Use Of Radiopharmaceuticals Research Articles

The influence of the sizes of nanodiamond aggregates in their suspensions on the efficiency of sorption of <sup>90</sup>Y and <sup>177</sup>Lu isotopes for their subsequent use in nuclear medicine

Nanodiamonds (NDs) are promising carriers of radionuclides in radiopharmaceuticals for use in nuclear medicine. In this work, we investigated the influence of the properties of ND suspensions, including the sizes of their aggregates, in aqueous solutions with different pH on their binding of medical isotopes 90Y and 177Lu and found the conditions for obtaining promising conjugates for further in vivo studies. It was shown that sorption is influenced by the composition of the solution, which determines the properties of the ND surface, while the forms of cations of the studied nuclides in the solution do not affect the degree of sorption.

Diagnosis of Melanoma with 61Cu-Labeled PET Tracer.

Until the recent years, substances containing radioactive 61Cu were strongly considered as potential positron-emitting radiopharmaceuticals for use in positron emission tomography (PET) applications; however, due to their suitably long half-life, and generator-independent and cost-effective production, they seem to be economically viable for human imaging. Since malignant melanoma (MM) is a major public health problem, its early diagnosis is a crucial contributor to long-term survival, which can be achieved using radiolabeled α-melanocyte-stimulating hormone analog NAPamide derivatives. Here, we report on the physicochemical features of a new CB-15aneN5-based Cu(II) complex ([Cu(KFTGdiac)]-) and the ex vivo and in vivo characterization of its NAPamide conjugate. The rigid chelate possesses prompt complex formation and suitable inertness (t1/2 = 18.4 min in 5.0 M HCl at 50 °C), as well as excellent features in the diagnosis of B16-F10 melanoma tumors (T/M(SUVs) (in vivo): 12.7, %ID/g: 6.6 ± 0.3, T/M (ex vivo): 22).

Resolução espacial de um tomógrafo PET de pequenos animais usando o isótopo <sup>68</sup>Ga

Nuclear Medicine is a modality that has been growing a lot in Brazil and in the world, bringing new radiopharmaceuticals and technologies for the diagnosis and treatment of diseases, making them more effective and accurate. In the development of new radiopharmaceuticals for use in positron emission tomography (PET), the preclinical studies step largely uses PET scanners dedicated to small animals. To achieve this, quality control tests must be carried out to ensure the efficiency of the equipment. Thus, this work aimed to evaluate the spatial resolution of the small animals PET scanner of the CDTN using the isotope 68Ga. In this sense, a microPET hot rod phantom and a commercial 68Ge/68Ga generator were used to obtain PET images. The analysis of the 68Ga-PET images of the simulator was carried out qualitatively and quantitatively and revealed that the spatial resolution of the system using the 68Ga is 3.5 mm.

An Overview of In Vitro Assays of 64Cu-, 68Ga-, 125I-, and 99mTc-Labelled Radiopharmaceuticals Using Radiometric Counters in the Era of Radiotheranostics.

Radionuclides are unstable isotopes that mainly emit alpha (α), beta (β) or gamma (γ) radiation through radiation decay. Therefore, they are used in the biomedical field to label biomolecules or drugs for diagnostic imaging applications, such as positron emission tomography (PET) and/or single-photon emission computed tomography (SPECT). A growing field of research is the development of new radiopharmaceuticals for use in cancer treatments. Preclinical studies are the gold standard for translational research. Specifically, in vitro radiopharmaceutical studies are based on the use of radiopharmaceuticals directly on cells. To date, radiometric β- and γ-counters are the only tools able to assess a preclinical in vitro assay with the aim of estimating uptake, retention, and release parameters, including time- and dose-dependent cytotoxicity and kinetic parameters. This review has been designed for researchers, such as biologists and biotechnologists, who would like to approach the radiobiology field and conduct in vitro assays for cellular radioactivity evaluations using radiometric counters. To demonstrate the importance of in vitro radiopharmaceutical assays using radiometric counters with a view to radiogenomics, many studies based on 64Cu-, 68Ga-, 125I-, and 99mTc-labeled radiopharmaceuticals have been revised and summarized in this manuscript.

