Radiopharmaceutical Activity Research Articles

National Diagnostic Reference Levels for Nuclear Medicine in Kuwait

The diagnostic reference level (DRL) is a patient-exposure optimization tool used to evaluate and provide guidance for radiation doses in medical imaging. In the past few decades, there has been a global increase in the number of diagnostic imaging procedures, including nuclear medicine procedures, and consequently in patient radiation exposure. This increase has encouraged international and national health-care organizations to take action and keep up with such changes to meet the expectation of increasing use of ionizing radiation in medicine. Methods: DRLs in Kuwait were established by investigating the administered activity of radiopharmaceuticals and CT radiation doses in hybrid imaging systems. The DRLs were determined on the basis of the 75th percentile of radiopharmaceutical administered activity distribution as recommended by the International Commission on Radiological Protection. Results: The DRLs determined in Kuwait agree well with other published DRLs in Europe, Japan, Korea, Australia, and the United States. Conclusion: This study presents the establishment process and the results of the first national DRLs for nuclear medicine procedures in Kuwait as a way to optimize radiation exposure.

Simple model for estimation of absorbed dose by organs and tumors after PRRT from a single SPECT/CT study

BackgroundFollowing each cycle of peptide receptor radionuclide therapy (PRRT), absorbed doses by tumors and normal organs are typically calculated from three quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT) studies acquired at t1 = 24 h, t2 = 96 h, t3 = 168 h after the first cycle of treatment and from a single study at t1 after the subsequent cycles. In the present study, we have assessed the feasibility of a single SPECT/CT study after each PRRT cycle using a trained multiple linear regression (MLR) model for absorbed dose calculation and have evaluated its impact on patient management. Quantitative [177Lu]-DOTA-TATE SPECT/CT data after PRRT of seventy-two consecutive metastatic neuroendocrine tumors patients were retrospectively evaluated. A set of 40 consecutive studies was used to train the MLR model. The two independent variables of the model included the time of imaging after administration of the treatment and the radiopharmaceutical activity concentration in a given organ/tumor. The dependent variable was the dose absorbed by the organ/tumor obtained with the standard protocol. For bone marrow dosimetry, the independent variables included the time of imaging, and the blood and remainder of the body activity concentration. The model was evaluated in 32 consecutive patients. Absorbed doses were assessed for kidneys, bone marrow, liver, spleen and tumor sites.ResultsThere was no difference in management decisions, whether PRRT can be safely continued or not because unsafe absorbed dose to risk organs between the standard and the MLR model-based protocol using a single SPECT/CT study performed at t3 = 168 h after the first cycle and at t1 = 24 h after the subsequent cycles. Cumulative absorbed doses were obtained with mean relative differences of − 0.5% ± 5.4%, 1.6% ± 15.1%, − 6.2% ± 7.3%, − 5.5% ± 5.8% and 2.9% ± 12.7% for kidneys, bone marrow, liver, spleen and tumors, respectively (Pearson’s r correlation coefficient 0.99, 0.91, 0.99, 0.99 and 0.97, respectively).ConclusionDosimetry calculations using a MLR model with a single SPECT/CT study are in good agreement with the standard protocol, while avoiding the use of dosimetry software and enabling improved patient comfort and reduced scanner and staff time.

Occupational exposures in PET procedures with 18F-FDG in adult and pediatric patients

Diagnosis through positron emission tomography (PET) is an increasingly used procedure in cerebral, cardiac and especially oncology diseases. It is performed in nuclear medicine clinics, mainly using 18F-Fluorodeoxyglucose (18F-FDG), which has one of the longest half-lives among positron emitters. The gamma rays, produced in the annihilations, require strict radiation control to guarantee the safety of the occupationally exposed individuals working in PET exam facilities. To evaluate occupational exposures, in this study, the MCNPX2.7.0 radiation transport code was used. The professionals were represented by the FASH3 (female) and MASH3 (male) adult virtual anthropomorphic phantoms, which have anthropometric characteristics like those of real individuals. Four exposure scenarios were modeled: radiopharmaceutical preparation, administration to the patient, patient follow-up, and patient placement in PET equipment. The results are presented in terms of the mean effective dose by PET procedure (μSv/procedure) and the mean effective dose by radiopharmaceutical activity (nSv/MBq). Using the set of conversion coefficients presented in this study, it is possible to calculate the absolute values of effective doses for nuclear medicine professionals who are in contact with the radioactive material or the patient. The differences between our study and the literature were only 3%. The effective occupational doses, with an adult patient, were 14% higher than those with pediatric patients.

