Walker, Marisa H. Miceli, Laurie Jones-Jackson. Edwin L.
Positron Emission Tomography (PET)
Palmer, James A. Scott, Thomas F. Todd M. Blodgett, Sanjay Paidisetty, Paul Shreve. Back Matter Pages The chapters provide practicing imaging physicians with a concise, practical guide, presenting PET-CT as an integrated anatomic-metabolic imaging procedure applied to cancer imaging. Physics and instrumentation chapters are oriented to provide an overview of the available technology and some physical concepts.
Comprehensive clinical chapters are structured to provide concise and structured background regarding the clinical management of each cancer and the role of PET-CT imaging in all phases of patient management.
Each clinical chapter will help the imaging physician more completely understand the relationship and role of the integrated modality imaging with respect to the overall treatment of the cancer patient. Editors and affiliations. Townsend 2 1.
Clinical PET and PETCT
Buy options. Following treatment for brain tumors, the differentiation of treatment-related changes from progression remains challenging 1 , 4 , 8 , 49 , 50 and is of pivotal clinical relevance. The erroneous interpretation of treatment-related changes as tumor progression may lead to a premature cessation of an effective treatment with a potentially negative impact on survival and an overestimation of the efficacy of the subsequent treatment.
A year-old patient with an anaplastic astrocytoma. Contrast-enhanced MRI 31 months after radiation therapy suggests tumor progression. In contrast, O- 2-[ 18 F]-fluoroethyl - l -tyrosine FET PET shows only slight metabolic activity, and the time—activity curve shows a constantly increasing FET uptake, consistent with treatment-related changes.
In patients with brain tumor, changes in the MRI contrast enhancement extent are typically used as an indicator of treatment response or tumor relapse. In gliomas, frequently used systemic treatment options are conventional alkylating chemotherapy and antiangiogenic therapy.
Using MET PET, a reliable response assessment to temozolomide and nitrosourea-based chemotherapy has been demonstrated in patients with high-grade glioma at recurrence. In newly diagnosed patients with IDH-wild-type glioblastoma, prospective studies assessed the predictive value of early FET uptake changes 6—8 weeks after postoperative chemoradiation with temozolomide.
Furthermore, amino acid PET has been investigated as an alternative imaging method for the assessment of treatment response to antiangiogenic therapy such as bevacizumab. Regarding PET tracers that assess cellular proliferation, previous studies in glioma patients suggest that FLT is able to predict favorable survival after bevacizumab therapy. Although PET plays only a minor role in the initial diagnosis of meningiomas, SSTR imaging may be of value regarding meningioma detection.
Clinically, this is highly relevant because meningiomas located at the skull base or nearby the falx cerebri, with transosseous extension, or equivocal imaging findings related to artifacts or calcifications were difficult to detect by anatomical MRI alone. At suspicion of recurrence, contrast-enhanced MRI is the imaging modality of choice for both diagnostic evaluation and treatment planning. However, the diagnostic accuracy of standard MRI is limited, especially in complex anatomic situations in which bone infiltration or scar tissue is present.
Additional imaging modalities to detect tumor remnants or recurrence more precisely are therefore needed. It has been demonstrated that SSTR PET adds important clinical information in discriminating meningioma tissue from posttherapeutic reactive changes eg, scars related to pretreatment , usually presenting as equivocal radiological findings on contrast-enhanced MRI. Regarding the assessment of treatment response to radiotherapy using PET in meningioma patients, however, only a limited number of studies is currently available.
Throughout the long-term follow-up of these patients over 10 years, MET tumor-to-brain ratios showed a further decrease in the majority of patients, whereas the tumor size was predominantly unchanged. The definition of the target volume is crucial for the planning of radiosurgery or fractionated radiotherapy. In meningiomas, target volumes are frequently delineated based on coregistered contrast-enhanced tomographic images MRI and CT. Moreover, in transosseous meningiomas, it is difficult to exactly define the degree of infiltration, despite using the bone window on CT images.
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In the setting of the identification of meningioma remnants after incomplete resection Figure 2 , PET imaging seems to be helpful for adjuvant radiotherapy planning. Amino acid PET can also be helpful for radiation therapy target volume delineation in patients with meningioma. Astner et al. As a consequence, areas without tumor infiltration could be excluded from the gross tumor volume and critical anatomical structures such as the optic chiasm, optic nerves, and pituitary gland could be preserved more effectively.
