Methionine positron emission tomography for differentiation of recurrent brain tumor and radiation necrosis after stereotactic radiosurgery —In malignant glioma—

Short report: Plasma based biomarkers detect radiation induced brain injury in cancer patients treated for brain metastasis: A pilot study

BACKGROUND

Radiotherapy has an important role in the treatment of brain metastases but carries risk of short and/or long-term toxicity, termed radiation-induced brain injury (RBI). As the diagnosis of RBI is crucial for correct patient management, there is an unmet need for reliable biomarkers for RBI. The aim of this proof-of concept study is to determine the utility of brain-derived circulating free DNA (BncfDNA), identified by specific methylation patterns for neurons, astrocytes, and oligodendrocytes, as biomarkers brain injury induced by radiotherapy.

METHODS

Twenty-four patients with brain metastases were monitored clinically and radiologically before, during and after brain radiotherapy, and blood for BncfDNA analysis (98 samples) was concurrently collected. Sixteen patients were treated with whole brain radiotherapy and eight patients with stereotactic radiosurgery.

RESULTS

During follow-up nine RBI events were detected, and all correlated with significant increase in BncfDNA levels compared to baseline. Additionally, resolution of RBI correlated with a decrease in BncfDNA. Changes in BncfDNA were independent of tumor response.

CONCLUSIONS

Elevated BncfDNA levels reflects brain cell injury incurred by radiotherapy. further research is needed to establish BncfDNA as a novel plasma-based biomarker for brain injury induced by radiotherapy.

Glioblastoma Recurrence Versus Radiotherapy Injury: Combined Model of Diffusion Kurtosis Imaging and 11C-MET Using PET/MRI May Increase Accuracy of Differentiation

PURPOSE

To evaluate the diagnostic potential of decision-tree model of diffusion kurtosis imaging (DKI) and 11C-methionine (11C-MET) PET, for the differentiation of radiotherapy (RT) injury from glioblastoma recurrence.

METHODS

Eighty-six glioblastoma cases with suspected lesions after RT were retrospectively enrolled. Based on histopathology or follow-up, 48 patients were diagnosed with local glioblastoma recurrence, and 38 patients had RT injury between April 2014 and December 2019. All the patients underwent PET/MRI examinations. Multiple parameters were derived based on the ratio of tumor to normal control (TNR), including SUVmax and SUVmean, mean value of kurtosis and diffusivity (MK, MD) from DKI, and histogram parameters. The diagnostic models were established by decision trees. Receiver operating characteristic analysis was used for evaluating the diagnostic accuracy of each independent parameter and all the diagnostic models.

RESULTS

The intercluster correlations of DKI, PET, and texture parameters were relatively weak, whereas the intracluster correlations were strong. Compared with models of DKI alone (sensitivity =1.00, specificity = 0.70, area under the curve [AUC] = 0.85) and PET alone (sensitivity = 0.83, specificity = 0.90, AUC = 0.89), the combined model demonstrated the best diagnostic accuracy (sensitivity = 1.00, specificity = 0.90, AUC = 0.95).

CONCLUSIONS

Diffusion kurtosis imaging, 11C-MET PET, and histogram parameters provide complementary information about tissue. The decision-tree model combined with these parameters has the potential to further increase diagnostic accuracy for the discrimination between RT injury and glioblastoma recurrence over the standard Response Assessment in Neuro-Oncology criteria. 11C-MET PET/MRI may thus contribute to the management of glioblastoma patients with suspected lesions after RT.

The Utility of Conventional Amino Acid PET Radiotracers in the Evaluation of Glioma Recurrence also in Comparison with MRI

AIM

In this comprehensive review we present an update on the most relevant studies evaluating the utility of amino acid PET radiotracers for the evaluation of glioma recurrence as compared to magnetic resonance imaging (MRI).

METHODS

A literature search extended until June 2020 on the PubMed/MEDLINE literature database was conducted using the terms "high-grade glioma", "glioblastoma", "brain tumors", "positron emission tomography", "PET", "amino acid PET", "[11C]methyl-l-methionine", "[18F]fluoroethyl-tyrosine", "[18F]fluoro-l-dihydroxy-phenylalanine", "MET", "FET", "DOPA", "magnetic resonance imaging", "MRI", "advanced MRI", "magnetic resonance spectroscopy", "perfusion-weighted imaging", "diffusion-weighted imaging", "MRS", "PWI", "DWI", "hybrid PET/MR", "glioma recurrence", "pseudoprogression", "PSP", "treatment-related change", and "radiation necrosis" alone and in combination. Only original articles edited in English and about humans with at least 10 patients were included.

RESULTS

Forty-four articles were finally selected. Conventional amino acid PET tracers were demonstrated to be reliable diagnostic techniques in differentiating tumor recurrence thanks to their high uptake from tumor tissue and low background in normal grey matter, giving additional and early information to standard modalities. Among them, MET-PET seems to present the highest diagnostic value but its use is limited to on-site cyclotron facilities. [18F]labelled amino acids, such as FDOPA and FET, were developed to provide a more suitable PET tracer for routine clinical applications, and demonstrated similar diagnostic performance. When compared to the gold standard MRI, amino acid PET provides complementary and comparable information to standard modalities and seems to represent an essential tool in the differentiation between tumor recurrence and other entities such as pseudoprogression, radiation necrosis, and pseudoresponse.

CONCLUSIONS

Despite the introduction of new advanced imaging techniques, the diagnosis of glioma recurrence remains challenging. In this scenario, the growing knowledge about imaging techniques and analysis, such as the combined PET/MRI and the application of artificial intelligence (AI) and machine learning (ML), could represent promising tools to face this difficult and debated clinical issue.

Role of circulating tumor cell detection in differentiating tumor recurrence from treatment necrosis of brain gliomas

Differentiating treatment necrosis from tumor recurrence poses a diagnostic conundrum for many clinicians in neuro-oncology. To investigate the potential role of circulating tumor cells (CTCs) detection in differentiating tumor recurrence and treatment necrosis in brain gliomas, we retrospectively analyzed the data of 22 consecutive patients with tumor totally removed and new enhancing mass lesion(s) showed on MRI after initial radiotherapy. The 22 patients were finally classified into tumor recurrence group (n = 10) and treatment necrosis group (n = 12), according to evidence from the clinical course (n = 11) and histological confirmation (n = 11). All 22 patients received CTCs detection, and DSC-MRP and 11C-MET-PET were performed on 20 patients (90.9%) and 17patients (77.3%) respectively. The data of the diagnosis efficacy to differentiate the two lesions by CTC detection, MPR and PET were analyzed by ROC analysis. The mean CTCs counts were significantly higher in the tumor recurrence group (6.10 ± 3.28) compared to the treatment necrosis group (1.08 ± 2.54, p < 0.001). The ROC curve showed that an optimized cell count threshold of 2 had 100% sensitivity and 91.2% specificity with AUC = 0.933 to declare tumor recurrence. The diagnostic efficacy of CTC detection was superior to rCBV of DSC-MRP and rSUV_max in MET-PET. Furthermore, we observed that CTCs detection could have a potential role in predicting tumor recurrence in one patient. Our research results preliminarily showed the potential value of CTC detection in differentiating treatment necrosis from tumor recurrence in brain gliomas, and is worthy of further confirmation with large samples involved.

Pseudoprogression versus true progression in glioblastoma patients: A multiapproach literature review. Part 2 - Radiological features and metric markers

After chemoradiotherapy for glioblastoma, pseudoprogression can occur and must be distinguished from true progression to correctly manage glioblastoma treatment and follow-up. Conventional treatment response assessment is evaluated via conventional MRI (contrast-enhanced T1-weighted and T2/FLAIR), which is unreliable. The emergence of advanced MRI techniques, MR spectroscopy, and PET tracers has improved pseudoprogression diagnostic accuracy. This review presents a literature review of the different imaging techniques and potential imaging biomarkers to differentiate pseudoprogression from true progression.

