Comparison of (11)C-methionine, (11)C-choline, and (18)F-fluorodeoxyglucose-PET for distinguishing glioma recurrence from radiation necrosis

Metabolic imaging in recurrent gliomas: comparative performance of 18F-FDOPA, 18F-fluorocholine and 18F-FDG PET/CT

PURPOSE

The aim of this study was to directly evaluate glucose, amino-acid and membrane metabolism in tumor cells for diagnosis and prognostication of recurrent gliomas.

METHODS

Fifty-five patients (median age = 36 years; 33 men) with histologically proven gliomas and suspected recurrence were prospectively recruited and underwent 18F-FDG (Fluorodeoxyglucose), 18F-FDOPA (fluorodopa) and 18F-Fluorocholine-PET/CT. Images were evaluated by two physicians visually and quantitatively [lesion-SUVmax, tumor (T) to gray-matter (G) and metabolically-active tumor volumes (MTV)]. After median follow-up of 51.5 months, recurrence was diagnosed in 49 patients. Thirty-one patients died with a median survival of 14 months.

RESULTS

Diagnostic-accuracies for 18F-FDOPA, 18F-Fluorocholine,18F-FDG and contrast-enhanced-MRI were 92.7% (95% CI 82.7-97.1), 81.8% (69.7-89.8), 45.5% (33.0-58.5) and 44.7% (30.2-60.3), respectively. Among the 20 lesions, missed by MRI; 18F-FDOPA, 18F-Fluorocholine and 18F-FDG were able to detect 19, 14 and 4 lesions. Corresponding area-under-the-curves (T/G ratios) were 0.817 (0.615-1.000), 0.850 (0.736-0.963) and 0.814 (0.658-0.969), when differentiating recurrence from treatment-induced changes. In univariate-survival-analysis, 18F-FDOPA-T/G, visually detectable recurrence in 18F-FDG, 18F-FDOPA-MTV, cell-lineage and treatment-type were significant parameters. In Multivariate-Cox-regression analysis, 18F-FDOPA-MTV [HR = 1.009 (1.001-1.017); P  = 0.024 (~0.9% increase in hazard for every mL increase of MTV)] and cell-lineage [3.578 (1.447-8.846); P  = 0.006] remained significant. 18F-FDOPA-MTV cutoff <29.59 mL predicted survival higher than 2 years. At cutoff ≥29.59 mL, HR at 2 years was 2.759 (1.310-5.810).

CONCLUSION

18F-FDOPA-PET/CT can diagnose recurrence with high accuracy and MTV predicts survival. 18F-Fluorocholine is a good alternative. Higher 18F-FDG uptake is an adverse prognostic indicator.

Methionine-PET to differentiate between brain lesions appearing similar on conventional CT/MRI scans

BACKGROUND AND PURPOSE

11 C-Methionine (MET)-PET is a useful tool in neuro-oncology. This study aimed to examine whether a combination of diagnostic variables associated with MET uptake could help distinguish between brain lesions that are often difficult to discriminate in conventional CT and MRI.

METHODS

MET-PET was assessed in 129 patients with glioblastoma multiforme, primary central nervous lymphoma, metastatic brain tumor, tumefactive multiple sclerosis, or radiation necrosis. The accuracy of the differential diagnosis was analyzed using five diagnostic characteristics in combination: higher maximum standardized uptake value (SUV) of MET in the lesion/the mean normal cortical SUV of MET ratio, overextension beyond gadolinium, peripheral pattern indicating abundant MET accumulation in the peripheral region, central pattern denoting abundant MET accumulation in the central region, and dynamic-up suggesting increased MET accumulation during dynamic study. The analysis was conducted on sets of two of the five brain lesions.

RESULTS

Significant differences in the five diagnostic traits were observed among the five brain lesions, and differential diagnosis could be achieved by combining these diagnostic features. The area under the curve between each set of two of the five brain lesions using MET-PET features ranged from .85 to 1.0.

CONCLUSIONS

According to the findings, combining the five diagnostic criteria could help with the differential diagnosis of the five brain lesions. MET-PET is an auxiliary diagnostic technique that could help in distinguishing these five brain lesions.

Advances in the application of neuroinflammatory molecular imaging in brain malignancies

The prevalence of brain cancer has been increasing in recent decades, posing significant healthcare challenges. The introduction of immunotherapies has brought forth notable diagnostic imaging challenges for brain tumors. The tumor microenvironment undergoes substantial changes in induced immunosuppression and immune responses following the development of primary brain tumor and brain metastasis, affecting the progression and metastasis of brain tumors. Consequently, effective and accurate neuroimaging techniques are necessary for clinical practice and monitoring. However, patients with brain tumors might experience radiation-induced necrosis or other neuroinflammation. Currently, positron emission tomography and various magnetic resonance imaging techniques play a crucial role in diagnosing and evaluating brain tumors. Nevertheless, differentiating between brain tumors and necrotic lesions or inflamed tissues remains a significant challenge in the clinical diagnosis of the advancements in immunotherapeutics and precision oncology have underscored the importance of clinically applicable imaging measures for diagnosing and monitoring neuroinflammation. This review summarizes recent advances in neuroimaging methods aimed at enhancing the specificity of brain tumor diagnosis and evaluating inflamed lesions.

The Role of PET Imaging in the Differential Diagnosis between Radiation Necrosis and Recurrent Disease in Irradiated Adult-Type Diffuse Gliomas: A Systematic Review

Adult-type diffuse gliomas are treated with a multimodality treatment approach that includes radiotherapy both in the primary setting, and in the case of progressive or recurrent disease. Radiation necrosis represents a major complication of radiotherapy. Recurrent disease and treatment-related changes are often indistinguishable using conventional imaging methods. The present systematic review aims at assessing the diagnostic role of PET imaging using different radiopharmaceuticals in differentiating radiation necrosis and disease relapse in irradiated adult-type diffuse gliomas. We conducted a comprehensive literature search using the PubMed/MEDLINE and EMBASE databases for original research studies of interest. In total, 436 articles were assessed for eligibility. Ten original papers, published between 2014 and 2022, were selected. Four articles focused on [¹⁸F]FDG, seven on amino acid tracers ([¹⁸F]FET n = 3 and [¹¹C]MET n = 4), one on [¹¹C]CHO, and one on [⁶⁸Ga]Ga-PSMA. Visual assessment, semi-quantitative methods, and radiomics were applied for image analysis. Furthermore, 2/10 papers were comparative studies investigating different radiopharmaceuticals. The present review, the first one on the topic in light of the new 2021 CNS WHO classification, highlighted the usefulness of PET imaging in distinguishing radiation necrosis and tumour recurrence, but revealed high heterogeneity among studies.

Challenges and opportunities for advanced neuroimaging of glioblastoma

Glioblastoma is the most aggressive of glial tumours in adults. On conventional magnetic resonance (MR) imaging, these tumours are observed as irregular enhancing lesions with areas of infiltrating tumour and cortical expansion. More advanced imaging techniques including diffusion-weighted MRI, perfusion-weighted MRI, MR spectroscopy and positron emission tomography (PET) imaging have found widespread application to diagnostic challenges in the setting of first diagnosis, treatment planning and follow-up. This review aims to educate readers with regard to the strengths and weaknesses of the clinical application of these imaging techniques. For example, this review shows that the (semi)quantitative analysis of the mentioned advanced imaging tools was found useful for assessing tumour aggressiveness and tumour extent, and aids in the differentiation of tumour progression from treatment-related effects. Although these techniques may aid in the diagnostic work-up and (post-)treatment phase of glioblastoma, so far no unequivocal imaging strategy is available. Furthermore, the use and further development of artificial intelligence (AI)-based tools could greatly enhance neuroradiological practice by automating labour-intensive tasks such as tumour measurements, and by providing additional diagnostic information such as prediction of tumour genotype. Nevertheless, due to the fact that advanced imaging and AI-diagnostics is not part of response assessment criteria, there is no harmonised guidance on their use, while at the same time the lack of standardisation severely hampers the definition of uniform guidelines.

