Administered Activities in Pediatric Nuclear Medicine and the Impact of the 2010 North American Consensus Guidelines on General Hospitals in the United States

Radiation Dose to Pediatric Patients From Radiopharmaceuticals

Nuclear medicine provides methods and techniques in that has benefited pediatric patients and their referring physicians for over 40 years. Nuclear medicine provides qualitative and quantitative information about overall and regional function of organs, systems, and lesions in the body. This involves applications in many organ systems including the skeleton, the brain, the kidneys and the heart as well as in the diagnosis and treatment of cancer. The practice of nuclear medicine requires the administration of radiopharmaceuticals which expose the patient to very low levels of ionizing radiation. Advanced approaches in the estimation of radiation dose from the internal distribution of radiopharmaceuticals in patients of various sizes and shapes have been developed in the past 20 years. Although there is considerable uncertainty in the estimation of the risk of adverse health effects from radiation at the very low exposure levels typically associated with nuclear medicine, some considers it prudent to be more cautious when applied to children as they are generally considered to be at higher risk than adults. Standard guidelines for administered activities for nuclear medicine procedures in children have been established including the North American consensus guidelines and the Paediatric Dosage Card developed by the European Association of Nuclear Medicine. As we move into the future, these guidelines would likely be reviewed in response to changes in clinical practice, a better understanding of radiation dosimetry as applied to children as well as new clinical applications, new advancements in the field with respect to both instrumentation and image reconstruction and processing.

Preparation and Logistic Considerations in Performing PET and PET/Computed Tomography in Pediatric Patients

It is good for the nuclear medicine technologist to be aware of the normal variants and the appearance of a good-quality scan. The primary responsibility as a nuclear medicine technologist is to provide an optimal quality scan that maximizes the reading physician's ability to correctly interpret while using current radiation safety practices as the best possible experience is created for patients and families. Combining the radiation safety aspects (nuclear) with how care is provided (medicine) and the use of the most recent equipment (technology) is what defines a nuclear medicine technologist.

Paediatric nuclear medicine practice: an international survey by the IAEA

PURPOSE

The International Atomic Energy Agency (IAEA) decided to initiate a survey to evaluate the current status of the practice of paediatric nuclear medicine worldwide, with the focus mainly on low and middle-income countries specifically in Latin America, Eastern Europe, Africa and Asia. This investigation sought to determine if the practice in paediatric nuclear medicine in these countries differed from that indicated by the survey of the Nuclear Medicine Global Initiative (NMGI) and if nuclear medicine practitioners were following established paediatric nuclear medicine guidelines.

METHODS

A total of 133 institutes took part in the survey from 62 different IAEA member states within Africa (29), Asia (39), Europe (29) and Latin America (36). The four most frequent conventional (single-photon) nuclear medicine procedures were 99mTc labelled MDP, DSMA, MAG3 and pertechnetate thyroid scans. In addition, 46 centres provided data on FDG PET/CT, including exposure data for the CT component. Nearly half of the sites (48%) perform less than 200 paediatric nuclear medicine studies per year, while 11% perform more than 1000 such studies per year.

RESULTS

Administered activities largely exceeded the recommendations for most of the sites for DMSA, MAG3 and pertechnetate, while compliance with international standards was somehow better for MDP studies. For FDG PET, the results were more uniform than for conventional nuclear medicine procedures. However, the use of CT in PET/CT for paediatric nuclear medicine revealed a high variability and, in some cases, high, dose-length product (DLP) values. This observation indicates that further attention is warranted for optimizing clinical practice in FDG PET/CT.

CONCLUSIONS

Overall, in most parts of the world, efforts have been undertaken to comply either with the EANM dosage card or with the North American Consensus Guidelines. However, variability in the practice of paediatric nuclear medicine still exists. The results of this survey provide valuable recommendations for a path towards global standardization of determining the amount of activity to be administered to children undergoing nuclear medicine procedures.

