FDG PET/MRI Coregistration Helps Predict Response to Gamma Knife Radiosurgery in Patients With Brain Metastases

Advancements in dendritic cell vaccination: enhancing efficacy and optimizing combinatorial strategies for the treatment of glioblastoma

Glioblastomas (GBM) are highly invasive, malignant primary brain tumors. The overall prognosis is poor, and management of GBMs remains a formidable challenge, necessitating novel therapeutic strategies such as dendritic cell vaccinations (DCVs). While many early clinical trials demonstrate an induction of an antitumoral immune response, outcomes are mixed and dependent on numerous factors that vary between trials. Optimization of DCVs is essential; the selection of GBM-specific antigens and the utilization of 18F-fludeoxyglucose Positron Emission Tomography (FDG-PET) may add significant value and ultimately improve outcomes for patients undergoing treatment for glioblastoma. This review provides an overview of the mechanism of DCV, assesses previous clinical trials, and discusses future strategies for the integration of DCV into glioblastoma treatment protocols. To conclude, the review discusses challenges associated with the use of DCVs and highlights the potential of integrating DCV with standard therapies.

The Role of Molecular Imaging in Patients with Brain Metastases: A Literature Review

Over the last several years, molecular imaging has gained a primary role in the evaluation of patients with brain metastases (BM). Therefore, the "Response Assessment in Neuro-Oncology" (RANO) group recommends amino acid radiotracers for the assessment of BM. Our review summarizes the current use of positron emission tomography (PET) radiotracers in patients with BM, ranging from present to future perspectives with new PET radiotracers, including the role of radiomics and potential theranostics approaches. A comprehensive search of PubMed results was conducted. All studies published in English up to and including December 2022 were reviewed. Current evidence confirms the important role of amino acid PET radiotracers for the delineation of BM extension, for the assessment of response to therapy, and particularly for the differentiation between tumor progression and radionecrosis. The newer radiotracers explore non-invasively different biological tumor processes, although more consistent findings in larger clinical trials are necessary to confirm preliminary results. Our review illustrates the role of molecular imaging in patients with BM. Along with magnetic resonance imaging (MRI), the gold standard for diagnosis of BM, PET is a useful complementary technique for processes that otherwise cannot be obtained from anatomical MRI alone.

Radiosurgery imaging

The most important imaging technology for GKNS continues to be magnetic resonance. The introduction of 3 Tesla machines permits quicker studies with better signal to noise ratio. The more powerful magnet increases the chances of heating the points of contact between patient and frame, but this has been solved with non-conducting nuts. There are several sequences for special functions. CISS studies are optimal for demonstrating cranial nerves in their passage through the subarachnoid space. FLAIR studies facilitate the distinction between CSF and edema due to inflammation. DTI permits the visualization of nerve fiber tracts. This has at least two current applications. In treatment planning of visible lesions, DTI permits a more efficient avoidance of important tracts. In functional work, tracts can be used to improve the definition of functional targets. Non stereotactic MRI can be imported into GammaPlan and co-registered to a non-distorted CT image.

Consensus recommendations for a standardized brain tumor imaging protocol for clinical trials in brain metastases

A recent meeting was held on March 22, 2019, among the FDA, clinical scientists, pharmaceutical and biotech companies, clinical trials cooperative groups, and patient advocacy groups to discuss challenges and potential solutions for increasing development of therapeutics for central nervous system metastases. A key issue identified at this meeting was the need for consistent tumor measurement for reliable tumor response assessment, including the first step of standardized image acquisition with an MRI protocol that could be implemented in multicenter studies aimed at testing new therapeutics. This document builds upon previous consensus recommendations for a standardized brain tumor imaging protocol (BTIP) in high-grade gliomas and defines a protocol for brain metastases (BTIP-BM) that addresses unique challenges associated with assessment of CNS metastases. The "minimum standard" recommended pulse sequences include: (i) parameter matched pre- and post-contrast inversion recovery (IR)-prepared, isotropic 3D T1-weighted gradient echo (IR-GRE); (ii) axial 2D T2-weighted turbo spin echo acquired after injection of gadolinium-based contrast agent and before post-contrast 3D T1-weighted images; (iii) axial 2D or 3D T2-weighted fluid attenuated inversion recovery; (iv) axial 2D, 3-directional diffusion-weighted images; and (v) post-contrast 2D T1-weighted spin echo images for increased lesion conspicuity. Recommended sequence parameters are provided for both 1.5T and 3T MR systems. An "ideal" protocol is also provided, which replaces IR-GRE with 3D TSE T1-weighted imaging pre- and post-gadolinium, and is best performed at 3T, for which dynamic susceptibility contrast perfusion is included. Recommended perfusion parameters are given.

