11C Dosimetry Scans Should Be Abandoned

[18F]SF51, a novel 18F-labeled PET radioligand for translocator protein 18kDa (TSPO) in brain, works well in monkeys but fails in humans

[18F]SF51 is a novel radioligand for imaging translocator protein 18 kDa (TSPO) that previously displayed excellent imaging properties in nonhuman primates. This study assessed its performance in human brain and its dosimetry. Seven healthy participants underwent brain PET imaging to measure TSPO binding using a two-tissue compartment model (2TCM) to calculate total distribution volume (VT). This cohort included two high-affinity binders (HABs), three mixed-affinity binders (MABs), and two low-affinity binders (LABs). Two other participants received whole-body scans to assess radiation exposure. Peak brain radioactivity reached a standardized uptake value (SUV) of 1.4 at 3 minutes post-injection, diminishing to 30% of peak by 120 minutes. The average VT for all genotype groups was notably low (<1 mL·cm-3), emphasizing the radioligand's poor binding in brain. [18F]SF51 remained sensitive to the TSPO polymorphism in vivo, as shown by a two-fold difference in VT between HABs and LABs. VT stabilization by 80 minutes post-injection suggested minimal radiometabolite accumulation in brain. The average effective dose was 13.8 ± 0.9 µSv/MBq. Contrary to previously published animal data, [18F]SF51 showed low binding to human TSPO, with uptake remaining influenced by the rs6971 polymorphism. These findings highlight the challenges of developing TSPO radioligands and underscore the significant species differences that may influence translational outcomes.ClinicalTrials.gov identifier: NCT05564429; registered 10/03/2022.

First-in-human evaluation of 6-bromo-7-[11C]methylpurine, a PET tracer for assessing the function of multidrug resistance-associated proteins in different tissues

PURPOSE

Multidrug resistance-associated protein 1 (MRP1) is a transport protein with a widespread tissue distribution, which has been implicated in the pathophysiology of Alzheimer's and chronic respiratory disease. PET with 6-bromo-7-[11C]methylpurine ([11C]BMP) has been used to measure MRP1 function in rodents. In this study, [11C]BMP was for the first time characterised in humans to assess the function of MRP1 and other MRP subtypes in different tissues.

METHODS

Thirteen healthy volunteers (7 men, 6 women) underwent dynamic whole-body PET scans on a long axial field-of-view (LAFOV) PET/CT system after intravenous injection of [11C]BMP. Three subjects of each sex were scanned a second time to assess reproducibility. Volumes of interest were outlined for MRP-expressing tissues (cerebral cortex, cerebellum, choroid plexus, retina, lungs, myocardium, kidneys, and liver). From the time-activity curves, the elimination rate constant (kE, h- 1) was derived as a parameter for tissue MRP function and its test-retest variability (TRTV, %) was calculated. Radiation dosimetry was calculated using the Medical Internal Radiation Dose (MIRD) methodology.

RESULTS

Mean kE and corresponding TRTV values were: cerebral cortex: 0.055 ± 0.010 h- 1 (- 4 ± 24%), cerebellum: 0.033 ± 0.009 h- 1 (1 ± 39%), choroid plexus: 0.292 ± 0.059 h- 1 (0.1 ± 16%), retina: 0.234 ± 0.045 h- 1 (30 ± 38%), lungs: 0.875 ± 0.095 h- 1 (- 3 ± 11%), myocardium: 0.641 ± 0.105 h- 1 (11 ± 25%), kidneys: 1.378 ± 0.266 h- 1 (14 ± 16%), and liver: 0.685 ± 0.072 h- 1 (7 ± 9%). Significant sex differences were found for kE in the cerebellum, lungs and kidneys. Effective dose was 4.67 ± 0.18 µSv/MBq for men and 4.55 ± 0.18 µSv/MBq for women.

CONCLUSION

LAFOV PET/CT with [11C]BMP potentially allows for simultaneous assessment of MRP function in multiple human tissues. Mean TRTV of kE in different tissues was in an acceptable range, except for the retina. The radiation dosimetry of [11C]BMP was in the typical range of 11C-tracers. LAFOV PET/CT holds great potential to assess at a whole-body, multi-tissue level molecular targets relevant for drug disposition in humans.