Carbon-11: Radiochemistry and Target-Based PET Molecular Imaging Applications in Oncology, Cardiology, and Neurology

The positron emission tomography (PET) molecular imaging technique has gained its universal value as a remarkable tool for medical diagnosis and biomedical research. Carbon-11 is one of the promising radiotracers that can report target-specific information related to its pharmacology and physiology to understand the disease status. Currently, many of the available carbon-11 (t_1/2 = 20.4 min) PET radiotracers are heterocyclic derivatives that have been synthesized using carbon-11 inserted different functional groups obtained from primary and secondary carbon-11 precursors. A spectrum of carbon-11 PET radiotracers has been developed against many of the upregulated and emerging targets for the diagnosis, prognosis, prediction, and therapy in the fields of oncology, cardiology, and neurology. This review focuses on the carbon-11 radiochemistry and various target-specific PET molecular imaging agents used in tumor, heart, brain, and neuroinflammatory disease imaging along with its associated pathology.

Non-FDG PET/CT

The major applications for molecular imaging with PET in clinical practice concern cancer imaging. Undoubtedly, 18F-FDG represents the backbone of nuclear oncology as it remains so far the most widely employed positron emitter compound. The acquired knowledge on cancer features, however, allowed the recognition in the last decades of multiple metabolic or pathogenic pathways within the cancer cells, which stimulated the development of novel radiopharmaceuticals. An endless list of PET tracers, substantially covering all hallmarks of cancer, has entered clinical routine or is being investigated in diagnostic trials. Some of them guard significant clinical applications, whereas others mostly bear a huge potential. This chapter summarizes a selected list of non-FDG PET tracers, described based on their introduction into and impact on clinical practice.

[Positron emission tomography with 11C-methionine in primary brain tumor diagnosis]

OBJECTIVE

To investigate the variations in ¹¹C-methionine uptake in the intact brain tissue and in glial brain tumors of different types.

MATERIAL AND METHODS

Forty patients (21 men, 19 women) with gliomas, Grade I-IV, underwent ¹¹C-methionine PET-CT and contrast-enhanced MRI. Standardized uptake value (SUV), tumor-to-normal (T/N) ratios and tumor volume were analyzed.

RESULTS

The high inter-subject variability was detected in the intact brain tissue (SUV in the frontal lobe (FL) varies from 0.47 to 1.73). Amino acid metabolism was more active in women than in men (FL SUV 1.32±0.22 and 1.05±0.24, respectively). T/N ratio better differentiates gliomas by the degree of anaplasia compared to SUV. Gliomas of Grade III (T/N=2.64±0.98) were significantly different (p<0.05) from those of Grade IV (T/N=3.83±0.75). The lowest level of methionine uptake was detected in diffuse astrocytomas (T/N=1.52±0.57), which was lower than with anaplastic astrocytomas (T/N=2.34±0.77, p<0.05).

CONCLUSIONS

¹¹C-methionine PET-CT was informative in the high/low degree of malignancy differentiation (T/N 1.66±0.71 for Grade I-II and 3.18±1.06 for Grade III-IV, p<0.05). The method was also useful in separating astrocytomas of Grade II and III. The considerable variation of SUV in the intact brain tissue as well as the difference in uptake between selected areas of the brain were revealed.

Differentiation of Recurrence from Radiation Necrosis in Gliomas Based on the Radiomics of Combinational Features and Multimodality MRI Images

Purpose

To classify radiation necrosis versus recurrence in glioma patients using a radiomics model based on combinational features and multimodality MRI images.

Methods

Fifty-one glioma patients who underwent radiation treatments after surgery were enrolled in this study. Sixteen patients revealed radiation necrosis while 35 patients showed tumor recurrence during the follow-up period. After treatment, all patients underwent T1-weighted, T1-weighted postcontrast, T2-weighted, and fluid-attenuated inversion recovery scans. A total of 41,284 handcrafted and 24,576 deep features were extracted for each patient. The 0.623 + bootstrap method and the area under the curve (denoted as 0.632 + bootstrap AUC) metric were used to select the features. The stepwise forward method was applied to construct 10 logistic regression models based on different combinations of image features.

Results

For handcrafted features on multimodality MRI, model 7 with seven features yielded the highest AUC of 0.9624, sensitivity of 0.8497, and specificity of 0.9083 in the validation set. These values were higher than the accuracy of using handcrafted features on single-modality MRI (paired t-test, p < 0.05, except sensitivity). For combined handcrafted and AlexNet features on multimodality MRI, model 6 with six features achieved the highest AUC of 0.9982, sensitivity of 0.9941, and specificity of 0.9755 in the validation set. These values were higher than the accuracy of using handcrafted features on multimodality MRI (paired t-test, p < 0.05).

Conclusions

Handcrafted and deep features extracted from multimodality MRI images reflecting the heterogeneity of gliomas can provide useful information for glioma necrosis/recurrence classification.

Targeting MMP-14 for dual PET and fluorescence imaging of glioma in preclinical models

PURPOSE

There is a clinical need for agents that target glioma cells for non-invasive and intraoperative imaging to guide therapeutic intervention and improve the prognosis of glioma. Matrix metalloproteinase (MMP)-14 is overexpressed in glioma with negligible expression in normal brain, presenting MMP-14 as an attractive biomarker for imaging glioma. In this study, we designed a peptide probe containing a near-infrared fluorescence (NIRF) dye/quencher pair, a positron emission tomography (PET) radionuclide, and a moiety with high affinity to MMP-14. This novel substrate-binding peptide allows dual modality imaging of glioma only after cleavage by MMP-14 to activate the quenched NIRF signal, enhancing probe specificity and imaging contrast.

METHODS

MMP-14 expression and activity in human glioma tissues and cells were measured in vitro by immunofluorescence and gel zymography. Cleavage of the novel substrate and substrate-binding peptides by glioma cells in vitro and glioma xenograft tumors in vivo was determined by NIRF imaging. Biodistribution of the radiolabeled MMP-14-binding peptide or substrate-binding peptide was determined in mice bearing orthotopic patient-derived xenograft (PDX) glioma tumors by PET imaging.

RESULTS

Glioma cells with MMP-14 activity showed activation and retention of NIRF signal from the cleaved peptides. Resected mouse brains with PDX glioma tumors showed tumor-to-background NIRF ratios of 7.6-11.1 at 4 h after i.v. injection of the peptides. PET/CT images showed localization of activity in orthotopic PDX tumors after i.v. injection of ⁶⁸Ga-binding peptide or ⁶⁴Cu-substrate-binding peptide; uptake of the radiolabeled peptides in tumors was significantly reduced (p < 0.05) by blocking with the non-labeled-binding peptide. PET and NIRF signals correlated linearly in the orthotopic PDX tumors. Immunohistochemistry showed co-localization of MMP-14 expression and NIRF signal in the resected tumors.

CONCLUSIONS

The novel MMP-14 substrate-binding peptide enabled PET/NIRF imaging of glioma models in mice, warranting future image-guided resection studies with the probe in preclinical glioma models.

Is the Hoffman Effect for Methionine Overuse Analogous to the Warburg Effect for Glucose Overuse in Cancer?

The general cancer-specific metabolic defect of methionine (MET) dependence is due to MET overuse for aberrant transmethylation reactions. The excess use of MET for aberrant transmethylation reactions apparently diverts methyl groups from DNA. The resulting global DNA hypomethylation is also a general phenomenon in cancer and leads to unstable genomes and aneuploid karyotypes. The excessive and aberrant use of MET in cancer is readily observed in [¹¹C]-MET-PET imaging, where high uptake of [¹¹C]-MET results in a very strong and selective tumor signal compared to normal tissue background for brain cancer and possibly other cancers. [¹¹C]-MET is superior to [¹⁸C]-fluorodeoxyglucose (FDG) for PET imaging, suggesting that MET overuse in cancer ("Hoffman effect") is greater than glucose overuse in cancer ("Warburg effect").

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.

Utility of Dynamic Susceptibility Contrast Perfusion-Weighted MR Imaging and 11C-Methionine PET/CT for Differentiation of Tumor Recurrence from Radiation Injury in Patients with High-Grade Gliomas

BACKGROUND AND PURPOSE

Both ¹¹C-methionine PET/CT and DSC-PWI could be used to differentiate radiation injury from recurrent brain tumors. Our aim was to assess the performance of MET PET/CT and DSC-PWI for differentiation of recurrence and radiation injury in patients with high-grade gliomas and to quantitatively analyze the diagnostic values of PET and PWI parameters.