Iatrogenic Influence on Prognosis of Radiation-Induced Contrast Enhancements in Patients with Glioma WHO 1-3 following Photon and Proton Radiotherapy

BACKGROUND AND PURPOSE

Radiation-induced contrast enhancement (RICE) is a common side effect following radiotherapy for glioma, but both diagnosis and handling are challenging. Due to the potential risks associated with RICE and its challenges in differentiating RICE from tumor progression, it is critical to better understand how RICE prognosis depends on iatrogenic influence.

MATERIALS AND METHODS

We identified 99 patients diagnosed with RICE who were previously treated with either photon or proton therapy for World Health Organization (WHO) grade 1-3 primary gliomas. Post-treatment brain MRI-based volumetric analysis and clinical data collection was performed at multiple time points.

RESULTS

The most common histologic subtypes were astrocytoma (50%) and oligodendroglioma (46%). In 67%, it was graded WHO grade 2 and in 86% an IDH mutation was present. RICE first occurred after 16 months (range: 1 - 160) in median. At initial RICE occurrence, 39% were misinterpreted as tumor progression. A tumor-specific therapy including chemotherapy or re-irradiation led to a RICE size progression in 86% and 92% of cases, respectively and RICE symptom progression in 57% and 65% of cases, respectively. A RICE-specific therapy such as corticosteroids or Bevacizumab for larger or symptomatic RICE led to a RICE size regression in 81% of cases with symptom stability or regression in 62% of cases.

CONCLUSIONS

While with chemotherapy and re-irradiation a RICE progression was frequently observed, anti-edematous or anti-VEGF treatment frequently went along with a RICE regression. For RICE, correct diagnosis and treatment decisions are challenging and critical and should be made interdisciplinarily.

Congress of Neurological Surgeons systematic review and evidence-based guidelines update on the role of imaging in the management of progressive glioblastoma in adults

TARGET POPULATION

These recommendations apply to adults with glioblastoma who have been previously treated with first-line radiation or chemoradiotherapy and who are suspected of experiencing tumor progression.

QUESTION

In patients with previously treated glioblastoma, is standard contrast-enhanced magnetic resonance imaging including diffusion weighted imaging useful for diagnosing tumor progression and differentiating progression from treatment-related changes?

LEVEL II

Magnetic resonance imaging with and without gadolinium enhancement including diffusion weighted imaging is recommended as the imaging surveillance method to detect the progression of previously diagnosed glioblastoma.

QUESTION

In patients with previously treated glioblastoma, does magnetic resonance spectroscopy add useful information for diagnosing tumor progression and differentiating progression from treatment-related changes beyond that derived from standard magnetic resonance imaging with and without gadolinium enhancement?

LEVEL II

Magnetic resonance spectroscopy is recommended as a diagnostic method to differentiate true tumor progression from treatment-related imaging changes or pseudo-progression in patients with suspected progressive glioblastoma.

QUESTION

In patients with previously treated glioblastoma, does magnetic resonance perfusion add useful information for diagnosing tumor progression and differentiating progression from treatment-related changes beyond that derived from standard magnetic resonance imaging with and without gadolinium enhancement?

LEVEL III

Magnetic resonance perfusion is suggested as a diagnostic method to differentiate true tumor progression from treatment-related imaging changes or pseudo-progression in patients with suspected progressive glioblastoma.

QUESTION

In patients with previously treated glioblastoma, does the addition of single-photon emission computed tomography (SPECT) provide additional useful information for diagnosing tumor progression and differentiating progression from treatment-related changes beyond that derived from standard magnetic resonance imaging with and without gadolinium enhancement?

LEVEL III

Single-photon emission computed tomography imaging is suggested as a diagnostic method to differentiate true tumor progression from treatment-related imaging changes or pseudo-progression in patients with suspected progressive glioblastoma.

QUESTION

In patients with previously treated glioblastoma, does 18F-fluorodeoxyglucose positron emission tomography add useful information for diagnosing tumor progression and differentiating progression from treatment-related changes beyond that derived from standard magnetic resonance imaging with and without gadolinium enhancement?

LEVEL III

The routine use of 18F-fluorodeoxyglucose positron emission tomography to identify progression of glioblastoma is not recommended.

QUESTION

In patients with previously treated glioblastoma, does positron emission tomography with amino acid agents add useful information for diagnosing tumor progression and differentiating progression from treatment-related changes beyond that derived from standard magnetic resonance imaging with and without gadolinium enhancement?

LEVEL III

It is suggested that amino acid positron emission tomography be considered to assist in the differentiation of progressive glioblastoma from treatment related changes.

Long-term survival of a patient with diffuse midline glioma in the pineal region: A case report and literature review

Background:

Diffuse midline glioma (DMG) is an invasive astrocytic tumor arisen from midline structures, such as the pons and thalamus. Five cases of DMG in the pineal region have been reported, but the clinical course was poor; there was no case of survival for more than 2 years.

Case Description:

We report the case of a 12-year-old boy with DMG in the pineal region who is living a normal daily life for more than 6 years following multimodal treatment. He complained of a headache accompanied by vomiting that had gradually worsened 1 month previously, and initial magnetic resonance imaging revealed a pineal tumor. Germinoma was initially suspected; however, a combination of chemotherapy using carboplatin and etoposide was ineffective. The first surgery was performed through the left occipital transtentorial approach (OTA); the diagnosis was DMG. After 60 Gy radiotherapy concomitant with temozolomide (TMZ), the tumor enlarged. Second surgery was performed through bilateral OTAs, and 90% of the tumor was removed. In addition, stereotactic radiotherapy (30 Gy, six fractions) was administered, and the local equivalent dose in 2 Gy/fraction reached 97.5 Gy. Maintenance chemotherapy using TMZ and bevacizumab was continued for 2 years. After finishing chemotherapy, the enhancing lesion enlarged again, and bevacizumab monotherapy was effective. Now, at 6 years after diagnosis, the patient leads an ordinary life as a student.

Conclusion:

Maximum resection and high-dose radiotherapy followed by bevacizumab may have been effective in the present case.

Neuroinflammation and immunoregulation in glioblastoma and brain metastases: Recent developments in imaging approaches

Brain tumors and brain metastases induce changes in brain tissue remodeling that lead to immunosuppression and trigger an inflammatory response within the tumor microenvironment. These immune and inflammatory changes can influence invasion and metastasis. Other neuroinflammatory and necrotic lesions may occur in patients with brain cancer or brain metastases as sequelae from treatment with radiotherapy. Glioblastoma (GBM) is the most aggressive primary malignant brain cancer in adults. Imaging methods such as positron emission tomography (PET) and different magnetic resonance imaging (MRI) techniques are highly valuable for the diagnosis and therapeutic evaluation of GBM and other malignant brain tumors. However, differentiating between tumor tissue and inflamed brain tissue with imaging protocols remains a challenge. Here, we review recent advances in imaging methods that have helped to improve the specificity of primary tumor diagnosis versus evaluation of inflamed and necrotic brain lesions. We also comment on advances in differentiating metastasis from neuroinflammation processes. Recent advances include the radiosynthesis of ¹⁸ F-FIMP, an L-type amino acid transporter 1 (LAT1)-specific PET probe that allows clearer differentiation between tumor tissue and inflammation compared to previous probes, and the combination of different advanced imaging protocols with the inclusion of radiomics and machine learning algorithms.

