Combined use of 18F-fluorodeoxyglucose and 11C-methionine in 45 positron emission tomography—guided stereotactic brain biopsies

Surgical management of Glioma Grade 4: technical update from the neuro-oncology section of the Italian Society of Neurosurgery (SINch®): a systematic review

PURPOSE

The extent of resection (EOR) is an independent prognostic factor for overall survival (OS) in adult patients with Glioma Grade 4 (GG4). The aim of the neuro-oncology section of the Italian Society of Neurosurgery (SINch®) was to provide a general overview of the current trends and technical tools to reach this goal.

METHODS

A systematic review was performed. The results were divided and ordered, by an expert team of surgeons, to assess the Class of Evidence (CE) and Strength of Recommendation (SR) of perioperative drugs management, imaging, surgery, intraoperative imaging, estimation of EOR, surgery at tumor progression and surgery in elderly patients.

RESULTS

A total of 352 studies were identified, including 299 retrospective studies and 53 reviews/meta-analysis. The use of Dexamethasone and the avoidance of prophylaxis with anti-seizure medications reached a CE I and SR A. A preoperative imaging standard protocol was defined with CE II and SR B and usefulness of an early postoperative MRI, with CE II and SR B. The EOR was defined the strongest independent risk factor for both OS and tumor recurrence with CE II and SR B. For intraoperative imaging only the use of 5-ALA reached a CE II and SR B. The estimation of EOR was established to be fundamental in planning postoperative adjuvant treatments with CE II and SR B and the stereotactic image-guided brain biopsy to be the procedure of choice when an extensive surgical resection is not feasible (CE II and SR B).

CONCLUSIONS

A growing number of evidences evidence support the role of maximal safe resection as primary OS predictor in GG4 patients. The ongoing development of intraoperative techniques for a precise real-time identification of peritumoral functional pathways enables surgeons to maximize EOR minimizing the post-operative morbidity.

A Systematic Review of Amino Acid PET Imaging in Adult-Type High-Grade Glioma Surgery: A Neurosurgeon's Perspective

Amino acid PET imaging has been used for a few years in the clinical and surgical management of gliomas with satisfactory results in diagnosis and grading for surgical and radiotherapy planning and to differentiate recurrences. Biological tumor volume (BTV) provides more meaningful information than standard MR imaging alone and often exceeds the boundary of the contrast-enhanced nodule seen in MRI. Since a gross total resection reflects the resection of the contrast-enhanced nodule and the majority of recurrences are at a tumor's margins, an integration of PET imaging during resection could increase PFS and OS. A systematic review of the literature searching for "PET" [All fields] AND "glioma" [All fields] AND "resection" [All fields] was performed in order to investigate the diffusion of integration of PET imaging in surgical practice. Integration in a neuronavigation system and intraoperative use of PET imaging in the primary diagnosis of adult high-grade gliomas were among the criteria for article selection. Only one study has satisfied the inclusion criteria, and a few more (13) have declared to use multimodal imaging techniques with the integration of PET imaging to intentionally perform a biopsy of the PET uptake area. Despite few pieces of evidence, targeting a biologically active area in addition to other tools, which can help intraoperatively the neurosurgeon to increase the amount of resected tumor, has the potential to provide incremental and complementary information in the management of brain gliomas. Since supramaximal resection based on the extent of MRI FLAIR hyperintensity resulted in an advantage in terms of PFS and OS, PET-based biological tumor volume, avoiding new neurological deficits, deserves further investigation.

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.

Frameless stereotactic biopsy for precision neurosurgery: diagnostic value, safety, and accuracy

BACKGROUND

Stereotactic biopsy is consistently employed to characterize cerebral lesions in patients who are not suitable for microsurgical resection. In the past years, technical improvement and neuroimaging advancements contributed to increase the diagnostic yield, the safety, and the application of this procedure. Currently, in addition to histological diagnosis, the molecular analysis is considered essential in the diagnostic process to properly select therapeutic and prognostic algorithms in a personalized approach. The present study reports our experience with frameless stereotactic brain biopsy in this molecular era.

METHODS

One hundred forty consecutive patients treated from January 2013 to September 2018 were analyzed. Biopsies were performed using the Brainlab Varioguide® frameless stereotactic system. Patients' clinical and demographic data, the time of occupation of the operating room, the surgical time, the morbidity, and the diagnostic yield in providing a histological and molecular diagnosis were recorded and evaluated.

