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Positron Emission Tomography (PET) in Oncology
Cancers, 2014
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.
Methodological considerations in quantification of oncological FDG PET studies
European Journal of Nuclear Medicine and Molecular Imaging, 2010
Purpose This review aims to provide insight into the factors that influence quantification of glucose metabolism by FDG PET images in oncology as well as their influence on repeated measures studies (i.e. treatment response assessment), offering improved understanding both for clinical practice and research. Methods Structural PubMed searches have been performed for the many factors affecting quantification of glucose metabolism by FDG PET. Review articles and references lists have been used to supplement the search findings.
Objectives: The use of dynamic positron emission tomography/computed tomography (dPET/CT) studies with [ 18 F]deoxyglucose (FDG) in oncological patients is limited and primarily confined to research protocols. A more widespread application is, however, desirable, and may help to assess small therapeutic effects early after therapy as well as to differentiate borderline differences between tumour and non-tumour lesions, e.g., lipomas versus low-grade liposarcomas. The aim is to present quantification approaches that can be used for the evaluation of dPET/CT series in combination with parametric imaging and to demonstrate the feasibility with regard to tumour diagnostics and therapy management. Methods: A 60-min data acquisition and short acquisition protocols (20-min dynamic series and a static image 60 min post injection) are discussed. A combination of a modified two-tissue compartment model and non-compartmental approaches from the chaos theory (fractal dimension of the timeactivity curves) are presented. Fused PET/CT images as well as regression-based parametric images fused with CT or with PET/standardised uptake value images are demonstrated for the exact placement of volumes of interest. Results: The two-tissue compartmental method results in the calculation of 5 kinetic parameters, the fractional blood volume V B (known also as the distribution volume), and the transport rates k 1 to k 4 . Furthermore, the influx according to Patlak can be calculated from the transport rates. The fractal dimension of the timeactivity curves describes the heterogeneity of the tracer distribution. The use of the regression-based parametric images of FDG helps to visualise the transport/ perfusion and the transport/phosphorylation-dependent FDG uptake, and adds a new dimension to the existing conventional PET or PET/CT images. Conclusions: More sophisticated quantification methods and dedicated software as well as high computational power and faster acquisition protocols can facilitate the assessment of dPET/CT, and may find use in clinical routine, in particular for the assessment of early therapeutic effects or new treatment protocols in combination with the new generation of PET/CT scanners.
Biases affecting the measurements of tumor-to-background activity ratio in PET
IEEE Transactions on Nuclear Science, 2002
The influence of various factors on the biases affecting tumor-to-background activity ratio (TBR) estimates in positron emission tomography (PET) was studied using analytical simulations of an anthropomorphic phantom. The impact of attenuation correction (AC) on TBR as a function of tumor location and tumor-to-background density ratio was studied. The TBR changes that would be observed when a tumor with uniform uptake turns to a tumor with nonuniform uptake due a necrotic process were characterized. Major parameters affecting the bias in TBR estimates were the tumor diameter, the TBR, whether AC had been performed and the spatial resolution of the PET scanner. Our results suggest that a necrotic process gets detectable if the necrotic volume is at least 50% of the total tumor volume for a necrosis-to-tumor activity ratio of 0.5. We discuss how our results regarding TBR biases translate into standardized uptake values biases.
EJNMMI physics, 2016
For tumour imaging with PET, the literature proposes to administer a patient-specific FDG activity that depends quadratically on a patient's body weight. However, a practical approach on how to implement such a protocol in clinical practice is currently lacking. We aimed to provide a practical method to determine a FDG activity formula for whole-body PET examinations that satisfies both the EANM guidelines and this quadratic relation. We have developed a methodology that results in a formula describing the patient-specific FDG activity to administer. A PET study using the NEMA NU-2001 image quality phantom forms the basis of our method. This phantom needs to be filled with 2.0 and 20.0 kBq FDG/mL in the background and spheres, respectively. After a PET acquisition of 10 min, a reconstruction has to be performed that results in sphere recovery coefficients (RCs) that are within the specifications as defined by the EANM Research Ltd (EARL). By performing reconstructions based on s...
2014
a b s t r a c t PET/MRI has recently been introduced onto the market after several years of research and development. The simple notion of combining the molecular capabilities of the PET and its different available radiotracers with the excellent tissue resolution of the MRI and wide range of multiparametric imaging techniques has generated great expectations upon the possible uses of this technology. Many challenges must be worked out. However, the most urgent one is the derivation of the MRI-based attenuation correction map. This is especially true because the PET/CT has already demonstrated a huge clinical impact within oncology, neurology and cardiology during its short existence. Despite these difficulties, research is being carried out at a rapid pace in the clinical setting in order to find areas in which the PET/MRI is superior to other existing imaging modalities. In the few initial publications found up to date that have analyzed its clinical role, areas have been identified where PET/CT can migrate to PET/MRI, even if only to suppress the CT scan's ionizing radiation. Nonetheless, there are many theoretical applications in which the PET/MRI can further improve the field of diagnostic imaging. In this article, we will review those applications, the evidence existing regarding the MRI and PET that support those premises as well as that which we have learned in the short period of one year with our experience using the PET/MRI.
