PET and PET/CT in pediatric oncology

Treatment-related mortality among children with cancer in Denmark during 2001-2021

BACKGROUND

Survival of children with cancer has markedly improved over recent decades, largely due to intensified treatment regimes. The intensive treatment may, however, result in fatal complications. In this retrospective cohort study, we assessed temporal variation in the incidence of treatment-related death and associated risk factors among children diagnosed with cancer in Denmark during 2001-2021.

METHOD

Among all children diagnosed with first incident cancer before age 15 years recorded in the Danish Childhood Cancer Register (n = 3,255), we estimated cumulative incidence of treatment-related death (death in the absence of progressive cancer) within 5 years from diagnosis using Aalen-Johansen estimators and assessed associated risk factors using Cox regression.

RESULTS

Among all 3,255 children with cancer, 93 (20% of all 459 deaths) died from treatment. Of these treatment-related deaths, 39 (42%) occurred within 3 months of diagnosis. The 5-year cumulative incidences of treatment-related death were 3.3% during 2001-2010 and 2.5% during 2011-2021 (p = 0.20). During 2011-2021, treatment-related deaths accounted for more than half of all deaths among children with haematological cancers. Risk factors varied according to cancer group and included female sex, age below 1 year at diagnosis, disease relapse, stem cell transplantation, central nervous system involvement, and metastasis at diagnosis.

INTERPRETATION

Despite increasing treatment intensities, the incidence of treatment-related death has remained stable during the past 20 years in Denmark. Still, clinical attention is warranted to prevent treatment-related deaths, particularly among children with haematological cancers. Patient characteristics associated with increased treatment-related death risk support patient-specific treatment approaches to avoid these fatalities.

A third of the radiotracer dose: two decades of progress in pediatric [18F]fluorodeoxyglucose PET/CT and PET/MR imaging

OBJECTIVES

To assess the evolution of administered radiotracer activity for F-18-fluorodeoxyglucose (18F-FDG) PET/CT or PET/MR in pediatric patients (0-16 years) between years 2000 and 2021.

METHODS

Pediatric patients (≤ 16 years) referred for 18F-FDG PET/CT or PET/MR imaging of the body during 2000 and 2021 were retrospectively included. The amount of administered radiotracer activity in megabecquerel (MBq) was recorded, and signal-to-noise ratio (SNR) was measured in the right liver lobe with a 4 cm3 volume of interest as an indicator for objective image quality. Descriptive statistics were computed.

RESULTS

Two hundred forty-three children and adolescents underwent a total of 466 examinations. The median injected 18F-FDG activity in MBq decreased significantly from 296 MBq in 2000-2005 to 100 MBq in 2016-2021 (p < 0.001), equaling approximately one-third of the initial amount. The median SNR ratio was stable during all years with 11.7 (interquartile range [IQR] 10.7-12.9, p = 0.133).

CONCLUSIONS

Children have benefited from a massive reduction in the administered 18F-FDG dose over the past 20 years without compromising objective image quality.

CLINICAL RELEVANCE STATEMENT

Radiotracer dose was reduced considerably over the past two decades of pediatric F-18-fluorodeoxyglucose PET/CT and PET/MR imaging highlighting the success of technical innovations in pediatric PET imaging.

KEY POINTS

• The evolution of administered radiotracer activity for F-18-fluorodeoxyglucose (18F-FDG) PET/CT or PET/MR in pediatric patients (0-16 years) between 2000 and 2021 was assessed. • The injected tracer activity decreased by 66% during the study period from 296 megabecquerel (MBq) to 100 MBq (p < 0.001). • The continuous implementation of technical innovations in pediatric hybrid 18F-FDG PET has led to a steady decrease in the amount of applied radiotracer, which is particularly beneficial for children who are more sensitive to radiation.

Revising and exploring the variations in methodologies for establishing the diagnostic reference levels for paediatric PET/CT imaging

PET-computed tomography (PET/CT) is a hybrid imaging technique that combines anatomical and functional information; to investigate primary cancers, stage tumours, and track treatment response in paediatric oncology patients. However, there is debate in the literature about whether PET/CT could increase the risk of cancer in children, as the machine is utilizing two types of radiation, and paediatric patients have faster cell division and longer life expectancy. Therefore, it is essential to minimize radiation exposure by justifying and optimizing PET/CT examinations and ensure an acceptable image quality. Establishing diagnostic reference levels (DRLs) is a crucial quantitative indicator and effective tool to optimize paediatric imaging procedures. This review aimed to distinguish and acknowledge variations among published DRLs for paediatric patients in PET/CT procedures. A search of relevant articles was conducted using databases, that is, Embase, Scopus, Web of Science, and Medline, using the keywords: PET-computed tomography, computed tomography, PET, radiopharmaceutical, DRL, and their synonyms. Only English and full-text articles were included, with no limitations on the publication year. After the screening, four articles were selected, and the review reveals different DRL approaches for paediatric patients undergoing PET/CT, with primary variations observed in patient selection criteria, reporting of radiation dose values, and PET/CT equipment. The study suggests that future DRL methods for paediatric patients should prioritize data collection in accordance with international guidelines to better understand PET/CT dose discrepancies while also striving to optimize radiation doses without compromising the quality of PET/CT images.

Pediatric Imaging Using PET/MR Imaging

PET/MR imaging is a one-stop shop technique for pediatric diseases allowing not only an accurate clinical assessment of tumors at staging and restaging but also the diagnosis of neurologic, inflammatory, and infectious diseases in complex cases. Moreover, applying PET kinetic analyses and sequences such as diffusion-weighted imaging as well as quantitative analysis investigating the relationship between disease metabolic activity and cellularity can be applied. Complex radiomics analysis can also be performed.