ANALYSIS OF HAND EXPOSURE AMONG NUCLEAR MEDICINE TECHNOLOGISTS IN SAUDI ARABIA.

The increase in the amount of radioactive materials administered to patients as well as the number of procedures performed has focused attention on the issue of radiation exposure to the hands of workers in nuclear medicine departments worldwide. The study aims to estimate the equivalent doses to the hands of individuals in nuclear medicine departments in Saudi. A cross-sectional analysis was conducted for 404 annual dose records in 16 nuclear medicine departments from 2016 to 2019. The monitoring of individual doses to the hands was performed using a Harshaw ring dosemeters. During the study period, the average annual equivalent doses per handled activity ranged from 0.21 to 0.41μSv/GBq. The estimated annual activities of radiopharmaceuticals ranged from 2 to 930MBq per exam. The hand dose averaged over the 4-year study period was determined to be 1.81±0.25mSv. The collective annual hand dose increased by 265% from 2016 to 2019.

Calculation Models of Radiopharmaceutical Activities of An Open 4-Compartment Model using The MIRD Method

An open 4-compartment model has been created which includes heart, thyroid, kidney, and liver organs using the MIRD method. Based on the compartment model, models of differential equations can be made as a function of the activities of the four organs. By ignoring the absorption function of radiopharmaceuticals from breast organs (absorption of radiopharmaceuticals by breast organs is very small) and using boundary conditions of the radiopharmaceutical activities function that enters or goes out of the heart organ has the same exponential factor function and ignores all disturbance, we get model of the activity equation is obtained from the heart, thyroid, kidney and liver organs. This activity equation model is only at the conceptual stage of a simple model through simple boundary conditions as well. This model is very difficult to apply to patients because there are many disturbing factors to the dose flow pattern such as organ function abnormalities, internal disease, internal and external disorders, etc.

Vplyv metodického postupu scintigrafie žalúdka na radiačnú záťaž pacientov

Introduction: Gastric emptying scintigraphy (GES) is a safe, noninvasive method for assessing the ability of the stomach to empty which has been used clinically for many years. It is considered as a “gold standard” to assess gastric emptying of both solids and liquids allowing assessment of early, mid and late emptying, each of which may be altered by pathology. The aim of the study was to analyse standard diagnostic approach and evaluate patients` radiation exposure, who underwent GES in Slovakia. Methods: A retrospective cohort study included 55 patients from 2 departments of nuclear medicine (department A, B). Patients’ radiation exposure was determined by dosimetry program IDAC-Dose2.1. The radiopharmaceutical 99mTc-DTPA, always with the same activity, was applied orally to patients at Department B. The applied activity of the radiopharmaceutical at GES was 185 MBq. The radiopharmaceutical 99mTc MAA, with various activity, was applied orally to patients at Department A. Results: According to ICRP60, the eff ective dose (ED) of every patient undergoing GES was 0.77 mSv and, according to ICRP103, the dose was 0.836 mSv at Department B. Patients at Department A were exposed to ionizing radiation with 5-times lower intensity, compared with patients at Department B. It was caused by radiopharmaceutical activity correction. The ED medians according to ICRP60, and according to ICRP103 were 0.167 mSv (range 0.105–0.208 mSv) and 0.181 mSv (range 0.113–0.226 mSv) at Department A, respectively. Discussion: Adequate correction of applied radiopharmaceutical activity is an essential part of GES guidelines and in accordance with ALARA principles. For the accuracy of GES examination, it is necessary to follow a standard 4-hour protocol and an approach which ensures full-featured utilization of the examination while decreasing patient`s radiation exposure. Conclusion: The results of our study show relatively low ED associated with GES, but also confi rm that the GES methodology significantly affects the patient`s radiation exposure