Electrochemical separation and purification of no-carrier-added 177Lu for radiopharmaceutical preparation: Translation from bench to bed

The entry of no-carrier-added (NCA) 177Lu in the arena of clinical nuclear medicine has revolutionized the practice of targeted radionuclide tumor therapy. In this study, we report the development of an electrochemical separation and purification procedure to obtain NCA 177Lu in a clinically usable form. The overall yield of the process developed was > 70% and it was reproducible in multiple batches. The effective specific activity of NCA 177Lu was 3.32 ± 0.04 TBq/mg and the radioisotope was found suitable for formulation of therapeutically relevant doses of [177Lu]Lu-DOTA-TATE with >98% radiolabeling yield. As a proof of concept, [177Lu]Lu-DOTA-TATE synthesized using electrochemically purified NCA 177Lu was administered in patients with proven neuroendocrine tumor (NET) and satisfactory preliminary clinical outcome was obtained. The feasibility of recovery of enriched (in 176Yb) target in chemical form suitable for reuse in the production of a fresh batch of NCA 177Lu was demonstrated, which makes the process economically viable. Overall, this robust and efficient radiochemical separation and purification technology might aid towards introduction of new 177Lu-based radiopharmaceuticals for use in clinical context in the foreseeable future.

Radiolabeled nanoporous hydroxyapatite microspheres: An advanced material for potential use in radiation synovectomy

The design and fabrication of porous and biocompatible inorganic materials having high adsorption capacity for therapeutic radioisotopes can trigger development of ‘next-generation’ radiopharmaceuticals for use in clinical nuclear medicine. In this study, nanoporous hydroxyapaptite (HA) microspheres of 1–10 μm diameter were synthesized by sol-gel technique followed by spray drying. The synthesized microparticles exhibited remarkably high sorption capacity for 90Y (141 ± 5 mg Y/mg) and 166Ho (262 ± 3 mg Ho/mg), which enabled the use of low specific activity radioisotopes produced in medium flux research reactors. Sorption of 90Y and 166Ho in nanoporous HA followed Langmuir-Freundlich adsorption isotherm and pseudo second order kinetics, indicating that the process was chemisorption. A chelator-free radiolabeling technique was developed for loading clinically relevant doses of radioisotopes such as 90Y and 166Ho in the HA matrix for use in treatment of arthritis. As a proof of concept, 90Y labeled formulation was administered in a patient with painful arthritis of knee joint. Selective localization of the radiolabeled agent in the synovial cavity was demonstrated by SPECT/CT imaging which demonstrated its potential for use in radiation synovectomy.

Radiochemical Quality Control Methods for Radium-223 and Thorium-227 Radiotherapies.

Background: The majority of radiopharmaceuticals for use in disease detection and targeted treatment undergo a single radioactive transition (decay) to reach a stable ground state. Complex emitters, which produce a series of daughter radionuclides, are emerging as novel radiopharmaceuticals. The need for validation of chemical and radiopurity with such agents using common quality control instrumentation is an area of active investigation. Here, we demonstrate novel methods to characterize 227Th and 223Ra. Materials and Methods: A radio-TLC scanner and a γ-counter, two common and widely accessible technologies, as well as a solid-state α-particle spectral imaging camera were evaluated for their ability to characterize and distinguish 227Th and 223Ra. We verified these results through purity evaluation of a novel 227Th-labeled protein construct. Results: The γ-counter and α-camera distinguished 227Th from 223Ra, enabling rapid and quantitative determination of radionuclidic purity. The radio-TLC showed limited ability to describe purity, although use under α-particle-specific settings enhanced resolution. All three methods were able to distinguish a pure from impure 227Th-labeled protein. Conclusions: The presented quality control evaluation for 227Th and 223Ra on three different instruments can be applied to both research and clinical settings as new alpha particle therapies are developed.