TRIAL REGISTRATION

EudraCT 2021-006348-29. Registered 15 December 2021.

Process validation and preclinical development of a new PET cerebral blood flow tracer [11C]MMP for initial clinical trials

BACKGROUND

2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is commonly used for diagnosis of dementia because brain glucose metabolism reflects neuronal activity. However, as [18F]FDG is an analogue of glucose, accumulation of tracer in the brain is affected by plasma glucose levels. In contrast, cerebral blood flow (CBF) tracers are theoretically unaffected by plasma glucose levels and are therefore expected to be useful alternatives for the diagnosis of dementia in patients with diabetes. The techniques currently used for CBF imaging using single photon emission computed tomography (SPECT) and [15O]H2O positron emission tomography (PET), but these are limited by their insufficient resolution and sensitivity for regional brain imaging, especially in patients with brain atrophy. N-isopropyl-4-[11C]methylamphetamine ([11C]MMP) is a possible CBF tracer with high resolution and sensitivity that exhibits comparable performance to that of [15O]H2O in conscious monkey brains. We performed process validation of the radiosynthesis and preclinical development of [11C]MMP prior to clinical translation.

RESULTS

The decay-corrected yields of [11C]MMP at the end of synthesis were 41.4 ± 6.5%, with 99.7 ± 0.3% radiochemical purity, and 192.3 ± 22.5 MBq/nmol molar activity. All process validation batches complied with the product specifications. The acute toxicity of MMP was evaluated at a dose of 3.55 mg/kg body weight, which is 10,000 times the potential maximum clinical dose of [11C]MMP. The acute toxicity of [11C]MMP injection at 150 or 200 times, to administer a postulated dose of 740 MBq of [11C]MMP, was also evaluated after the decay-out of 11C. No acute toxicity of MMP and [11C]MMP injection was found. No mutagenic activity was observed for MMP. The effective dose calculated according to the Medical Internal Radiation Dose (MIRD) method was 5.4 µSv/MBq, and the maximum absorbed dose to the bladder wall was 57.6 µGy/MBq. MMP, a derivative of phenylalkylamine, showed binding to the sigma receptor, but had approximately 1/100 of the affinity of existing sigma receptor imaging agents. The affinity for other brain neuroreceptors was low.

CONCLUSIONS

[11C]MMP shows acceptable pharmacological safety at the dose required for adequate PET imaging. The potential risk associated with [11C]MMP PET imaging is well within the acceptable dose limit.

Preclinical validation of a novel brain-penetrant PET ligand for visualization of histone deacetylase 6: a potential imaging target for neurodegenerative diseases

PURPOSE

Histone deacetylase 6 (HDAC6) has emerged as a therapeutic target for neurodegenerative diseases such as Alzheimer's disease. Noninvasive imaging of HDAC6 in the brain by positron emission tomography (PET) would accelerate research into its roles in these diseases. We recently discovered an 18F-labeled derivative of the selective HDAC6 inhibitor SW-100 ([18F]FSW-100) as a potential candidate for brain HDAC6 radioligand. As a mandatory step prior to clinical translation, we performed preclinical validation of [18F]FSW-100.

METHODS

Process validation of [18F]FSW-100 radiosynthesis for clinical use and assessment of preclinical toxicity and radiation dosimetry estimated from mouse distribution data were performed. In vitro selectivity of FSW-100 for 28 common receptors in the brain and HDAC isoforms was characterized. [18F]FSW-100 PET imaging was performed in non-human primates in a conscious state to estimate the feasibility of HDAC6 imaging in humans.

RESULTS

Three consecutive validation runs of the automated radiosynthesis gave [18F]FSW-100 injections with radiochemical yields of 12%, and the injections conformed to specified quality control criteria for batch release. No acute toxicity was observed for non-radiolabeled FSW-100 or radioactivity decayed [18F]FSW-100 injection, and the former was negative in the Ames test. The whole-body effective dose estimated from biodistribution in mice was within the range of that of previously reported 18F-radioligands in humans. In vitro selectivity against common receptors and other HDAC isoforms was confirmed. [18F]FSW-100 demonstrated good penetration in monkey brain, and in vivo blocking studies suggested that the uptake was specific.