РЕЗУЛЬТАТЫ ДОКЛИНИЧЕСКИХ ИССЛЕДОВАНИЙ БЕЗОПАСНОСТИ РАДИОФАРМПРЕПАРАТА С 90Y ДЛЯ ВНУТРИАРТЕРИАЛЬНОЙ РАДИОЭМБОЛИЗАЦИИ ЗЛОКАЧЕСТВЕННЫХ НОВООБРАЗОВАНИЙ ПЕЧЕНИ

Purpose: Performing a safety study of a radiopharmaceutical drug with yttrium-90 for intra-arterial radioembolization of inoperable patients with primary and metastatic liver cancer.
 Material and methods: The developed radiopharmaceutical is a microspheres of human blood albumin with a diameter of 25-40 microns, modified with diethylenetriaminpentaacetic acid and labeled with 90Y radionuclide. The safety of the radiopharmaceutical was studied by the following indicators: acute toxicity of lyophilized reagents, subchronic toxicity of the radiopharmaceutical on two types of animals, local irritant effect of the radiopharmaceutical therapeutic activity in equivalent terms on laboratory animals, specific toxicity (allergizing effect) of lyophilized reagents for the preparation of a radiopharmaceutical drug. Female and male BALB/C mice, Wistar rats, chinchilla rabbits, and albino Guinea pigs were taken as experimental animals. All animals were obtained from certified laboratory animal nurseries.
 Results: During acute toxicity studies, the maximum safe dose of an inactive drug was determined. In terms of per person, it exceeds the intended dose for clinical use by almost 20 times. The study of the subchronic toxicity of the radiopharmaceutical did not reveal any symptoms of intoxication. The survival rate of the animals during the entire observation period was absolute. Standard behavior and appearance were observed in animals. The dynamics of body weight was positive, and the body temperature of rats and rabbits did not exceed the limits allowed. Samples of the finished dosage form of the drug did not have a local irritant effect. The solution of inactive components of lyophilized reagents for the preparation of a radiopharmaceutical drug did not have an allergenic effect in quantities ten times higher than the doses administered to a person.
 Conclusion: According to the results of preclinical studies, the radiopharmaceutical should be considered safe for use. The results of preclinical studies allow us to recommend the drug for clinical research.

Assessment Relation of Myocardial Detector Counts and Administered Activity of 99mTc-SestaMIBI in MPI: The Effects of Body Weight, BMI, and Gender.

In myocardial perfusion imaging, reducing the number of photons in images of obese patients causes poor image quality. To solve this problem, we need to inject the tracer according to the patients' weight. Therefore, this study aimed to investigate the relationship between myocardial photon counts with patients' weight, BMI, and gender. A total of 129 patients underwent myocardial perfusion imaging in a twoday stress-first protocol, but only rest images were included in this study. Multiplication factor <img src="/images/article-115470.png" /> was used to determine the amount of radiopharmaceutical activity injected into the patients. For evaluating the effect of gender, the photon counts of 22 female patients were also assessed when the breast tissue was pulled upward (Breast Up). The total myocardial detector counts in the raw images were calculated from the summation of 32 projections. A multiple linear regression test was used to simultaneously examine the effects of weight, BMI, and gender on photon counts. There was no significant relationship between photon counts and patients' weight (p=0.129) and BMI (0.406), but gender had significant effects on photon counts, and myocardial detector counts were found to be higher in males (p=0.00). There was a statistically significant difference between the images of Breast Up and Non-Breast Up, and myocardial detector counts were higher in the Breast Up imaging method (p=0.00). Using the bodyweight formula, the image quality was comparable in obese and lean patients, but myocardial detector counts were lower in females, and this formula needs to be adjusted according to the patient's gender.