Biomarkers of Systemic Inflammation in Patients with Glioblastoma: An Analysis of Correlation with Tumour-Related Factors and Survival

Background

Biomarkers of systemic inflammation (BMSIs), including haemogram cell counts (CC, e.g., absolute neutrophil count) and cell count-ratios (CCR, e.g., the neutrophil-lymphocyte ratio, etc.), have been found to have prognostic significance in many solid-organ cancers.

Aims

In this three-part study, we first examined if the CCs and CCRs were altered in patients with glioblastoma (GBM) when compared with healthy controls. Second, we evaluated for any correlation between the BMSIs and patient- and tumour-related factors. Third, we evaluated the influence of the CCs and CCRs on survival.

Methods

This was a retrospective analysis of patients who underwent surgery/biopsy for a newly diagnosed brain tumour that was subsequently confirmed to be GBM (Cases). Controls were healthy individuals who underwent pre-employment screening blood tests.

Statistical Methods

Parametric tests were used to compare normally distributed continuous variables, whereas non-normally distributed variables were compared using non-parametric tests. Thresholds for the BMSIs were determined using X-tile analysis. Cox regression using the proportional hazards model was used for survival analyses around the determined thresholds.

Results

All CCs and CCRs were altered in Cases compared with Controls. Presentation with raised intracranial pressure, altered sensorium, poor performance status, loss of ATRX, and lack of p53 overexpression was associated with an inflammatory phenotype of changes in the BMSIs. The inflammatory phenotype of changes was associated with poor survival.

Conclusions

A significant inflammatory response was found in patients with GBM and correlated with clinical features, the molecular profile of the tumour and poor survival.

Combined amino acid PET-MRI for identifying recurrence in post-treatment gliomas: together we grow

PURPOSE

The aim of this study is to compare the diagnostic accuracy of amino acid PET, MR perfusion and diffusion as stand-alone modalities and in combination in identifying recurrence in post-treatment gliomas and to qualitatively assess spatial concordance between the three modalities using simultaneous PET-MR acquisition.

METHODS

A retrospective review of 48 cases of post-treatment gliomas who underwent simultaneous PET-MRI using C11 methionine as radiotracer was performed. MR perfusion and diffusion sequences were acquired during the PET study. The following parameters were obtained: TBR_max, TBR_mean, SUV_max, and SUV_mean from the PET images; rCBV from perfusion; and ADC_mean and ADC_ratio from the diffusion images. The final diagnosis was based on clinical/imaging follow-up and histopathology when available. ROC curve analysis in combination with logistic regression analysis was used to compare the diagnostic performance. Spatial concordance between modalities was graded as 0, 1, and 2 representing discordance, < 50% and > 50% concordance respectively.

RESULTS

There were 35 cases of recurrence and 13 cases of post-treatment changes without recurrence. The highest area under curve (AUC) was obtained for TBR_max followed by rCBV and ADC_ratio. The AUC increased significantly with a combination of rCBV and TBR_max. Amino acid PET showed the highest diagnostic accuracy and maximum agreement with the final diagnosis. There was discordance between ADC and PET in 22.9%, between rCBV and PET in 16.7% and between PET and contrast enhancement in 14.6% cases.

CONCLUSION

Amino acid PET had the highest diagnostic accuracy in identifying recurrence in post-treatment gliomas. Combination of PET with MRI further increased the AUC thus improving the diagnostic performance.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Determination of brain tumor recurrence using 11 C-methionine positron emission tomography after radiotherapy

We conducted a prospective multicenter trial to compare the usefulness of ¹¹C‐methionine (MET) and ¹⁸F‐fluorodeoxyglucose (FDG) positron emission tomography (PET) for identifying tumor recurrence. Patients with clinically suspected tumor recurrence after radiotherapy underwent both ¹¹C‐MET and ¹⁸F‐FDG PET. When a lesion showed a visually detected uptake of either tracer, it was surgically resected for histopathological analysis. Patients with a lesion negative to both tracers were revaluated by magnetic resonance imaging (MRI) at 3 months after the PET studies. The primary outcome measure was the sensitivity of each tracer in cases with histopathologically confirmed recurrence, as determined by the McNemar test. Sixty‐one cases were enrolled, and 56 cases could be evaluated. The 38 cases where the lesions showed uptake of either ¹¹C‐MET or ¹⁸F‐FDG underwent surgery; 32 of these cases were confirmed to be subject to recurrence. Eighteen cases where the lesions showed uptake of neither tracer received follow‐up MRI; the lesion size increased in one of these cases. Among the cases with histologically confirmed recurrence, the sensitivities of ¹¹C‐MET PET and ¹⁸F‐FDG PET were 0.97 (32/33, 95% confidence interval [CI]: 0.85‐0.99) and 0.48 (16/33, 95% CI: 0.33‐0.65), respectively, and the difference was statistically significant (P < .0001). The diagnostic accuracy of ¹¹C‐MET PET was significantly better than that of ¹⁸F‐FDG PET (87.5% vs. 69.6%, P = .033). No examination‐related adverse events were observed. The results of the study demonstrated that ¹¹C‐MET PET was superior to ¹⁸F‐FDG PET for discriminating between tumor recurrence and radiation‐induced necrosis.

Diagnostic Accuracy of PET for Differentiating True Glioma Progression From Post Treatment-Related Changes: A Systematic Review and Meta-Analysis

Purpose: To evaluate the diagnostic accuracy of PET with different radiotracers and parameters in differentiating between true glioma progression (TPR) and post treatment-related change (PTRC). Methods: Studies on using PET to differentiate between TPR and PTRC were screened from the PubMed and Embase databases. By following the PRISMA checklist, the quality assessment of included studies was performed, the true positive and negative values (TP and TN), false positive and negative values (FP and FN), and general characteristics of all the included studies were extracted. Results of PET consistent with reference standard were defined as TP or TN. The pooled sensitivity (Sen), specificity (Spe), and hierarchical summary receiver operating characteristic curves (HSROC) were generated to evaluate the diagnostic accuracy. Results: The 33 included studies had 1,734 patients with 1,811 lesions suspected of glioma recurrence. Fifteen studies tested the accuracy of 18F-FET PET, 12 tested 18F-FDG PET, seven tested 11C-MET PET, and three tested 18F-DOPA PET. 18F-FET PET showed a pooled Sen and Spe of 0.88 (95% CI: 0.80, 0.93) and 0.78 (0.69, 0.85), respectively. In the subgroup analysis of FET-PET, diagnostic accuracy of high-grade gliomas (HGGs) was higher than that of mixed-grade gliomas (P interaction = 0.04). 18F-FDG PET showed a pooled Sen and Spe of 0.78 (95% CI: 0.71, 0.83) and 0.87 (0.80, 0.92), the Spe of the HGGs group was lower than that of the low-grade gliomas group (0.82 vs. 0.90, P = 0.02). 11C-MET PET had a pooled Sen and Spe of 0.92 (95% CI: 0.83, 0.96) and 0.78 (0.69, 0.86). 18F-DOPA PET had a pooled Sen and Spe of 0.85 (95% CI: 0.80, 0.89) and 0.70 (0.60, 0.79). FET-PET combined with MRI had a pooled Sen and Spe of 0.88 (95% CI: 0.78, 0.94) and 0.76 (0.57, 0.88). Multi-parameters analysis of FET-PET had pooled Sen and Spe values of 0.88 (95% CI: 0.81, 0.92) and 0.79 (0.63, 0.89). Conclusion: PET has a moderate diagnostic accuracy in differentiating between TPR and PTRC. The high Sen of amino acid PET and high Spe of FDG-PET suggest that the combination of commonly used FET-PET and FDG-PET may be more accurate and promising, especially for low-grade glioma.