MATERIALS AND METHODS

Forty-two patients with high-grade gliomas were enrolled in this study. The final diagnosis was determined by histopathologic analysis or clinical follow-up. PWI and PET parameters were recorded and compared between patients with recurrence and those with radiation injury using Student t tests. Receiver operating characteristic and logistic regression analyses were used to determine the diagnostic performance of each parameter.

RESULTS

The final diagnosis was recurrence in 33 patients and radiation injury in 9. PET/CT showed a patient-based sensitivity and specificity of 0.909 and 0.556, respectively, while PWI showed values of 0.667 and 0.778, respectively. The maximum standardized uptake value, mean standardized uptake value, tumor-to-background maximum standardized uptake value, and mean relative CBV were significantly higher for patients with recurrence than for patients with radiation injury. All these parameters showed a high discriminative power in receiver operating characteristic analysis. The optimal cutoff values for the tumor-to-background maximum standardized uptake value and mean relative CBV were 1.85 and 1.83, respectively, and corresponding sensitivities and specificities for the diagnosis of recurrence were 0.97 and 0.667 and 0.788 and 0.88, respectively. Areas under the curve for the tumor-to-background maximum standardized uptake value and mean relative CBV were 0.847 ± 0.077 and 0.845 ± 0.078, respectively. Combined assessment of the tumor-to-background maximum standardized uptake value and mean relative CBV showed the largest area under the curve (0.953 ± 0.031), with corresponding sensitivity and specificity of 0.848 and 1.0, respectively.

CONCLUSIONS

Both ¹¹C-methionine PET/CT and PWI are equally accurate in the differentiation of recurrence from radiation injury in patients with high-grade gliomas, and a combination of the 2 modalities could result in increased diagnostic accuracy.

L-[Methyl-11C] Methionine-Positron-Emission Tomography (MET-PET)

Methionine (MET) dependence is a cancer-specific metabolic abnormality that is due to MET overuse for aberrant transmethylation reactions. [¹¹C]-MET is very useful for positron-emission tomography (PET) due to MET overuse in malignant tumors. Many benefits of MET-PET have been demonstrated. MET-PET can differentiate recurrent glioma and necrosis. [¹¹C]-MET-PET can also predict prognosis in gliomas better than [¹⁸F]-FDG PET. [¹¹C]-MET-PET is better than MRI for predicting survival in low-grade glioma (LGG). MET-PET has greater specificity for detecting residual tumor after surgery than MRI.

Molecular PET imaging in adaptive radiotherapy: brain

INTRODUCTION

Owing to their heterogeneity and radioresistance, the prognosis of primitive brain tumors, which are mainly glial tumors, remains poor. Dose escalation in radioresistant areas is a potential issue for improving local control and overall survival. This review focuses on advances in biological and metabolic imaging of brain tumors that are proving to be essential for defining tumor target volumes in radiation therapy (RT) and for increasing the use of DPRT (dose painting RT) and ART (adaptative RT), to optimize dose in radio-resistant areas.

EVIDENCE ACQUISITION

Various biological imaging modalities such as PET (hypoxia, glucidic metabolism, protidic metabolism, cellular proliferation, inflammation, cellular membrane synthesis) and MRI (spectroscopy) may be used to identify these areas of radioresistance. The integration of these biological imaging modalities improves the diagnosis, prognosis and treatment of brain tumors.

EVIDENCE SYNTHESIS

Technological improvements (PET and MRI), the development of research, and intensive cooperation between different departments are necessary before using daily metabolic imaging (PET and MRI) to treat patients with brain tumors.

CONCLUSIONS

The adaptation of treatment volumes during RT (ART) seems promising, but its development requires improvements in several areas and an interdisciplinary approach involving radiology, nuclear medicine and radiotherapy. We review the literature on biological imaging to outline the perspectives for using DPRT and ART in brain tumors.

Glioblastoma radiomics: can genomic and molecular characteristics correlate with imaging response patterns?

PURPOSE

For glioblastoma (GBM), imaging response (IR) or pseudoprogression (PSP) is frequently observed after chemoradiation and may connote a favorable prognosis. With tumors categorized by the Cancer Genome Atlas Project (mesenchymal, classical, neural, and proneural) and by methylguanine-methyltransferase (MGMT) methylation status, we attempted to determine if certain genomic or molecular subtypes of GBM were specifically associated with IR or PSP.

METHODS

Patients with GBM treated at two institutions were reviewed. Kaplan-Meier method was used to estimate overall survival (OS) and progression-free survival (PFS). Mantel-cox test determined effect of IR and PSP on OS and PFS. Fisher's exact test was utilized to correlate IR and PSP with genomic subtypes and MGMT status.

RESULTS

Eighty-two patients with GBM were reviewed. The median OS and PFS were 17.9 months and 8.9 months. IR was observed in 28 (40%) and was associated with improved OS (median 29.4 vs 14.5 months p < 0.01) and PFS (median 17.7 vs 5.5 months, p < 0.01). PSP was observed in 14 (19.2%) and trended towards improved PFS (15.0 vs 7.7 months p = 0.08). Tumors with a proneural component had a higher rate of IR compared to those without a proneural component (IR 60% vs 28%; p = 0.03). MGMT methylation was associated with IR (58% vs 24%, p = 0.032), but not PSP (34%, p = 0.10).

CONCLUSION

IR is associated with improved OS and PFS. The proneural subtype and MGMT methylated tumors had higher rates of IR.

Accuracy of 11C-choline positron emission tomography in differentiating glioma recurrence from radiation necrosis: A systematic review and meta-analysis

OBJECTIVES

Distinguishing glioma recurrence from the necrosis after radiation therapy and/or chemotherapy is a crucial clinical issue, for the different diagnosis will lead to divergent treatments. The accurate judgment is barely achieved by conventional imaging methods. We therefore assume it is of need to exert a meta-analysis to evaluate the diagnostic accuracy of 11C-choline positron emission tomography (PET), to achieve this goal.

MATERIAL AND METHODS

We searched the PubMed, Embase, and Chinese Biomedical databases comprehensively to select eligible studies and assessed the quality of each article included (up to May 31, 2018). Fixed-effects models were used. Summary diagnostic accuracy of 11C-choline PET was obtained from pooled analysis.

RESULTS

Five articles comprising 6 studies with total 118 patients (134 scans) were enrolled for the meta-analysis. There was no heterogeneity or publication bias among the included studies. The pooled sensitivity and specificity were 0.87 (95% confidence interval [CI]: 0.78, 0.93) and 0.820 (95% CI: 0.69, 0.91), respectively. The pooled diagnostic odds ratio was 35.50 (95% CI: 11.70, 107.75). The area under the curve was 0.9170 (95% CI: 0.8504, 0.9836), with Q* index equaling to 0.8499. The diagnostic accuracy of each subgroup showed no statistical differences with that of the overall group.

CONCLUSIONS

This meta-analysis indicated 11C-choline has high diagnostic accuracy for the identification of tumor relapse from radiation induced necrosis in gliomas.

Magnetic Resonance Spectroscopy, Positron Emission Tomography and Radiogenomics-Relevance to Glioma

Advances in metabolic imaging techniques have allowed for more precise characterization of gliomas, particularly as it relates to tumor recurrence or pseudoprogression. Furthermore, the emerging field of radiogenomics where radiographic features are systemically correlated with molecular markers has the potential to achieve the holy grail of neuro-oncologic neuro-radiology, namely molecular diagnosis without requiring tissue specimens. In this section, we will review the utility of metabolic imaging and discuss the current state of the art related to the radiogenomics of glioblastoma.

Carbon-11 and Fluorine-18 Labeled Amino Acid Tracers for Positron Emission Tomography Imaging of Tumors

Tumor cells have an increased nutritional demand for amino acids (AAs) to satisfy their rapid proliferation. Positron-emitting nuclide labeled AAs are interesting probes and are of great importance for imaging tumors using positron emission tomography (PET). Carbon-11 and fluorine-18 labeled AAs include the [1-11C] AAs, labeling alpha-C- AAs, the branched-chain of AAs and N-substituted carbon-11 labeled AAs. These tracers target protein synthesis or amino acid (AA) transport, and their uptake mechanism mainly involves AA transport. AA PET tracers have been widely used in clinical settings to image brain tumors, neuroendocrine tumors, prostate cancer, breast cancer, non-small cell lung cancer (NSCLC) and hepatocellular carcinoma. This review focuses on the fundamental concepts and the uptake mechanism of AAs, AA PET tracers and their clinical applications.