ARRONAX Cyclotron: Setting up of In-House Hospital Radiopharmacy.

Whilst radiopharmaceuticals have an important role to play in both imaging and treatment of patients, most notably cancer patients, nuclear medicine and radiopharmacy are currently facing challenges to create innovative new drugs. Traditional radiopharmaceutical manufacture can be considered as either a routine hospital production or a large-scale industrial production. The gap between these two practices has meant that there is an inability to supply innovative radiopharmaceuticals for use at the local level for mono- or multicentric clinical trials with satisfactory quality and safety specifications. This article highlights the regulatory requirements in aseptic pharmaceutical processing and in nuclear medicine to be able to locally produce radiopharmaceuticals. We validate the proof-of-concept for an “in-house” hospital-based radiopharmacy including an on-site cyclotron, that can fulfill the conflicting requirements between radiation safety and aseptic processing. The ARRONAX in-house radiopharmacy is currently able to provide sterile and pyrogenic-free injectable radiopharmaceutical compounds for both industrial and institutional clinical trials.

An assessment of bone-seeking radionuclides for palliation of metastatic bone pain in a vertebral model.

Bone-seeking radiopharmaceuticals have the main role in the treatment of painful bone metastases. The aim of this study was to dosimetrically compare radiopharmaceuticals in use for bone pain palliation therapy and bone scan. The MCNPX code was used to simulate the radiation transport in a vertebral phantom. Absorbed fractions were calculated for monoenergetic electrons, photons and alpha particles. S values were obtained for radionuclides 32P, 33P, 89Sr, 90Y, 99mTc, 117mSn, 153Sm, 166Ho, 169Er, 177Lu, 186Re, 188Re, 223Ra, 224Ra and their progenies for target regions including the active marrow and the bone endosteum. The results demonstrated the dependence of dosimetric parameters on the source or target size, particle energy and location of the source. The electron emitters including 33P, 117mSn, 169Er and 177Lu and 223Ra as an α-emitter gave the lower absorbed dose to the active marrow. These radionuclides gave the highest values of the Relative Advantage Factor (RAF). According to the results,33P, 117mSn, 169Er, 177Lu and 223Ra have fewer side effects on the active marrow than other investigated radionuclides. Therefore, these radionuclides may be a better choice for use in palliative radiotherapy.

Diagnostic nuclear medicine procedures in Germany between 1996 and 2002: application frequencies and collective effective doses.

Man-made radiation exposure to the German population predominantly results from the medical use of ionizing radiation. It was therefore the aim of the present study, to provide public health information concerning diagnostic nuclear medicine procedures carried out in Germany between 1996 and 2002. Application frequencies for 10 groups of procedures were estimated from official reimbursement data provided by the German health insurance companies. Mean effective doses for these examinations were estimated from data provided by 14 clinics and 10 practices concerning the radiopharmaceuticals in use and the activities administered. During the period 1996-2002, a total of (3.83 +/- 0.31) million nuclear medicine procedures were performed in average per year, which corresponds to a mean annual application frequency of approximately 47 examinations per 1 000 inhabitants. More than 90% of the examinations were scintigraphies of the thyroid (37%), skeleton (25%), myocardium (13%), lungs (8%) and kidneys (8%). The averaged collective effective dose was (10.2 +/- 1.4) . 10(3) mSv per year, which corresponds to a mean annual per caput effective dose of about (0.12 +/- 0.02) mSv. Three types of procedures were responsible for about 80% of the total collective effective dose: scintigraphies of the myocardium (36%), skeleton (33%) and thyroid (10%). Averaged over all procedures carried-out, the mean effective dose per examination was (2.7 +/- 0.8) mSv. The average effective dose per inhabitant and year caused by nuclear medicine examinations is markedly lower than that resulting from medical X-ray procedures (0.12 vs. 1.8 mSv). Reduction of patient exposure may be achieved, for example, by replacing (201)Tl-labeled radiopharmaceuticals by (99m)Tc-labeled compounds.

