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- Clinical PET and PET/CT - Principles and Applications | E. Edmund Kim | Springer
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Although some modern treatment planning systems model the dose buildup empirically, the parameters used to model the buildup should be validated. Moreover, because only a few high-dose fractions are used, tissue responses based on conventional fractionation schemes may not be valid. Consequently, models of dose response, such as those that generate biologically equivalent doses, may be more appropriate for evaluating hypofractionated treatment plans.
David D. Hou, John A. Carrino, in Pain Management , The most significant advancement in nuclear medicine recently is positron emission tomography PET and the combination of PET CT scanners with important implications for oncology, especially for soft tissue neoplasms or postoperative cancer patients. PET is a nuclear medicine technique that only recently has been widely used in clinical oncology in part because in order to have ready availability of the agents an on-site cyclotron was required.
PET uses short-lived positron-emitting radioisotopes that annihilate to form two photons that have trajectories approximately degrees apart at a particular energy level keV.
The coincidental detection of these photons by a ring detector is reconstructed via a filtered back projection similar to CT to form images of tracer distribution. FDG accumulation reflects the rate of glucose utilization in a tissue because FDG is transported into a tissue by the same mechanisms of glucose transport and trapped in a tissue as FDGphosphate, which is a poor substrate for the further enzyme systems of glycolysis or glycogen storage. The use of FDG in evaluation of the musculoskeletal system is based on increased glycolytic rate in pathologic tissues.
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Thus, PET has proven to be the gold standard in metabolic imaging. FDG provides a means of quantitating the glucose metabolism, with the amount of tracer accumulation reflecting the glucose metabolism: high-grade malignancies tend to have higher rates of glycolysis than do low-grade malignancies and benign lesions; therefore, high-grade malignancies have greater uptake of FDG than that of low-grade or benign lesions. PET, as a metabolic imaging technique, demonstrates advantages over and complements structural imaging methods and also shows differences from conventional nuclear medicine, all of which have led to its growth in clinical applications in recent years.
PET applications are evolving, but now it is approved for the diagnosis, staging, and restaging of many common malignancies and has shown efficacy for the detection of osseous metastasis from several malignancies, including lung carcinoma, breast carcinoma, and lymphoma.
However, the significance of FDG PET in evaluations of primary bone tumors and tumor-like lesions has not been extensively elucidated. Several investigators have reported the usefulness of FDG-PET in oncologic applications for primary musculoskeletal tumors.
Clinical PET and PET/CT - Principles and Applications | E. Edmund Kim | Springer
Preliminary reports suggest a good correlation between glucose consumption measured by FDG PET and the aggressiveness of musculoskeletal tumors. However, not an insignificant overlap exists between benign and malignant groups; therefore, PET is not a solo method for differential diagnosis between benign and malignant bone lesions. Both neoplastic and inflammatory processes can cause increase in FDG activity, so tissue sampling may not be obviated but should be directed to the most metabolically active regions identified by PET.
Therefore, PET has a role as a very useful adjunct to anatomic imaging techniques because it can provide an in-vivo method for quantifying functional metabolism in normal and diseased tissues.
Gary A. Under idealized conditions we expect there to be perfect alignment of the PET and CT images; however, this is virtually never the case. This is common in the head and neck, if the head is not immobilized. This will also produce incorrect attenuation correction maps from the CT images and lead to incorrect calculation of standardized uptake values SUVs. Motion of the diaphragm will cause misregistration between CT and PET images in the lower lungs and upper abdomen, sometimes quite significantly.
This could result in artifactual placement of liver lesions over the lung on PET Fig.
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Incorrect localization of photons and suboptimal attenuation correction maps from diaphragmatic motion will artifactually lower SUVs for lesions near the diaphragm. In the extreme, this problem may cause lesions in the lower lungs or upper abdomen to artifactually disappear from PET images Fig.
Careful evaluation of the CT images near the diaphragm is important to prevent these errors. A FDG maximum intensity projection MIP in a patient with metastatic paraganglioma demonstrates substantial abnormal FDG avidity overlying the midline abdomen arrow and an abnormal focus overlying the lower right chest arrowhead.
No therapy in the interim.
The primary esophageal malignancy arrow in unchanged, but metastases in the superior portion of the liver have disappeared arrowhead. Note the flattening of the superior surface of the liver near the arrowhead, which is a clue to the problem on PET. Motion at the diaphragm between CT and PET images, and the arms-down positioning, has contributed to obscuring the metastases that should be seen on the superior aspect of the liver.
Alireza Rezaee, However, there are only a few studies reported in the literature. Timothy Fox PhD, Automated image registration methods for PET imaging have been implemented in commercial treatment planning and imaging systems for radiation therapy. The decision to possibly use PET-CT images for treatment simulation can avoid the image registration step in treatment planning. However, many radiation therapy centers will still perform CT simulation with the image registration of the transmission PET or transmission CT images.
The use of both semiautomated landmark-based anatomical points and automated intensity-based mutual information image registration methods using rigid transformations can be performed with acceptable accuracy. The errors of image registration should be determined for each system and disease site such that these uncertainties can be incorporated into the margins used for tumor delineation.
Over the next few years, non-rigid deformable image registration methods will be investigated to determine the validity of these techniques in nuclear medicine.
In the future, the design of an automated registration method that can recognize the type of task such as disease site and determine the most appropriate solution may motivate the development of expert systems for image registration. Esther Y. To overcome imaging specific limitations in resolution, sensitivity, and penetration depth, the combination of multiple imaging modalities has gained increasing popularity. The design of multimodal contrast agents is hence a major issue of medicinal research as it offers reduced stress for patients by performing a single administration for multiple measurements.
Long-circulation half-lives, as well as high-tumor uptake could be obtained leading to sensitive tumor detections with high resolutions. As-prepared bioconjugated platforms were dually labeled with fluorophores Cy5. As prepared systems exhibited strong contrast for MRI, CT, and ultrasonography and simultaneously demonstrated efficient therapeutic treatments of diabetes. The process of PET-CT simulation will vary depending on the type of scanner used and departmental policy. Patients undergo a combined PET-CT scan in the radiotherapy treatment position that serves as both a diagnostic and radiotherapy planning scan.
Simulation is performed according to standard protocols for patients with esophageal cancer receiving 3D-CRT in our department. Oncology—Male Reproductive System Pages Oncology—Urology Pages Oncology—Lymphoma Pages Oncology—Melanoma Pages Infection and Inflammation Pages Pediatrics Pages Variants and Pitfalls Pages Show next xx. Read this book on SpringerLink. Recommended for you.
Jadvar J. Fellows are exposed to research that is being conducted by senior faculty, other trainees, graduate students and other members of the Johns Hopkins community in various specialties. This includes opportunity for viewing PET studies performed for evaluation of research radiotracers and clinical trials. Fellows are encouraged to pursue any relevant line of research that excites their interest, with the assistance of a faculty mentor.
Opportunities for research collaboration both within and outside the department are vast. Fellows are expected to complete research projects in an area of their interest, present their findings in national meetings and publish in leading nuclear medicine, internal medicine, cardiology and radiology journals.