The standardized uptake value (SUV) is the most commonly used parameter to quantify the intensity of radiotracer uptake in tumors. Previous studies suggested that measurements of 18 F-FDG accumulation in tissue might be affected by the image reconstruction method, but the clinical relevance of these findings has not been assessed. Methods: Phantom studies were performed and clinical whole-body 18 F-FDG PET images of 85 cancer patients were analyzed. All images were reconstructed using either filtered backprojection (FBP) with measured attenuation correction (MAC) or iterative reconstruction (IR) with segmented attenuation correction (SAC). In a subset of 15 patients, images were reconstructed using all 4 combinations of IRϩSAC, IRϩMAC, FBPϩSAC, and FBPϩMAC. For phantom studies, a sphere containing 18 F-FDG was placed in a waterfilled cylinder and the activity concentration of that sphere was measured in FBP and IR reconstructed images using all 4 combinations. Clinical studies were displayed simultaneously and identical regions of interest (ROIs, 50 pixels) were placed in liver, urinary bladder, and tumor tissue in both image sets. SUV max (maximal counts per pixel in ROI) and SUV avg (average counts per pixel) were measured. Results: In phantom studies, measurements from FBP images underestimated the true activity concentration to a greater degree than those from IR images (20% vs. 5% underestimation). In patient studies, SUV derived from FBP images were consistently lower than those from IR images in both normal and tumor tissue: Tumor SUV max with IRϩSAC was 9.6 Ϯ 4.5, with IRϩMAC it was 7.7 Ϯ 3.5, with FBPϩMAC it was 6.9 Ϯ 3.0, and with FBPϩSAC it was 8.6 Ϯ 4.1 (all P Ͻ 0.01 vs. IRϩSAC). Compared with IRϩSAC, SUV from FBPϩMAC images were 25%-30% lower. Similar discrepancies were noted for liver and bladder. Discrepancies between measurements became more apparent with increasing 18 F-FDG concentration in tissue. Conclusion: SUV measurements in whole-body PET studies are affected by the applied methods for both image reconstruction and attenuation correction. This should be considered when serial PET studies are done in cancer patients. Moreover, if SUV is used for tissue characterization, different cutoff values should be applied, de-pending on the chosen method for image reconstruction and attenuation correction.
The role of positron emission tomography in oncology and other whole-body applications
Seminars in Nuclear Medicine, 1992
Imaging and quantifying biochemical and physiological processes with PET clearly has major potential significance for all organ systems and many disease states. Although the full utility and potential of emerging new applications of PET in organs other than the heart and brain must be demonstrated in basic and clinical research studies, the rapidly accumulating aggregate experience in oncology in particular, and in other organ systems and disease states as well, indicares that PET is now truly becoming a modality of both clinical and investigative use for the body as a whole as well as for specific organ systems. Wholebody PET FDG imaging (Fig 9) illustrates the potential of biochemical imaging to map the distribution of cancer throught the body. With the growing list of radiopharmacautical and quantitative techniques applicable to cancer studies with PET, this field will continue to realize significant growth. Copyright 9 1992 by W.B. Saunders Company p OSITRON emission tomography (PET) began primarily as a research tool for biochemical and physiological investigations of the brain and heart. 1 PET has also been established as a clinical modality for selected diseases of the heart and brain, and it is also becoming more widely used in other organ systems and disease states. In addition to the brain and heart, organ systems investigated with positron emitting radiopharmaceuticals include the lungs, 2-5 thyroid, 6 liver, 7 and skeletal system, 8 among others. An emerging application of PET of potentially major significance for both research and clinical practice is in the field of oncology. 9,1~ Because of the often disseminated distribution of cancer, PET imaging methods capable of including large regions of the body in the field of view are advantageous. 14 Additionally, it is necessary to understand how biochemical and physiological characteristics of organ systems affect
The Use of FDG-PET to Target Tumors by Radiotherapy
Strahlentherapie und Onkologie, 2010
Fluorodeoxyglucose positron emission tomography (FDG-PET) plays an increasingly important role in radiotherapy, beyond staging and selection of patients. Especially for non-small cell lung cancer, FDG-PET has, in the majority of the patients, led to the safe decrease of radiotherapy volumes, enabling radiation dose escalation and, experimentally, redistribution of radiation doses within the tumor. In limited-disease small cell lung cancer, the role of FDG-PET is emerging. For primary brain tumors, PET based on amino acid tracers is currently the best choice, including high-grade glioma. This is especially true for low-grade gliomas, where most data are available for the use of 11 C-MET (methionine) in radiation treatment planning. For esophageal cancer, the main advantage of FDG-PET is the detection of otherwise unrecognized lymph node metastases. In Hodgkin's disease, FDG-PET is essential for involved-node irradiation and leads to decreased irradiation volumes while also decreasing geographic miss. FDG-PET's major role in the treatment of cervical cancer with radiation lies in the detection of para-aortic nodes that can be encompassed in radiation fields. Besides for staging purposes, FDG-PET is not recommended for routine radiotherapy delineation purposes. It should be emphasized that using PET is only safe when adhering to strictly standardized protocols.