Supplemental minimal-activity PET/CT to validate ambiguous findings with less than 1 mSv: Proof of concept.

Short-term follow-up examinations could verify ambiguous findings in PET/CT diagnostics, but are often avoided due to radiation and financial burdens. We demonstrate the feasibility of a focused, minimal-activity PET protocol as a supplemental examination for uncertain findings after standard PET/CT. After changing conditions, e.g. patient positioning, preparation and bypassing an interval as well as a targeted tracer change, an additional examination with less than 1mSv of additional radiation exposure was performed. Lowered administered activity of radiopharmaceuticals could be compensated by prolonged acquisition time, which was made possible by the limitation to a single body region. A sufficient visual and quantitative image quality of scans could be achieved. In all cases, the ambiguous finding could be clarified, so further diagnostic procedures or unnecessary interventions were avoided.

Body morphometry appropriate computational phantoms for dose and risk optimization in pediatric renal imaging with Tc-99m DMSA and Tc-99m MAG3

Current guidelines for administered activity (AA) in pediatric nuclear medicine imaging studies are based on a 2016 harmonization of the 2010 North American Consensus guidelines and the 2007 European Association of Nuclear Medicine pediatric dosage card. These guidelines assign AA scaled to patient body mass, with further constraints on maximum and minimum values of radiopharmaceutical activity. These guidelines, however, are not formulated based upon a rigor-ous evaluation of diagnostic image quality. In a recent study of the renal cortex imaging agent 99mTc-DMSA (Li Y et al 2019), body mass-based dosing guidelines were shown to not give the same level of image quality for patients of differing body mass. Their data suggest that patient girth at the level of the kidneys may be a better morphometric parameter to consider when selecting AA for renal nuclear medicine imaging. The objective of the present work was thus to develop a dedicated series of computational phantoms to support image quality and organ dose studies in pediatric renal imaging using 99mTc-DMSA or 99mTc-MAG3. The final library consists of 50 male and female phantoms of ages 0 to 15 years, with percentile variations (5th to 95th) in waist circumference (WC) at each age. For each phantom, nominal values of kidney volume, length, and depth were incorporated into the phantom design. Organ absorbed doses, detriment-weighted doses, and stochastic risks were assessed using ICRP reference biokinetic models for both agents. In Monte Carlo radiation transport simulations, organ doses for these agents yielded detriment-weighted dose coefficients (mSv/MBq) that were in general larger than current ICRP values of the effective dose coefficients (age and WC-averaged ratios of eDW/e were 1.40 for the male phantoms and 1.49 for the female phantoms). Values of risk index (ratio of radiation-induced to natural background cancer incidence risk x 100) varied between 0.062 (newborns) to 0.108 (15-year-olds) for 99mTc-DMSA and between 0.026 (newborns) to 0.122 (15-year-olds) for 99mTc-MAG3. Using tallies of photon exit fluence as a rough surrogate for uniform image quality, our study demonstrated that through body region-of-interest optimization of AA, there is the potential for further dose and risk reductions of between factors of 1.5 to 3.0 beyond simple weight-based dosing guidance.

An international multi-center investigation on the accuracy of radionuclide calibrators in nuclear medicine theragnostics