Bevacizumab for radiation necrosis following radiotherapy of brain metastatic disease: a systematic review & meta-analysis

Background

Radiotherapy is the mainstay of brain metastasis (BM) management. Radiation necrosis (RN) is a serious complication of radiotherapy. Bevacizumab (BV), an anti-vascular endothelial growth factor monoclonal antibody, has been increasingly used for RN treatment. We systematically reviewed the medical literature for studies reporting the efficacy and safety of bevacizumab for treatment of RN in BM patients.

Materials and methods

PubMed, Medline, EMBASE, and Cochrane library were searched with various search keywords such as “bevacizumab” OR “anti-VEGF monoclonal antibody” AND “radiation necrosis” OR “radiation-induced brain necrosis” OR “RN” OR “RBN” AND “Brain metastases” OR “BM” until 1st Aug 2020. Studies reporting the efficacy and safety of BV treatment for BM patients with RN were retrieved. Study selection and data extraction were carried out by independent investigators. Open Meta Analyst software was used as a random effects model for meta-analysis to obtain mean reduction rates.

Results

Two prospective, seven retrospective, and three case report studies involving 89 patients with RN treated with BV were included in this systematic review and meta-analysis. In total, 83 (93%) patients had a recorded radiographic response to BV therapy, and six (6.7%) had experienced progressive disease. Seven studies (n = 73) reported mean volume reductions on gadolinium-enhanced T1 (mean: 47.03%, +/− 24.4) and T2-weighted fluid-attenuated inversion recovery (FLAIR) MRI images (mean: 61.9%, +/− 23.3). Pooling together the T1 and T2 MRI reduction rates by random effects model revealed a mean of 48.58 (95% CI: 38.32–58.85) for T1 reduction rate and 62.017 (95% CI: 52.235–71.799) for T2W imaging studies. Eighty-five patients presented with neurological symptoms. After BV treatment, nine (10%) had stable symptoms, 39 (48%) had improved, and 34 (40%) patients had complete resolution of their symptoms. Individual patient data was available for 54 patients. Dexamethasone discontinuation or reduction in dosage was observed in 30 (97%) of 31 patients who had recorded dosage before and after BV treatment. Side effects were mild.

Conclusions

Bevacizumab presents a promising treatment strategy for patients with RN and brain metastatic disease. Radiographic response and clinical improvement was observed without any serious adverse events. Further class I evidence would be required to establish a bevacizumab recommendation in this group of patients.

Deep Learning Methodology for Differentiating Glioma Recurrence From Radiation Necrosis Using Multimodal Magnetic Resonance Imaging: Algorithm Development and Validation

BACKGROUND

The radiological differential diagnosis between tumor recurrence and radiation-induced necrosis (ie, pseudoprogression) is of paramount importance in the management of glioma patients.

OBJECTIVE

This research aims to develop a deep learning methodology for automated differentiation of tumor recurrence from radiation necrosis based on routine magnetic resonance imaging (MRI) scans.

METHODS

In this retrospective study, 146 patients who underwent radiation therapy after glioma resection and presented with suspected recurrent lesions at the follow-up MRI examination were selected for analysis. Routine MRI scans were acquired from each patient, including T1, T2, and gadolinium-contrast-enhanced T1 sequences. Of those cases, 96 (65.8%) were confirmed as glioma recurrence on postsurgical pathological examination, while 50 (34.2%) were diagnosed as necrosis. A light-weighted deep neural network (DNN) (ie, efficient radionecrosis neural network [ERN-Net]) was proposed to learn radiological features of gliomas and necrosis from MRI scans. Sensitivity, specificity, accuracy, and area under the curve (AUC) were used to evaluate performance of the model in both image-wise and subject-wise classifications. Preoperative diagnostic performance of the model was also compared to that of the state-of-the-art DNN models and five experienced neurosurgeons.

RESULTS

DNN models based on multimodal MRI outperformed single-modal models. ERN-Net achieved the highest AUC in both image-wise (0.915) and subject-wise (0.958) classification tasks. The evaluated DNN models achieved an average sensitivity of 0.947 (SD 0.033), specificity of 0.817 (SD 0.075), and accuracy of 0.903 (SD 0.026), which were significantly better than the tested neurosurgeons (P=.02 in sensitivity and P<.001 in specificity and accuracy).

CONCLUSIONS

Deep learning offers a useful computational tool for the differential diagnosis between recurrent gliomas and necrosis. The proposed ERN-Net model, a simple and effective DNN model, achieved excellent performance on routine MRI scans and showed a high clinical applicability.

Treatment-induced brain tissue necrosis: a clinical challenge in neuro-oncology

Cancer therapy-induced adverse effects on the brain are a major challenge in neuro-oncology. Brain tissue necrosis (treatment necrosis [TN]) as a consequence of brain directed cancer therapy remains an insufficiently characterized condition with diagnostic and therapeutic difficulties and is frequently associated with significant patient morbidity. A better understanding of the underlying mechanisms, improvement of diagnostic tools, development of preventive strategies, and implementation of evidence-based therapeutic practices are pivotal to improve patient management. In this comprehensive review, we address existing challenges associated with current TN-related clinical and research practices and highlight unanswered questions and areas in need of further research with the ultimate goal to improve management of patients affected by this important neuro-oncological condition.

Metabolic Imaging of Brain Tumor Recurrence

OBJECTIVE. Diagnosing brain tumor recurrence, especially with changes that occur after treatment, is a challenge. MRI has an exceptional structural resolution, which is important from the perspective of treatment planning. However, its reliability in diagnosing recurrence is relatively lower, when compared to metabolic imaging. The latter is more sensitive to the early changes associated with recurrence and relatively immune to confounding by treatment related changes. CONCLUSION. There is no one-stop shop for the diagnosis of recurrence in brain tumors. The sensitivity of metabolic imaging is not a substitute for the resolution of the MRI, making a multi-modal approach the only way forward.

Diagnostic Performance of PET and Perfusion-Weighted Imaging in Differentiating Tumor Recurrence or Progression from Radiation Necrosis in Posttreatment Gliomas: A Review of Literature

Tumor resection followed by chemoradiation remains the current criterion standard treatment for high-grade gliomas. Regardless of aggressive treatment, tumor recurrence and radiation necrosis are 2 different outcomes. Differentiation of tumor recurrence from radiation necrosis remains a critical problem in these patients because of considerable overlap in clinical and imaging presentations. Contrast-enhanced MR imaging is the universal imaging technique for diagnosis, treatment evaluation, and detection of recurrence of high-grade gliomas. PWI and PET with novel radiotracers have an evolving role for monitoring treatment response in high-grade gliomas. In the literature, there is no clear consensus on the superiority of either technique or their complementary information. This review aims to elucidate the diagnostic performance of individual and combined use of functional (PWI) and metabolic (PET) imaging modalities to distinguish recurrence from posttreatment changes in gliomas.