Recombinant methioninase (rMETase) is an effective therapeutic for BRAF-V600E-negative as well as -positive melanoma in patient-derived orthotopic xenograft (PDOX) mouse models

Melanoma is a recalcitrant disease. Melanoma patients with the BRAF-V600E mutation have been treated with the drug vemurafenib (VEM) which targets this mutation. However, we previously showed that VEM is not very effective against a BRAF-V600E melanoma mutant in a patient-derived orthotopic xenograft (PDOX) model. In contrast, we demonstrated that recombinant methioninase (rMETase) which targets the general metabolic defect in cancer of methionine dependence, was effective against the BRAF-V600E mutant melanoma PDOX model. In the present study, we demonstrate that rMETase is effective against a BRAF-V600E-negative melanoma PDOX which we established. Forty BRAF-V600E-negative melanoma PDOX mouse models were randomized into four groups of 10 mice each: untreated control (n = 10); temozolomide (TEM) (25 mg/kg, p.o., 14 consecutive days, n = 10); rMETase (100 units, i.p., 14 consecutive days, n = 10); TEM + rMETase (TEM: 25 mg/kg, p.o., rMETase: 100 units, i.p., 14 consecutive days, n = 10). All treatments inhibited tumor growth compared to untreated control (TEM: p = 0.0003, rMETase: p = 0.0006, TEM/rMETase: p = 0.0002) on day 14 after initiation. Combination therapy of TEM and rMETase was significantly more effective than either mono-therapy (TEM: p = 0.0113, rMETase: p = 0.0173). The present study shows that TEM combined with rMETase is effective for BRAF-V600E-negative melanoma PDOX similar to the BRAF-V600E-positive mutation melanoma. These results suggest rMETase in combination with first-line chemotherapy can be highly effective in both BRAF-V600E-negative as well as BRAF-V600E-positive melanoma and has clinical potential for this recalcitrant disease.

Methionine Dependency Determination of Human Patient Tumors in Gelfoam® Histoculture

The elevated requirement of methionine by cancer cells (methionine dependence) is a general metabolic abnormality in cancer. Methionine-dependent cancer cells are unable to proliferate and arrest in the late S/G₂ phase of the cell cycle when methionine is restricted in vitro or in vivo. Cell-cycle arrest in late S/G₂ was used as a biomarker of methionine dependence for patient tumors in Gelfoam^® histoculture. Human cancer patient tumors, including tumors of the colon, breast, ovary, prostate, and a melanoma, were observed to be methionine dependent in Gelfoam^® histoculture based on cell cycle analysis. This simple method can be used to screen patient tumors for methionine dependence and then subsequently apply appropriate chemotherapy for these patients to target this cancer-specific metabolic abnormality.

11C-MET PET/MRI for detection of recurrent glioma

INTRODUCTION

Radiological assessment of brain tumors is widely based on the Radiology Assessment of Neuro-Oncology (RANO) criteria that consider non-specific T1 and T2 weighted images. Limitation of the RANO criteria is that they do not include metabolic imaging techniques that have been reported to be helpful to differentiate treatment related changes from true tumor progression. In the current study, we assessed if the combined use of MRI and PET with hybrid ¹¹C-MET PET/MRI can improve diagnostic accuracy and diagnostic confidence of the readers to differentiate treatment related changes from true progression in recurrent glioma.

METHODS

Fifty consecutive patients with histopathologically proven glioma were prospectively enrolled for a hybrid ¹¹C-MET PET/MRI to differentiate recurrent glioma from treatment induced changes. Sole MRI data were analyzed based on RANO. Sole PET data and in a third evaluation hybrid ¹¹C-MET-PET/MRI data were assessed for metabolic respectively metabolic and morphologic glioma recurrence. Diagnostic performance and diagnostic confidence of the reader were calculated for the different modalities, and the McNemar test and Mann-Whitney U Test were applied for statistical analysis.

RESULTS

Hybrid ¹¹C-MET PET/MRI was successfully performed in all 50 patients. Glioma recurrence was diagnosed in 35 of the 50 patients (70%). Sensitivity and specificity were calculated for MRI (86.11% and 71.43%), for ¹¹C-MET PET (96.77% and 73.68%), and for hybrid ¹¹C-MET-PET/MRI (97.14% and 93.33%). For diagnostic accuracy hybrid ¹¹C-MET-PET/MRI (96%) showed significantly higher values than MRI alone (82%), whereas no significant difference was found for 11C-MET PET (88%). Furthermore, by rating on a five-point Likert scale significantly higher scores were found for diagnostic confidence when comparing ¹¹C-MET PET/MRI (4.26 ± 0,777) to either PET alone (3.44 ± 0.705) or MRI alone (3.56 ± 0.733).

CONCLUSION

This feasibility study showed that hybrid PET/MRI might strengthen RANO classification by adding metabolic information to conventional MRI information. Future studies should evaluate the clinical utility of the combined use of ¹¹C-MET PET/MRI in larger patient cohorts.

Differentiation between Treatment-Induced Necrosis and Recurrent Tumors in Patients with Metastatic Brain Tumors: Comparison among 11C-Methionine-PET, FDG-PET, MR Permeability Imaging, and MRI-ADC-Preliminary Results

BACKGROUND AND PURPOSE

In patients with metastatic brain tumors after gamma knife radiosurgery, the superiority of PET using ¹¹C-methionine for differentiating radiation necrosis and recurrent tumors has been accepted. To evaluate the feasibility of MR permeability imaging, it was compared with PET using ¹¹C-methionine, FDG-PET, and DWI for differentiating radiation necrosis from recurrent tumors.

MATERIALS AND METHODS

The study analyzed 18 lesions from 15 patients with metastatic brain tumors who underwent gamma knife radiosurgery. Ten lesions were identified as recurrent tumors by an operation. In MR permeability imaging, the transfer constant between intra- and extravascular extracellular spaces (/minute), extravascular extracellular space, the transfer constant from the extravascular extracellular space to plasma (/minute), the initial area under the signal intensity-time curve, contrast-enhancement ratio, bolus arrival time (seconds), maximum slope of increase (millimole/second), and fractional plasma volume were calculated. ADC was also acquired. On both PET using ¹¹C-methionine and FDG-PET, the ratio of the maximum standard uptake value of the lesion divided by the maximum standard uptake value of the symmetric site in the contralateral cerebral hemisphere was measured (¹¹C-methionine ratio and FDG ratio, respectively). The receiver operating characteristic curve was used for analysis.

RESULTS

The area under the receiver operating characteristic curve for differentiating radiation necrosis from recurrent tumors was the best for the ¹¹C-methionine ratio (0.90) followed by the contrast-enhancement ratio (0.81), maximum slope of increase (millimole/second) (0.80), the initial area under the signal intensity-time curve (0.78), fractional plasma volume (0.76), bolus arrival time (seconds) (0.76), the transfer constant between intra- and extravascular extracellular spaces (/minute) (0.74), extravascular extracellular space (0.68), minimum ADC (0.60), the transfer constant from the extravascular extracellular space to plasma (/minute) (0.55), and the FDG-ratio (0.53). A significant difference in the ¹¹C-methionine ratio (P < .01), contrast-enhancement ratio (P < .01), maximum slope of increase (millimole/second) (P < .05), and the initial area under the signal intensity-time curve (P < .05) was evident between radiation necrosis and recurrent tumor.

CONCLUSIONS

The present study suggests that PET using ¹¹C-methionine may be superior to MR permeability imaging, ADC, and FDG-PET for differentiating radiation necrosis from recurrent tumors after gamma knife radiosurgery for metastatic brain tumors.