BackgroundPersonalized molecular radiotherapy based on theragnostics requires accurate quantification of the amount of radiopharmaceutical activity administered to patients both in diagnostic and therapeutic applications. This international multi-center study aims to investigate the clinical measurement accuracy of radionuclide calibrators for 7 radionuclides used in theragnostics: 99mTc, 111In, 123I, 124I, 131I, 177Lu, and 90Y.MethodsIn total, 32 radionuclide calibrators from 8 hospitals located in the Netherlands, Belgium, and Germany were tested. For each radionuclide, a set of four samples comprising two clinical containers (10-mL glass vial and 3-mL syringe) with two filling volumes were measured. The reference value of each sample was determined by two certified radioactivity calibration centers (SCK CEN and JRC) using two secondary standard ionization chambers. The deviation in measured activity with respect to the reference value was determined for each radionuclide and each measurement geometry. In addition, the combined systematic deviation of activity measurements in a theragnostic setting was evaluated for 5 clinically relevant theragnostic pairs: 131I/123I, 131I/124I, 177Lu/111In, 90Y/99mTc, and 90Y/111In.ResultsFor 99mTc, 131I, and 177Lu, a small minority of measurements were not within ± 5% range from the reference activity (percentage of measurements not within range: 99mTc, 6%; 131I, 14%; 177Lu, 24%) and almost none were outside ± 10% range. However, for 111In, 123I, 124I, and 90Y, more than half of all measurements were not accurate within ± 5% range (111In, 51%; 123I, 83%; 124I, 63%; 90Y, 61%) and not all were within ± 10% margin (111In, 22%; 123I, 35%; 124I, 15%; 90Y, 25%). A large variability in measurement accuracy was observed between radionuclide calibrator systems, type of sample container (vial vs syringe), and source-geometry calibration/correction settings used. Consequently, we observed large combined deviations (percentage deviation > ± 10%) for the investigated theragnostic pairs, in particular for 90Y/111In, 131I/123I, and 90Y/99mTc.ConclusionsOur study shows that substantial over- or underestimation of therapeutic patient doses is likely to occur in a theragnostic setting due to errors in the assessment of radioactivity with radionuclide calibrators. These findings underline the importance of thorough validation of radionuclide calibrator systems for each clinically relevant radionuclide and sample geometry.

The 2020 national diagnostic reference levels for nuclear medicine in Japan

The diagnostic reference levels (DRLs) are one of several effective tools for optimizing nuclear medicine examinations and reducing patient exposure. With the advances in imaging technology and alterations of examination protocols, the DRLs must be reviewed periodically. The first DRLs in Japan were established in 2015, and since 5 years have passed, it is time to review and revise the DRLs. We conducted a survey to investigate the administered activities of radiopharmaceuticals and the radiation doses of computed tomography (CT) in hybrid CT accompanied by single photon emission computed tomography (SPECT)/CT and positron emission tomography (PET)/CT. We distributed a Web-based survey to 915 nuclear medicine facilities throughout Japan and survey responses were provided by 256 nuclear medicine facilities (response rate 28%). We asked for the facility's median actual administered activity and median radiation dose of hybrid CT when SPECT/CT or PET/CT was performed for patients with standard habitus in the standard protocol of the facility for each nuclear medicine examination. We determined the new DRLs based on the 75th percentile referring to the 2015 DRLs, drug package inserts, and updated guidelines. The 2020 DRLs are almost the same as the 2015 DRLs, but for the relatively long-lived radionuclides, the DRLs are set low due to the changes in the Japanese delivery system. There are no items set higher than the previous values. Although the DRLs determined this time are roughly equivalent to the DRLs used in the US, overall they tend to be higher than the European DRLs. The DRLs of the radiation dose of CT in hybrid CT vary widely depending on each imaging site and the purpose of the examination.

177Lu Effect of Geometry Factors in Radionuclide Calibrator

The accuracy of radiopharmaceutical activity which will be administered to the patients is very important in nuclear medicine, especially in the case of therapeutical procedure. Hence, all safety aspects should be considered, including the standardization of the dose calibrator. From the reference, the accuracy of dose calibrator is influenced by various factors, such as the geometrical factors of the syringes or vials. The aim of this work was to investigate the effect of different container such as syringes and vials on the accuracy of dose calibrator. The initial work was done by preparing 5 cc glass ampoule and 1 cc syringes containing 177Lu. Both samples was measured using the Capintec CRC 7-BT dose calibrator. The ampoule and syringe activity was measured at the base of the chamber and 5 cm above the base of the chamber, respectively. The result shows that the correction factor was 2.5 % for the syringe and 1.03 % for the ampoule. The correction factor should be considered when the dose calibrator will be used for measuring the administered to the patient to get more accurate activity measurement and patient safety.

