- The impact of functional imaging on radiation medicine | SpringerLink
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- Image-Guided Radiation Therapy in Lymphoma Management
For patients with metastatic disease, there is an increasing range of therapies but these must be individualized to the specific subtype of tumor expressed, which varies in aggressiveness from well to poorly differentiated phenotypes. The ability to perform this as a whole body study is highlighting the limitations of relying on histopathology obtained from a single site. Through earlier diagnosis, improved selection of the most appropriate therapy and better assessment of therapeutic response for an individual patient, molecular imaging is improving the outcome for patients with NET.
Tags: FDG , fluorodeoxyglucose , ostreotide , somatostatin analog. Author s : Bhupesh Parashar , A. Clifford Chao. Materials and Methods : Fourteen patients have been accrued and analyzed. The lesions were base of tongue, tonsil, nodes, hypopharynx, maxilla, palate, lung, pancreas, brain, uterine, and rectal. Median tumor size was 4. Median RT dose was 66 Gy.
The impact of functional imaging on radiation medicine | SpringerLink
Fourteen The median percentage change between the 1 st and 2 nd scan was Median follow-up was 12 months. Tags: FDG , fluorocholine , fluorodeoxyglucose , radionuclide. Abstract: The challenges of diagnosing rheumatic diseases are the high prevalence of certain rheumatic diseases, the existence of orphan disease, and the different pathophysiological backgrounds including infection and autoimmune mechanisms.
During recent decades, more and more attention has been drawn to early diagnosis and achievement of full remission. Accordingly, new classification criteria have been developed and more biomarkers introduced into clinical practice. Specific laboratory parameters as well as wider use of functional imaging tools like ultrasound and magnetic resonance further support the early diagnostic process.
Besides diagnosis early after disease onset, achievement of remission during follow-up is another important clinical aim of rheumatologists. In parallel with the development of new therapeutic approaches, both quality of life and treatment outcome especially of chronic inflammatory diseases could be improved. Both specific outcome parameters and global disease activity assessments are important to verify treatment goals of full remission, and at the same time may also predict response to treatment regimens.
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Author s : Sandip Basu. Abstract: Behavioral heterogeneity within a given patient cohort has been a major challenge in clinical practice and is probably most prominently observed in the field of oncology. This has been the prime impetus of the cutting-edge preclinical and clinical research studies over recent times, many of which seek to further stratify patients based on patients' genetic, proteomic, and metabolic profile the three key components of "-omics" research , in order to select the appropriate therapy according to an individual's best-fit. Solid tumors that are commonly treated with radiotherapy or chemoradiotherapy show variable resistance to therapy, ranging from very sensitive tumors e.
For resistant tumors, changes in tumor glucose metabolic activity may be small and occur only late during the course of radiotherapy. This article provides a comprehensive and contemporary overview of molecular imaging applications in radiation therapy, particularly for target definition and treatment response assessment. Specific quantitative imaging requirements for use in radiation therapy, and potential confounding artifacts that limit image interpretation, will be highlighted.
Future perspectives for full exploration of molecular imaging, particularly for biologically conformal applications of radiotherapy, will be discussed. Molecular images should be of high quality for effective application in radiotherapy target delineation and treatment response assessment. The quality of molecular images depends on a combination of multiple factors, including patient preparation, technologist training, imaging protocol design, scanner technology, software algorithms, and data analysis methods.
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Several guidelines are available that provide recommendations on imaging procedures for 18 F-FDG 1 , 2 , as well as for other PET radiotracers 3 , 4. Practice guidelines for certain functional MRI procedures have also been suggested by the American College of Radiology 5. Molecular imaging for radiation therapy applications, however, requires an additional level of reproducibility and image quality beyond what is required for diagnostic imaging.
It is important that patients undergo similar preparations before imaging and before receipt of each fraction of radiation therapy. For example, for abdominal tumors, fasting before imaging and treatment increases the likelihood that the stomach and bowels are the same size during treatment planning as they will be for each treatment session. Blood glucose levels should be checked before 18 F-FDG injection, and the scan should be rescheduled if levels are outside a predetermined range 2.