Is True Whole-Body 18F-FDG PET/CT Required in Pediatric Lymphoma? An IAEA Multicenter Prospective Study

Guidelines recommend true whole-body ¹⁸F-FDG PET/CT scans from vertex to toes in pediatric lymphoma patients, although this suggestion has not been validated in large clinical trials. The objective of the study was to evaluate the incidence and clinical impact of lesions outside the "eyes to thighs" regular field of view (R-FOV) in ¹⁸F-FDG PET/CT staging (sPET) and interim (iPET) scans in pediatric lymphoma patients. Methods: True whole-body sPET and iPET scans were prospectively obtained in pediatric lymphoma patients (11 worldwide centers). Expert panel central review of sPET and iPET scans were evaluated for lymphoma lesions outside the R-FOV and clinical relevance of these findings. Results: A total of 610 scans were obtained in 305 patients. The sPET scans did not show lesions outside the R-FOV in 91.8% of the patients, whereas in 8.2% patients the sPET scans demonstrated lesions also outside the R-FOV (soft tissue, bone, bone marrow, and skin); however, the presence of these lesions did not change the clinical stage of any patient and did not affect treatment decision. Among the 305 iPET scans, there were no new positive ¹⁸F-FDG-avid lesions outside the R-FOV, when compared with their paired sPET scans. A single lesion outside the R-FOV on iPET occurred in 1 patient (0.3%), with the primary lesion diagnosed in the femur on sPET that persisted on iPET. Conclusion: The identification of additional lesions outside the R-FOV (eyes to thighs) using ¹⁸F-FDG PET/CT has no impact in the definition of the clinical stage of disease and minimal impact in the treatment definition of patients with pediatric lymphoma. As so, R-FOV for both sPET and iPET scans could be performed.

Investigation of the relation between administered dose and image quality for pediatric 99mTc-DMSA renal scintigraphy: clinical study applying the JSNM (Japanese Society of Nuclear Medicine) pediatric dosage card : The Japanese Society of Nuclear Medicine Technology (JSNMT), the Optimization of Imaging Technique Committee for Pediatric Nuclear Medicine Studies

PURPOSE

In 2013, the Japanese Society of Nuclear Medicine (JSNM) announced consensus guidelines for pediatric nuclear medicine. These JSNM guidelines proposed use of lower administered doses compared with traditionally determined doses, which were estimated from age, weight or body surface area (BSA) based on the administered dose for adults in Japan. When the JSNM guidelines are used, the relationship between this recommended administered dose and image quality remains unclear. In this study, we clarified the relationship between administered dose and image quality for pediatric ^99mTc-DMSA renal scan retrospectively, and verified the diagnosable image quality with the recommended administered dose of the JSNM guidelines.

MATERIALS AND METHODS

Data from 7 pediatric patients who underwent ^99mTc-DMSA dynamic renal scans according to the guidelines' recommended doses were collected. Scan frame rate was 1 frame/min, and scan time was up to 8 min. Eight images, which had different acquired time periods from 1 min to 8 min were prepared by adding each frame. Nine nuclear medicine specialists determined 8 images with different acquired times as diagnosable or undiagnosable. A region of interest (ROI) with 50% thresholds was placed on each kidney of every image. Coefficient of variation (CV) was calculated by dividing the standard deviation (σ) by the mean counts (µ) of each ROI (CV = σ/µ × 100). ^99mTc-DMSA renal scans (total of 2821 cases) that were performed previously in collaboration with 6 hospitals were collected, and CVs of these images were calculated in all cases. These 2821 cases were separated into 5 groups for every 10 kg weight; i.e., (1) less than 10 kg, (2) 10-19.9 kg, (3) 20-29.9 kg, (4) 30-39.9 kg, and (5) above 40 kg. Regression line of each group was analyzed in relation to the CV and administered dose. The CV at the point of intersection with the recommended dose range from the guideline was determined for each group. This CV value was considered as the estimated CV of the image obtained when the recommended dose of the guideline was used. Thus, if the CV was equal to or less than the estimated CV value, then the diagnostic image quality was deemed satisfactory.