Pharmacokinetic model and calculation of absorbed doses in radionuclide therapy of thyroid cancer

Purpose. To create a model of pharmacokinetics of thyroid-stimulating radiopharmaceuticals (Na131I), to determine the transport constants of thyroid metabolism and excretion by comparing the model results with quantitative radiometric data of patients with thyroid cancer, as well as to calculate the threshold and therapeutic absorbed doses in the thyroid gland on the basis of this model taking into account the effects of ablation. Materials and methods. The principles and methods of pharmacokinetics (compartment simulation), method of Hooke-Jeeves for finding the minimum of function of several variables when determining the values of the parameters of communications between compartments using quantitative data radiometry of the thyroid tissue of five patients entered radiopharmaceutical, methods of calculation of absorbed doses was found through the process of modeling the cumulative activity of the radiopharmaceutical in the thyroid gland. Results. A two-compartment model of the kinetics of a thyroid-stimulating radiopharmaceutical was developed taking into account the radiation damage of thyroid tissue residual after thyroidectomy as a result of internal irradiation during radionuclide therapy. Kinetic curves of changes in radiopharmaceutical activity (time-activity curves) in the model compartments for five patients with thyroid cancer were obtained. On the basis of this model calculations of individual threshold and total absorbed doses in thyroid tissue are carried out. Conclusion. The developed pharmacokinetic model allows to describe the kinetics of radiopharmaceuticals in patients with thyroid cancer. On the Activity-time curves for thyroid tissue there is a characteristic fracture at the time of reaching the threshold dose and then a sharp decline due to the destruction of thyroid tissue as a result of the effects of ablation.

Quality assurance and quality control at dose calibrator to support nuclear medicine services

One of the most important factors in health services is the quality and speed of service. However, the speed of service must be supported by the quality of service. Quality is often used as a benchmark and differentiator for a health service. Therefore, all producers and providers of health services must looking for ways to maintain and improve their quality. In this paper quality assurance (QA) and quality control (QC) will be presented at the dose calibrator (DC) to support nuclear medicine services. DC is a very useful tool for measuring radiopharmaceutical activity / dose (which will be given to patients) for diagnostic or therapeutic purposes. For accurate measurements, DC must be calibrated routinely, must pay attention to electronic factors, statistical considerations, ion recombination, background radiation, the source and volume container effects, source position, source adsorption, pure beta transmitter measurements and the presence of contaminants. One of the successes of patient care in nuclear medicine (NM) is by giving accurate doses, according to the type of cancer, the volume and severity of cancer cells. Accurate doses can be achieved by implementing QA and QC at DC, which starts from the calibration stage, checks stability, linearity, and pays attention to parameters that can affect measurement. The aim is to ensure that the measurement results meet the requirements and quality standards set. There are 5 parameters that can support QC implementation, namely PC3M: Person, Chain, Machine, Material and Method. If one of these 5 parameters is missing then QC cannot be implemented.

EANM procedural guidelines for myocardial perfusion scintigraphy using cardiac-centered gamma cameras

An increasing number of Nuclear Medicine sites in Europe are using cardiac-centered gamma cameras for myocardial perfusion scintigraphy (MPS). Three cardiac-centered gamma cameras are currently the most frequently used in Europe: the D-SPECT (Spectrum Dynamics), the Alcyone (Discovery NM 530c and Discovery NM/CT 570c; General Electric Medical Systems), and the IQ-SPECT (Siemens Healthcare). The increased myocardial count sensitivity of these three cardiac-centered systems has allowed for a decrease in the activities of radiopharmaceuticals injected to patients for myocardial perfusion imaging and, consequently, radiation exposure of patients. When setting up protocols for MPS, the overall objective should be to maintain high diagnostic accuracy of MPS, while injecting the lowest activities reasonably achievable to reduce the level of radiation exposure of patient and staff. These guidelines aim at providing recommendations for acquisition protocols and image interpretation using cardiac-centered cameras. As each imaging system has specific design and features for image acquisition and analysis, these guidelines have been separated into three sections for each gamma camera system. These recommendations have been written by the members of the Cardiovascular Committee of EANM and were based on their own experience with each of these systems and on the existing literature.