Diagnostic and management roles of FDG PET/CT imaging in post-transplant lympho-proliferation in pediatric heart transplantation

BACKGROUND

Post-transplant lymphoproliferative disorder (PTLD) is a serious complication of pediatric heart transplant (PHTx). 18F-FDG PET/CT has been used to differentiate early lympho-proliferation from more advanced PTLD. We report our experience with PET/CT in the management of PTLD following PHTx.

METHODS

This was a retrospective study of 100 consecutive PHTx recipients at our institution between 2004 and 2018. Patients who underwent PET/CT or conventional CT scans to evaluate for PTLD or high Epstein-Barr viral load were included.

RESULTS

Males, eight females. Median age at transplant was 3.5 months (IQR = 1.5-27.5). Median age at PTLD diagnosis was 13.3 years (IQR = 9.2-16.1). Median time between transplant and PTLD diagnosis was 9.5 (IQR = 4.5-15) years. Induction agents were used in 12 patients (50%): Thymoglobulin (N = 9), anti-IL2 (N = 2), and Rituximab (N = 1). Eighteen patients (75%) had PET/CT, of whom 14 had 18FDG-avid PTLD. Six had conventional CT. Nineteen patients (79.2%) had diagnostic biopsy confirmation of PTLD, and 5 (20.8%) had excisional biopsies. Two patients had Hodgkin's lymphoma; nine had monomorphic PTLD; eight had polymorphic PTLD; five were classified as other. Nine patients had monomorphic PTLD, including seven with diffuse large cell lymphoma (DLBC) and one with T cell lymphoma. The majority (16/24) had multi-site involvement at PTLD diagnosis, and PET/CT showed that 31.3% (5/16) had easily accessible subcutaneous nodes. Seventeen patients (overall survival 71%) underwent successful treatment without recurrence of PTLD. Of seven deaths (7/24, 29%), five had DLBC lymphoma, one had polymorphic PTLD and one had T-cell lymphoma.

CONCLUSION

PET-CT allowed simultaneous anatomical and functional assessment of PTLD lesions, while guiding biopsy. In patients with multiple lesions, PET/CT revealed the most prominent and active lesions, improving diagnostic accuracy.

The Impact of PET/CT on Paediatric Oncology

This review paper will discuss the use of positron emission tomography/computed tomography (PET/CT) in paediatric oncology. Functional imaging with PET/CT has proven useful to guide treatment by accurately staging disease and limiting unnecessary treatments by determining the metabolic response to treatment. 18F-Fluorodeoxyglucose (2-[18F]FDG) PET/CT is routinely used in patients with lymphoma. We highlight specific considerations in the paediatric population with lymphoma. The strengths and weaknesses for PET/CT tracers that compliment Meta-[123I]iodobenzylguanidine ([123I]mIBG) for the imaging of neuroblastoma are summarized. 2-[18F]FDG PET/CT has increasingly been used in the staging and evaluation of disease response in sarcomas. The current recommendations for the use of PET/CT in sarcomas are given and potential future developments and highlighted. 2-[18F]FDG PET/CT in combination with conventional imaging is currently the standard for disease evaluation in children with Langerhans-cell Histiocytosis (LCH) and the non-LCH disease spectrum. The common pitfalls of 2-[18F]FDG PET/CT in this setting are discussed.

Changing Role of PET/CT in Cancer Care With a Focus on Radiotherapy

Positron emission tomography (PET) integrated with computed tomography (CT) has brought revolutionary changes in improving cancer care (CC) for patients. These include improved detection of previously unrecognizable disease, ability to identify oligometastatic status enabling more aggressive treatment strategies when the disease burden is lower, its use in better defining treatment targets in radiotherapy (RT), ability to monitor treatment responses early and thus improve the ability for early interventions of non-responding tumors, and as a prognosticating tool as well as outcome predicting tool. PET/CT has enabled the emergence of new concepts such as radiobiotherapy (RBT), radioimmunotherapy, theranostics, and pharmaco-radiotherapy. This is a rapidly evolving field, and this primer is to help summarize the current status and to give an impetus to developing new ideas, clinical trials, and CC outcome improvements.

SNMMI Procedure Standard/EANM Practice Guideline on Pediatric 18F-FDG PET/CT for Oncology 1.0

The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote the science, technology, and practical application of nuclear medicine. The European Association of Nuclear Medicine (EANM) is a professional nonprofit medical association founded in 1985 to facilitate communication worldwide among individuals pursuing clinical and academic excellence in nuclear medicine. SNMMI and EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine.

The SNMMI and EANM will periodically put forth new standards/guidelines for nuclear medicine practice to help advance the science of nuclear medicine and improve service to patients. Existing standards/guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each standard/guideline, representing a policy statement by the SNMMI/EANM, has undergone a thorough consensus process, entailing extensive review. The SNMMI and EANM recognize that the safe and effective use of diagnostic nuclear medicine imaging requires particular training and skills, as described in each document. These standards/guidelines are educational tools designed to assist practitioners in providing appropriate and effective nuclear medicine care for patients. These guidelines are consensus documents, and are not inflexible rules or requirements of practice. They are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, the SNMMI and the EANM cautions against the use of these standards/guidelines in litigation in which the clinical decisions of a practitioner are called into question.