RESULTS

Average CV of the lower limit of diagnosable images in 7 cases as determined by 9 nuclear medicine specialists was 19.9%. Estimated CV was 21.2-24.2% in the group weighing < 10 kg (group 1), 19.9-20.6% in the group weighing > 10 kg and < 20 kg (group 2), 19.6% in group weighing > 20 kg and < 30 kg (group 3), 19.4-19.5% in the group weighing > 30 kg and < 40 kg (group 4), and 19.8% in the group weighing > 40 kg (group 5). The estimated CVs from groups 1 and 2 with weight < 20 kg exceeded 19.9%.

CONCLUSIONS

Although ^99mTc-DMSA renal scan can be carried out using the guidelines' recommended dose with conventional image acquisition time in patients weighing 20 kg or more, those < 20 kg need consideration for a longer image acquisition time to obtain diagnosable images.

Radionuclide Imaging of Infection and Inflammation in Children: a Review

With the exception of radiolabeled monoclonal antibodies, antibody fragments and radiolabeled peptides which have seen little application in the pediatric population, the nuclear medicine imaging procedures used in the evaluation of infection and inflammation are the same for both adults and children. These procedures include (1) either a two- or a three-phase bone scan using technetium-99m methylene diphosphonate; (2) Gallium 67-citrate; (3) in vitro radiolabeled white blood cell imaging (using ¹¹¹Indium-oxine or ^99mTechnetium hexamethyl-propylene-amine-oxime-labeled white blood cells); and (4) hybrid imaging with ¹⁸F-FDG. But children are not just small adults. Not only are the disease processes encountered in children different from those in adults, but there are developmental variants that can mimic, but should not be confused with, pathology. This article discusses some of the differences between adults and children with osteomyelitis, illustrates several of the common developmental variants that can mimic disease, and, finally, focuses on the increasing use of ¹⁸F-FDG PET/CT in the diagnosis and response monitoring of children with infectious and inflammatory processes. The value of and need for pediatric specific imaging protocols are reviewed.

Effects of body habitus on internal radiation dose calculations using the 5-year-old anthropomorphic male models

Computational phantoms are commonly used in internal radiation dosimetry to assess the amount and distribution pattern of energy deposited in various parts of the human body from different internal radiation sources. Radiation dose assessments are commonly performed on predetermined reference computational phantoms while the argument for individualized patient-specific radiation dosimetry exists. This study aims to evaluate the influence of body habitus on internal dosimetry and to quantify the uncertainties in dose estimation correlated with the use of fixed reference models. The 5-year-old IT'IS male phantom was modified to match target anthropometric parameters, including body weight, body height and sitting height/stature ratio (SSR), determined from reference databases, thus enabling the creation of 125 5-year-old habitus-dependent male phantoms with 10th, 25th, 50th, 75th and 90th percentile body morphometries. We evaluated the absorbed fractions and the mean absorbed dose to the target region per unit cumulative activity in the source region (S-values) of F-18 in 46 source regions for the generated 125 anthropomorphic 5-year-old hybrid male phantoms using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code and calculated the absorbed dose and effective dose of five ¹⁸F-labelled radiotracers for children of various habitus. For most organs, the S-value of F-18 presents stronger statistical correlations with body weight, standing height and sitting height than BMI and SSR. The self-absorbed fraction and self-absorbed S-values of F-18 and the absorbed dose and effective dose of ¹⁸F-labelled radiotracers present with the strongest statistical correlations with body weight. For ¹⁸F-Amino acids, ¹⁸F-Brain receptor substances, ¹⁸F-FDG, ¹⁸F-L-DOPA and ¹⁸F-FBPA, the mean absolute effective dose differences between phantoms of different habitus and fixed reference models are 11.4%, 11.3%, 10.8%, 13.3% and 11.4%, respectively. Total body weight, standing height and sitting height have considerable effects on human internal dosimetry. Radiation dose calculations for individual subjects using the most closely matched habitus-dependent computational phantom should be considered as an alternative to improve the accuracy of the estimates.