Étude dosimétrique de préparations de médicaments radiopharmaceutiques au 68Ga

AimProduction of 68Ga-radiopharmaceuticals is a rapidly growing field in France. However, operators may already be involved in other radiopharmaceutical activities. It is thus necessary to know the exposure of this new activity. Material and methodsFor passive dosimetry, a radiophotoluminescent (RPL) dosimeter, a thermoluminescent (TLD) chip, 2 TLD rings and a passive dosimeter for crystalline were used. For active dosimetry, an extremity dosimeter and a whole body dosimeter were used. This study was performed during semi-automatized production of 68Ga-investigational medicinal products. Values were normalized to 500MBq manipulated (median activity using a 1850MBq 68Ga-generator), 60 radiosynthesis (maximum enrollment ability of our center) and 2 operators. A LB123 proportional counter was used for quantification of external exposition to 10MBq 68Ge and internal exposition by inhalation was theoretically assessed. 68Ga emission attenuation by collective protection equipments was also discussed. ResultsConsidering passive dosimetry, the equivalent dose to extremities was 21.75±0.34mSv, the whole-body effective dose was 0.189±0.011mSv and the dose to crystalline was 0.925±0.009mSv. Considering active dosimetry, the equivalent dose to extremities was 8,75±0.12mSv and the whole-body effective dose was 0,088±0.009mSv. Total exposure to 68Ge was 1.75μSv. ConclusionIn our hands, 68Ga is a directly transposable activity in radiopharmacies already equipped for 18F because of a dosimetry complying with regulatory limits and suitable radiation protection of collective equipments.

84. Ionization chamber calibration for 90Y at OPBG by the ENEA-INMRI portable TDCR

Purpose Short-lived beta-emitting radionuclides, such as 90Y, start to be commonly used in Nuclear Medicine (NM) for Molecular Radiotherapy (MRT). The instruments, such as Ionization Chambers (ICs), typically used in the NM departments for measuring the activity of radiopharmaceuticals need to be calibrated in order to meet the demands of the European Pharmacopoeia [1] . The OPBG IC was then calibrated for the 90Y by using the ENEA-INMRI portable TDCR counter [2] . Methods The 90 YCl 3 solution was kindly provided by Sirtex company. A set of 6 sources (2 in 10 mL UG + 20 mL glass vial, 2 in 10 mL H2O + plastic vial, 2 in 10 mL H2O + 20 mL glass vial with 20 mg and 40 mg of radioactive in each one) and 1 source in the OPBG IC vial geometry were prepared directly at OPBG to be measured by TDCR and IC devices. Results The achieved results show that, in the typical operative conditions of a hospital structure, the uncertainties in determining the IC calibration factor are less equal to 2%. Conclusions The paper highlights how the TDCR-Cherenkov technique, developed at ENEA-INMRI, allows to calibrate on site an IC in use at a Hospital structure. In particular, this technique turns out to be more practical, because the sources to be characterized in activity, for the IC calibration, can be prepared directly in water. The whole work was performed in the framework of the project “Metrology for clinical implementation of dosimetry in Molecular Radiotherapy” (MRTDosimetry) funded by the European Metrology Program for Innovation and Research (EMPIR) [3] .

OA109] Validation of a radio-guided surgery technique based on beta-radiation: Test on ex-vivo specimens