Radiotherapy to volumes defined by metabolic imaging in gliomas: time to abandon monstrous margins?

The survival in patients with high grade gliomas (HGG) remains poor even after the adoption post-operative radiotherapy (RT) to magnetic resonance imaging (MRI) based volumes. Despite delivery of 'standardized' doses of radiation, recurrence is the norm, rather than the exception. Recurrences occur both within, and outside of the volume of irradiation, leading us to two questions-firstly concerning the adequacy of the dose of radiation used, and secondly about the current methods of treatment volume delineation. The emergence of newer radiopharmaceuticals for use in positron emission tomography (PET) have kindled the hope of more precise volume localizations for post-operative RT, and it is likely that these new radiopharmaceuticals can help us define accurate areas at highest risk of recurrence and thus allow us to use increased doses of radiation with confidence.

Feasibility analysis of I-131 production in the Moroccan TRIGA research reactor

Since the commissioning of the Moroccan 2MW TRIGA MARK II research reactor hosted by the Centre National de l’Energie des Sciences et des Techniques Nucléaires (CNESTEN), the latter institution has established a radioisotope production program to supply radiopharmaceuticals for use in nuclear medicine. This paper presents a feasibility analysis for I-131 production using two in-core irradiation positions within the Moroccan TRIGA MARK II research reactor. The MCNPX v2.7 code, with its depletion capabilities, was used for the evaluation of two different production scenarios using several masses of TeO2 target samples. The maximum achievable activities were found to be 3.90Ci/week for scenario 1 and 4.63Ci/week for scenario 2. Thermal analysis shows that safety limits of capsules used for these experiments were not violated.

Erbium-169 labeled hydroxyapatite particulates for use in radiation synovectomy of digital joints – a preliminary investigation

Abstract Erbium-169 [T 1/2 = 9.4 d, E β( max ) = 342 keV (45%) and 351 keV (55%), E γ = 110.5 KeV (0.0014%)] is the most preferred radionuclide for radiation synovectomy (RSV) of digital joints. Radiolabeled particulates of appropriate size, wherein the radionuclide is irreversibly attached to the preformed particles, offer distinct advantages as the radiopharmaceuticals for use in RSV over other radiotherapeutic agents in terms of minimal leakage of radioactivity from the joint cavity. Hyroxyapatite (HA) particles, regarded as one of the most suitable carrier moiety for radiosynoviortheses applications, have been envisaged for labeling with 169Er with an aim to developing an agent for RSV of digital joints. Erbium-169 was produced with a specific activity of 415 ± 23 MBq/mg and radionuclidic purity of 99.22 ± 0.17% (both at the end of bombardment) by thermal neutron irradiation of enriched (98.2% in 168Er) erbium target at a flux of ∼ 8 · 1013 n/cm2 s for 21 d. HA particles (1–10 micrometer size), synthesized in-house, were labeled with 169Er in high yield and radiochemical purity (> 99%) using 5 mg of HA particulates at pH 7.5. The radiolabeled particulates showed excellent in vitro stability in normal saline and human serum. Biodistribution and imaging studies (using 171Er-HA) carried out in normal Wistar rats following intra-articular injection of 169Er-HA particulates in the knee joint showed near-complete retention of injected radioactivity within the synovial cavity with almost no activity leaching out to the other organs/tissue.