Glioma surveillance imaging: current strategies, shortcomings, challenges and outlook

Inaccurate assessment of surveillance imaging to assess response to glioma therapy may have life-changing consequences. Varied management plans including chemotherapy, radiotherapy or immunotherapy may all contribute to heterogeneous post-treatment appearances and the overlap between the morphological features of pseudoprogression, pseudoresponse and radiation necrosis can make their discrimination very challenging. Therefore, there has been a drive to develop objective strategies for post-treatment assessment of brain gliomas. This review discusses the most important of these approaches such as the RANO "Response Assessment in Neuro-Oncology", iRANO "Immunotherapy Response Assessment in Neuro-Oncology" and RAPNO "Response Assessment in Paediatric Neuro-Oncology" models. In addition to these systematic approaches for glioma surveillance, the relatively limited information provided by conventional imaging modalities alone has motivated the development of novel advanced magnetic resonance (MR) and metabolic imaging methods for further discrimination between viable tumour and treatment induced changes. Multiple clinical trials and meta-analyses have investigated the diagnostic performance of these novel techniques in the follow up of brain gliomas, including both single modality descriptive studies and comparative imaging assessment. In this manuscript, we review the literature and discuss the promises and pitfalls of frequently studied modalities in glioma surveillance imaging, including MR perfusion, MR diffusion and MR spectroscopy. In addition, we evaluate other promising MR techniques such as chemical exchange saturation transfer as well as fludeoxyglucose and non-FDG positron emission tomography techniques.

Combined PET/MRI in brain glioma imaging

Gliomas are the most common primary brain tumours in children and adults, consisting of a heterogeneous group of neoplastic diseases arise from the supporting cells of the CNS (glial cells). Their histopathological and molecular characteristics vary considerably as do their management and prognosis. Conventional gadolinium-enhanced magnetic resonance imaging (MRI) is considered the primary imaging modality for initial work up and follow up of patients with gliomas, although it has some limitations, especially in differentiating high from low grade tumours and in distinguishing disease recurrence from post-therapy changes. Hybrid positron emission tomography (PET)/MRI is a relatively novel tool that combines MRI sequences with metabolic information from PET, and therefore different PET radiotracers, in a single scan. This article discusses the main advantages and disadvantages of combined PET/MRI compared to other conventional or more widely available imaging tools, such as MRI or combined positron emission tomography-computed tomography. The main uses of PET/MRI and the most commonly used PET radiotracers in providing diagnostic, prognostic and predictive information in patients with glioma are covered.

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.

Contribution of Different Positron Emission Tomography Tracers in Glioma Management: Focus on Glioblastoma

Although rare, glioblastomas account for the majority of primary brain lesions, with a dreadful prognosis. Magnetic resonance imaging (MRI) is currently the imaging method providing the higher resolution. However, it does not always succeed in distinguishing recurrences from non-specific temozolomide, have been shown to improve -related changes caused by the combination of radiotherapy, chemotherapy, and targeted therapy, also called pseudoprogression. Strenuous attempts to overcome this issue is highly required for these patients with a short life expectancy for both ethical and economic reasons. Additional reliable information may be obtained from positron emission tomography (PET) imaging. The development of this technique, along with the emerging of new classes of tracers, can help in the diagnosis, prognosis, and assessment of therapies. We reviewed the current data about the commonly used tracers, such as 18F-fluorodeoxyglucose (18F-FDG) and radiolabeled amino acids, as well as different PET tracers recently investigated, to report their strengths, limitations, and relevance in glioblastoma management.

The Role of Metabolic Plasticity in Blood and Brain Stem Cell Pathophysiology

Our understanding of intratumoral heterogeneity in cancer continues to evolve, with current models incorporating single-cell signatures to explore cell-cell interactions and differentiation state. The transition between stem and differentiation states in nonneoplastic cells requires metabolic plasticity, and this plasticity is increasingly recognized to play a central role in cancer biology. The insights from hematopoietic and neural stem cell differentiation pathways were used to identify cancer stem cells in leukemia and gliomas. Similarly, defining metabolic heterogeneity and fuel-switching signals in nonneoplastic stem cells may also give important insights into the corresponding molecular mechanisms controlling metabolic plasticity in cancer. These advances are important, because metabolic adaptation to anticancer therapeutics is rooted in this inherent metabolic plasticity and is a therapeutic challenge to be overcome.

The Molecular Effects of Ionizing Radiations on Brain Cells: Radiation Necrosis vs. Tumor Recurrence

The central nervous system (CNS) is generally resistant to the effects of radiation, but higher doses, such as those related to radiation therapy, can cause both acute and long-term brain damage. The most important results is a decline in cognitive function that follows, in most cases, cerebral radionecrosis. The essence of radio-induced brain damage is multifactorial, being linked to total administered dose, dose per fraction, tumor volume, duration of irradiation and dependent on complex interactions between multiple brain cell types. Cognitive impairment has been described following brain radiotherapy, but the mechanisms leading to this adverse event remain mostly unknown. In the event of a brain tumor, on follow-up radiological imaging often cannot clearly distinguish between recurrence and necrosis, while, especially in patients that underwent radiation therapy (RT) post-surgery, positron emission tomography (PET) functional imaging, is able to differentiate tumors from reactive phenomena. More recently, efforts have been done to combine both morphological and functional data in a single exam and acquisition thanks to the co-registration of PET/MRI. The future of PET imaging to differentiate between radionecrosis and tumor recurrence could be represented by a third-generation PET tracer already used to reveal the spatial extent of brain inflammation. The aim of the following review is to analyze the effect of ionizing radiations on CNS with specific regard to effect of radiotherapy, focusing the attention on the mechanism underling the radionecrosis and the brain damage, and show the role of nuclear medicine techniques to distinguish necrosis from recurrence and to early detect of cognitive decline after treatment.

Usefulness of positron emission tomography for differentiating gliomas according to the 2016 World Health Organization classification of tumors of the central nervous system

OBJECTIVE

Positron emission tomography (PET) is important in the noninvasive diagnostic imaging of gliomas. There are many PET studies on glioma diagnosis based on the 2007 WHO classification; however, there are no studies on glioma diagnosis using the new classification (the 2016 WHO classification). Here, the authors investigated the relationship between uptake of 11C-methionine (MET), 11C-choline (CHO), and 18F-fluorodeoxyglucose (FDG) on PET imaging and isocitrate dehydrogenase (IDH) status (wild-type [IDH-wt] or mutant [IDH-mut]) in astrocytic and oligodendroglial tumors according to the 2016 WHO classification.

METHODS

In total, 105 patients with newly diagnosed cerebral gliomas (6 diffuse astrocytomas [DAs] with IDH-wt, 6 DAs with IDH-mut, 7 anaplastic astrocytomas [AAs] with IDH-wt, 24 AAs with IDH-mut, 26 glioblastomas [GBMs] with IDH-wt, 5 GBMs with IDH-mut, 19 oligodendrogliomas [ODs], and 12 anaplastic oligodendrogliomas [AOs]) were included. All OD and AO patients had both IDH-mut and 1p/19q codeletion. The maximum standardized uptake value (SUV) of the tumor/mean SUV of normal cortex (T/N) ratios for MET, CHO, and FDG were calculated, and the mean T/N ratios of DA, AA, and GBM with IDH-wt and IDH-mut were compared. The diagnostic accuracy for distinguishing gliomas with IDH-wt from those with IDH-mut was assessed using receiver operating characteristic (ROC) curve analysis of the mean T/N ratios for the 3 PET tracers.