The Role of Dual-Phase FDG PET/CT in the Diagnosis and Follow-Up of Brain Tumors

OBJECTIVE. FDG PET/CT of brain tumors is limited by background activity. Dual-phase FDG PET/CT can eliminate this limitation and allow discernment of viable tumors. Our aim was to assess the diagnostic capability of dual-phase FDG PET/CT qualitatively and quantitatively and to determine cutoff values for dual-phase FDG PET/CT in brain tumor imaging. MATERIALS AND METHODS. Retrospectively, 51 malignant brain tumors were evaluated with dual-phase FDG PET/CT in 32 patients. Acquisitions were performed 30 minutes (time 1) and 3 hours (time 2) after administration of 10 mCi (370 MBq) FDG and 6 hours of fasting. Two observers independently and qualitatively evaluated lesions. A weighted Cohen kappa was used to calculate interrater reliability and accuracy. Quantitatively, maximum standardized uptake value (SUV_max) was measured in the lesions, contralateral white matter (CWM), contralateral caudate nucleus head, and ipsilateral cerebellar cortex (CC). Lesion-to-CWM SUV_max, lesion-to-contralateral caudate nucleus head SUV_max, and lesion-to-ipsilateral CC SUV_max ratios at time 1 and time 2 were calculated. ROC analysis was used to determine optimum cutoff values, and AUC ratios were compared among quantitative parameters. Lesion outcome was determined by pathologic results (available in 15 lesions), lesion stability on serial MRI examinations (representing nonviable tumor), or decreased tumor size on serial MRI examinations after new treatment (representing viable tumor). RESULTS. Thirty-seven viable and 14 nonviable lesions were evaluated. Qualitatively, the diagnostic accuracy (first observer: κ = 0.45 to κ = 0.59; second observer: κ = 0.41 to κ = 0.66) and interrater reliability (at time 1: κ = 0.51; at time 2: κ = 0.83) improved with delayed imaging. AUC and ROC analysis showed comparably high sensitivity, specificity, and accuracy profiles for early and delayed dual-phase FDG PET/CT. Some of the proposed cutoff values were as follows: lesion SUV_max at time 1, 7.20 (sensitivity, 89.2%; specificity, 85.7%); lesion SUV_max at time 2, 7.80 (sensitivity, 97.3%; specificity, 71.4%); lesion-to-CWM SUV_max at time 1, 2.05 (sensitivity, 78.4%; specificity, 92.9%); and lesion-to-CWM SUV_max at time 2, 2.36 (sensitivity, 81.1%; specificity, 85.7%). CONCLUSION. Dual-phase FDG PET/CT improves lesion detection and diagnostic accuracy in malignant brain tumors.

Radiological diagnosis of brain radiation necrosis after cranial irradiation for brain tumor: a systematic review

Introduction

This systematic review aims to elucidate the diagnostic accuracy of radiological examinations to distinguish between brain radiation necrosis (BRN) and tumor progression (TP).

Methods

We divided diagnostic approaches into two categories as follows—conventional radiological imaging [computed tomography (CT) and magnetic resonance imaging (MRI): review question (RQ) 1] and nuclear medicine studies [single photon emission CT (SPECT) and positron emission tomography (PET): RQ2]—and queried. Our librarians conducted a comprehensive systematic search on PubMed, the Cochrane Library, and the Japan Medical Abstracts Society up to March 2015. We estimated summary statistics using the bivariate random effects model and performed subanalysis by dividing into tumor types—gliomas and metastatic brain tumors.

Results

Of 188 and 239 records extracted from the database, we included 20 and 26 studies in the analysis for RQ1 and RQ2, respectively. In RQ1, we used gadolinium (Gd)-enhanced MRI, diffusion-weighted image, MR spectroscopy, and perfusion CT/MRI to diagnose BRN in RQ1. In RQ2, ²⁰¹Tl-, ^99mTc-MIBI-, and ^99mTc-GHA-SPECT, and ¹⁸F-FDG-, ¹¹C-MET-, ¹⁸F-FET-, and ¹⁸F-BPA-PET were used. In meta-analysis, Gd-enhanced MRI exhibited the lowest sensitivity [63%; 95% confidence interval (CI): 28–89%] and diagnostic odds ratio (DOR), and combined multiple imaging studies displayed the highest sensitivity (96%; 95% CI: 83–99%) and DOR among all imaging studies. In subanalysis for gliomas, Gd-enhanced MRI and ¹⁸F-FDG-PET revealed low DOR. Conversely, we observed no difference in DOR among radiological imaging in metastatic brain tumors. However, diagnostic parameters and study subjects often differed among the same imaging studies. All studies enrolled a small number of patients, and only 10 were prospective studies without randomization.

Conclusions

Differentiating BRN from TP using Gd-enhanced MRI and ¹⁸F-FDG-PET is challenging for patients with glioma. Conversely, BRN could be diagnosed by any radiological imaging in metastatic brain tumors. This review suggests that combined multiparametric imaging, including lesional metabolism and blood flow, could enhance diagnostic accuracy, compared with a single imaging study. Nevertheless, a substantial risk of bias and indirectness of reviewed studies hindered drawing firm conclusion about the best imaging technique for diagnosing BRN.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1228-x) contains supplementary material, which is available to authorized users.