Synthesis and biological evaluation of two agents for imaging estrogen receptor β by positron emission tomography: challenges in PET imaging of a low abundance target

Independent measurement of the levels of both the estrogen receptors, ERα and ERβ, in breast cancer could improve prediction of benefit from endocrine therapies. While ERα levels can be measured by positron emission tomography (PET) using 16α-[(18)F]fluoroestradiol (FES), no effective agent for imaging ERβ by PET has yet been reported. We have prepared the fluorine-18 labeled form of 8β-(2-fluoroethyl)estradiol (8BFEE(2)), an analog of an ERβ-selective steroidal estrogen, 8β-vinylestradiol; efficient incorporation of fluorine-18 was achieved, but required very vigorous conditions. We have examined the biodistribution of this compound, as well as of Br-041, an analog of a known non-steroidal ERβ-selective ligand (ERB-041), labeled with bromine-76. Studies were done in immature female rodents, with various pharmacological and endocrine perturbations to assess ERβ selectivity of uptake. Little evidence of ERβ-mediated uptake was observed with either [(18)F]8BFEE(2) or [(76)Br]Br-041. Attempts to increase the ERβ content of target tissues were not effective and failed to improve biodistribution selectivity. Because on an absolute basis level, ERβ levels are low in all target tissues, these studies have highlighted the need to develop improved in vivo models for evaluating ERβ-selective radiopharmaceuticals for use in PET imaging. Genetically engineered breast cancer cells that are being developed to express either ERα or ERβ in a regulated manner, grown as xenografts in immune-compromised mice, could prove useful for future studies to develop ER subtype-selective radiopharmaceuticals.

Zur Messung der Nierenfunktion durch Clearancebestimmungen: Methoden und Indikationen – ein Update

Um die Nierenfunktion quantitativ zu beurteilen, gibt es viele Methoden. Meist benützen die Kliniker die simple Bestimmung des Plasmakreatinins, einige wählen jedoch die Kreatininclearance mit Urinsammlungen und andere alternative, aber indirekte Verfahren. Die Isotopenclearancebestimmungen sind jedoch im Vergleich mit allen anderen Methoden einfach durchzuführen und ergeben eine hohe Genauigkeit bei äußerst geringer Strahlenexposition. In diesem Überblick werden der Clearancebegriff, die unterschiedlichen Radiopharmaka, deren Vor- und Nachteile, die unterschiedlichen Clearancetechniken sowie die klinischen Indikationen zu Clearanceuntersuchungen besprochen. Dabei handelt es sich um ein Update eines entsprechenden Artikels, der 2003 in „Der Nuklearmediziner” publiziert wurde.

In vitro kinetic studies on the mechanism of oxygen-dependent cellular uptake of copper radiopharmaceuticals

The development of hypoxia-selective radiopharmaceuticals for use as therapeutic and/or imaging agents is of vital importance for both early identification and treatment of cancer and in the design of new drugs. Radiotracers based on copper for use in positron emission tomography have received great attention due to the successful application of copper(II) bis(thiosemicarbazonato) complexes, such as [60/62/64Cu(II)ATSM] and [60/62/64Cu(II)PTSM], as markers for tumour hypoxia and blood perfusion, respectively. Recent work has led to the proposal of a revised mechanism of hypoxia-selective cellular uptake and retention of [Cu(II)ATSM]. The work presented here describes non-steady-state kinetic simulations in which the reported pO2-dependent in vitro cellular uptake and retention of [64Cu(II)ATSM] in EMT6 murine carcinoma cells has been modelled by using the revised mechanistic scheme. Non-steady-state (NSS) kinetic analysis reveals that the model is in very good agreement with the reported experimental data with a root-mean-squared error of less than 6% between the simulated and experimental cellular uptake profiles. Estimated rate constants are derived for the cellular uptake and washout (k1 = 9.8 ± 0.59 × 10−4 s−1 and k2 = 2.9 ± 0.17 × 10−3 s−1), intracellular reduction (k3 = 5.2 ± 0.31 × 10−2 s−1), reoxidation (k4 = 2.2 ± 0.13 mol−1 dm3 s−1) and proton-mediated ligand dissociation (k5 = 9.0 ± 0.54 × 10−5 s−1). Previous mechanisms focused on the reduction and reoxidation steps. However, the data suggest that the origins of hypoxia-selective retention may reside with the stability of the copper(I) anion with respect to protonation and ligand dissociation. In vitro kinetic studies using the nicotimamide adenine dinucleotide (NADH)-dependent ferredoxin reductase enzyme PuR isolated from the bacterium Rhodopseudomonas palustris have also been conducted. NADH turnover frequencies are found to be dependent on the structure of the ligand and the results confirm that the proposed reduction step in the mechanism of hypoxia selectivity is likely to be mediated by NADH-dependent enzymes. Further understanding of the mechanism of hypoxia selectivity may facilitate the development of new imaging and radiotherapeutic agents with increased specificity for tumour hypoxia.