Nevertheless, the most commonly used imaging modality for brain metastases detection with the highest sensitivity remains thin-slice contrast-enhanced MRI. Depending on the performance status of the patient and the number of brain metastases, radiotherapy is an effective treatment option, either as whole-brain radiotherapy or stereotactic radiosurgery. Several FDG PET studies with considerable differences in methodology evaluated the value of this tracer to differentiate brain metastasis relapse from radiation-induced changes. Furthermore, reactive changes may also occur following systemic treatment and can also be difficult to distinguish from brain metastases relapse.
Pseudoprogression may occur in brain metastases treated with immune checkpoint inhibitors using CTLA-4 eg, ipilimumab or PD-1 eg, nivolumab or pembrolizumab inhibitors. A pilot study highlighted the potential of amino acid PET using FET to identify pseudoprogression in patients with brain metastases secondary to malignant melanoma treated with ipilimumab. The advent of immunotherapy using immune checkpoint inhibitors and targeted therapy has dramatically improved the treatment of extracranial cancer, especially in patients with skin, lung, or breast cancers.
Moreover, recent trials have shown that patients with brain metastases may also benefit from these agents. In patients with melanoma brain metastases undergoing immune checkpoint blockade or targeted therapy, a pilot study observed that metabolic responders may show a proliferative reduction on FLT PET despite unchanged findings on standard MRI. Studies evaluating amino acid PET for the assessment of treatment response remain scarce.
Single reports suggest that amino acid PET has the potential to add valuable information to standard MRI for the assessment of treatment response. A year-old female patient with a brain metastasis secondary to a v-Raf murine sarcoma viral oncogene homolog B BRAF -mutated malignant melanoma treated with dabrafenib and trametinib. The metabolic response was associated with an overall survival of 9 months after treatment initiation reproduced from Galldiks et al.
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It has to be pointed out that a considerable number of studies were performed in single centers only or were based on a retrospective PET data collection. Thus, the clinical value and the additional biological information of these methods warrants further investigation including neuropathological validation, preferentially in prospective multicenter clinical trials.
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The present literature provides strong evidence that PET can be of great clinical value for the most important diagnostic indications in the field of neuro-oncology Table 1. Especially PET using amino acid tracers and SSTR ligands offers a variety of insights for the assessment of brain tumors with the potential to overcome the limitations of conventional MRI. The diagnostic improvement probably results in relevant benefits for patients with brain tumor and justifies a more widespread use of this diagnostic tool.
Moreover, additional costs of this method can be potentially saved by the incurred costs of less reliable diagnostic imaging techniques. Especially amino acid PET is a robust and attractive approach for clinicians for many indications including easy scan reading. Importantly, most studies using amino acid PET provide comparable results across different scanners, which is also a consequence of national and international efforts concerning the standardization of amino acid PET acquisition and evaluation in brain tumor imaging. The addition of advanced MRI techniques eg, MR spectroscopic imaging, perfusion- and diffusion-weighted imaging to amino acid or SSTR PET has the potential for a more profound evaluation of biological characteristics in patients with primary or secondary brain cancer.
The complementary information derived from these imaging techniques suggests differential biological information, which therefore warrants further evaluation.
In the light of emerging high-throughput analysis methods such as radiomics and machine learning, this is also of great clinical interest; for example, it has been demonstrated that combined PET and MRI radiomics encodes more important diagnostic information than either modality alone. Furthermore, the combination of diagnostics and therapy theranostics has been introduced to meningioma treatment.
In patients with progressive, treatment-refractory meningiomas, a disease stabilization has been reported in a considerable number of patients, suggesting that this therapy modality is a promising treatment alternative, which should be evaluated in further studies to determine its role in meningioma management. Study design, writing of manuscript drafts: NG. Revising manuscript, approving final content of the manuscript: All.
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Article Contents. Key Points. PET Tracers. Summary and Outlook. Authorship statement:. Oxford Academic. Google Scholar. Philipp Lohmann. Nathalie L Albert. Karl-Josef Langen. Cite Citation. Permissions Icon Permissions. Abstract Over the past decades, a variety of PET tracers have been used for the evaluation of patients with brain tumors.
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