This article reviews routine quality-control (QC) procedures for current nuclear medicine instrumentation, including the survey meter, dose calibrator, well counter, intraoperative probe, organ ...("thyroid") uptake probe, gamma-camera, SPECT and SPECT/CT scanner, and PET and PET/CT scanner. It should be particularly useful for residents, fellows, and other trainees in nuclear medicine, nuclear cardiology, and radiology. The procedures described and their respective frequencies are presented only as general guidelines.
A first-in-human clinical trial of ultrasmall inorganic hybrid nanoparticles, "C dots" (Cornell dots), in patients with metastatic melanoma is described for the imaging of cancer. These renally ...excreted silica particles were labeled with (124)I for positron emission tomography (PET) imaging and modified with cRGDY peptides for molecular targeting. (124)I-cRGDY-PEG-C dot particles are inherently fluorescent, containing the dye, Cy5, so they may be used as hybrid PET-optical imaging agents for lesion detection, cancer staging, and treatment management in humans. However, the clinical translation of nanoparticle probes, including quantum dots, has not kept pace with the accelerated growth in minimally invasive surgical tools that rely on optical imaging agents. The safety, pharmacokinetics, clearance properties, and radiation dosimetry of (124)I-cRGDY-PEG-C dots were assessed by serial PET and computerized tomography after intravenous administration in patients. Metabolic profiles and laboratory tests of blood and urine specimens, obtained before and after particle injection, were monitored over a 2-week interval. Findings are consistent with a well-tolerated inorganic particle tracer exhibiting in vivo stability and distinct, reproducible pharmacokinetic signatures defined by renal excretion. No toxic or adverse events attributable to the particles were observed. Coupled with preferential uptake and localization of the probe at sites of disease, these first-in-human results suggest safe use of these particles in human cancer diagnostics.
Ionizing radiation has contributed enormously to dramatic improvements in medical care. The potential risks of radiation-based medical imaging have, however, drawn considerable attention in recent ...years. Although such concern is beneficial in terms of critical evaluation and optimization of imaging procedures, it can create the misconception that radiation is the only risk of medical imaging. In contrast to expression of radiation risks, quantitative estimates of the benefits of medical imaging are notably lacking. Expression of benefit in purely qualitative terms vs. expression of risk in quantitative, and thus apparently more concrete, terms may contribute to a biased judgement of the relative benefits and risks of medical imaging among health care professionals as well as the public. This paper, therefore, quantitatively compares the benefits of diagnostic imaging in several cases, based on actual mortality or morbidity data if ionizing radiation were not employed, with the linear no-threshold model derived (i.e., theoretical) estimates of radiogenic cancer mortality and illustrates the large benefit-to-risk ratios typical of medical imaging procedures.
Metastatic thyroid cancers that are refractory to radioiodine (iodine-131) are associated with a poor prognosis. In mouse models of thyroid cancer, selective mitogen-activated protein kinase (MAPK) ...pathway antagonists increase the expression of the sodium-iodide symporter and uptake of iodine. Their effects in humans are not known.
We conducted a study to determine whether the MAPK kinase (MEK) 1 and MEK2 inhibitor selumetinib (AZD6244, ARRY-142886) could reverse refractoriness to radioiodine in patients with metastatic thyroid cancer. After stimulation with thyrotropin alfa, dosimetry with iodine-124 positron-emission tomography (PET) was performed before and 4 weeks after treatment with selumetinib (75 mg twice daily). If the second iodine-124 PET study indicated that a dose of iodine-131 of 2000 cGy or more could be delivered to the metastatic lesion or lesions, therapeutic radioiodine was administered while the patient was receiving selumetinib.
Of 24 patients screened for the study, 20 could be evaluated. The median age was 61 years (range, 44 to 77), and 11 patients were men. Nine patients had tumors with BRAF mutations, and 5 patients had tumors with mutations of NRAS. Selumetinib increased the uptake of iodine-124 in 12 of the 20 patients (4 of 9 patients with BRAF mutations and 5 of 5 patients with NRAS mutations). Eight of these 12 patients reached the dosimetry threshold for radioiodine therapy, including all 5 patients with NRAS mutations. Of the 8 patients treated with radioiodine, 5 had confirmed partial responses and 3 had stable disease; all patients had decreases in serum thyroglobulin levels (mean reduction, 89%). No toxic effects of grade 3 or higher attributable by the investigators to selumetinib were observed. One patient received a diagnosis of myelodysplastic syndrome more than 51 weeks after radioiodine treatment, with progression to acute leukemia.