CONCLUSION

These results support the clinical utility of [18F]FSW-100 for in vivo imaging of HDAC6 in the brain.

Advancing 6-bromo-7-[11C]methylpurine to clinical use: improved regioselective radiosynthesis, non-clinical toxicity data and human dosimetry estimates

BACKGROUND

6-Bromo-7-[11C]methylpurine ([11C]BMP) is a radiotracer for positron emission tomography (PET) to measure multidrug resistance-associated protein 1 (MRP1) transport activity in different tissues. Previously reported radiosyntheses of [11C]BMP afforded a mixture of 7- and 9-[11C]methyl regioisomers. To prepare for clinical use, we here report an improved regioselective radiosynthesis of [11C]BMP, the results of a non-clinical toxicity study as well as human dosimetry estimates based on mouse PET data.

RESULTS

[11C]BMP was synthesised by regioselective N7-methylation of 6-bromo-7H-purine (prepared under good manufacturing practice) with [11C]methyl triflate in presence of 2,2,6,6-tetramethylpiperidine magnesium chloride in a TRACERlab™ FX2 C synthesis module. [11C]BMP was obtained within a total synthesis time of approximately 43 min in a decay-corrected radiochemical yield of 20.5 ± 5.2%, based on starting [11C]methyl iodide, with a radiochemical purity > 99% and a molar activity at end of synthesis of 197 ± 130 GBq/μmol (n = 28). An extended single-dose toxicity study conducted in male and female Wistar rats under good laboratory practice after single intravenous (i.v.) administration of unlabelled BMP (2 mg/kg body weight) revealed no test item related adverse effects. Human dosimetry estimates, based on dynamic whole-body PET data in female C57BL/6J mice, suggested that an i.v. injected activity amount of 400 MBq of [11C]BMP will deliver an effective dose in the typical range of 11C-labelled radiotracers.

CONCLUSIONS

[11C]BMP can be produced in sufficient amounts and acceptable quality for clinical use. Data from the non-clinical safety evaluation showed no adverse effects and suggested that the administration of [11C]BMP will be safe and well tolerated in humans.

[18F]FNDP PET neuroimaging test-retest repeatability and whole-body dosimetry in humans

PURPOSE

Soluble epoxide hydrolase (sEH) is an enzyme that shapes immune signaling through its role in maintaining the homeostasis of polyunsaturated fatty acids and their related byproducts. [18F]FNDP is a radiotracer developed for use with positron emission tomography (PET) to image sEH, which has been applied to imaging sEH in the brains of healthy individuals. Here, we report the test-retest repeatability of [18F]FNDP brain PET binding and [18F]FNDP whole-body dosimetry in healthy individuals.

METHODS

Seven healthy adults (4 men, 3 women, ages 40.1 ± 4.6 years) completed [18F]FNDP brain PET on two occasions within a period of 14 days in a test-retest study design. [18F]FNDP regional total distribution volume (VT) values were derived from modeling time-activity data with a metabolite-corrected arterial input function. Test-retest variability, mean absolute deviation, and intraclass correlation coefficient (ICC) were investigated. Six other healthy adults (3 men, 3 women, ages 46.0 ± 7.0 years) underwent [18F]FNDP PET/CT for whole-body dosimetry, which was acquired over 4.5 h, starting immediately after radiotracer administration. Organ-absorbed doses and the effective dose were then estimated.

RESULTS

The mean test-retest difference in regional VT (ΔVT) was 0.82 ± 5.17%. The mean absolute difference in regional VT was 4.01 ± 3.33%. The ICC across different brain regions ranged from 0.92 to 0.99. The organs with the greatest radiation-absorbed doses included the gallbladder (0.081 ± 0.024 mSv/MBq), followed by liver (0.077 ± 0.018 mSv/MBq) and kidneys (0.063 ± 0.006 mSv/MBq). The effective dose was 0.020 ± 0.003 mSv/MBq.