177Lu-EDTMP: A Viable Bone Pain Palliative in Skeletal Metastasis

Designing ideal radiopharmaceuticals for use as bone pain palliatives require the use of a moderate energy beta() emitter as a radionuclide and a suitable polyaminophosphonic acid as a carrier molecule. Owing to its suitable decay characteristics [T(1/2) = 6.73 d, E((max)) = 497 keV, E() = 113 keV (6.4%), 208 keV (11%)] as well as the feasibility of large-scale production in adequate specific activity and radionuclidic purity using a moderate flux reactor, 177Lu could be considered as a promising radionuclide for palliative care in painful bone metastasis. The present study was therefore, oriented toward the preparation and biologic evaluation of 177Lu complex of ethylenediaminetetramethylene phosphonic acid (EDTMP) in various animal models, with an aim to prepare a viable radiopharmaceutical for bone pain palliation. 177Lu was produced with a specific activity of approximately 12 GBq/mg (approximately 324 mCi/mg) and radionuclidic purity of 99.98% by irradiation of natural Lu2O3 targeted at a thermal neutron flux of approximately 6 x 10(13) n/cm(2).s for 21 days. 177Lu-EDTMP complex was prepared in high-yield and excellent radiochemical purity (>99%), using EDTMP synthesized and characterized in-house. The complex exhibited excellent in vitro stability at room temperature. Biodistribution studies in Wistar rats showed a rapid skeletal accumulation of injected activity [(1.74 +/- 0.30)% per gram in femur at 3 hours postinjection] with a fast clearance from blood and minimal uptake in any of the major organs. Scintigraphic imaging studies carried out in normal Wistar rats, New Zealand white rabbits, as well as in Beagle dogs also demonstrated significant accumulation of the agent in the skeleton and almost no retention of activity in any other vital organs.

Radiopharmaceuticals for Drug Development: United States Regulatory Perspective

Imaging with radiopharmaceuticals is playing an increasingly important role in the development of new drugs. At nearly every step of the process imaging may be used to assess the status of the candidate drugs and assist in determining the lead molecules for further evaluation. Incorporating imaging studies into the paradigm may ameliorate the temporal and economic cost of drug development. Since 1975 radiopharmaceuticals have been regulated as drugs and all human studies must be carried out under an investigational new drug (IND) or radioactive drug research committee (RDRC) protocol. The FDA released the exploratory IND guidance in 2006 to highlight the flexibility in the IND process while trying to stimulate new drug entry into the approval pipeline. The exploratory IND also provides a lower threshold for radiopharmaceutical and candidate drug first in human studies, using the microdosing concept, that may not be conducted under an RDRC protocol. The RDRC mechanism permits the basic research studies with limited dose and numbers of subjects. The RDRC regulations are 30 years old and the full IND process remains burdensome for radiopharmaceutical development. Therefore, it is essential that the regulatory framework permit the approval of radiopharmaceuticals for use in humans that is commensurate with the safety and applications of the probes. Beyond diagnosing and staging disease, monitoring progression or therapeutic intervention, imaging is playing an increasingly important role in the drug discovery and development process. Nuclear imaging, positron emission tomography (PET) and single photon emission computed tomography (SPECT), with radiolabeled molecular entities, radiopharmaceuticals, permits the visualization of the distribution of potential drugs as well as interrogating their effect on disease, organ systems and the whole body. Imaging probes may be applied in two ways to drug development, i) to define the pharmacokinetic (PK) properties of labeled drug candidates or ii) to assess the pharmacodynamic (PD) properties of new drugs. Molecular imaging's role in drug discovery and development has grown significantly over the last decade and it will continue to have a major impact on the assessment and profiling of new drugs for the foreseeable future. Since 1975 radioactive labeled entities, small molecules and biologics, have been considered by the United States Food and Drug Administration (FDA) to be drugs and are regulated as such. In spite of the fact that imaging probes, by their very nature, are tracers with minimal mass and no expected pharmacological or toxicological properties, they must undergo extensive safety evaluation prior to approval by the FDA. All human studies involving radioactively labeled molecules, unless exempt, must be performed under FDA guidelines using either an investigational new drug (IND) a or Radioactive Drug Research Committee (RDRC) b approval mechanism. This article describes the United States regulatory pathways that are involved to permit the use of new and existing radiopharmaceuticals in the drug discovery and development process.