Selumetinib produces clinically meaningful increases in iodine uptake and retention in a subgroup of patients with thyroid cancer that is refractory to radioiodine; the effectiveness may be greater in patients with RAS-mutant disease. (Funded by the American Thyroid Association and others; ClinicalTrials.gov number, NCT00970359.).
Nanoparticle-based materials, such as drug delivery vehicles and diagnostic probes, currently under evaluation in oncology clinical trials are largely not tumor selective. To be clinically ...successful, the next generation of nanoparticle agents should be tumor selective, nontoxic, and exhibit favorable targeting and clearance profiles. Developing probes meeting these criteria is challenging, requiring comprehensive in vivo evaluations. Here, we describe our full characterization of an approximately 7-nm diameter multimodal silica nanoparticle, exhibiting what we believe to be a unique combination of structural, optical, and biological properties. This ultrasmall cancer-selective silica particle was recently approved for a first-in-human clinical trial. Optimized for efficient renal clearance, it concurrently achieved specific tumor targeting. Dye-encapsulating particles, surface functionalized with cyclic arginine-glycine-aspartic acid peptide ligands and radioiodine, exhibited high-affinity/avidity binding, favorable tumor-to-blood residence time ratios, and enhanced tumor-selective accumulation in αvβ3 integrin-expressing melanoma xenografts in mice. Further, the sensitive, real-time detection and imaging of lymphatic drainage patterns, particle clearance rates, nodal metastases, and differential tumor burden in a large-animal model of melanoma highlighted the distinct potential advantage of this multimodal platform for staging metastatic disease in the clinical setting.
In internal radionuclide therapy, a growing interest in voxel-level estimates of tissue-absorbed dose has been driven by the desire to report radiobiologic quantities that account for the biologic ...consequences of both spatial and temporal nonuniformities in these dose estimates. This report presents an overview of 3-dimensional SPECT methods and requirements for internal dosimetry at both regional and voxel levels. Combined SPECT/CT image-based methods are emphasized, because the CT-derived anatomic information allows one to address multiple technical factors that affect SPECT quantification while facilitating the patient-specific voxel-level dosimetry calculation itself. SPECT imaging and reconstruction techniques for quantification in radionuclide therapy are not necessarily the same as those designed to optimize diagnostic imaging quality. The current overview is intended as an introduction to an upcoming series of MIRD pamphlets with detailed radionuclide-specific recommendations intended to provide best-practice SPECT quantification-based guidance for radionuclide dosimetry.
Gamma probes are now an important, well-established technology in the management of cancer, particularly in the detection of sentinel lymph nodes. Intraoperative sentinel lymph node as well as tumor ...detection may be improved under some circumstances by the use of beta (negatron or positron), rather than gamma detection, because the very short range (∼1 mm or less) of such particulate radiations eliminates the contribution of confounding counts from activity other than in the immediate vicinity of the detector. This has led to the development of intraoperative beta probes. Gamma camera imaging also benefits from short source-to-detector distances and minimal overlying tissue, and intraoperative small field-of-view gamma cameras have therefore been developed as well. Radiation detectors for intraoperative probes can generally be characterized as either scintillation or ionization detectors. Scintillators used in scintillation-detector probes include thallium-doped sodium iodide, thallium- and sodium-doped cesium iodide, and cerium-doped lutecium orthooxysilicate. Alternatives to inorganic scintillators are plastic scintillators, solutions of organic scintillation compounds dissolved in an organic solvent that is subsequently polymerized to form a solid. Their combined high counting efficiency for beta particles and low counting efficiency for 511-keV annihilation γ-rays make plastic scintillators well-suited as intraoperative beta probes in general and positron probes in particular Semiconductors used in ionization-detector probes include cadmium telluride, cadmium zinc telluride, and mercuric iodide. Clinical studies directly comparing scintillation and semiconductor intraoperative probes have not provided a clear choice between scintillation and ionization detector-based probes. The earliest small field-of-view intraoperative gamma camera systems were hand-held devices having fields of view of only 1.5-2.5 cm in diameter that used conventional thallium-doped sodium iodide or sodium-doped cesium iodide scintillation detectors. Later units used 2-dimensional arrays (mosaics) of scintillation crystals connected to a position-sensitive photomultiplier tube and, more recently, semiconductors such as cadmium telluride or cadmium zinc telluride. The main problems with the early units were their very small fields of view and the resulting large number of images required to interrogate the surgical field and the difficulty in holding the device sufficiently still for the duration (up to 1 min) of the image acquisition. More recently, larger field-of-view (up to 5 × 5 cm) devices have developed which are attached to an articulating arm for easy and stable positioning. These systems are nonetheless fully portable and small enough overall to be accommodated in typical surgical suites.