CONCLUSION

These data support a favorable test-retest repeatability of [18F]FNDP brain PET regional VT. The radiation dose to humans from each [18F]FNDP PET scan is similar to that of other 18F-based PET radiotracers.

Intravenous and oral whole body ketone dosimetry, biodistribution, metabolite correction and kinetics studied by (R)-[1-11C]β-hydroxybutyrate ([11C]OHB) PET in healthy humans

BACKGROUND

Ketones are increasingly recognized as an important and possibly oxygen sparing source of energy in vital organs such as the heart, the brain and the kidneys. Drug treatments, dietary regimens and oral ketone drinks designed to deliver ketones for organ and tissue energy production have therefore gained popularity. However, whether ingested ketones are taken up by various extra-cerebral tissues and to what extent is still largely unexplored. It was therefore the aim of this study to use positron emission tomography (PET) to explore the whole body dosimetry, biodistribution and kinetics of the ketone tracer (R)-[1-¹¹C]β-hydroxybutyrate ([¹¹C]OHB). Six healthy subjects (3 women and 3 men) underwent dynamic PET studies after both intravenous (90 min) and oral (120 min) administration of [¹¹C]OHB. Dosimetry estimates of [¹¹C]OHB was calculated using OLINDA/EXM software, biodistribution was assessed visually and [¹¹C]OHB tissue kinetics were obtained using an arterial input function and tissue time-activity curves.

RESULTS

Radiation dosimetry yielded effective doses of 3.28 [Formula: see text]Sv/MBq (intravenous administration) and 12.51 [Formula: see text]Sv/MBq (oral administration). Intravenous administration of [¹¹C]OHB resulted in avid radiotracer uptake in the heart, liver, and kidneys, whereas lesser uptake was observed in the salivary glands, pancreas, skeletal muscle and red marrow. Only minimal uptake was noted in the brain. Oral ingestion of the tracer resulted in rapid radiotracer appearance in the blood and radiotracer uptake in the heart, liver and kidneys. In general, [¹¹C]OHB tissue kinetics after intravenous administration were best described by a reversible 2-tissue compartmental model.

CONCLUSION

The PET radiotracer [¹¹C]OHB shows promising potential in providing imaging data on ketone uptake in various physiologically relevant tissues. As a result, it may serve as a safe and non-invasive imaging tool for exploring ketone metabolism in organs and tissues of both patients and healthy individuals. Trial registration Clinical trials, NCT0523812, Registered February 10th 2022, https://clinicaltrials.gov/ct2/show/NCT05232812?cond=NCT05232812&draw=2&rank=1 .

Biodistribution and dosimetry in human healthy volunteers of the PET radioligands [11C]CHDI-00485180-R and [11C]CHDI-00485626, designed for quantification of cerebral aggregated mutant huntingtin

PURPOSE

Huntington's disease is caused by a trinucleotide expansion in the HTT gene, which leads to aggregation of mutant huntingtin (mHTT) protein in the brain and neurotoxicity. Direct in vivo measurement of mHTT aggregates in human brain parenchyma is not yet possible. In this first-in-human study, we investigated biodistribution and dosimetry in healthy volunteers of [11C]CHDI-00485180-R ([11C]CHDI-180R) and [11C]CHDI-00485626 ([11C]CHDI-626), two tracers designed for PET imaging of aggregated mHTT in the brain that have been validated in preclinical models.

METHODS

Biodistribution and radiation dosimetry studies were performed in 3 healthy volunteers (age 25.7 ± 0.5 years; 2 F) for [11C]CHDI-180R and in 3 healthy volunteers (age 35.3 ± 6.8 years; 2 F) for [11C]CHDI-626 using sequential whole-body PET-CT. Source organs were delineated in 3D using combined PET and CT data. Individual organ doses and effective doses were determined using OLINDA 2.1.