Molecular imaging for radiation therapy planning requires equipment and procedures additional to those typically used for diagnostic imaging. Unlike diagnostic images, images for radiation therapy planning will eventually need to be coregistered with treatment-planning CT images. Reliable target delineation is contingent on the accuracy of registration between the functional image and the planning CT image. As such, molecular imaging acquisitions for radiation therapy planning need to follow principles similar to those recommended for planning CT or simulation CT acquisitions 6.
The patient should be positioned and immobilized during image acquisition in the same manner as during receipt of each fraction of therapy.
Because flat-top couches are used for radiation therapy delivery to ensure repeatable positioning, a flat-top table should be placed on top of the patient table. Any immobilization devices, padding, or bolus material should be in place during the scan. For nuclear medicine, placement of positioning equipment outside the transaxial imaging field of view but within the scanner bore should be avoided, as it can lead to attenuation artifacts 7. Scanners with large bores are preferred to accommodate the extra equipment.
Positioning for functional MRI can be more challenging, depending on the tumor site 8. For example, for head and neck cancer, personalized masks are often used to ensure reproducible positioning and immobilization, but these masks often do not fit inside standard head coils. Furthermore, MRI bores are often smaller than CT bores, potentially limiting the use of some positioning devices. In these cases, creative solutions may be necessary 9. The positioning of the lasers should be precise and maintained at a known spatial relationship to the image center, so that patients can be marked in a way that will ensure repeatable positioning at subsequent treatment sessions.
The alignment of the external laser should be tested for accuracy; such quality assurance tests have been described by the American Association of Physicists in Medicine AAPM task group 66 6. Attenuation and scatter correction for PET image reconstruction can typically be performed using either low-dose CT or high-quality diagnostic CT.
The preference is to acquire a single high-quality CT scan together with the PET scan, which can then be used for treatment planning. In this case, no additional image registration is needed to align the PET image and the planning CT image.
Image-Guided Radiation Therapy in Lymphoma Management
Treatment-planning CT, however, is sometimes performed with intravenous contrast material. Unless corrected for, contrast-enhanced CT can cause the PET voxel values in regions of high contrast density to be increased when the scan is used for attenuation correction In these cases or when the planning CT scan has been acquired separately , an additional low-dose CT scan should be acquired together with the PET scan.
This low-dose CT scan can be used for attenuation and scatter correction but is not suitable for treatment planning. Although several methods to improve the accuracy of pseudo CT mapping e. When the planning CT image is not already registered to the functional images, the two image coordinate systems need to be aligned.
Rigid registration algorithms rotate and translate two images to maximize the spatial similarity of their intensity values. Most modern image-analysis software packages include methods for performing rigid registration. Voxel sizes for PET images are larger than CT voxel sizes and, depending on the software, may need to be up-sampled before PET can be used for target delineation. Unless nearest-neighbor resampling is used, this resampling step will alter the quantitative SUVs; therefore, quantitative image analysis for treatment response assessment should be performed before the PET image registration.
Special software may be required to register anatomic MRI and CT images, as the imaging values for different tissues are inherently different between the two imaging modalities. In many cases, patient positioning will not be identical in the molecular images and in the planning CT image. This issue can make rigid registration difficult and can occasionally cause algorithms to converge to strange solutions results should always be checked. One option, if the software allows it, is to crop the template image, leaving only the regions of interest to be registered. Another option is to use deformable registration algorithms.
Like rigid registration, deformable registration algorithms maximize the similarities between two images but allow for morphologic changes beyond rotation and translation. These algorithms ultimately warp the template image to match the reference image. There are several deformable registration algorithms, each with different similarity measures or regularization constraints. Because the resulting solution will differ depending on the algorithm used, an algorithm should not be arbitrarily chosen Quality assurance processes for image registration have been proposed 14 , and an upcoming report from task group of the AAPM will further describe the proper use and quality assurance of image registration algorithms.
Patient motion during imaging causes the image to be blurred over the path of motion, elongating target volumes.