Neuroendocrine tumours (NETs) arise from secondary epithelial cell lines in the gastrointestinal or respiratory system organs. The rate of development of these tumours varies from an indolent to an aggressive course, typically being initially asymptomatic. The identification of these tumours is difficult, particularly because the primary tumour is often small and undetectable by conventional anatomical imaging. Consequently, diagnosis of NETs is complicated and has been a significant challenge until recently. In the last 30 years, the advent of novel nuclear medicine diagnostic procedures has led to a substantial increase in NET detection. Great varieties of exclusive single photon emission computed tomography (SPECT) and positron emission tomography (PET) radiopharmaceuticals for detecting NETs are being applied successfully in clinical settings, including [111In]In-pentetreotide, [99mTc]Tc-HYNIC-TOC/TATE, [68Ga]Ga-DOTA-TATE, and [64Cu]Cu-DOTA-TOC/TATE. Among these tracers for functional imaging, PET radiopharmaceuticals are clearly and substantially superior to planar or SPECT imaging radiopharmaceuticals. The main advantages include higher resolution, better sensitivity and increased lesion-to-background uptake. An advantage of diagnosis with a radiopharmaceutical is the capacity of theranostics to provide concomitant diagnosis and treatment with particulate radionuclides, such as beta and alpha emitters including Lutetium-177 (177Lu) and Actinium-225 (225Ac). Due to these unique challenges involved with diagnosing NETs, various PET tracers have been developed. This review compares the clinical characteristics of radiolabelled somatostatin analogues for NET diagnosis, focusing on the most recently FDA-approved [64Cu]Cu-DOTA-TATE as a state-of-the art NET-PET/CT radiopharmaceutical.
Purposewe aimed to investigate the effect of various β-value in BSREM algorithm under different lesion sizes, in order to determine an optimal penalty factor for clinical use.
MethodsThe NEMA IQ phantom and 15 patients with prostate cancer were injected with 68Ga-PSMA and scanned by GE Discovery IQ PET/CT scanner. Images were reconstructed using OSEM and BSREM with different β-values and then background variability (BV), contrast recovery (CR), signal-to-noise ratio (SNR), and lung residual error (LE) from phantom data, and Signal-to-Background Ratio (SBR), contrast from clinical data were measured.
ResultsThe increment of BV using β-value of 100 was 120% and the decrement of BV using β-value 1000 were 40.5% compared to OSEM. As the β decreased from 1000 to 100, the SUV max increased by 59% and 26.4% for sphere with diameter of 10 mm and 37 mm, respectively.Δ SNR (100-1000) % increased by 140.5 and 29.0 in the smallest and the largest sphere, respectively. The Δ LE OSEM-100 and Δ LE OSEM-1000 was − 41.1% and − 36.7% respectively. In the clinical study, the lowest SBR and contrast was related to the OSEM. The SBR and contrast, respectively increased by 69.7% and 71.8% in small lesions and 35.6% and 33% in large lesions, respectively, when β-value was decreased from 500 to 100.
ConclusionsAs the lesion size decreased, the optimum β-value decreased. In both studies, a β value of 400 would be optimal for reconstruction of small lesions, whereas for large lesions in phantom and clinical studies respectively, β-value of 600 and 500 is recommended.
Nuclear medicine technicians would receive unavoidable exposures during the preparation and administration of radiopharmaceuticals. Based on the staff dose monitoring, the dose reduction efficiencies of the radiation protection shields and the need to implement additional strategies to reduce the staff doses could be evaluated. In this study, medical staff doses during the preparation and administration of Tc-99 m, I-131, and Kr-81 radiopharmaceuticals were evaluated. The dose reduction efficiencies of the lead apron and thyroid shield were also investigated. GR-207 thermoluminescent dosimeter (TLD) chips were used for quantifying the medical staff doses. The occupational dose magnitudes were determined in five organs at risk including eye lens, thyroid, fingers, chest, and gonads. TLDs were located under and over the protective shields for evaluating the dose reduction efficiencies of the lead apron and thyroid shield. The occupational doses were normalized to the activities used in the working shifts. During preparation and injection of Tc-99 m radiopharmaceutical, the average annual doses were higher in the chest (4.49 mGy) and eye lenses (4 mGy). For I-131 radiopharmaceutical, the average annual doses of the point-finger (15.8 mGy) and eye lenses (1.23 mGy) were significantly higher than other organs. During the preparation and administration of Kr-81, the average annual doses of the point-finger (0.65 mGy) and chest (0.44 mGy) were higher. The significant dose reductions were achieved using the lead apron and thyroid shield. The radiation protection shields and minimum contact with the radioactive sources, including patients, are recommended to reduce the staff doses.
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