 (1977) and the subsequent Publication 604 (1991). The highest ICRP Publication 60 wT is that of the gonads (0.2), followed by the bone marrow, colon, lung, and stomach (each 0.12). Minor changes to ICRP Publication 60 tissue weighting factors were suggested in subsequent reports. On March 21, 2007, a comprehensive update to ICRP Publication 60 was approved; this is scheduled for publication as ICRP Publication 103.9 Based on more current data, it introduces a new set of tissue weighting factors, summarized in Table 1. The major difference is a higher wT for the female breast and a lower factor for the gonads. The actual dose received by a person from a given radiation exposure can be estimated by 1 of several methods, tailored to the nature of the radiation exposure. TABLE 1. Tissue Weighting Factors in ICRP Publication 26, ICRP Publication 60, and the 2007 Draft of ICRP Publication 103ICRP 268 (1977)ICRP 604 (1991)ICRP 1039 (2007)Ellipses indicate no tissue weighting factor associated with organ.Bladder…0.050.04Bone0.030.010.01Brain……0.01Breasts0.150.050.12Colon……0.12Esophagus…0.050.04Liver…0.050.04Lower large intestine…0.12…Lungs0.120.120.12Ovaries/testes0.250.200.08Red marrow0.120.120.12Remainder tissues0.300.050.12Salivary glands……0.01Skin…0.010.01Stomach…0.120.12Thyroid0.030.050.04Limitations in Dose EstimationIt is important to note that all reported radiation doses, both for a typical study in a population and for a particular study in a particular patient, are estimates in a statistical sense, obtained with the use of measured quantities but making numerous assumptions that may result in variation from the "true" value. For example, current radiopharmaceutical dosimetry models yield an estimate of E that is not patient-specific but rather is based on a number of assumptions, including standard patient weights and organ sizes, generic rather than patient-specific biokinetic data, and uniform radiopharmaceutical activity within organs.10 Thus, reported doses should properly be viewed as dose estimates.11 Although point estimates of typical doses of cardiac imaging studies have been reasonably well documented in the literature, the quantitative characterization of uncertainty in dose estimation has lagged behind and remains an important area for future investigation.For all modalities, gender-specific dosimetry has been lacking and is only beginning to be addressed. The effect of body habitus, and obesity in particular, on dosimetry remains unclear, and dose estimation will continue to evolve as more data are available. Even so, the dose estimates here are useful in comparing different modalities and study protocols.Nuclear Cardiology DosimetryTerminology and MethodologyThe activity (A) of a radionuclide is the average number of spontaneous nuclear decays in a given period of time. The SI unit for activity is the becquerel (Bq), which was formally defined at the 15th CGPM as seconds−1 but is commonly used to mean decays per second. The traditional unit for activity is the curie, originally standardized in 1910 by Marie Curie and now equal to exactly 3.7×1010 Bq.Radiation dosimetry from a study using a radiopharmaceutical is typically estimated on the basis of a mathematical biokinetic model that quantifies the distribution and metabolism of that agent in the body. Such models incorporate biokinetic data from animal and human models. They enable the determination of tissue or organ absorbed doses per unit of activity administered (DT/A) and whole-body effective dose per unit of activity (E/A), referred to as dose coefficients.Values for DT/A are referred to here as tissue dose coefficients, and those for E/A are referred to as effective dose coefficients. A widely respected series of such models for commonly used radiopharmaceuticals has been compiled by the ICRP, drawing on the work of the Medical Internal Radiation Dose committee of the Society of Nuclear Medicine, as well as research done at Oak Ridge National Laboratories. ICRP Publication 17 (1968) and its successor ICRP Publication 5312 (1987) contain an extensive set of dosimetry tables for a variety of radiopharmaceuticals