The performance of 11C-Methionine PET in the differential diagnosis of glioma recurrence

Despite the advancement of neuroimaging techniques, it often remains a diagnostic challenge to distinguish recurrent glioma from lesions representing treatment effect. Preliminary reports suggest that 11C-methionine Positron emission tomography (PET) can assist in diagnosing true glioma recurrence. We present here a meta-analysis to assess the accuracy of 11C-methionine PET in identifying recurrent glioma in patients who had undergone prior therapy. A comprehensive search of the PubMed, Embase and Chinese Biomedical (CBM) databases yielded 23 eligible articles comprising 29 studies listed prior to November 20, 2016, representing 891 patients. In this report, we assess the methodological quality of each article individually and perform a meta-analysis to obtain the summary diagnostic accuracy of 11C-methionine PET in correctly identifying recurrent glioma. The pooled sensitivity and specificity are 0.88 (95% CI: 0.85, 0.91) and 0.85 (95% CI: 0.80, 0.89), respectively, with an area under the curve (AUC) for the summary receiver-operating characteristic curve (SROC) of 0.9352. We conclude that 11C-methionine PET has excellent diagnostic performance for differentiating glioma recurrence from treatment effect.

Optimization of diagnostic performance for differentiation of recurrence from radiation necrosis in patients with metastatic brain tumors using tumor volume-corrected 11C-methionine uptake

Background

Tumor to normal tissue ratio (T/N ratio) on ¹¹C-methionine (¹¹C-MET) positron emission tomography/computed tomography (PET/CT) is affected by variable factors. We investigated whether T/N ratio cutoff values corrected according to metabolic tumor volume (MTV) could improve the diagnostic performance of ¹¹C-MET PET/CT for diagnosis of recurrence in patients with metastatic brain tumor.

Forty-eight patients with metastatic brain tumors underwent ¹¹C-MET PET/CT for differential diagnosis between recurrence and radiation necrosis after gamma knife radiosurgery (GKR). Both T/N ratio and MTV were estimated in each lesion on ¹¹C-MET PET/CT. The lesions were classified into three groups based on MTV criteria (≤ 0.5 cm³; > 0.5, ≤ 4.0 cm³; and > 4.0 cm³). The optimal cutoff values of the T/N ratio from receiver operating characteristic (ROC) curve were determined in each group (MTV-corrected) as well as total lesions (non-corrected). Finally, diagnostic performance of ¹¹C-MET PET/CT was compared with the MTV-corrected cutoff values.

Results

Among 77 lesions, 51 were diagnosed with recurrence. The mean T/N ratio was 2.25 (± 1.12) for recurrent lesions and 1.44 (± 0.22) for radiation necrosis (P < 0.001). T/N ratio of 1.61 (non-corrected) provided the best sensitivity, specificity, and diagnostic accuracy (70.6, 80.8, and 74.0%, respectively). Using the MTV criteria, optimal cutoff values of the T/N ratios in each group were 1.23 (MTV ≤ 0.5 cm³), 1.54 (0.5 cm³ < MTV ≤ 4.0 cm³), and 1.85 (MTV > 4.0 cm³). In small-sized lesions (MTV ≤ 0.5 cm³), MTV-corrected cutoff values (1.23) could maintain favorable diagnostic performance with sensitivity, specificity, and diagnostic accuracy (70.0, 80.0, and 73.3%, respectively), compared to non-corrected cutoff values.

Conclusions

MTV-corrected cutoff values of T/N ratio could maintain the diagnostic performance of ¹¹C-MET PET/CT in small sized, metastatic brain tumors. We expect our results to contribute to reproducible and standardized interpretation of ¹¹C-MET PET/CT.

Is DNA methylation the new guardian of the genome?

BACKGROUND

It has been known for more than 100 years that aneuploidy is an essence of cancer. The question is what keeps the genome stable, thereby preventing aneuploidy. For the past 25 years, it has been proposed that p53 is the "guardian of the genome." However, it has been shown that inactivation of p53 does not cause aneuploidy. Another essence of cancer is global DNA hypomethylation, which causes destabilization of the genome and subsequent aneupoloidy. Yet, another essence of cancer is excessive use of methionine, resulting in methionine dependence. Methionine dependence is due to possible "metabolic reprogramming" due to carcinogens, including chemical agents and infectious organisms, such as Helicobacter pylori, that result in altered and excessive transmethylation in cancer cells. Cancer cells appear to have a "methyl-sink" whereby methyl groups are diverted from DNA.

CONCLUSION

DNA hypomethylation destabilizes the genome, leading to aneuploidy and subsequent selection and speciation into autonomous cancers, leading to the conclusion that DNA methylation is the "guardian of the genome."

The wayward methyl group and the cascade to cancer

We propose here a hypothesis of the cause of cancer that brings together fundamental changes in methyl-group metabolism resulting in methionine dependence and global DNA hypomethylation which destabilizes the genome leading to aneuploid karyotypes which evolve and stabilize into autonomous cancer. Experimental support for this hypothesis is that methioine dependence is a general metabolic defect in caner. Methionine dependence is due to excess use of methionene for aberrant transmethylation reactions that apparently divert methyl groups from DNA. The resulting global DNA hypomethylation is also a general phenomena in cancer. Global hypomethylation leads to an unstable genomes and aneuploid karyotypes, another general phenomena in cancer. The excessive and aberrant use of methionine in cancer is strongly observed in [¹¹C]methionine PET imaging, where high uptake of [¹¹C]methionine results in a very strong and selective tumor signal compared with normal tissue background. [¹¹C]methionine is superior to [¹⁸C] fluorodeoxyglucose (FDG)-PET for PET imaging, suggesting methionine dependence is more tumor-specific than glucose dependence.

The usefulness of 18F-fluorocholine PET/CT in the detection of recurrence of central nervous system primary neoplasms

AIM

To study the usefulness of ¹⁸F-fluorocholine (FCH) in detecting the recurrence of primary brain tumours.

MATERIAL AND METHODS

A prospective study was conducted on brain PET/CT with FCH for compassionate use in 21 patients with suspected recurrence of a primary brain tumour. The distribution by pathology was: three grade ii astrocytomas, three grade iii astrocytomas, one grade ii oligodendroglioma, three grade iii oligodendrogliomas, one grade iii oligoastrocytoma, four glioblastoma multiform, one gliomatosis cerebri, and five meningiomas. Studies in which there was a visually significant uptake in the brain parenchyma were classified as positive.

RESULTS

A total of 17 patients were classified as positive, with the results being confirmed by histology (10 cases) or clinical follow-up and imaging, with no false positives or negatives. The mean SUVmax for positive patients was 8.02 and 0.94 for the negative ones, which was significantly different (P=.003) CONCLUSION: PET/CT with FCH shows encouraging results in the evaluation of patients with suspected recurrence of primary brain neoplasms.

Evaluation of a novel sodium borocaptate-containing unnatural amino acid as a boron delivery agent for neutron capture therapy of the F98 rat glioma

BACKGROUND

Boron neutron capture therapy (BNCT) is a unique particle radiation therapy based on the nuclear capture reactions in boron-10. We developed a novel boron-10 containing sodium borocaptate (BSH) derivative, 1-amino-3-fluorocyclobutane-1-carboxylic acid (ACBC)-BSH. ACBC is a tumor selective synthetic amino acid. The purpose of this study was to assess the biodistribution of ACBC-BSH and its therapeutic efficacy following Boron Neutron Capture Therapy (BNCT) of the F98 rat glioma.

METHODS

We evaluated the biodistribution of three boron-10 compounds, ACBC-BSH, BSH and boronophenylalanine (BPA), in vitro and in vivo, following intravenous (i.v.) administration and intratumoral (i.t.) convection-enhanced delivery (CED) in F98 rat glioma bearing rats. For BNCT studies, rats were stratified into five groups: untreated controls, neutron-irradiation controls, BNCT with BPA/i.v., BNCT with ACBC-BSH/CED, and BNCT concomitantly using BPA/i.v. and ACBC-BSH/CED.

RESULTS

In vitro, ACBC-BSH attained higher cellular uptake F98 rat glioma cells compared with BSH. In vivo biodistribution studies following i.v. administration and i.t. CED of ACBC-BSH attained significantly higher boron concentrations than that of BSH, but much lower than that of BPA. However, following convection enhanced delivery (CED), ACBC-BSH attained significantly higher tumor concentrations than BPA. The i.t. boron-10 concentrations were almost equal between the ACBC-BSH/CED group and BPA/i.v. group of rats. The tumor/brain boron-10 concentration ratio was higher with ACBC-BSH/CED than that of BPA/i.v. group. Based on these data, BNCT studies were carried out in F98 glioma bearing rats using BPA/i.v. and ACBC-BSH/CED as the delivery agents. The corresponding mean survival times were 37.4 ± 2.6d and 44.3 ± 8.0d, respectively, and although modest, these differences were statistically significant.

