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Medical Specialties / Radiology / PET

Current and Emerging Roles of Functional Imaging in Radiation Therapy

Abstract: The advent of functional imaging facilitates the acquisition of patient-specific tumor characteristics, including its metabolic state and regional oxygen tension. Recent advances promote incorporating this information with data obtained from current imaging techniques, such as MRI and CT, to manage various malignancies. Functional imaging's vital roles progressively evolved to include: aiding in diagnosis, improving radiation treatment planning, differentiating tumor volume from surrounding normal tissues which enables dose escalation to the former while improving sparing of the latter, adapting radiation therapy regimens according to a tumor's response to initial treatment, and assessing radiation therapy response and toxicity. This review explores functional imaging in radiation oncology in the context of these five applications, as well as its comparison to, and integration with, existing imaging modalities. In parallel with advances in functional imaging and understanding of tumor microbiology, the emergence of diverse tracers provides a plethora of options to distinguish and manage malignancies on the basis of specific metabolic processes and changing microenvironmental cues. Current limitations, potential concerns, and future innovations of functional imaging are also discussed. ... Read more

Changing Paradigms with Molecular Imaging of Neuroendocrine Tumors

Abstract: Molecular imaging is changing diagnostic and treatment paradigms in patients with neuroendocrine tumors through its ability to non-invasively characterize disease, supplementing the traditional role of using imaging for localizing and measuring disease. 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. Positron emission tomography (PET) is now able to characterize these subtypes through its ability to quantify somatostatin receptor cell surface (SSTR) expression and glycolytic metabolism with SSTR and fluorodeoxyglucose (FDG) PET, respectively. 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. ... Read more

Early Assessment of Radiation Response Using a Novel Functional Imaging Modality -- [18F]Fluorocholine PET (FCH-PET): A Pilot Study

Abstract: Aim: [18F]Fluorodeoxyglucose-positron emission tomography/computerized tomography (FDG-PET) is commonly used to assess response to patients treated with radiation (RT) or combination of chemotherapy and RT (CRT). The intent of this pilot study is to explore whether [18F]fluorocholine PET (FCH-PET) can serve as an early predictive biomarker for early detection of RT/CRT response. 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. There were 16 lesions that were considered target lesion and were followed for correlation between change in FCH-PET SUVmax readings and clinical outcome. Median tumor size was 4.4 cm. Median RT dose was 66 Gy. The change in SUVmax (Δ SUVmax) of FCH-PET scans performed before and during RT was correlated with clinical outcome at the last follow-up. Results: The median FCH-PET SUVmax for the 1st and 2nd scans was 6.15 and 4.65, respectively. Fourteen (87.5%) lesions showed a reduction in SUVmax in either a complete response (CR) or a partial response (PR), and 2 lesions showed an increase in SUVmax both of which were determined to be non-response (NR). The median percentage change between the 1st and 2nd scan was -19.5%. Forty-four percent of lesions (7/16) had CR, 44% (7/16) had PR, and 12% (2/16) had NR (no response). Median follow-up was 12 months. The results showed a difference between NR and PR, between NR and CR, and a trend towards significance (p=0.06). Conclusion: FCH-PET scan demonstrated changes in SUVmax during RT that were predictive of final outcome. ... Read more

The Scope and Potentials of Functional Radionuclide Imaging Towards Advancing Personalized Medicine in Oncology: Emphasis on PET-CT

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. Data from functional radionuclide imaging particularly that obtained from PET-CT, with regard to characterization of an individual's tumor phenotype, can play a very important role in answering some of the critical decision-making questions on an individual basis. The role of molecular imaging with PET, SPECT, and planar radionuclide technologies is not confined to early response assessment of administered therapeutics (which is its major benefit compared to conventional methods), rather it has a much broader perspective and encompasses multiple steps in decision making steps of patient management. The immense impact of the radionuclide-based molecular imaging techniques on the selection of an appropriate treatment (at initial diagnosis, during therapy, or after therapy) or in defining the tumor biology has been documented and increasingly recognized through both large and small-scale studies. However, there has been relatively less systematic effort towards the development of a successful and definitive clinical model of "personalized cancer medicine" (based on accurate disease triaging on an individual basis) by the medical community that would be suitable for routine adoption. In this paper, an endeavor has been made to explore the potential of this approach and underscore the areas that would require further critical evaluation to make this a reality. ... Read more

Direct Sagittal Image Registration and Tumor Delineation on Sagittal Magnetic Resonance Imaging Sequences for Image-Guided Brachytherapy of Cervical Cancer