RESULTS

There were no clinically relevant adverse events. The mean effective dose (ED) for [11C]CHDI-180R was 4.58 ± 0.65 μSv/MBq, with highest absorbed doses for liver (16.9 μGy/MBq), heart wall (15.9 μGy/MBq) and small intestine (15.8 μGy/MBq). Mean ED for [11C]CHDI-626 was 5.09 ± 0.06 μSv/MBq with the highest absorbed doses for the gallbladder (26.5 μGy/MBq), small intestine (20.4 μGy/MBq) and liver (19.6 μGy/MBq). Decay-corrected brain uptake curves showed promising kinetics for [11C]CHDI-180R, but for [11C]CHDI-626 an increasing signal over time was found, probably due to accumulation of a brain-penetrant metabolite.

CONCLUSION

[11C]CHDI-180R and [11C]CHDI-626 are safe for in vivo PET imaging in humans. The estimated radiation burden is in line with most 11C-ligands. While [11C]CHDI-180R has promising kinetic properties in the brain, [11C]CHDI-626 is not suitable for human in vivo mHTT PET due to the possibility of a radiometabolite accumulating in brain parenchyma.

TRIAL REGISTRATION

EudraCT number 2020-002129-27.

CLINICALTRIALS

gov NCT05224115 (retrospectively registered).

Biodistribution and dosimetry of the GluN2B-specific NMDA receptor PET radioligand (R)-[11C]Me-NB1

BACKGROUND

The NMDA receptor (NMDAR) plays a key role in the central nervous system, e.g., for synaptic transmission. While synaptic NMDARs are thought to have protective characteristics, activation of extrasynaptic NMDARs might trigger excitotoxic processes linked to neuropsychiatric disorders. Since extrasynaptic NMDARs are typically GluN2B-enriched, the subunit is an interesting target for drug development and treatment monitoring. Recently, the novel GluN2B-specific PET radioligand (R)-[11C]Me-NB1 was investigated in rodents and for the first time successfully translated to humans. To assess whether (R)-[11C]Me-NB1 is a valuable radioligand for (repeated) clinical applications, we evaluated its safety, biodistribution and dosimetry.

METHODS

Four healthy subjects (two females, two males) underwent one whole-body PET/MR measurement lasting for more than 120 min. The GluN2B-specific radioligand (R)-[11C]Me-NB1 was administered simultaneously with the PET start. Subjects were measured in nine passes and six bed positions from head to mid-thigh. Regions of interest was anatomically defined for the brain, thyroid, lungs, heart wall, spleen, stomach contents, pancreas, liver, kidneys, bone marrow and urinary bladder contents, using both PET and MR images. Time-integrated activity coefficients were estimated to calculate organ equivalent dose coefficients and the effective dose coefficient. Additionally, standardized uptake values (SUV) were computed to visualize the biodistribution.

RESULTS

Administration of the radioligand was safe without adverse events. The organs with the highest uptake were the urinary bladder, spleen and pancreas. Organ equivalent dose coefficients were higher in female in almost all organs, except for the urinary bladder of male. The effective dose coefficient was 6.0 µSv/MBq.

CONCLUSION

The GluN2B-specific radioligand (R)-[11C]Me-NB1 was well-tolerated without reported side effects. Effective dose was estimated to 1.8 mSv when using 300 MBq of presented radioligand. The critical organ was the urinary bladder. Due to the low effective dose coefficient of this radioligand, longitudinal studies for drug development and treatment monitoring of neuropsychiatric disorders including neurodegenerative diseases are possible. Trial registration Registered on 11th of June 2019 at https://www.basg.gv.at (EudraCT: 2018-002933-39).