CONCLUSIONS

Our findings suggest that further studies are warranted to evaluate ACBC-BSH/CED as a boron delivery agent.

Optimization of scan initiation timing after 11C-methionine administration for the diagnosis of suspected recurrent brain tumors

OBJECTIVE

¹¹C-Methionine (MET) positron emission tomography (PET) imaging is a valuable technique for the evaluation of primary and recurrent brain tumors. Many studies have used MET-PET for data acquisition starting at 20 min after the tracer injection, while others have used scan initiation times at 5-15 min postinjection. No previous studies have identified the best acquisition timing during MET-PET imaging for suspected recurrent brain tumors. Here we sought to determine the optimal scan initiating timing after MET administration for the detection of recurrent brain tumors.

MATERIALS AND METHODS

Twenty-three consecutive patients with suspected recurrent brain tumors underwent MET-PET examinations. Brain PET images were reconstructed from the four serial data sets (10-15, 15-20, 20-25, and 25-30 min postinjection) that were obtained using the list-mode acquisition technique. We determined the maximal standardized uptake values (SUVmax) of the target lesions and the target-to-normal-tissue ratios (TNRs), calculated as the SUVmax to the SUVmean of a region of interest placed on the normal contralateral frontal cortex. Target lesions without significant MET uptake were excluded.

RESULTS

Thirty-one lesions from 23 patients were enrolled. There were no significant differences in MET SUVmax or TNR values among the PET images that were reconstructed with the data extracted from the four phases postinjection.

CONCLUSION

The MET uptake in the suspected recurrent brain tumors was comparable among all data extraction time phases from 10 to 30 min postinjection. The scan initiation time of MET-PET at 10 min after the injection is allowable for the detection of recurrent brain tumors. The registration identification number of the original study is 1002.

The value of 11C-methionine PET in the early differentiation between tumour recurrence and radionecrosis in patients treated for a high-grade glioma and indeterminate MRI

OBJECTIVE

To evaluate the contribution of ¹¹C-Methionine PET in the early differentiation between tumour recurrence and radionecrosis in patients treated for a high grade glioma.

METHOD

The study included 30 patients with glioma (III/IV grade) treated with surgery/radiotherapy/chemotherapy (5-8 months) and with an indeterminate MRI. All patients underwent a ¹¹C-Methione PET (within 15 days of MRI) and studies were visually analysed (intensity and morphology of uptake), quantified (SUV max/SUV mean background), and coregistered to MRI (3D-Flair). Patient management was decided by the neuro-oncology committee to clinical and imaging follow-up, second-line treatment, or surgery.

RESULTS

There were 23 ¹¹C-Methionine PET studies visually positive. Morphology of uptake was focal in 15, diffuse in 4, and ring-shaped in 4. Three out of the focal uptake cases underwent resection (Histopathology +). Sixteen underwent second-line therapy (11 responded; 5 progressed). The 4 cases with ring-shaped uptake were followed-up, and progression was found in 2 (true-positive), and disease-free in 2 (follow-up of 6 and 7 months, respectively) (false-positive). Seven out of ¹¹C-Methionine studies PET were visually negative, and all of them were disease-free (follow-up of 3-12 months). SUV lesion/background was 2.79±1.35 in tumour recurrence, and 1.53±0.39 in radionecrosis (P<.05). Taking into account a SUV lesion/background threshold of 2.35, the sensitivity and specificity values were 90.5% and 100%, respectively.

CONCLUSION

Visual analysis, quantitative and PET/MRI coregistration of ¹¹C-Methionine PET showed their complementary role in patients with indeterminate MRI results, thus allowing early differentiation between tumour recurrence and radionecrosis, and helping in the individual therapy approach.

Prognostic value of post-treatment metabolic tumor volume from 11C-methionine PET/CT in recurrent malignant glioma

We investigated the diagnostic and prognostic significance of metabolic parameters from ¹¹C-methionine (MET) positron emission tomography (PET) in patients with malignant glioma. The MET-PET was examined in 42 patients who had been previously treated with adjuvant treatment for malignant glioma. Both ratios of maximal MET uptake of the tumors to those of the contralateral normal gray matter (T/N ratio) and metabolic tumor volume (MTV) were estimated in each lesion. The diagnostic performance for recurrence was investigated in all enrolled patients. A definitive diagnosis was done with pathologic confirmation or clinical follow-up. Among recurrent patients, we evaluated the prognostic value of metabolic parameters (T/N ratio and MTV) as well as clinical factors. Among 42 patients, 35 patients were revealed with recurrence. Both T/N ratios (p = 0.009) and MTV (p = 0.001) exhibited statistical significance to differentiate between recurrence and post-treatment radiation effect. A T/N ratio of 1.43 provided the best sensitivity and specificity for recurrence (91.4 and 100 %, respectively), and a MTV of 6.72 cm³ provided the best sensitivity and specificity (77.1 % and 100 %, respectively). To evaluate the prognostic impact, different cutoffs of MTV were examined in patients with recurrent tumor and a threshold of 60 cm³ was determined as a best cutoff value to separate the patients in two prognostic groups. Univariate analysis revealed improved overall survival (OS) for patients with Karnofsky performance scale (KPS) score ≥70 (p < 0.001) or MTV <60 cm³ (p = 0.049). Multivariate analysis showed that patients with KPS score ≥70 (p < 0.001; hazard ratio = 0.104; 95 % CI, 0.029-0.371) or MTV < 60 cm³ (p = 0.031; hazard ratio = 0.288; 95 % CI, 0.093-0.895) were significantly associated with a longer OS. However, T/N ratio was not correlated with patients' outcome. Metabolic parameters had the diagnostic value to differentiate recurrence from post-treatment radiation effect. Compared with T/N ratio, MTV was an independent significant prognostic factor with KPS score in patients with recurrent tumor. Our study had a potential to manage these patients according to prognostic information using MET-PET.

Response Assessment in Neuro-Oncology working group and European Association for Neuro-Oncology recommendations for the clinical use of PET imaging in gliomas

This guideline provides recommendations for the use of PET imaging in gliomas. The review examines established clinical benefit in glioma patients of PET using glucose ((18)F-FDG) and amino acid tracers ((11)C-MET, (18)F-FET, and (18)F-FDOPA). An increasing number of studies have been published on PET imaging in the setting of diagnosis, biopsy, and resection as well radiotherapy planning, treatment monitoring, and response assessment. Recommendations are based on evidence generated from studies which validated PET findings by histology or clinical course. This guideline emphasizes the clinical value of PET imaging with superiority of amino acid PET over glucose PET and provides a framework for the use of PET to assist in the management of patients with gliomas.

A comparison study of (11)C-methionine and (18)F-fluorodeoxyglucose positron emission tomography-computed tomography scans in evaluation of patients with recurrent brain tumors

Introduction:

¹¹C-methonine ([¹¹C]-MET) positron emission tomography-computed tomography (PET-CT) is a well-established technique for evaluation of tumor for diagnosis and treatment planning in neurooncology. [¹¹C]-MET reflects amino acid transport and has been shown to be more sensitive than magnetic resonance imaging (MRI) in stereotactic biopsy planning. This study compared fluorodeoxyglucose (FDG) PET-CT and MET PET-CT in the detection of various brain tumors.

Materials and Methods:

Sixty-four subjects of brain tumor treated by surgery, chemotherapy, and/or radiotherapy were subjected to [¹⁸F]-FDG, [¹¹C]-MET, and MRI scan. The lesion was analyzed semiquantitatively using tumor to normal contralateral ratio. The diagnosis was confirmed by surgery, stereotactic biopsy, clinical follow-up, MRI, or CT scans.