based on these models. ICRP Publication 8013 (1998) and the still-unpublished Addendum 5 to ICRP Publication 5314 use more updated methodology to recalculate dosimetry for common radionuclides and correct errors in dosimetry calculations found in ICRP Publication 53. The manufacturers of radiopharmaceuticals also provide such tables in the package inserts (PIs) for these products. Some of these tables provide a total body dose rather than E/A. Total body dose is an older term, defined as the total radiation energy absorbed in the body divided by the mass of the body (70 kg is typically used). However, the total body dose does not account for the nonuniformity in dose distribution among body organs, and it is always lower than the effective dose.15 Tables II and III in the online-only Data Supplement compile dose coefficients for commonly used cardiac radiopharmaceuticals from the most recent ICRP publications reporting these quantities, as well as from current manufacturers' PIs. Although for 99mTc sestamibi and tetrofosmin, separate dose coefficients are reported for injection at stress versus at rest, demonstrating modestly (8% to 22%) decreased stress doses, these data are unavailable for other agents or for injection after pharmacological stress agents.With the use of these dose coefficients, the equivalent dose to tissue T from a radiopharmaceutical with activity A0 can be estimated from the equation equationDownload figureFor each radiopharmaceutical, E can be estimated either with a set of tissue dose coefficients {D/AT}, using equationDownload figureor, alternatively, from an effective dose coefficient using equationDownload figureHere we use E1 to denote an effective dose derived from tissue dose coefficients and E2 to denote an effective dose derived from an effective dose coefficient.Dosimetry of Nuclear Cardiology StudiesWith the use of ICRP or PI dose coefficients, a set of tissue weighting factors, the radionuclide activities for a standard protocol, and Equations 3 and 4 above, one can estimate the effective dose to a typical patient of a standard cardiac radiopharmaceutical study. Table 216–18 summarizes E1 and E2 for commonly performed studies, with calculations performed with the use of ICRP Publication 60 tissue weighting factors and average radionuclide activities specified in current American Society of Nuclear Cardiology guidelines.16 No additional radiation dose for attenuation correction is included. Performed in a minority of nuclear cardiology laboratories, attenuation correction scans performed with either radioisotope sources or low-dose CT have Es that are small compared with those of radionuclide studies.19,20Table 3 demonstrates the effect of the tissue weighting factors on effective dose, using the 3 ICRP wT schema, and compares E1 determined with the use of dose coefficients from ICRP tables with those from manufacturers' PIs. Organ doses for selected protocols are summarized in Table IV in the online-only Data Supplement, which lists the organs receiving the highest equivalent doses for each protocol. Figure 2 demonstrates the components (weighted equivalent doses) contributing to the total effective dose for selected protocols. TABLE 2. Estimates of Effective Doses of Standard Myocardial Perfusion Imaging ProtocolsProtocolInjected Activity (mCi)Effective Doses, mSvFrom ICRP TablesFrom Manufacturers' PIsRestStressE1E2E1E2E1 indicates effective dose estimated from tissue dose coefficients, using ICRP Publication 60 tissue weighting factors. Calculations were performed with the use of the "splitting rule,"4 arithmetic averaging rather than mass averaging of individual remainder organ dose contributions,18 and upper large intestine rather than extrathoracic airways as a remainder organ, as was originally specified in ICRP Publication 60. If dose to the colon was not specified in a data source, then the average of the upper large intestine and lower large intestine doses was substituted. E2 indicates effective dose estimated from effective dose coefficients, using ICRP Publication 60 tissue weighting factors. NR indicates not reported in PI (total body dose provided rather than effective dose); NA, not available for cyclotron-produced tracers.