Essential Principles and Recent Progress in the Development of TSPO PET Ligands for Neuroinflammation Imaging

The translocator protein 18kDa (TSPO) is expressed in the outer mitochondrial membrane and is implicated in several functions, including cholesterol transport and steroidogenesis. Under normal physiological conditions, TSPO is present in very low concentrations in the human brain but is markedly upregulated in response to brain injury and inflammation. This upregulation is strongly associated with activated microglia. Therefore, TSPO is particularly suited for assessing active gliosis associated with brain lesions following injury or disease. For over three decades, TSPO has been studied as a biomarker. Numerous radioligands for positron emission tomography (PET) that target TSPO have been developed for imaging inflammatory progression in the brain. Although [11C]PK11195, the prototypical first-generation PET radioligand, is still widely used for in vivo studies, mainly now as its single more potent R-enantiomer, it has severe limitations, including low sensitivity and poor amenability to quantification. Second-generation radioligands are characterized by higher TSPO specific signals but suffer from other drawbacks, such as sensitivity to the TSPO single nucleotide polymorphism (SNP) rs6971. Therefore, their applications in human studies have the burden of needing to genotype subjects. Consequently, recent efforts are focused on developing improved radioligands that combine the optimal features of the second generation with the ability to overcome the differences in binding affinities across the population. This review presents essential principles in the design and development of TSPO PET ligands and discusses prominent examples among the main chemotypes.

Practical considerations for navigating the regulatory landscape of non-clinical studies for clinical translation of radiopharmaceuticals

Background

The development of radiopharmaceuticals requires extensive evaluation before they can be applied in a diagnostic or therapeutic setting in Nuclear Medicine. Chemical, radiochemical, and pharmaceutical parameters must be established and verified to ensure the quality of these novel products.

Main body

To provide supportive evidence for the expected human in vivo behaviour, particularly related to safety and efficacy, additional tests, often referred to as “non-clinical” or “preclinical” are mandatory. This document is an outcome of a Technical Meeting of the International Atomic Energy Agency. It summarises the considerations necessary for non-clinical studies to accommodate the regulatory requirements for clinical translation of radiopharmaceuticals. These considerations include non-clinical pharmacology, radiation exposure and effects, toxicological studies, pharmacokinetic modelling, and imaging studies. Additionally, standardisation of different specific clinical applications is discussed.

Conclusion

This document is intended as a guide for radiopharmaceutical scientists, Nuclear Medicine specialists, and regulatory professionals to bring innovative diagnostic and therapeutic radiopharmaceuticals into the clinical evaluation process in a safe and effective way.

Strategic, feasibility, economic, and cultural aspects of phase 0 approaches: Is it time to change the drug development process in order to increase productivity?

Research conducted over the past 2 decades has enhanced the validity and expanded the applications of microdosing and other phase 0 approaches in drug development. Phase 0 approaches can accelerate drug development timelines and reduce attrition in clinical development by increasing the quality of candidates entering clinical development and by reducing the time to "go-no-go" decisions. This can be done by adding clinical trial data (both healthy volunteers and patients) to preclinical candidate selection, and by applying methodological and operational advantages that phase 0 have over traditional approaches. The main feature of phase 0 approaches is the limited, subtherapeutic exposure to the test article. This means a reduced risk to research volunteers, and reduced regulatory requirements, timelines, and costs of first-in-human (FIH) testing. Whereas many operational aspects of phase 0 approaches are similar to those of other early phase clinical development programs, they have some unique strategic, regulatory, ethical, feasibility, economic, and cultural aspects. Here, we provide a guidance to these operational aspects and include case studies to highlight their potential impact in a range of clinical development scenarios.

Radiation Absorbed Dose to the Embryo and Fetus from Radiopharmaceuticals

Nuclear medicine procedures are generally avoided during pregnancy out of concern for the radiation dose to the fetus. However, for clinical reasons, radiopharmaceuticals must occasionally be administered to pregnant women. The procedures most likely to be performed voluntarily during pregnancy are lung scans to diagnose pulmonary embolism and 18F-fluoro-2-deoxyglucose (18F-FDG) scans for the staging of cancers. This article focuses on the challenges of fetal dose calculation after administering radiopharmaceuticals to pregnant women. In particular, estimation of the fetal dose is hampered by the lack of fetal biokinetic data of good quality and is subject to the variability associated with methodological choices in dose calculations, such as the use of various anthropomorphic phantoms and modeling of the maternal bladder. Despite these sources of uncertainty, the fetal dose can be reasonably calculated within a range that is able to inform clinical decisions. Current dose estimates suggest that clinically justified nuclear medicine procedures should be performed even during pregnancy because the clinical benefits for the mother and the fetus outweigh the small and purely hypothetical radiation risk to the fetus. In addition, the fetal radiation dose should be minimized without compromising image quality, such as by encouraging bladder voiding and by using positron emission tomography (PET)/magnetic resonance imaging (MRI) devices or high-sensitivity PET scanners that generate images of good quality with a lower injected activity.