The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by medical professionals taking into account the unique circumstances of each case. Thus, there is no implication that action differing from what is laid out in the standards/guidelines, standing alone, is below standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the standards/guidelines when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the standards/guidelines.

The practice of medicine involves not only the science, but also the art of dealing with the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible for general guidelines to consistently allow for an accurate diagnosis to be reached or a particular treatment response to be predicted. Therefore, it should be recognized that adherence to these standards/guidelines will not ensure a successful outcome. All that should be expected is that the practitioner follows a reasonable course of action, based on their level of training, the current knowledge, the available resources, and the needs/context of the particular patient being treated.

PET and computerized tomography (CT) have been widely used in oncology. ¹⁸F-FDG is the most common radiotracer used for PET imaging. The purpose of this document is to provide imaging specialists and clinicians guidelines for recommending, performing, and interpreting ¹⁸F-FDG PET/CT in pediatric patients in oncology. There is not a high level of evidence for all recommendations suggested in this paper. These recommendations represent the expert opinions of experienced leaders in this field. Further studies are needed to have evidence-based recommendations for the application of ¹⁸F-FDG PET/CT in pediatric oncology. These recommendations should be viewed in the context of good practice of nuclear medicine and are not intended to be a substitute for national and international legal or regulatory provisions.

Clinical pediatric positron emission tomography/magnetic resonance program: a guide to successful implementation

Children with malignancies undergo recurrent imaging as part of tumor diagnosis, staging and therapy response assessment. Simultaneous positron emission tomography (PET) and magnetic resonance (MR) allows for decreased radiation exposure and acts as a one-stop shop for disease in which MR imaging is required. Nevertheless, PET/MR is still less readily available than PET/CT across institutions. This article serves as a guide to successful implementation of a clinical pediatric PET/MR program based on our extensive clinical experience. Challenges include making scanners more affordable and increasing patient throughput by decreasing total scan time. With improvements in workflow and robust acquisition protocols, PET/MR imaging is expected to play an increasingly important role in pediatric oncology.

Pediatric airway tumors: A report from the International Network of Pediatric Airway Teams (INPAT)

OBJECTIVE

Primary tracheobronchial tumors (PTTs) are rare heterogeneous lesions arising from any part of the tracheobronchial tree. Nonspecific symptoms may lead to delayed diagnosis that requires more aggressive surgical treatment. An analysis of cases collected by the International Network of Pediatric Airway Team was undertaken to ensure proper insight into the behavior and management of PTTs.

METHODS

Patients <18 years of age with a histological confirmation of PTT diagnosed from 2000 to 2015 were included in this multicenter international retrospective study. Medical records, treatment modalities, and outcomes were analyzed. The patient presentation, tumor management, and clinical course were compared between malignant and benign histotypes. Clinical and surgical variables that might influence event-free survival were considered.

RESULTS

Among the 78 children identified, PTTs were more likely to be malignant than benign; bronchial carcinoid tumor (n = 31; 40%) was the most common histological subtype, followed by inflammatory myofibroblastic tumor (n = 19; 25%) and mucoepidermoid carcinoma (n = 15; 19%). Regarding symptoms at presentation, wheezing (P = 0.001) and dyspnea (P = 0.03) were more often associated with benign growth, whereas hemoptysis was more frequently associated with malignancy (P = 0.042). Factors that significantly worsened event-free survival were age at diagnosis earlier than 112 months (P = 0.0035) and duration of symptoms lasting more than 2 months (P = 0.0029).

CONCLUSION

The results of this international study provide important information regarding the clinical presentation, diagnostic workup, and treatment of PTTs in children, casting new light on the biological behavior of PTTs to ensure appropriate treatments.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:E243-E251, 2020.

FDG PET in response evaluation of bulky masses in paediatric Hodgkin's lymphoma (HL) patients enrolled in the Italian AIEOP-LH2004 trial

PURPOSE

We present the results of an investigation of the role of FDG PET in response evaluation of bulky masses in paediatric patients with Hodgkin's lymphoma (HL) enrolled in the Italian AIEOP-LH2004 trial.

METHODS

We analysed data derived from 703 patients (388 male, 315 female; mean age 13 years) with HL and enrolled in 41 different Italian centres from March 2004 to September 2012, all treated with the AIEOP-LH2004 protocol. The cohort comprised 309 patients with a bulky mass, of whom 263 were evaluated with FDG PET at baseline and after four cycles of chemotherapy. Responses were determined according to combined functional and morphological criteria. Patients were followed up for a mean period of 43 months and for each child we calculated time-to-progression (TTP) and relapse rates considering clinical monitoring, and instrumental and histological data as the reference standard. Statistical analyses were performed for FDG PET and morphological responses with respect to TTP. Multivariate analysis was used to define independent predictive factors.

RESULTS

Overall, response evaluation revealed 238 PET-negative patients (90.5%) and 25 PET-positive patients (9.5%), with a significant difference in TTP between these groups (mean TTP: 32.67 months for negative scans, 23.8 months for positive scans; p < 0.0001, log-rank test). In the same cohort, computed tomography showed a complete response (CR) in 85 patients (32.3%), progressive disease (PD) in 6 patients (2.3%), and a partial response (PR) in 165 patients (62.7%), with a significant difference in TTP between patients with CR and patients with PD (31.1 months and 7.9 months, respectively; p < 0.001, log-rank test). Similarly, there was a significant difference in relapse rates between PET-positive and PET-negative patients (p = 0000). In patients with PR, there was also a significant difference in TTP between PET-positive and PET-negative patients (24.6 months and 34.9 months, respectively; p < 0.0001). In the multivariate analysis with correction for multiple testing, only the PET result was an independent predictive factor in both the entire cohort of patients and the subgroup showing PR on CT (p < 0.01).