RESULTS

There were significant differences in the mean T/N ratios for all 3 PET tracers between the IDH-wt and IDH-mut groups of all histological classifications (p < 0.001). Among the 27 gliomas with mean T/N ratios higher than the cutoff values for all 3 PET tracers, 23 (85.2%) were classified into the IDH-wt group using ROC analysis. In DA, there were no significant differences in the T/N ratios for MET, CHO, and FDG between the IDH-wt and IDH-mut groups. In AA, the mean T/N ratios of all 3 PET tracers in the IDH-wt group were significantly higher than those in the IDH-mut group (p < 0.01). In GBM, the mean T/N ratio in the IDH-wt group was significantly higher than that in the IDH-mut group for both MET (p = 0.034) and CHO (p = 0.01). However, there was no significant difference in the ratio for FDG.

CONCLUSIONS

PET imaging using MET, CHO, and FDG was suggested to be informative for preoperatively differentiating gliomas according to the 2016 WHO classification, particularly for differentiating IDH-wt and IDH-mut tumors.

Direct comparison of [11C] choline and [18F] FET PET to detect glioma infiltration: a diagnostic accuracy study in eight patients

Background

Positron emission tomography (PET) is increasingly used to guide local treatment in glioma. The purpose of this study was a direct comparison of two potential tracers for detecting glioma infiltration, O-(2-[¹⁸F]-fluoroethyl)-l-tyrosine ([¹⁸F] FET) and [¹¹C] choline.

Methods

Eight consecutive patients with newly diagnosed diffuse glioma underwent dynamic [¹¹C] choline and [¹⁸F] FET PET scans. Preceding craniotomy, multiple stereotactic biopsies were obtained from regions inside and outside PET abnormalities. Biopsies were assessed independently for tumour presence by two neuropathologists. Imaging measurements were derived at the biopsy locations from 10 to 40 min [¹¹C] choline and 20–40, 40–60 and 60–90 min [¹⁸F] FET intervals, as standardized uptake value (SUV) and tumour-to-brain ratio (TBR). Diagnostic accuracies of both tracers were compared using receiver operating characteristic analysis and generalized linear mixed modelling with consensus histopathological assessment as reference.

Results

Of the 74 biopsies, 54 (73%) contained tumour. [¹¹C] choline SUV and [¹⁸F] FET SUV and TBR at all intervals were higher in tumour than in normal samples. For [¹⁸F] FET, the diagnostic accuracy of TBR was higher than that of SUV for intervals 40–60 min (area under the curve: 0.88 versus 0.81, p = 0.026) and 60–90 min (0.90 versus 0.81, p = 0.047). The diagnostic accuracy of [¹⁸F] FET TBR 60–90 min was higher than that of [¹¹C] choline SUV 20–40 min (0.87 versus 0.67, p = 0.005).

Conclusions

[¹⁸F] FET was more accurate than [¹¹C] choline for detecting glioma infiltration. Highest accuracy was found for [¹⁸F] FET TBR for the interval 60–90 min post-injection.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0523-8) contains supplementary material, which is available to authorized users.

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.

Dissociation Between 11C-Methionine-Positron Emission Tomography and Gadolinium-Enhanced Magnetic Resonance Imaging in Longitudinal Features of Glioblastoma After Postoperative Radiotherapy

The aims of the present study were to compare the longitudinal changes of glioblastoma multiforme after radiotherapy (RT) between 11C-methionine positron emission tomography (MET-PET) and gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) and to clarify whether these changes were predictive of survival. We included 30 patients, who had undergone MET-PET and Gd-MRI before and every 3 months after RT. The lesion/normal brain uptake (L/N) ratio and contrast-enhancing lesion volume were examined. The L/N ratio was decreased until 9 months after RT with significance until 3 months. The contrast-enhancing lesion volume was decreased until 3 months and thereafter increased until 9 months with significance. The variation rates of the L/N ratio between pre-RT and 3 months differentiated survival of >23 months from ≤23 months. A dissociation could exist in the longitudinal changes of GBM after RT between MET-PET and Gd-MRI. The variation rate of the L/N ratio could be related to survival.

Emerging Functional Imaging Biomarkers of Tumour Responses to Radiotherapy

Tumour responses to radiotherapy are currently primarily assessed by changes in size. Imaging permits non-invasive, whole-body assessment of tumour burden and guides treatment options for most tumours. However, in most tumours, changes in size are slow to manifest and can sometimes be difficult to interpret or misleading, potentially leading to prolonged durations of ineffective treatment and delays in changing therapy. Functional imaging techniques that monitor biological processes have the potential to detect tumour responses to treatment earlier and refine treatment options based on tumour biology rather than solely on size and staging. By considering the biological effects of radiotherapy, this review focusses on emerging functional imaging techniques with the potential to augment morphological imaging and serve as biomarkers of early response to radiotherapy.

18F-DOPA PET/CT in brain tumors: impact on multidisciplinary brain tumor board decisions

PURPOSE

This study aimed to assess the therapeutic impact and diagnostic accuracy of ¹⁸F-DOPA PET/CT in patients with glioblastoma or brain metastases.

METHODS

Patients with histologically proven glioblastoma or brain metastases were prospectively included in this monocentric clinical trial (IMOTEP). Patients were included either due to a clinical suspicion of relapse or to assess residual tumor infiltration after treatment. Multimodality brain MRI and ¹⁸F-DOPA PET were performed. Patients' data were discussed during a Multidisciplinary Neuro-oncology Tumor Board (MNTB) meeting. The discussion was first based on clinical and MRI data, and an initial diagnosis and treatment plan were proposed. Secondly, a new discussion was conducted based on the overall imaging results, including ¹⁸F-DOPA PET. A second diagnosis and therapeutic plan were proposed. A retrospective and definitive diagnosis was obtained after a 3-month follow-up and considered as the reference standard.

RESULTS

One hundred six cases were prospectively investigated by the MNTB. All patients with brain metastases (N = 41) had a clinical suspicion of recurrence. The addition of ¹⁸F-DOPA PET data changed the diagnosis and treatment plan in 39.0% and 17.1% of patients' cases, respectively. Concerning patients with a suspicion of recurrent glioblastoma (N = 12), the implementation of ¹⁸F-DOPA PET changed the diagnosis and treatment plan in 33.3% of cases. In patients evaluated to assess residual glioblastoma infiltration after treatment (N = 53), ¹⁸F-DOPA PET data had a lower impact with only 5.7% (3/53) of diagnostic changes and 3.8% (2/53) of therapeutic plan changes. The definitive reference diagnosis was available in 98/106 patients. For patients with tumor recurrence suspicion, the adjunction of ¹⁸F-DOPA PET increased the Younden's index from 0.44 to 0.53 in brain metastases and from 0.2 to 1.0 in glioblastoma, reflecting an increase in diagnostic accuracy.

CONCLUSION

¹⁸F-DOPA PET has a significant impact on the management of patients with a suspicion of brain tumor recurrence, either glioblastoma or brain metastases, but a low impact when used to evaluate the residual glioblastoma infiltration after a first-line radio-chemotherapy or second-line bevacizumab.