Results:

Tumor recurrence was found in 5 out of 22 patients on [F-18] FDG scan while [¹¹C]-MET was able to detect recurrence in 18 out of 22 patients in low-grade gliomas. Two of these patients were false positive for the presence of recurrence of tumor and later found to be harboring necrosis. Among oligodendroglioma, medulloblastoma and high-grade glioma out of 42 patients 39 were found to be concordant MET and FDG scans. On semiquantitative analysis, mean T/NT ratio was found to be 2.96 ± 0.94 for lesions positive for recurrence of tumors and 1.18 ± 0.74 for lesions negative for recurrence of tumor on [¹¹C]-MET scan. While the ratio for FDG scan on semiquantitative analysis was found to be 2.05 ± 1.04 for lesions positive for recurrence of tumors and 0.52 ± 0.15 for lesions negative for recurrence of tumors.

Conclusion:

The study highlight that [¹¹C]-MET is superior to [¹⁸F]-FDG PET scans to detect recurrence in low-grade glioma. A cut-off value of target to nontarget value of 1.47 is a useful parameter to distinguish benign from malignant lesion on an [¹¹C]-MET Scan. Both [¹⁸F]-FDG and [¹¹C]-MET scans were found to be useful in high-grade astrocytoma, oligodendroglioma, and medulloblastoma.

A prospective, multicentre, single-arm clinical trial of bevacizumab for patients with surgically untreatable, symptomatic brain radiation necrosis†

Background

Brain radiation necrosis (BRN) can be a complication of radiotherapy for primary and secondary brain tumors, as well as head and neck tumors. Since vascular endothelial growth factor (VEGF) is also a vascular permeability factor in the brain, bevacizumab, a humanized antibody that inhibits VEGF, would be expected to reduce perilesional edema that often accompanies BRN.

Methods

Patients with surgically untreatable, symptomatic BRN refractory to conventional medical treatments (eg, corticosteroid, anticoagulants, or hyperbaric oxygen therapy) were enrolled. We judged that a major cause of perilesional edema with a lesion-to-normal brain ratio ≤1.8 on ¹¹C-methionine or ≤2.5 on ¹⁸F-boronophenylalanine PET was BRN, not tumor recurrence, and 6 cycles of biweekly bevacizumab (5 mg/kg) were administered. The primary endpoint was a ≥30% reduction from the patients' registration for perilesional edema continuing for ≥1 month.

Results

Of the 41 patients enrolled, 38 were fully eligible for the response assessment. The primary endpoint was achieved in 30 of the 38 (78.9%) patients at 3.0 months (median) after enrollment. Sixteen patients (42.1%) experienced improvement of their Karnofsy Performance Score. Corticosteroid use could be reduced in 29 patients (76.3%). Adverse events at grade ≥3 occurred in 10 patients (24.4%).

Conclusions

Bevacizumab treatment offers certain clinical benefits for patients with surgically untreatable, symptomatic BRN. The determination of BRN using amino-acid PET, not biopsy, is adequate and less invasive for determining eligibility to receive bevacizumab.

Treating recurrent glioblastoma: an update

Glioblastoma, the most aggressive of the gliomas, has a high recurrence and mortality rate. The nature of this poor prognosis resides in the molecular heterogeneity and phenotypic features of this tumor. Despite research advances in understanding the molecular biology, it has been difficult to translate this knowledge into effective treatment. Nearly all will have tumor recurrence, yet to date very few therapies have established efficacy as salvage regimens. This challenge is further complicated by imaging confounders and to an even greater degree by the ever increasing molecular heterogeneity that is thought to be both sporadic and treatment-induced. The development of novel clinical trial designs to support the development and testing of novel treatment regimens and drug delivery strategies underscore the need for more precise techniques in imaging and better surrogate markers to help determine treatment response. This review summarizes recent approaches to treat patients with recurrent glioblastoma and considers future perspectives.

Role of [(11)C] methionine positron emission tomography in the diagnosis and prediction of survival in brain tumours

OBJECTIVE

[(11)C] methionine (MET) positron-emission tomography (PET) is a useful diagnostic and therapeutic tool in neuro-oncology. The aim of this study was to evaluate the relationship between MET uptake and the histopathological grade in both primary brain tumours and brain metastases. A secondary goal was to assess the relationship between MET uptake and patients' survival after surgery.

METHODS

We reviewed a consecutive series of 43 PET studies performed at our institution. Out of the 43 patients studied, 35 harboured primary brain tumours (3 grade I, 12 grade II, 7 grade III and 13 grade IV) and 8 patients had brain metastases. We measured the tumour/cortex ratio (T/C ratio) on each PET study and we investigated the correlations among the tracer uptake, tumour grade, tumour type, MRI parameters and outcome.

RESULTS

The mean T/C ratio was 1.8 ± 0.9 for benign lesions and low grade gliomas (grade I and II) and 2.7 ± 1 for high grade gliomas (grade III and IV). In brain metastases it was 2.5 ± 0.7, with a significant difference in MET uptake between low and high grades gliomas (P=0.03). There was no statistically significant difference among all different histologic types. We found that both contrast enhancement and perfusion studies correlate with MET uptake in brain tumours. Moreover, in Kaplan-Meier curves, the T/C ratio adversely affects long term survival in patients with brain tumours (P=0.01).

CONCLUSIONS

MET PET appears to be useful in diagnosis and evaluation of potential malignancy in brain tumours. MET uptake is also related with the overall survival in patients with brain tumours. Nevertheless, further studies are needed in order to define its possible clinical implications in identifying patients at high risk of tumour progression or resistance to therapy.

11C-MET PET/CT and advanced MRI in the evaluation of tumor recurrence in high-grade gliomas

OBJECTIVES

The purpose of this study was to evaluate the performance of l-[methyl-()11C]methionine (11C-MET) PET/CT and MRI (with the inclusion of advanced imaging techniques, namely, MR spectroscopy and MR perfusion) in the assessment of tumor recurrence in high-grade gliomas.

PATIENTS AND METHODS

Twenty-nine patients with high-grade gliomas who underwent surgical resection, external beam radiation therapy, and standard regimens of chemotherapy were subjected to MRI (conventional, MR perfusion, and MR spectroscopy) and 11C-MET PET/CT scans. A definitive diagnosis was made based on histopathology and/or long-term clinical and radiological follow-up. Several indices were obtained for lesion characterization, namely, SUVmean, SUVmax, and mean lesion-to-normal tissue on PET/CT, as well as relative cerebral blood volume and choline-to-creatine ratio on MRI.

RESULTS

Histological examination revealed viable tumor cells in 19 cases, whereas the remaining 10 were deemed to be negative based on histology (3 cases) or long-term follow-up (7 cases). All the quantitative indices mentioned previously tended to be higher in patients with tumor recurrence/residual. The sensitivity, specificity, and accuracy of 11C-MET PET/CT in identifying tumor recurrence/residual were 94.7%, 80%, and 89.6%, respectively, whereas that of MRI were 84.2%, 90%, and 86.2%, respectively.

CONCLUSIONS

Both 11C-MET PET/CT and MRI (with the inclusion of advanced MRI techniques) demonstrated a high diagnostic performance in the identification of tumor residual/recurrence in high-grade gliomas posttherapy. Although 11C-MET PET/CT seemed to be more sensitive, whereas advanced MRI seemed more specific, there was no statistically significant difference in the diagnostic performance of either modality in the present study. Further studies with a larger group of patients are warranted.

Tumour progression or pseudoprogression? A review of post-treatment radiological appearances of glioblastoma

Glioblastoma (GBM) is a common brain tumour in adults, which, despite multimodality treatment, has a poor median survival. Efficacy of therapy is assessed by clinical examination and magnetic resonance imaging (MRI) features. There is now a recognised subset of treated patients with imaging features that indicate "progressive disease" according to Macdonald's criteria, but subsequently, show stabilisation or resolution without a change in treatment. In these cases of "pseudoprogression", it is believed that non-tumoural causes lead to increased contrast enhancement and conventional MRI is inadequate in distinguishing this from true tumour progression. Incorrect diagnosis is important, as failure to identify pseudoprogression could lead to an inappropriate change of effective therapy. The purpose of this review is to outline the current research into radiological assessment with MRI and molecular imaging of post-treatment GBMs, specifically the differentiation between pseudoprogression and tumour progression.