CONCLUSION

After four cycles of chemotherapy, FDG PET response assessment in paediatric HL patients with a bulky mass is a good predictor of TTP and disease outcome. Moreover, in patients with a PR on CT, PET was able to differentiate those with a longer TTP. In paediatric HL patients with a bulky mass and in patients with a PR on CT, response on FDG PET was an independent predictive factor.

Radiation absorbed dose estimates for 18F-BPA PET

Background Boron neutron capture therapy (BNCT) is a molecular radiation therapy approach based on the ¹⁰B (n, α) ⁷Li nuclear reaction in cancer cells. In BNCT, delivery of ¹⁰B in the form of 4-borono-phenylalanine conjugated with fructose (BPA-fr) to the cancer cells is important. The PET tracer 4-borono-2-18F-fluoro-phenylalanine (FBPA) has been used to predict the accumulation of BPA-fr before BNCT. Purpose To determine the biodistribution and dosimetric parameters in 18F-BPA PET/CT studies. Material and Methods Human biokinetic data were obtained during clinical 18F-BPA PET studies between February and June 2015 at one institution. Nine consecutive patients were studied prospectively. The internal radiation dose was calculated on the basis of radioactivity data from blood, urine, and normal tissue of the heart, liver, spleen, kidney, and other parts of the body at each time point using OLINDA/EXM1.1 program. We compared our calculations with published 18F-FDG data. Results Adult patients (3 men, 3 women; age range, 28-68 years) had significantly smaller absorbed doses than pediatric patients (3 patients; age range, 5-12 years) ( P = 0.003). The mean effective dose was 57% lower in adult patients compared with pediatric patients. Mean effective doses for 18F-BPA were 25% lower than those for 18F-FDG presented in International Commission of Radiation Protection (ICRP) publication 106. Conclusion We found significant differences in organ absorbed doses for 18F-BPA against those for 18F-FDG presented in ICRP publication 106. Mean effective doses for 18F-BPA were smaller than those for 18F-FDG in the publication by 0.5-38% (mean difference, 25%).

Primary osseous Burkitt lymphoma with nodal and intracardiac metastases in a child

Burkitt lymphoma (BL) is the most frequent non-Hodgkin lymphoma in pediatric patients, accounting for approximately 34% of the cases of lymphoma in children. This subtype of non-Hodgkin lymphoma was first described in 1958 as a monoclonal proliferation of B cell lymphocytes. Cardiac involvement of BL in association with osseous compromise and lymphadenopathy is rare and poorly documented. We report a case of femur primary BL in an 8-year-old boy with metastatic cardiac involvement, retroperitoneal and iliofemoral lymphadenopathy, and hepatosplenomegaly. We highlight the diagnostic challenge in a patient with clinical nonspecific findings and systemic disease.

PET/CT in paediatric malignancies - An update

¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a well-established imaging modality in adult oncological practice. Its role in childhood malignancies needs to be discussed as paediatric malignancies differ from adults in tumor subtypes and they have different tumor biology and FDG uptake patterns. This is also compounded by smaller body mass, dosimetric restrictions, and physiological factors that can affect the FDG uptake. It calls for careful planning of the PET study, preparing the child, the parents, and expertise of nuclear physicians in reporting pediatric positron emission tomography/computed tomography (PET/CT) studies. In a broad perspective, FDG-PET/CT has been used in staging, assessment of therapy response, identifying metastases and as a follow-up tool in a wide variety of pediatric malignancies. This review outlines the role of PET/CT in childhood malignancies other than hematological malignancies such as lymphoma and leukemia.

Physiological Activity of Spinal Cord in Children: An 18F-FDG PET-CT Study

STUDY DESIGN

Retrospective study.

OBJECTIVE

To evaluate, in a pediatric population, F-Fluoro-deoxy-glucose (F-FDG) metabolic activity of normal spinal cord and to assess the correlation with demographic, clinical, and environmental variables.

SUMMARY OF BACKGROUND DATA

F-FDG uptake of normal spinal cord is variable in children. The knowledge of physiological metabolism of spinal cord is essential to distinguish normal from pathological findings by positron emission tomography-computed tomography (PET-CT).

METHODS

We retrospectively evaluated F-FDG positron emission tomography-computed tomography scans from a total of 167 pediatric patients (97 males; 3.9-18.9 yr) divided into 4 age groups (0-4.9 yr, 5-9.9 yr, 10-14.9 yr, and 15-18.9 yr), excluding those submitted to previous or recent therapeutic procedures influencing spinal cord metabolism or with central nervous system diseases. Spinal cord was divided into 3 levels (C1-C7; D1-D6; and D7-L1), and maximum standardized uptake value (SUVmax) of each cord level was measured. Correlations between SUVmax and spinal cord level, age, body weight, sex, type of disease, and season were statistically assessed.

RESULTS

Median SUVmax was similar and significantly (P < 0.01) higher at C1-C7 and D7-L1 levels than at D1-D6 level and it significantly (P < 0.01) increased with age in all spinal cord levels. A positive and significant association between SUVmax and body weight, female sex, and Hodgkin lymphoma was found. No significant association with season was observed. By multivariate analysis, only weight and female sex remained significant.

CONCLUSION

Knowledge of physiological F-FDG spinal cord activity in children is essential for a correct interpretation of positron emission tomography-computed tomography, especially in oncologic pediatric patients to avoid potential pitfalls.