Radiation Necrosis, Pseudoprogression, Pseudoresponse, and Tumor Recurrence: Imaging Challenges for the Evaluation of Treated Gliomas

Glioblastoma (GBM) is the most common primary malignant type of brain neoplasm in adults and carries a dismal prognosis. The current standard of care for GBM is surgical excision followed by radiation therapy (RT) with concurrent and adjuvant temozolomide-based chemotherapy (TMZ) by six additional cycles. In addition, antiangiogenic therapy with an antivascular endothelial growth factor (VEGF) agent has been used for recurrent glioblastoma. Over the last years, new posttreatment entities such as pseudoprogression and pseudoresponse have been recognized, apart from radiation necrosis. This review article focuses on the role of different imaging techniques such as conventional magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI), dynamic contrast enhancement (DCE-MRI) and dynamic susceptibility contrast (DSE-MRI) perfusion, magnetic resonance spectroscopy (MRS), and PET/SPECT in differentiation of such treatment-related changes from tumor recurrence.

PET imaging in glioma: techniques and current evidence

PET holds potential to provide additional information about tumour metabolic processes, which could aid brain tumour differential diagnosis, grading, molecular subtyping and/or the distinction of therapy effects from disease recurrence. This review discusses PET techniques currently in use for untreated and treated glioma characterization and aims to critically assess the evidence for different tracers ([F]Fluorodeoxyglucose, choline and amino acid tracers) in this context.

Investigational PET tracers for high-grade gliomas

High-grade gliomas (HGGs) are the most common primary malignant tumors of the brain, with glioblastoma (GBM) constituting over 50% of all the gliomas in adults. The disease carries very high mortality, and even with optimal treatment, the median survival is 2-5 years for anaplastic tumors and 1-2 years for GBMs. Neuroimaging is critical to managing patients with HGG for diagnosis, treatment planning, response assessment, and detecting recurrent disease. Magnetic resonance imaging (MRI) is the cornerstone of imaging in neuro-oncology, but molecular imaging with positron emission tomography (PET) can overcome some of the inherent limitations of MRI. Additionally, PET has the potential to target metabolic and molecular alterations in HGGs relevant to prognosis and therapy that cannot be assessed with anatomic imaging. Many classes of PET tracers have been evaluated in HGG including agents that target cell membrane biosynthesis, protein synthesis, amino acid transport, DNA synthesis, the tricarboxylic acid (TCA) cycle, hypoxic environments, cell surface receptors, blood flow, vascular endothelial growth factor (VEGF), epidermal growth factor (EGFR), and the 18-kDa translocator protein (TSPO), among others. This chapter will provide an overview of PET tracers for HGG that have been evaluated in human subjects with a focus on tracers that are not yet in widespread use for neuro-oncology.

Discriminating radiation injury from recurrent tumor with [18F]PARPi and amino acid PET in mouse models

Background

Radiation injury can be indistinguishable from recurrent tumor on standard imaging. Current protocols for this differential diagnosis require one or more follow-up imaging studies, long dynamic acquisitions, or complex image post-processing; despite much research, the inability to confidently distinguish between these two entities continues to pose a significant dilemma for the treating clinician. Using mouse models of both glioblastoma and radiation necrosis, we tested the potential of poly(ADP-ribose) polymerase (PARP)-targeted PET imaging with [¹⁸F]PARPi to better discriminate radiation injury from tumor.

Results

In mice with experimental radiation necrosis, lesion uptake on [¹⁸F]PARPi-PET was similar to contralateral uptake (1.02 ± 0.26 lesion/contralateral %IA/cc_max ratio), while [¹⁸F]FET-PET clearly delineated the contrast-enhancing region on MR (2.12 ± 0.16 lesion/contralateral %IA/cc_max ratio). In mice with focal intracranial U251 xenografts, tumor visualization on PARPi-PET was superior to FET-PET, and lesion-to-contralateral activity ratios (max/max, p = 0.034) were higher on PARPi-PET than on FET-PET.

Conclusions

A murine model of radiation necrosis does not demonstrate [¹⁸F]PARPi avidity, and [¹⁸F]PARPi-PET is better than [¹⁸F]FET-PET in distinguishing radiation injury from brain tumor. [¹⁸F]PARPi-PET can be used for discrimination between recurrent tumor and radiation injury within a single, static imaging session, which may be of value to resolve a common dilemma in neuro-oncology.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0399-z) contains supplementary material, which is available to authorized users.

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.

Circulating Cell-Free DNA as a Prognostic and Molecular Marker for Patients with Brain Tumors under Perillyl Alcohol-Based Therapy

Tumor infiltration into brain tissue usually remains undetected even by high-resolution imaging. Molecular markers are used to increase diagnostic accuracy, but with limited continuous monitoring application. We evaluated the potential of circulating cell-free DNA (cfDNA) as a molecular indicator of the response to therapy by the intranasal administration (ITN) of perillyl alcohol (POH) in brain tumors. The cohort included 130 healthy subjects arranged as control-paired groups and patients at terminal stages with glioblastoma (GBM, n = 122) or brain metastasis (BM, n = 55) from stage IV adenocarcinomas. Serum cfDNA was isolated and quantified by fluorimetry. Compared with the controls (40 ng/mL), patients with brain tumors before ITN-POH treatment had increased (p < 0.0001) cfDNA median levels: GBM (286 ng/mL) and BM (588 ng/mL). ITN-POH treatment was significantly correlated (rho = −0.225; p = 0.024) with survival of >6 months at a concentration of 599 ± 221 ng/mL and of <6 months at 1626 ± 505 ng/mL, but a sharp and abrupt increase of cfDNA and tumor recurrence occurred after ITN-POH discontinuation. Patients under continuous ITN-POH treatment and checked with brain magnetic resonance imaging (MRI) compatible with complete response had cfDNA levels similar to the controls. cfDNA may be used as a noninvasive prognostic and molecular marker for POH-based therapy in brain tumors and as an accurate screening tool for the early detection of tumor progression.

Potential use of prostate specific membrane antigen (PSMA) for detecting the tumor neovasculature of brain tumors by PET imaging with 89Zr-Df-IAB2M anti-PSMA minibody

Tumor angiogenesis has attracted increasing attention because of its potential as a valuable marker in the differential diagnosis of brain tumors as well as a novel therapeutic target. Prostate-specific membrane antigen (PSMA) is expressed by the neovasculature endothelium of some tumors, with little to no expression by the tumor cells or normal vasculature endothelium. The aim of this study was to investigate the potential of PSMA for the evaluation of the tumor neovasculature of various brain tumors and the possibility of detecting PSMA expression in brain tumors using PET imaging with ⁸⁹Zr-Df-IAB2M (anti-PSMA minibody). Eighty-three tissue specimens including gliomas, metastatic brain tumors, primary central nervous system lymphomas (PCNSL), or radiation necroses were analyzed by immunohistochemical staining with PSMA antibody. ⁸⁹Zr-Df-IAB2M PET scans were performed in three patients with recurrent high-grade gliomas or metastatic brain tumor. PSMA was highly expressed in the vascular endothelium of high-grade glioma and metastatic brain tumor, whereas PSMA was poorly expressed in the vascular endothelium of PCNSL and radiation necrosis. PSMA expression in high-grade gliomas and a metastatic brain tumor was clearly visualized by PET imaging with ⁸⁹Zr-Df-IAB2M. Furthermore, a trend toward a positive correlation between the degree of ⁸⁹Zr-Df-IAB2M uptake and PSMA expression levels in tumor specimens was observed. PET imaging of PSMA using ⁸⁹Zr-Df-IAB2M may have potential value in the differential diagnosis of high-grade glioma from PCNSL or radiation necrosis as well as in the prediction of treatment efficacy and assessment of treatment response to bevacizumab therapy for high-grade glioma.