Optimization of Pediatric PET/CT

PET/CT, the most common form of hybrid imaging, has transformed oncologic imaging and is increasingly being used for nononcologic applications as well. Performing PET/CT in children poses unique challenges. Not only are children more sensitive to the effects of radiation than adults but, following radiation exposure, children have a longer postexposure life expectancy in which to exhibit adverse radiation effects. Both the PET and CT components of the study contribute to the total patient radiation dose, which is one of the most important risks of the study in this population. Another risk in children, not typically encountered in adults, is potential neurotoxicity related to the frequent need for general anesthesia in this patient population. Optimizing pediatric PET/CT requires making improvements to both the PET and the CT components of the procedure while decreasing the potential for risk. This can be accomplished through judicious performance of imaging, the use of recommended pediatric ¹⁸fluorine-2-fluoro-2-deoxy-d-glucose (¹⁸F-FDG) administered activities, thoughtful selection of pediatric-specific CT imaging parameters, careful patient preparation, and use of appropriate patient immobilization. In this article, we will review a variety of strategies for radiation dose optimization in pediatric ¹⁸F-FDG-PET/CT focusing on these processes. Awareness of and careful selection of pediatric-specific CT imaging parameters designed for appropriate diagnostic, localization, or attenuation correction only CT, in conjunction with the use of recommended radiotracer administered activities, will help to ensure image quality while limiting patient radiation exposure. Patient preparation, an important determinant of image quality, is another focus of this review. Appropriate preparative measures are even more crucial in children in whom there is a higher incidence of brown fat, which can interfere with study interpretation. Finally, we will discuss measures to improve the patient experience, the resource use, the departmental workflow, and the diagnostic performance of the study through the use of appropriate technology, all in the context of minimizing procedure-related risks.

Minimally invasive biomarkers of general anesthetic-induced developmental neurotoxicity

The association of general anesthesia with developmental neurotoxicity, while nearly impossible to study in pediatric populations, is clearly demonstrable in a variety of animal models from rodents to nonhuman primates. Nearly all general anesthetics tested have been shown to cause abnormal brain cell death in animals when administered during periods of rapid brain growth. The ability to repeatedly assess in the same subjects adverse effects induced by general anesthetics provides significant power to address the time course of important events associated with exposures. Minimally-invasive procedures provide the opportunity to bridge the preclinical/clinical gap by providing the means to more easily translate findings from the animal laboratory to the human clinic. Positron Emission Tomography or PET is a tool with great promise for realizing this goal. PET for small animals (microPET) is providing valuable data on the life cycle of general anesthetic induced neurotoxicity. PET radioligands (annexin V and DFNSH) targeting apoptotic processes have demonstrated that a single bout of general anesthesia effected during a vulnerable period of CNS development can result in prolonged apoptotic signals lasting for several weeks in the rat. A marker of cellular proliferation (FLT) has demonstrated in rodents that general anesthesia-induced inhibition of neural progenitor cell proliferation is evident when assessed a full 2weeks after exposure. Activated glia express Translocator Protein (TSPO) which can be used as a marker of presumed neuroinflammatory processes and a PET ligand for the TSPO (FEPPA) has been used to track this process in both rat and nonhuman primate models. It has been shown that single bouts of general anesthesia can result in elevated TSPO expression lasting for over a week. These examples demonstrate the utility of specific PET tracers to inform, in a minimally-invasive fashion, processes associated with general anesthesia-induced developmental neurotoxicity. The fact that PET procedures are also used clinically suggests an opportunity to confirm in humans what has been repeatedly observed in animals.