LEVEL OF EVIDENCE

N/A.

2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography/computed tomography imaging in paediatric oncology

Positron emission tomography (PET) is a minimally invasive technique which has been well validated for the diagnosis, staging, monitoring of response to therapy, and disease surveillance of adult oncology patients. Traditionally the value of PET and PET/computed tomography (CT) hybrid imaging has been less clearly defined for paediatric oncology. However recent evidence has emerged regarding the diagnostic utility of these modalities, and they are becoming increasingly important tools in the evaluation and monitoring of children with known or suspected malignant disease. Important indications for 2-deoxy-2-(¹⁸F)fluoro-D-glucose (FDG) PET in paediatric oncology include lymphoma, brain tumours, sarcoma, neuroblastoma, Langerhans cell histiocytosis, urogenital tumours and neurofibromatosis type I. This article aims to review current evidence for the use of FDG PET and PET/CT in these indications. Attention will also be given to technical and logistical issues, the description of common imaging pitfalls, and dosimetric concerns as they relate to paediatric oncology.

Positron Emission Tomography (PET) in Oncology

Since its introduction in the early nineties as a promising functional imaging technique in the management of neoplastic disorders, FDG-PET, and subsequently FDG-PET/CT, has become a cornerstone in several oncologic procedures such as tumor staging and restaging, treatment efficacy assessment during or after treatment end and radiotherapy planning. Moreover, the continuous technological progress of image generation and the introduction of sophisticated software to use PET scan as a biomarker paved the way to calculate new prognostic markers such as the metabolic tumor volume (MTV) and the total amount of tumor glycolysis (TLG). FDG-PET/CT proved more sensitive than contrast-enhanced CT scan in staging of several type of lymphoma or in detecting widespread tumor dissemination in several solid cancers, such as breast, lung, colon, ovary and head and neck carcinoma. As a consequence the stage of patients was upgraded, with a change of treatment in 10%-15% of them. One of the most evident advantages of FDG-PET was its ability to detect, very early during treatment, significant changes in glucose metabolism or even complete shutoff of the neoplastic cell metabolism as a surrogate of tumor chemosensitivity assessment. This could enable clinicians to detect much earlier the effectiveness of a given antineoplastic treatment, as compared to the traditional radiological detection of tumor shrinkage, which usually takes time and occurs much later.

Potential Pediatric Applications of PET/MR

Medical imaging with multimodality and whole-body technologies has continuously improved in recent years. The advent of combined modalities such as PET/CT and PET/MR offers new tools with an exact fusion of molecular imaging and high-resolution anatomic imaging. For noninvasive pediatric diagnostics, molecular imaging and whole-body MR have become important, especially in pediatric oncology. Because it has a lower radiation exposure than PET/CT, combined PET/MR is expected to be of special use in pediatric diagnostics. This review focuses on possible pediatric applications of PET/MR hybrid imaging, particularly pediatric oncology and neurology but also the diagnosis of infectious or inflammatory diseases.

Pediatric radiation dosimetry for positron-emitting radionuclides using anthropomorphic phantoms

PURPOSE

Positron emission tomography (PET) plays an important role in the diagnosis, staging, treatment, and surveillance of clinically localized diseases. Combined PET/CT imaging exhibits significantly higher sensitivity, specificity, and accuracy than conventional imaging when it comes to detecting malignant tumors in children. However, the radiation dose from positron-emitting radionuclide to the pediatric population is a matter of concern since children are at a particularly high risk when exposed to ionizing radiation.

METHODS

The authors evaluate the absorbed fractions and specific absorbed fractions (SAFs) of monoenergy photons/electrons as well as S-values of 9 positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Rb-82, Y-86, and I-124) in 48 source regions for 10 anthropomorphic pediatric hybrid models, including the reference newborn, 1-, 5-, 10-, and 15-yr-old male and female models, using the Monte Carlo N-Particle eXtended general purpose Monte Carlo transport code.

RESULTS

The self-absorbed SAFs and S-values for most organs were inversely related to the age and body weight, whereas the cross-dose terms presented less correlation with body weight. For most source/target organ pairs, Rb-82 and Y-86 produce the highest self-absorbed and cross-absorbed S-values, respectively, while Cu-64 produces the lowest S-values because of the low-energy and high-frequency of electron emissions. Most of the total self-absorbed S-values are contributed from nonpenetrating particles (electrons and positrons), which have a linear relationship with body weight. The dependence of self-absorbed S-values of the two annihilation photons varies to the reciprocal of 0.76 power of the mass, whereas the self-absorbed S-values of positrons vary according to the reciprocal mass.

CONCLUSIONS

The produced S-values for common positron-emitting radionuclides can be exploited for the assessment of radiation dose delivered to the pediatric population from various PET radiotracers used in clinical and research settings. The mass scaling method for positron-emitters can be used to derive patient-specific S-values from data of reference phantoms.

(18)F-FDG PET as a single imaging modality in pediatric neuroblastoma: comparison with abdomen CT and bone scintigraphy

OBJECTIVE

The purpose of this study was to evaluate the diagnostic performance of (18)F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG PET) as a single imaging agent in neuroblastoma in comparison with other imaging modalities.

METHODS

A total of 30 patients with pathologically proven neuroblastoma who underwent FDG PET for staging were enrolled. Diagnostic performance of FDG PET and abdomen CT was compared in detecting soft tissue lesions. FDG PET and bone scintigraphy (BS) were compared in bone metastases. Maximal standardized uptake value (SUVmax) of primary or recurrent lesions was calculated for quantitative analysis.