Purpose A very promising technique for radio-guided surgery (RGS) based on β -radiation is being developed. The lower background, with respect to the established approach with high penetrant γ radiation, can allow for a large diffusion of such a technique and extending the RGS to cases with a large uptake of surrounding healthy organs, such as abdominal and brain neoplastic disease or tumor of infancy. Methods To validate the β -RGS feasibility study, tests on ex-vivo specimens of brain meningioma and gastro-entero-pancreatic neuroendocrine tumors have been performed. These clinical cases were selected between the tumors known to express receptors to a β -emitting radio-tracer already in use in the clinical routine: 90Y-labelled DOTATOC. Voluntary patients were enrolled according to the standard uptake value (SUV) and the expected tumor-to-non-tumor ratios (TNR) estimated from PET/CT images after administration of 68 Ga-DOTATOC. All of them gave written informed consent to participate in the clinical trial, already approved by the Ethics Committee. After administration of a low activity (about 2.5 mCi) of 90Y-DOTATOC, the extracted ex-vivo specimens and the healthy tissue around the lesions were examined to assess the correlation between the counting rates measured by the developed β -detecting probe and the expected 90Y activity. Results All the neoplastic samples were correctly identified. A dependence of the counting rate both on the volume V and on the total activity of the sample were observed. Even injecting as low as 1.4 MBq/kg of radio-tracer, tumor remnants of 0.1 ml would be detectable in few seconds. Conclusions The results of the clinical tests showed the validity of the underlying assumptions and strengthening the feasibility studies already published. Small radiopharmaceutical activity is required to detect a tumor remnant as expected due to the low background rates. The negligible medical staff exposure was also confirmed.

A projection image database to investigate factors affecting image quality in weight-based dosing: application to pediatric renal SPECT

Balancing the tradeoff between radiation dose, acquisition duration and diagnostic image quality is essential for medical imaging modalities involving ionizing radiation. Lower administered activities to the patient can reduce absorbed dose, but can result in reduced diagnostic image quality or require longer acquisition durations. In pediatric nuclear medicine, it is desirable to use the lowest amount of administered radiopharmaceutical activity and the shortest acquisition duration that gives sufficient image quality for clinical diagnosis. However, diagnostic image quality is a complex function of patient factors including body morphometry. In this study, we present a digital population of 90 computational anatomic phantoms that model realistic variations in body morphometry and internal anatomy. These phantoms were used to generate a large database of projection images modeling pediatric SPECT imaging using a 99mTc-DMSA tracer. We used an analytic projection code that models attenuation, spatially varying collimator-detector response, and object-dependent scatter to generate the projections. The projections for each organ were generated separately and can be subsequently scaled by parameters extracted from a pharmacokinetics model to simulate realistic tracer biodistribution, including variations in uptake, inside each relevant organ or tissue structure for a given tracer. Noise-free projection images can be obtained by summing these individual organ projections and scaling by the system sensitivity and acquisition duration. We applied this database in the context of 99mTc-DMSA renal SPECT, the most common nuclear medicine imaging procedure in pediatric patients. Organ uptake fractions based on literature values and patient studies were used. Patient SPECT images were used to verify that the sum of counts in the simulated projection images was clinically realistic. For each phantom, 384 uptake realizations, modeling random variations in the uptakes of organs of interest, were generated, producing 34 560 noise-free projection datasets (384 uptake realizations times 90 phantoms). Noisy images modeling various count levels (corresponding to different products of acquisition duration and administered activity) were generated by appropriately scaling these images and simulating Poisson noise. Acquisition duration was fixed; six count levels were simulated corresponding to projection images acquired using 25%, 50%, 75%, 100%, 125%, and 150% of the original weight-based administrated activity as computed using the North American Guidelines (Gelfand et al 2011 J. Nucl. Med. 52 318–22). Combined, a total number of 207 360 noisy projection images were generated, creating a realistic projection database for use in renal pediatric SPECT imaging research. The phantoms and projection datasets were used to calculate three surrogate indices for factors affecting image quality: renal count density, average radius of rotation, and scatter-to-primary ratio. Differences in these indices were seen across the phantoms for dosing based on current guidelines, and especially for the phantom modeling the newborn. We also performed an image quality study using an anthropomorphic model observer that demonstrates that the weight-based dose scaling does not equalize image quality as measured by the area under the receiver-operating characteristics curve. These studies suggest that a dosing procedure beyond weight-based scaling of administered activities is required to equalize image quality in pediatric renal SPECT.