The potential medical applications of nanomaterials are shaping the landscape of the nanobiotechnology field and driving it forward. A key factor in determining the suitability of these nanomaterials ...must be how they interface with biological systems. Single walled carbon nanotubes (CNT) are being investigated as platforms for the delivery of biological, radiological, and chemical payloads to target tissues. CNT are mechanically robust graphene cylinders comprised of sp(2)-bonded carbon atoms and possessing highly regular structures with defined periodicity. CNT exhibit unique mechanochemical properties that can be exploited for the development of novel drug delivery platforms. In order to evaluate the potential usefulness of this CNT scaffold, we undertook an imaging study to determine the tissue biodistribution and pharmacokinetics of prototypical DOTA-functionalized CNT labeled with yttrium-86 and indium-111 ((86)Y-CNT and (111)In-CNT, respectively) in a mouse model.
The (86)Y-CNT construct was synthesized from amine-functionalized, water-soluble CNT by covalently attaching multiple copies of DOTA chelates and then radiolabeling with the positron-emitting metal-ion, yttrium-86. A gamma-emitting (111)In-CNT construct was similarly prepared and purified. The constructs were characterized spectroscopically, microscopically, and chromatographically. The whole-body distribution and clearance of yttrium-86 was characterized at 3 and 24 hours post-injection using positron emission tomography (PET). The yttrium-86 cleared the blood within 3 hours and distributed predominantly to the kidneys, liver, spleen and bone. Although the activity that accumulated in the kidney cleared with time, the whole-body clearance was slow. Differential uptake in these target tissues was observed following intravenous or intraperitoneal injection.
The whole-body PET images indicated that the major sites of accumulation of activity resulting from the administration of (86)Y-CNT were the kidney, liver, spleen, and to a much less extent the bone. Blood clearance was rapid and could be beneficial in the use of short-lived radionuclides in diagnostic applications.
Preclinical dosimetry is essential for guiding the design of animal radiopharmaceutical biodistribution, imaging, and therapy experiments, evaluating efficacy and/or toxicities in such experiments, ...ensuring compliance with ethical standards for animal research, and, perhaps most importantly, providing reasonable initial estimates of normal-organ doses in humans, required for clinical translation of new radiopharmaceuticals. This MIB Guide provides a basic protocol for obtaining preclinical dosimetry estimates with organ-level dosimetry software.
While it is implicitly recognized that the benefits of diagnostic imaging far outweigh any theoretical radiogenic risks, quantitative estimates of the benefits are rarely, if ever, juxtaposed with ...quantitative estimates of risk. This alone - expression of benefit in purely qualitative terms versus expression of risk in quantitative, and therefore seemingly more certain, terms - may well contribute to a skewed sense of the relative benefits and risks of diagnostic imaging among healthcare providers as well as patients. The current paper, therefore, briefly compares the benefits of diagnostic imaging in several cases, based on actual mortality or morbidity data if ionizing radiation were not employed, with theoretical estimates of radiogenic cancer mortality based on the "linear no-threshold" (LNT) dose-response model.
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