RESULTS

Tumor FDG uptake was detected in 29 of 30 patients with primary neuroblastoma. On initial FDG PET, SUVmax of primary lesions were lower in early stage (I-II) than in late stage (III-IV) (3.03 vs. 5.45, respectively, p = 0.019). FDG PET was superior to CT scan in detecting distant lymph nodes (23 vs. 18 from 23 lymph nodes). FDG PET showed higher accuracy to identify bone metastases than BS both on patient-based analyses (100 vs. 94.4 % in sensitivity, 100 vs. 77.8 % in specificity), and on lesion-based analyses (FDG PET: 203 lesions, BS: 86 lesions). Sensitivity and specificity of FDG PET to detect recurrence were 87.5 % and 93.8, respectively.

CONCLUSION

FDG PET was superior to CT in detecting distant LN metastasis and to BS in detecting skeletal metastasis in neuroblastoma. BS might be eliminated in the evaluation of neuroblastoma when FDG PET is performed.

Is there a role for PET-CT and SPECT-CT in pediatric oncology?

During the last decade, hybrid imaging has revolutionized nuclear medicine. Multimodal camera systems, integrating positron emission tomography (PET) or single photon emission computed tomography (SPECT) with computed tomography (CT) now combine the contrast provided by tumor-avid radioactive drugs with the anatomic precision of CT. While PET-CT to a great extent has replaced single-modality PET in adult oncology, the use of PET-CT in children has been controversial, since even the lowest dose CT protocols adds approximately 2 mSv to the radiation dose of about 4 mSv from the PET-study with F-18-fluorodeoxyglucose (F-18-FDG). The article describes the current techniques used, discusses radiation doses and gives an overview of current indications for PET-CT and SPECT-CT in children. Hybrid imaging with a tumor-avid radioactive drug provides extremely high contrast between tumor and background tissues, while the CT component helps to locate the lesion anatomically. Currently both PET-CT and SPECT-CT play a role in pediatric oncology; PET-CT using F-18-FDG particularly for staging and follow-up of lymphoma and brain cancer, bone and soft tissue sarcomas; SPECT-CT with I-123-metaiodobenzylguanidine (MIBG) for tumors of the sympathetic nervous system such as neuroblastoma and pheochromocytoma while the remaining neuroendocrine tumors are imaged with radioactively labeled somatostatin analogues. To reduce radiation dose, a low-dose CT in combination with ultrasound and/or magnetic resonance imaging for the assessment of anatomy is often preferred.

PET and MR imaging: the odd couple or a match made in heaven?

PET and MR imaging are modalities routinely used for clinical and research applications. Integrated scanners capable of acquiring PET and MR imaging data in the same session, sequentially or simultaneously, have recently become available for human use. In this article, we describe some of the technical advances that allowed the development of human PET/MR scanners; briefly discuss methodologic challenges and opportunities provided by this novel technology; and present potential oncologic, cardiac, and neuropsychiatric applications. These examples range from studies that might immediately benefit from PET/MR to more advanced applications on which future development might have an even broader impact.

PET/MR in children. Initial clinical experience in paediatric oncology using an integrated PET/MR scanner

Use of PET/MR in children has not previously been reported, to the best of our knowledge. Children with systemic malignancies may benefit from the reduced radiation exposure offered by PET/MR. We report our initial experience with PET/MR hybrid imaging and our current established sequence protocol after 21 PET/MR studies in 15 children with multifocal malignant diseases. The effective dose of a PET/MR scan was only about 20% that of the equivalent PET/CT examination. Simultaneous acquisition of PET and MR data combines the advantages of the two previously separate modalities. Furthermore, the technique also enables whole-body diffusion-weighted imaging (DWI) and statements to be made about the biological cellularity and nuclear/cytoplasmic ratio of tumours. Combined PET/MR saves time and resources. One disadvantage of PET/MR is that in order to have an effect, a significantly longer examination time is needed than with PET/CT. In our initial experience, PET/MR has turned out to be an unexpectedly stable and reliable hybrid imaging modality, which generates a complementary diagnostic study of great additional value.

Synthesis and high performance of magnetofluorescent polyelectrolyte nanocomposites as MR/near-infrared multimodal cellular imaging nanoprobes

Here, we describe an easy but robust chemical strategy to synthesize high-performance magnetic resonance (MR)/near-infrared (NIR) multimodal imaging nanoprobes. Poly(γ-glutamic acid) was used for the convenient phase transfer of MnFe(2)O(4) nanoparticles dispersed in organic solvents into aqueous solutions and facilitated further ionic gelation with poly(l-lysine). During the gelation process, MnFe(2)O(4) nanoparticulate satellites were encapsulated in the ionic nanocomplex, which induced synergistic magnetism and resulted in huge T(2) relaxivity (r(2)). The positively charged outer surfaces were assembled with other negatively charged NIR emitting fluorescent nanocrystals and enabled the highly efficient delivery of the magnetofluorescent polyelectrolyte nanocomposites (MagFL-PEN) into cancer cells. The enhancement of negative contrast of MagFL-PEN at 2 μg/mL concentration was similar to that of Resovist at 20 μg/mL concentration. The NIR fluorescence microscopy images of the MagFL-PEN-labeled cells even at 12.5 pM were able to be clearly observed. The labeling efficiency of MagFL-PEN was approximately 65-fold higher compared to that of the commercialized fluorescent nanocrystals, only after 3 h incubation period, even at the test concentration (100 pM). Due to the high-performance capabilities both in materials properties and cell labeling efficiency, the MagFL-PEN is expected to be used as a highly efficient MR/NIR dual-modality imaging nanoprobe in the detection of cancer cells and monitoring of therapeutic cells in vivo.