Abstract: Aim: To test and evaluate direct sagittal-plane tumor delineation for MRI-based image-guided brachytherapy (IGBT) planning for patients with cervical cancer. Materials and Methods: An image registration method based on the sagittal source MR images was developed and employed in ten patients with an indwelling ring/tandem applicator. The gross tumor volume (GTV) was delineated separately on the sagittal (GTV-S) and axial images (GTV-A). GTV conformity indices and dose-volume histogram analyses were compared among GTV-S and GTV-A (paired t-test). Results: Image quality and delineation in the sagittal images was graded superior to the axial images. The ratio of common volume of the axial and sagittal volumes to that of the axial volume was 0.77 +/- (standard deviation) 0.2. The GTV-S mean volume (19.6 +/- 13.8 mL) was significantly larger than the GTV-A mean volume (10.3 +/- 7.3 mL, p=0.003). The GTV-S mean D99 (5.2 +/- 2.5 Gy) was significantly lower than the GTV-A mean D99 (6.9 +/- 2.7 Gy, p=0.013). The GTV-S mean D90 (6.8 +/- 2.8 Gy) was significantly lower than the GTV-A mean D90 (8.5 +/- 3.1 Gy, p=0.016). Conclusions: Registration of the sagittal source MRI and contouring the GTV directly on the sagittal images is feasible and practical for IGBT. Consistently larger sagittal GTVs may be explained by the better visualization and more continuous tumor topology in the sagittal plane, compared to the discrete oblique sectioning of the uterus/tumor and partial volume loss in the axial plane. ... Read more

Recovery from Post-stroke Aphasia: Lessons from Brain Imaging and Implications for Rehabilitation and Biological Treatments

Abstract: Aphasia, a condition defined as the partial or complete loss of language function after brain damage, is one of the most devastating cognitive deficits produced by stroke lesions. Over the past decades, there have been great advances in the diagnosis and treatment of post-stroke language and communication deficits. In particular, the advent of functional brain imaging and other brain mapping methods has advanced our understanding of how the intact and lesioned brain takes over the activity of irretrievably damaged networks in aphasic patients. This review examines the contribution of these ancillary methods to elucidate the neural changes that take place to promote improvement of language function in early, late, and very late stages of recovery. Also, functional neuroimaging is helpful to identify brain areas involved in language recovery as well as to characterize the plastic reorganization of neural networks produced by scientifically-based language therapies and biological treatments (drugs, transcranial magnetic stimulation). ... Read more

Molecular Imaging Using Positron Emission Tomography in Colorectal Cancer

Abstract: Positron emission tomography (PET) is one of the most important recent advances in cancer imaging. Molecular imaging using PET is now an integral part of multidisciplinary cancer care. In this review, the role of PET in colorectal cancer (CRC) is discussed, including its well established role in the assessment of recurrent disease and emerging applications such as initial staging, monitoring therapy efficacy, and radiotherapy planning. The development of new hybrid devices such as PET-magnetic resonance imaging along with the use of novel molecular probes in targeting specific pathways in oncogenesis will further improve patient management. ... Read more

Stereotactic Body Radiation Therapy for Oligometastases

Abstract: There are data in the literature to suggest the presence of an oligometastatic state, and local aggressive therapy of the oligometastases may improve outcomes including survival. Stereotactic body radiation therapy has emerged as one of the local therapy options for oligometastases in various body sites, most commonly in the lung and the liver. Retrospective studies and clinical trials have demonstrated promising results with the use of stereotactic body radiation therapy for oligometastases. However, most of the studies have relatively short follow-up intervals. Longer follow-up is necessary to better define the role of stereotactic body radiation therapy in the management of patients with oligometastases. Given the high propensity for distant progression, the combination of novel systemic therapy and stereotactic body radiation therapy is to be explored. ... Read more

Stereotactic Body Radiation Therapy (Stereotactic Ablative Radiotherapy) for Stage I Non-Small Cell Lung Cancer - Updates of Radiobiology, Techniques, and Clinical Outcomes

Abstract: Stereotactic body radiation therapy (SBRT), also known as stereotactic ablative radiotherapy (SABR), has emerged as one of the standard treatment options for stage I non-small cell lung cancer (NSCLC), mainly in medically inoperable patients. Its use has also been explored in operable patients. A large body of experience, either from retrospective studies or clinical trials, has been accumulated over the years and more is known about the radiobiology, cancer biology, technical aspects, clinical outcomes, and toxicities of SBRT. This article provides updates of these aspects of SBRT for stage I NSCLC. ... Read more

The Neural Correlates of Impaired Consciousness in Coma and Unresponsive States

Abstract: Over the last few years, functional neuroimaging studies have provided new insights into cerebral activity in subjects with severe brain damage leading to coma and other clinical states characterized by unresponsiveness. The present paper introduces the clinical picture of patients with impaired consciousness, and reviews the nosological criteria and functional neuroanatomical basis for brain death, coma, vegetative state, minimally conscious state, and the locked-in syndrome. Converging evidence suggests that disrupted activity in higher-order association areas, especially prefrontal and posteromedial parietal regions, plays a pivotal role within the neural correlates of impaired consciousness in the unresponsive patient. ... Read more

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