Qualitative analysis of spinal intramedullary lesions using PET/CT

OBJECT Although the usefulness of PET for brain lesions has been established, few reports have examined the use of PET for spinal intramedullary lesions. This study investigated the diagnostic utility of PET/CT for spinal intramedullary lesions. METHODS l-[methyl-¹¹C]-methionine (MET)- or [¹⁸F]-fluorodeoxyglucose (FDG)-PET/CT was performed in 26 patients with spinal intramedullary lesions. The region of interest (ROI) within the spinal cord parenchyma was placed manually in the axial plane. Maximum pixel counts in the ROIs were normalized to the maximum standardized uptake value (SUV_max) using subject body weight. For FDG-PET the SUV_max was corrected for lean body mass (SUL_max) to exclude any influence of the patient's body shape. Each SUV was analyzed based on histopathological results after surgery. The diagnostic validity of the SUV was further compared with the tumor proliferation index using the MIB-1 monoclonal antibody (MIB-1 index). RESULTS A total of 16 patients underwent both FDG-PET and MET-PET, and the remaining 10 patients underwent either FDG-PET or MET-PET. Pathological diagnoses included high-grade malignancy such as glioblastoma multiforme, anaplastic astrocytoma, or anaplastic ependymoma in 5 patients; low-grade malignancy such as hemangioblastoma, diffuse astrocytoma, or ependymoma in 12 patients; and nonneoplastic lesion including cavernous malformation in 9 patients. Both FDG and MET accumulated significantly in high-grade malignancy, and the SUL_max and SUV_max correlated with the tumor proliferation index. Therapeutic response after chemotherapy or radiation in high-grade malignancy was well monitored. However, a significant difference in SUL_max and SUV_max for FDG-PET and MET-PET was not evident between low-grade malignancy and nonneoplastic lesions. CONCLUSIONS Spinal PET/CT using FDG or MET for spinal intramedullary lesions appears useful and practical, particularly for tumors with high-grade malignancy. Differentiation of tumors with low-grade malignancy from nonneoplastic lesions may still prove difficult. Further technological refinement, including the selection of radiotracer or analysis evaluation methods, is needed.

The use of 18F-FDG PET ratios in the differential diagnosis of common malignant brain tumors

OBJECTIVE

This study examined the use of positron emission tomography (PET) ratios to improve the diagnostic ability of 18F-FDG PET/computed tomography (CT) in the differentiation of enhancing brain metastases, central nervous system lymphomas, and gliomas.

MATERIALS AND METHODS

Seventy-six patients with malignant brain tumors and available magnetic resonance imaging and PET/CT examinations were included.

RESULTS

Among standardized uptake value (SUV)-related parameters tested, tumor maximum SUV to ipsilateral cortex maximum SUV ratio (Tmax:WMimax) and maximum SUV (SUVmax) proved to be the two most valuable parameters for differential diagnosis.

CONCLUSION

In addition to SUVmax, Tmax:WMimax also seems to provide helpful information for the differential diagnosis of lymphomas from other malignant brain tumors.

Differentiation of Brain Tumor Recurrence from Post-Radiotherapy Necrosis with 11C-Methionine PET: Visual Assessment versus Quantitative Assessment

Purpose

The aim of this multi-center study was to assess the diagnostic capability of visual assessment in L-methyl-¹¹C-methionine positron emission tomography (MET-PET) for differentiating a recurrent brain tumor from radiation-induced necrosis after radiotherapy, and to compare it to the accuracy of quantitative analysis.

Methods

A total of 73 brain lesions (glioma: 31, brain metastasis: 42) in 70 patients who underwent MET-PET were included in this study. Visual analysis was performed by comparison of MET uptake in the brain lesion with MET uptake in one of four regions (around the lesion, contralateral frontal lobe, contralateral area, and contralateral cerebellar cortex). The concordance rate and logistic regression analysis were used to evaluate the diagnostic ability of visual assessment. Receiver-operating characteristic curve analysis was used to compare visual assessment with quantitative assessment based on the lesion-to-normal (L/N) ratio of MET uptake.

Results

Interobserver and intraobserver κ-values were highest at 0.657 and 0.714, respectively, when assessing MET uptake in the lesion compared to that in the contralateral cerebellar cortex. Logistic regression analysis showed that assessing MET uptake in the contralateral cerebellar cortex with brain metastasis was significantly related to the final result. The highest area under the receiver-operating characteristic curve (AUC) with visual assessment for brain metastasis was 0.85, showing no statistically significant difference with L/Nmax of the contralateral brain (AUC = 0.89) or with L/Nmean of the contralateral cerebellar cortex (AUC = 0.89), which were the areas that were the highest in the quantitative assessment. For evaluation of gliomas, no specific candidate was confirmed among the four areas used in visual assessment, and no significant difference was seen between visual assessment and quantitative assessment.

Conclusion

The visual assessment showed no significant difference from quantitative assessment of MET-PET with a relevant cut-off value for the differentiation of recurrent brain tumors from radiation-induced necrosis.

The use of dynamic O-(2-18F-fluoroethyl)-l-tyrosine PET in the diagnosis of patients with progressive and recurrent glioma

BACKGROUND

We evaluated the diagnostic value of static and dynamic O-(2-[(18)F]fluoroethyl)-L-tyrosine ((18)F-FET) PET parameters in patients with progressive or recurrent glioma.

METHODS

We retrospectively analyzed 132 dynamic (18)F-FET PET and conventional MRI scans of 124 glioma patients (primary World Health Organization grade II, n = 55; grade III, n = 19; grade IV, n = 50; mean age, 52 ± 14 y). Patients had been referred for PET assessment with clinical signs and/or MRI findings suggestive of tumor progression or recurrence based on Response Assessment in Neuro-Oncology criteria. Maximum and mean tumor/brain ratios of (18)F-FET uptake were determined (20-40 min post-injection) as well as tracer uptake kinetics (ie, time to peak and patterns of the time-activity curves). Diagnoses were confirmed histologically (95%) or by clinical follow-up (5%). Diagnostic accuracies of PET and MR parameters for the detection of tumor progression or recurrence were evaluated by receiver operating characteristic analyses/chi-square test.

RESULTS

Tumor progression or recurrence could be diagnosed in 121 of 132 cases (92%). MRI and (18)F-FET PET findings were concordant in 84% and discordant in 16%. Compared with the diagnostic accuracy of conventional MRI to diagnose tumor progression or recurrence (85%), a higher accuracy (93%) was achieved by (18)F-FET PET when a mean tumor/brain ratio ≥2.0 or time to peak <45 min was present (sensitivity, 93%; specificity, 100%; accuracy, 93%; positive predictive value, 100%; P < .001).

CONCLUSION

Static and dynamic (18)F-FET PET parameters differentiate progressive or recurrent glioma from treatment-related nonneoplastic changes with higher accuracy than conventional MRI.

Post-treatment imaging changes in primary brain tumors

Discerning between primary brain tumor progression and treatment-related effect is a significant issue and a major challenge in neuro-oncology. The difficulty in differentiating tumor progression from treatment-related effects has important implications for treatment decisions and prognosis, as well as for clinical trial design and results. Conventional MRI is widely used to assess disease status, but cannot reliably distinguish between tumor progression and treatment-related effects. Several advanced imaging techniques are promising, but have yet to be prospectively validated for this use. This review explores two treatment-related effects, pseudoprogression and radiation necrosis, as well as the concept of pseudoresponse, and highlights several advanced imaging modalities and the evidence supporting their use in differentiating tumor progression from treatment-related effect.

Pathophysiology, diagnosis, and treatment of radiation necrosis in the brain

New radiation modalities have made it possible to prolong the survival of individuals with malignant brain tumors, but symptomatic radiation necrosis becomes a serious problem that can negatively affect a patient’s quality of life through severe and lifelong effects. Here we review the relevant literature and introduce our original concept of the pathophysiology of brain radiation necrosis following the treatment of brain, head, and neck tumors. Regarding the pathophysiology of radiation necrosis, we introduce two major hypotheses: glial cell damage or vascular damage. For the differential diagnosis of radiation necrosis and tumor recurrence, we focus on the role of positron emission tomography. Finally, in accord with our hypothesis regarding the pathophysiology, we describe the promising effects of the anti-vascular endothelial growth factor antibody bevacizumab on symptomatic radiation necrosis in the brain.