PET-CT in children: where is it appropriate?

The use of PET/PET-CT is a rapidly growing area of imaging and research in the care of children. Until recently, diagnostic imaging methods have provided either anatomical or functional assessment. The development of fused imaging modalities, such as PET-CT or PET-MRI, now provides the opportunity for simultaneously providing both anatomical and functional or physiological assessment. This review will discuss current established uses of PET-CT, possible uses and potential research investigations in the use of this modality in the pediatric population. The focus of this paper will be its use in children being treated for non-central nervous system and non-cardiac disorders.

Brown fat distribution in the chest wall of infants-normal appearance, distribution and evolution on CT scans of the chest

BACKGROUND

While reviewing chest CT scans of infants, we repeatedly observed hyperdense enhancing tissue in the chest wall that is not well described in radiology literature.

OBJECTIVE

This study was undertaken to describe the imaging features of this tissue in chest walls of infants.

MATERIALS AND METHODS

CT scans of the chest conducted on all infants between April 2008 and October 2009 were retrospectively reviewed. CT studies with any deviation from normal radiation or contrast dose or those with chest wall anatomical distortion were excluded.

RESULTS

One hundred eighty-eight infants were scanned, with 202 MDCTs, of which 180 (89.1%) received contrast agent. Fifty-four of 180 (30%) cases revealed focal areas of hyperdensity in various locations. All positive cases ranged between 2 days and 9 months of age. The areas of distribution of hyperdensity had excellent correlation with known areas of brown fat in the chest wall, known from nuclear medicine studies, and hence we concluded these to represent the same.

CONCLUSION

Brown fat in the chest wall can be seen as enhancing tissue on contrast CT scans done on infants. This is a normal morphological component with the brown fat converting to normal fat. It is important to recognize it in the chest wall of infants to avoid misinterpretation.

PET/CT: Current status in India

PET/CT is a new modality with integration of PET and CT systems. In India, since December 2004 there has been a steady increase in the number of imaging systems. From stand-alone PET/CT systems with on-site cyclotrons, mostly in the government sector, the modality has matured to such an extent that, today, the majority of the PET/CT scanners and cyclotrons are in the private setup; also, scanners situated in different locations (and even different cities) share the isotope produced from one cyclotron. This shows how much this field has developed and reflects the confidence of the end users. The current status of PET/CT in India is indeed healthy and heartening and the future certainly looks promising.

Matched pairs dosimetry: 124I/131I metaiodobenzylguanidine and 124I/131I and 86Y/90Y antibodies

The technological advances in imaging and production of radiopharmaceuticals are driving an innovative way of evaluating the targets for antineoplastic therapies. Besides the use of imaging to better delineate the volume of external beam radiation therapy in oncology, modern imaging techniques are able to identify targets for highly specific medical therapies, using chemotherapeutic drugs and antiangiogenesis molecules. Moreover, radionuclide imaging is able to select targets for radionuclide therapy and to give the way to in vivo dose calculation to target tissues and to critical organs. This contribution reports the main studies published on matched pairs dosimetry with (124)I/(131)I- and (86)Y/(90)Y-labelled radiopharmaceuticals, with an emphasis on metaiodobenzylguanidine (MIBG) and monoclonal antibodies.

18F-FDG PET/CT and 123I-metaiodobenzylguanidine imaging in high-risk neuroblastoma: diagnostic comparison and survival analysis

The aim of our study was to evaluate prospectively the diagnostic performance and prognostic significance of (18)F-FDG PET/CT in comparison with (123)I-metaiodobenzylguanidine ((123)I-MIBG) imaging in patients with high-risk neuroblastoma.

METHODS

Twenty-eight patients with refractory or relapsed high-risk neuroblastoma (16 male and 12 female patients; age range, 2-45 y; median age, 7.5 y) were simultaneously evaluated with (18)F-FDG PET/CT and (123)I-MIBG imaging before treatment with high-dose (131)I-MIBG. We compared the 2 methods in mapping tumor load, according to the extent of disease and intensity of positive lesions identified in each patient. Separate comparisons were performed for the soft-tissue and bone-bone marrow components of tumor burden. Survival analysis was performed to assess the prognostic significance of (18)F-FDG and (123)I-MIBG imaging parameters.

RESULTS

(18)F-FDG PET/CT results were positive in 24 of 28 (86%) patients, whereas (123)I-MIBG imaging results were positive in all patients. (18)F-FDG was superior in mapping tumor load in 4 of 28 (14%) patients, whereas (123)I-MIBG was better in 12 of 28 (43%) patients. In the remaining 12 (43%) patients, no major differences were noted between the 2 modalities. (18)F-FDG PET/CT missed 5 cases of bone-bone marrow disease, 4 cases of soft-tissue disease, and 6 cases of skull involvement that were positive on (123)I-MIBG scans. Cox regression and Kaplan-Meier survival curves showed that the group of patients (4/28) in whom (18)F-FDG was superior to (123)I-MIBG had a significantly lower survival rate than the others. Tumoral avidity for (18)F-FDG (maximum standardized uptake value) and extent of (18)F-FDG-avid bone-bone marrow disease were identified as adverse prognostic factors.

CONCLUSION

(123)I-MIBG imaging is superior to (18)F-FDG PET/CT in the assessment of disease extent in high-risk neuroblastoma. However, (18)F-FDG PET/CT has significant prognostic implications in these patients.