*American Society of Nuclear Cardiology guidelines16 do not prescribe a recommended dose. Stress and rest doses of 1100 MBq (29.7 mCi) used, as per European Association of Nuclear Medicine/European Society of Cardiology guidelines.1799mTc sestamibi rest-stress10.027.511.311.414.6NR99mTc sestamibi stress only0.027.57.98.010.0NR99mTc sestamibi 2-day25.025.015.715.620.6NR99mTc tetrofosmin rest-stress10.027.59.39.99.712.999mTc tetrofosmin stress only0.027.56.67.16.78.899mTc tetrofosmin 2-day25.025.012.813.513.718.3201Tl stress-redistribution0.03.522.022.028.7 (PI 1) 9.3 (PI 2) 28.4 (PI 3)46.6 (PI 1) NR (PI 2) 46.6 (PI 3)201Tl stress-reinjection1.53.031.431.543.0 (PI 1) 14.0 (PI 2) 42.6 (PI 3)69.9 (PI 1) NR (PI 2) 69.9 (PI 3)Dual isotope 201Tl-99mTc sestamibi3.525.029.229.337.8 (PI 1) 18.4 (PI 2) 37.5 (PI 3)NR (PI 1) NR (PI 2) NR (PI 3)99mTc-labeled erythrocytes22.50.05.75.82.3NR82Rb50.050.013.512.63.0NR13N-ammonia15.015.02.42.2NANA15O-water*29.729.72.52.4NANA18F-FDG10.00.07.07.0NANATABLE 3. Effect of ICRP Tissue Weighting Factors wT on Estimates of Effective Dose E1 (mSv)ProtocolDose Coefficients DT/A From ICRP TablesDose Coefficients DT/A From Manufacturers' PIsICRP 26 wTICRP 60 wTICRP 103 wTICRP 26 wTICRP 60 wTICRP 103 wTNA indicates not available for cyclotron-produced tracers.99mTc sestamibi rest-stress7.811.310.78.014.612.199mTc sestamibi stress only5.67.97.55.610.08.499mTc sestamibi 2-day10.715.714.811.220.617.099mTc tetrofosmin rest-stress5.79.38.67.19.78.999mTc tetrofosmin stress only4.16.66.24.96.76.299mTc tetrofosmin 2-day7.912.811.89.913.712.5201Tl stress-redistribution19.222.016.923.5 (PI 1) 7.5 (PI 2) 23.7 (PI 3)28.7 (PI 1) 9.3 (PI 2) 28.4 (PI 3)21.7 (PI 1) 6.4 (PI 2) 21.4 (PI 3)201Tl reinjection27.431.424.235.3 (PI 1) 11.3 (PI 2) 35.5 (PI 3)43.0 (PI 1) 14.0 (PI 2) 42.6 (PI 3)32.6 (PI 1) 9.5 (PI 2) 32.1 (PI 3)Dual isotope 201Tl-99mTc-sestamibi24.229.223.728.6 (PI 1) 12.6 (PI 2) 28.8 (PI 3)37.8 (PI 1) 18.4 (PI 2) 37.5 (PI 3)29.3 (PI 1) 14.0 (PI 2) 29.0 (PI 3)99mTc-labeled erythrocytes4.95.75.72.82.31.782Rb10.513.512.83.23.02.413N-ammonia2.02.42.3NANANA15O-water1.62.52.3NANANA18F-FDG6.47.06.4NANANADownload figureDownload PowerPointFigure 2. Estimated effective doses and weighted organ equivalent doses from some standard cardiac radionuclide studies. Top, Doses determined using ICRP Publication 103 (2007) tissue weighting factors. Bottom, Doses determined using ICRP Publication 60 (1990) tissue weighting factors. CTCA indicates 64-slice computed tomography coronary angiogram; CaSc, calcium scoring; and ECTCM, ECG-controlled tube current modulation. Calculations were performed with ImpactDose (VAMP GmbH, Erlangen, Germany); for Siemens Sensation 64 scanner with retrospective gating, voltage was 120 kVp, pitch 0.2, and scan length 15 cm. For CTCA, slice thickness was 0.6 mm and tube current-time product was 165 mAs; ECTCM was simulated by reducing tube current by a third, to 110 mAs. For CaSc, collimation was 20×1.2 mm, and tube current-time product was 27 mAs. Effective doses (E1) correspond to third and second numeric columns in Table 3, respectively. Doses shown are arithmetic means of doses to standardized male and female phantoms.As is seen in the tables and figures, effective doses of myocardial perfusion imaging (MPI) procedures are nontrivial and vary greatly between protocols. Substantial differences exist between procedures with the use of different radiopharmaceuticals and between different procedures with the use of the same agent. While the typical effective dose of a posteroanterior chest x-ray is 0.02 mSv,7 and the annual background radiation in the United States is 3.0 mSv,21 typical E1 values for MPI studies range from 2.2 to 31.5 mSv with the use of ICRP dose coefficients and ICRP Publication 60 wT. Of the most commonly performed studies, a rest-stress 99mTc sestamibi study averages 11.3 mSv, and a rest-stress 99mTc tetrofosmin study averages 9.3 mSv. Single-injection protocols are associated with a dose that is ≈30% lower. Doses are much higher for studies using 