Diagnostic nuclear medicine procedures in Germany between 1996 and 2002

Summary Aim: Man-made radiation exposure to the German population predominantly results from the medical use of ionizing radiation. It was therefore the aim of the present study, to provide public health information concerning diagnostic nuclear medicine procedures carried out in Germany between 1996 and 2002. Material and methods: Application frequencies for 10 groups of procedures were estimated from official reimbursement data provided by the German health insurance companies. Mean effective doses for these examinations were estimated from data provided by 14 clinics and 10 practices concerning the radiopharmaceuticals in use and the activities administered. Results: During the period 1996-2002, a total of (3.83 ± 0.31) million nuclear medicine procedures were performed in average per year, which corresponds to a mean annual application frequency of approximately 47 examinations per 1 000 inhabitants. More than 90% of the examinations were scintigraphies of the thyroid (37%), skeleton (25%), myocardium (13%), lungs (8%) and kidneys (8%). The averaged collective effective dose was (10.2 ± 1.4) ⋅103 manSv per year, which corresponds to a mean annual per caput effective dose of about (0.12 ± 0.02) mSv. Three types of procedures were responsible for about 80% of the total collective effective dose: scintigraphies of the myocardium (36%), skeleton (33%) and thyroid (10%). Averaged over all procedures carried-out, the mean effective dose per examination was (2.7 ± 0.8) mSv. Conclusion: The average effective dose per inhabitant and year caused by nuclear medicine examinations is markedly lower than that resulting from medical X-ray procedures (0.12 vs. 1.8 mSv). Reduction of patient exposure may be achieved, for example, by replacing 201Tl-labeled radiopharmaceuticals by 99mTc-labeled compounds.

The response of radiation portal monitors to medical radionuclides at border crossings

Radiopharmaceuticals are administered to a large number of individuals each year, and at any given time can be found at detectable levels in about one in 2600 Americans. Such individuals are among the population crossing international borders where equipment has been deployed for radiation detection, and the resulting “nuisance” alarms produced by these individuals must be resolved by further inspection like all other alarms. During 2001, a total of approximately 14.4 million medical procedures using radionuclides were performed in the US. This number rose to over 16.5 million in 2004. Of this total number of procedures, approximately 98% were diagnostic procedures and 2% were therapeutic procedures. Although there were over 45 different commercially-available products used in over 75 different types of medical procedures, only 17 different radioisotopes comprise the complete set of active radionuclides in the commercially-available radiopharmaceuticals in the US. There are other experimental radiopharmaceuticals in use, but their presence in the population is rare. Of these 17 radioisotopes, nine are customarily administered to outpatients and produce sufficiently energetic photons that can readily be detected. The radioisotope 99mTc is administered in about 90% of the procedures and is the one most likely to be detected by radiation screening equipment. This paper reports on various impacts of radiopharmaceuticals observed in people at border crossings. Calculations were performed to simulate the response of multi-lane portal radiation monitor deployments to these types of sources. Results are given for the time period during which radiopharmaceuticals might be detectable by radiation screening equipment at border crossings.