Evaluation of 18F-FDG PET and MRI associations in pediatric diffuse intrinsic brain stem glioma: a report from the Pediatric Brain Tumor Consortium

The purpose of this study was to assess (18)F-FDG uptake in children with a newly diagnosed diffuse intrinsic brain stem glioma (BSG) and to investigate associations with progression-free survival (PFS), overall survival (OS), and MRI indices.

METHODS

Two Pediatric Brain Tumor Consortium (PBTC) therapeutic trials in children with newly diagnosed BSG were designed to test radiation therapy combined with molecularly targeted agents (PBTC-007: phase I/II study of gefitinib; PBTC-014: phase I/II study of tipifarnib). Baseline brain (18)F-FDG PET scans were obtained in 40 children in these trials. Images were evaluated by consensus between 2 PET experts for intensity and uniformity of tracer uptake. Associations of (18)F-FDG uptake intensity and uniformity with both PFS and OS, as well as associations with tumor MRI indices at baseline (tumor volume on fluid-attenuated inversion recovery, baseline intratumoral enhancement, diffusion and perfusion values), were evaluated.

RESULTS

In most of the children, BSG (18)F-FDG uptake was less than gray-matter uptake. Survival was poor, irrespective of intensity of (18)F-FDG uptake, with no association between intensity of (18)F-FDG uptake and PFS or OS. However, hyperintense (18)F-FDG uptake in the tumor, compared with gray matter, suggested poorer survival rates. Patients with (18)F-FDG uptake in 50% or more of the tumor had shorter PFS and OS than did patients with (18)F-FDG uptake in less than 50% of the tumor. There was some evidence that tumors with higher (18)F-FDG uptake were more likely to show enhancement, and when the diffusion ratio was lower, the uniformity of (18)F-FDG uptake appeared higher.

CONCLUSION

Children with BSG for which (18)F-FDG uptake involves at least half the tumor appear to have poorer survival than children with uptake in less than 50% of the tumor. A larger independent study is needed to verify this hypothesis. Intense tracer uptake in the tumors, compared with gray matter, suggests decreased survival. Higher (18)F-FDG uptake within the tumor was associated with enhancement on MR images. Increased tumor cellularity as reflected by restricted MRI diffusion may be associated with increased (18)F-FDG uniformity throughout the tumor.

PET imaging for pediatric oncology: an assessment of the evidence

Positron emission tomography (PET) has shown potential benefits when used in therapeutic clinical trials for children with cancer. However, existing trials are limited in scope with small numbers of patients and varied observations, making accurate conclusions about the usefulness of PET scanning impossible. This review examines PET and its applications in pediatric oncology. While evidence is limited, there appears to be a basis for rigorous evaluation of this imaging modality before widespread application without validation from clinical trials.

Diffuse reflectance spectroscopy for in vivo pediatric brain tumor detection

The concept of using diffuse reflectance spectroscopy to distinguish intraoperatively between pediatric brain tumors and normal brain parenchyma at the edge of resection cavities is evaluated using an in vivo human study. Diffuse reflectance spectra are acquired from normal and tumorous brain areas of 12 pediatric patients during their tumor resection procedures, using a spectroscopic system with a handheld optical probe. A total of 400 spectra are acquired at the rate of 33 Hz from a single investigated site, from which the mean spectrum and the standard deviation are calculated. The mean diffuse reflectance spectra collected are divided into the normal and the tumorous categories in accordance with their corresponding results of histological analysis. Statistical methods are used to identify those spectral features that effectively separated the two tissue categories, and to quantify the spectral variations induced by the motion of the handheld probe during a single spectral acquisition procedure. The results show that diffuse reflectance spectral intensities between 600 and 800 nm are effective in terms of differentiating normal cortex from brain tumors. Furthermore, probe movements induce large variations in spectral intensities (i.e., larger standard deviation) between 400 and 600 nm.

(18)F-FDG PET in Pediatric Lymphomas: A Comparison with Conventional Imaging

This study reports on our experience with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in pediatric patients affected by Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL). We studied 20 pediatric subjects (12 males, 8 females; mean age, 10 years; range, 6 months to 14 years) with malignant lymphoma (9 HD, 11 NHL) for a 4-year period of time. Overall, 45 PET scans were performed: 7 at disease presentation and 38 for evaluation of response to therapy or follow-up study. All PET results were compared with conventional imaging (CI), mainly computed tomography (CT) and/or magnetic resonance imaging (MRI), and supported by clinical follow-up and/or histologic data. In 18 of 20 patients, PET findings correctly identified the status of disease. Two (2) subjects (respectively, 1 HD and 1 NHL, both at follow-up) resulted falsely positive: 1 due to prominent thymic uptake, and the other due to nonspecific inflammation. Of 45 scans, PET findings were consistent with clinical follow-up and other CI data in 43 cases (16 true-positive and 27 true-negative results) and resulted falsely positive in the remaining 2 scans. On a lesion-by-lesion basis (overall, 153 lesions: 84 nodal and 69 extranodal), we found a concordance between CI and PET findings in 25 nodal (29.8%) and in 22 extranodal sites (32%). PET was more accurate than CI, as it identified active disease in 1 patient negative at CI and excluded relapse in 6 patients with inconclusive CI and in 2 patients with a falsely positive CI. Overall, PET sensitivity and specificity was 100% and 93% versus 94% sensitivity and 72.4% specificity for CI. This comparative study shows FDG PET to be more accurate than CI in evaluating children with lymphoma. Our data also confirms that (18)F-FDG PET may show false-positive findings.