201Tl. A single-injection 201Tl MPI study has an E1 of 22 mSv. Dual isotope studies have the highest effective doses, with an E1 of 29.2 mSv for a 201Tl-99mTc sestamibi study, ≈3 times that of a single-injection protocol using a 99mTc-containing agent. The lowest doses are for positron emission tomography protocols using the cyclotron-produced radionuclides 13N ammonia and 15O water, for which E1 values were 2.4 and 2.5 mSv.Effective doses of MPI studies using the new 2007 wT are slightly lower than those using ICRP Publication 60 wT, as shown in Table 3 and Figure 2. The most significant factor appears to be the lower gonadal doses obtained with the new wT, which most affects effective doses of studies incorporating 201Tl.Comparison of Doses Determined Using ICRP Versus Manufacturers' Dose CoefficientsSome notable differences exist between effective doses estimated with the use of ICRP dose coefficients and those estimated with the use of dose coefficients provided in PIs, as illustrated in Table 3 and Figure 3. Most PIs were initially issued at the time of approval of a radiopharmaceutical, and dosimetry information included in subsequent revisions has not been updated to reflect new biokinetic data or changes in the ICRP dosimetry system. Determination of E2 is not possible from the PIs for 99mTc sestamibi, 99mTc-labeled erythrocytes, 82Rb, and 1 of the 3 manufacturers of 201Tl. Each of these reports total body dose per unit activity rather than effective dose per unit activity. Future revisions of these PIs should incorporate effective dose coefficients. Download figureDownload PowerPointFigure 3. Comparison of estimated effective doses (mSv) for standard myocardial perfusion imaging protocols, determined with the use of ICRP and manufacturers' PI dose coefficients. Weighted equivalent doses were determined with the use of ICRP Publication 60 tissue weighting factors. ULI indicates upper large intestine.For 99mTc sestamibi rest-stress imaging, good agreement exists between E1 from ICRP (11.3 mSv) and PI (14.6 mSv for 4.8-hour urinary void, 13.5 mSv for 2-hour void) dose coefficients. The higher E1 with the longer void time is primarily due to the higher equivalent dose to the bladder wall (41 versus 21 mSv) and demonstrates the potential dose-reduction benefit of hydration and early micturition after radiopharmaceutical administration. Much of the difference between ICRP- and PI-derived E1 is due to an idiosyncrasy in the methodology of ICRP Publication 60 for determining dose to "remainder" organs, which was later amended.22 For 99mTc tetrofosmin, even closer agreement exists between ICRP- and PI-derived E1 values, which are 9.3 and 9.7 mSv, respectively.201Tl dosimetry varies markedly between manufacturers' PIs. E1 for a 3.5-mCi injection determined with dose coefficients from ICRP Publication 53 Addendum 5 and PIs 1, 2, and 3 are 22.0, 28.7, 9.3, and 28.4 mSv, respectively. When we examine the dose coefficients in PI 2, included in Table III in the online-only Data Supplement, no doses are listed for many organs (this is noted as well for 99mTc-labeled erythrocytes), and dose coefficients are much lower in general than for the other sources of data. In contrast, E/A for 201Tl is much higher in PIs 1 and 3 (0.36 mSv/MBq) than in ICRP Publication 53 Addendum 5 (0.17 mSv/MBq), resulting in a discordance between PI-derived E1 and E2 and extremely high E2 for standard protocols, ie, 47 mSv. Data sources cited in these PIs date back to the 1980s, and even with the use of ICRP Publication 26 tissue weighting factors, the discordance between E1 and E2 remains. In sum, 2 PIs suggest a 201Tl effective dose even greater than that from ICRP data, and a third PI (reporting limited organ data and no effective dose coefficient) suggests a much lower effective dose. It appears that 201Tl dosimetry requires revisiting, and PIs should be updated, which will result in lower effective dose coefficients for 2 manufacturers if ICRP Publication 53 Addendum 5 dosimetry is confirmed.Another radiopharmaceutical for which significant differences e
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