Simultaneous radiomethylation of [11C]harmine and [11C]DASB and kinetic modeling approach for serotonergic brain imaging in the same individual

Simultaneous characterization of pathologies by multi-tracer positron emission tomography (PET) is among the most promising applications in nuclear medicine. Aim of this work was the simultaneous production of two PET-tracers in one module and test the relevance for human application. [11C]harmine and [11C]DASB were concurrently synthesized in a 'two-in-one-pot' reaction in quality for application. Dual-tracer protocol was simulated using 16 single PET scans in different orders of tracer application separated by different time intervals. Volume of distribution was calculated for single- and dual-tracer measurements using Logan's plot and arterial input function in 13 brain regions. The 'two-in-one-pot' reaction yielded equivalent amounts of both radiotracers with comparable molar activities. The simulations of the dual-tracer application were comparable to the single bolus injections in 13 brain regions, when [11C]harmine was applied first and [11C]DASB second, with an injection time interval of 45 min (rxy = 0.90). Our study shows the successful simultaneous dual-tracer production leading to decreased radiation burden and costs. The simulation of dual subject injection to quantify the monoamine oxidase-A and serotonin transporter distribution proved its high potential. Multi-tracer imaging may drive more sophisticated study designs and diminish the day-to-day differences in the same individual as well as increase PET scanner efficiency.

First-in-Human PET Imaging and Estimated Radiation Dosimetry of l-[5-11C]-Glutamine in Patients with Metastatic Colorectal Cancer

Altered metabolism is a hallmark of cancer. In addition to glucose, glutamine is an important nutrient for cellular growth and proliferation. Noninvasive imaging via PET may help facilitate precision treatment of cancer through patient selection and monitoring of treatment response. l-[5-11C]-glutamine (11C-glutamine) is a PET tracer designed to study glutamine uptake and metabolism. The aim of this first-in-human study was to evaluate the radiologic safety and biodistribution of 11C-glutamine for oncologic PET imaging. Methods: Nine patients with confirmed metastatic colorectal cancer underwent PET/CT imaging. Patients received 337.97 ± 44.08 MBq of 11C-glutamine. Dynamic PET acquisitions that were centered over the abdomen or thorax were initiated simultaneously with intravenous tracer administration. After the dynamic acquisition, a whole-body PET/CT scan was acquired. Volume-of-interest analyses were performed to obtain estimates of organ-based absorbed doses of radiation. Results:11C-glutamine was well tolerated in all patients, with no observed safety concerns. The organs with the highest radiation exposure included the bladder, pancreas, and liver. The estimated effective dose was 4.46E-03 ± 7.67E-04 mSv/MBq. Accumulation of 11C-glutamine was elevated and visualized in lung, brain, bone, and liver metastases, suggesting utility for cancer imaging. Conclusion: PET using 11C-glutamine appears safe for human use and allows noninvasive visualization of metastatic colon cancer lesions in multiple organs. Further studies are needed to elucidate its potential for other cancers and for monitoring response to treatment.

Long axial field of view PET scanners: a road map to implementation and new possibilities

In this contribution, several opportunities and challenges for long axial field of view (LAFOV) PET are described. It is an anthology in which the main issues have been highlighted. A consolidated overview of the camera system implementation, business and financial plan, opportunities and challenges is provided. What the nuclear medicine and molecular imaging community can expect from these new PET/CT scanners is the delivery of more comprehensive information to the clinicians for advancing diagnosis, therapy evaluation and clinical research.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

RESULTS

This commentary of highlights has resulted in 23 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals.

CONCLUSION

Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.