Amide proton transfer imaging seems to provide higher diagnostic performance in post-treatment high-grade gliomas than methionine positron emission tomography

OBJECTIVES

To compare the diagnostic performance of amide proton transfer (APT) imaging and 11-C methionine positron emission tomography (MET-PET) for in vivo molecular imaging of protein metabolism in post-treatment gliomas.

MATERIALS AND METHODS

This study included 43 patients (12 low and 31 high grade) with post-treatment gliomas who underwent both APT and MET-PET imaging within 3 weeks. APT-weighted voxel values and semi-quantitative tumour-to-normal ratios (TNR) were obtained from tumour portions. The voxel-wise relationships between TNR and APT were assessed. The diagnostic performance for recurrence of high-grade gliomas was calculated, using the area under the receiver operating characteristic curve (AUC) with maximum (TNR_max and APT_max) and 90% histogram values (TNR90 and APT90).

RESULTS

A moderate positive correlation between TNR and APT was found in low-grade recurrences (r = 0.47, p < 0.001), but not in high-grade ones (r = -0.24, p < 0.001). For distinguishing recurrence in post-treatment high-grade gliomas, APT_max (AUC, 0.88) and APT90 (AUC, 0.78-0.83) had a similar to better diagnostic performance than TNR_max (AUC, 0.71, p = 0.08) or TNR90 (AUC, 0.53-0.59, p = 0.01-0.05).

CONCLUSIONS

In post-treatment high-grade gliomas, APT provides different regional information to MET-PET and provides higher diagnostic performance. This difference needs to be considered when using APT or MET-PET as a surrogate marker for tumour protein metabolism.

KEY POINTS

• APT and TNR values in low-grade recurrence showed a moderate voxel-wise correlation. • APT and TNR demonstrated regional differences in post-treatment high-grade gliomas. • APT90 showed better diagnostic performance than TNR90 in high-grade recurrence.

Diagnostic Accuracy of Amino Acid and FDG-PET in Differentiating Brain Metastasis Recurrence from Radionecrosis after Radiotherapy: A Systematic Review and Meta-Analysis

BACKGROUND

Current studies that analyze the usefulness of amino acid and FDG-PET in distinguishing brain metastasis recurrence and radionecrosis after radiation therapy are limited by small cohort size.

PURPOSE

Our aim was to assess the diagnostic accuracy of amino acid and FDG-PET in differentiating brain metastasis recurrence from radionecrosis after radiation therapy.

DATA SOURCES

Studies were retrieved from PubMed, Embase, and the Cochrane Library.

STUDY SELECTION

Fifteen studies were included from the literature. Each study used PET to differentiate radiation necrosis from tumor recurrence in contrast-enhancing lesions on follow-up brain MR imaging after treating brain metastasis with radiation therapy.

DATA ANALYSIS

Data were analyzed with a bivariate random-effects model. Sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio were pooled, and a summary receiver operating characteristic curve was fit to the data.

DATA SYNTHESIS

The overall pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio of PET were 0.85, 0.88, 7.0, 0.17, and 40, respectively. The area under the receiver operating characteristic curve was 0.93. On subgroup analysis of different tracers, amino acid and FDG-PET had similar diagnostic accuracy. Meta-regression analysis demonstrated that the method of quantification based on patient, lesion, or PET scan (based on lesion versus not, P = .07) contributed to the heterogeneity.

LIMITATIONS

Our study was limited by small sample size, and 60% of the included studies were of retrospective design.

CONCLUSIONS

Amino acid and FDG-PET had good diagnostic accuracy in differentiating brain metastasis recurrence from radionecrosis after radiation therapy.

Prospective study of 11C-methionine PET for distinguishing between recurrent brain metastases and radiation necrosis: limitations of diagnostic accuracy and long-term results of salvage treatment

Background

On conventional diagnostic imaging, the features of radiation necrosis (RN) are similar to those of local recurrence (LR) of brain metastases (BM). ¹¹C–methionine positron emission tomography (MET-PET) is reportedly useful for making a differential diagnosis between LR and RN. In this prospective study, we aimed to investigate the diagnostic performance of MET-PET and the long-term results of subsequent patient management.

Methods

The eligible subjects had enlarging contrast-enhanced lesions (>1 cm) on MR imaging after any form of radiotherapy for BM, suggesting LR or RN. However, it was difficult to differentiate LR from RN in these cases. From August 2013 to February 2017, MET-PET was performed for 37 lesions in 32 eligible patients. Tracer accumulation in the regions of interest was analysed as the standardised uptake value (SUV) and maximal lesion SUV/maximal normal tissue SUV ratios (LNR) were calculated. The cut-off value for LNR was provisionally set at 1.40. Salvage treatment strategies determined based on MET-PET diagnosis and treatment results were investigated. The diagnostic accuracy of MET-PET was evaluated by receiver operating characteristic (ROC) curve analysis.

Results

The median interval from primary radiotherapy to MET-PET was 19 months and radiotherapy had been performed twice or more for 13 lesions. The MET-PET diagnoses were LR in 19 and RN in 18 lesions. The mean values and standard deviation of LNRs for each diagnostic category were 1.70 ± 0.30 and 1.09 ± 0.25, respectively. At the median follow-up time of 18 months, final diagnoses were confirmed histologically for 17 lesions and clinically for 20 lesions. ROC curve analysis indicated the optimal LNR cut-off value to be 1.40 (area under the curve: 0.84), and the sensitivity and specificity were 0.82 and 0.75, respectively. The median survival times of patient groups with LR and RN based on MET-PET diagnosis were 14.8 months and 35.1 months, respectively (P = 0.035, log-rank test).

Conclusions

MET-PET showed apparently reliable diagnostic performance for distinguishing between LR and RN. The provisional LNR cut-off value of 1.4 in our institution was found to be appropriate. Limitations of diagnostic accuracy should be recognised in cases with LNR close to this cut-off value.

High Expression of Glypican-1 Predicts Dissemination and Poor Prognosis in Glioblastomas

OBJECTIVE

Glioblastoma (GBM) relapses locally or in a disseminated pattern and is highly resistant to chemoradiotherapy. Although dissemination is associated with poor prognosis for patients with GBM, the clinicopathologic factors that promote dissemination have not been elucidated. Glypican-1 (GPC-1) is a heparin sulfate proteoglycan that is attached to the extracytoplasmic surface of the cell membrane and regulates cell motility. The aim of this study was to determine whether GPC-1 expression correlated with GBM dissemination and patient prognosis.

METHODS

GPC-1 expression was examined by immunohistochemistry in 53 patients with GBM who received radiotherapy and temozolomide treatment. We assessed the relationship between dissemination and clinicopathologic factors, including GPC-1 expression. We also evaluated the relationship between GPC-1 expression and overall survival (OS) by uni- and multivariate analyses of a range of clinicopathologic factors, including age, Karnofsky Performance Status, extent of resection, and O6-methylguanine-DNA methyltransferase (MGMT) status.

RESULTS

Logistic regression analysis revealed that GPC-1 expression correlated with dissemination (P = 0.0116). Log-rank tests revealed that age, Karnofsky Performance Status, extent of resection, MGMT status, dissemination (P = 0.0008) and GPC-1 expression (P = 0.0011) were significantly correlated with OS. Multivariate analysis indicated that age, MGMT status, and GPC-1 expression were significantly correlated with OS. GPC-1 expression had the highest hazard ratio (2.392) among all regressors.

CONCLUSIONS

GPC-1 expression significantly correlated with OS in patients with GBM who received radiotherapy and temozolomide treatment. GPC-1 expression can help predict the occurrence of dissemination and shorter OS in patients with GBM.