RESULTS

The overall diagnostic yield was 93.6% with nine procedures resulting non-diagnostic. Among 110 patients with glioma, the IDH-1 mutational status was characterized in 108 cases (98.2%), resulting wild-type in all subjects but 3; MGMT methylation was characterized in 96 cases (87.3%), resulting present in 60 patients, and 1p/19q codeletion was founded in 6 of the 20 cases of grade II-III gliomas analyzed. All the specimens were apt for molecular analysis when performed. Bleeding requiring surgical drainage occurred in 2.1% of the cases; 8 (5.7%) asymptomatic hemorrhages requiring no treatment were observed. No biopsy-related mortality was recorded. Median length of hospital stay was 5 days (IQR 4-8) with mean surgical time of 60.77 min (± 23.12) and 137.44 ± 24.1 min of total occupation time of the operative room.

CONCLUSIONS

Stereotactic frameless biopsy is a safe, feasible, and fast procedure to obtain a histological and molecular diagnosis.

Update on amino acid PET of brain tumours

PURPOSE OF REVIEW

The aim of this study was to give an update on the emerging role of PET using radiolabelled amino acids in the diagnostic workup and management of patients with cerebral gliomas and brain metastases.

RECENT FINDINGS

Numerous studies have demonstrated the potential of PET using radiolabelled amino acids for differential diagnosis of brain tumours, delineation of tumour extent for treatment planning and biopsy guidance, differentiation between tumour progression and recurrence versus treatment-related changes, and for monitoring of therapy. The Response Assessment in Neuro-Oncology (RANO) working group - an international effort to develop new standardized response criteria for clinical trials in brain tumours - has recently recommended the use of amino acid PET imaging for brain tumour management in addition to MRI at every stage of disease. With the introduction of F-18 labelled amino acids, a broader clinical application has become possible, but is still hampered by the lack of regulatory approval and of reimbursement in many countries.

SUMMARY

PET using radiolabelled amino acids is a rapidly evolving method that can significantly enhance the diagnostic value of MRI in brain tumours. Current developments suggest that this imaging technique will become an indispensable tool in neuro-oncological centres in the near future.

The Path Toward PET-Guided Radiation Therapy for Glioblastoma in Laboratory Animals: A Mini Review

Glioblastoma is the most aggressive and malignant primary brain tumor in adults. Despite the current state-of-the-art treatment, which consists of maximal surgical resection followed by radiation therapy, concomitant, and adjuvant chemotherapy, progression remains rapid due to aggressive tumor characteristics. Several new therapeutic targets have been investigated using chemotherapeutics and targeted molecular drugs, however, the intrinsic resistance to induced cell death of brain cells impede the effectiveness of systemic therapies. Also, the unique immune environment of the central nervous system imposes challenges for immune-based therapeutics. Therefore, it is important to consider other approaches to treat these tumors. There is a well-known dose-response relationship for glioblastoma with increased survival with increasing doses, but this effect seems to cap around 60 Gy, due to increased toxicity to the normal brain. Currently, radiation treatment planning of glioblastoma patients relies on CT and MRI that does not visualize the heterogeneous nature of the tumor, and consequently, a homogenous dose is delivered to the entire tumor. Metabolic imaging, such as positron-emission tomography, allows to visualize the heterogeneous tumor environment. Using these metabolic imaging techniques, an approach called dose painting can be used to deliver a higher dose to the tumor regions with high malignancy and/or radiation resistance. Preclinical studies are required for evaluating the benefits of novel radiation treatment strategies, such as PET-based dose painting. The aim of this review is to give a brief overview of promising PET tracers that can be evaluated in laboratory animals to bridge the gap between PET-based dose painting in glioblastoma patients.

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.

Clinical value of fluorine-18α-methyltyrosine PET in patients with gliomas: comparison with fluorine-18 fluorodeoxyglucose PET

Background

We investigated the relationship between metabolic activity and histological features of gliomas using fluorine-18α-methyltyrosine (¹⁸F-FAMT) positron emission tomography (PET) compared with fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) PET in 38 consecutive glioma patients. The tumor to normal brain ratios (T/N ratios) were calculated, and the relationships between T/N ratio and World Health Organization tumor grade or MIB-1 labeling index were evaluated. The diagnostic values of T/N ratios were assessed using receiver operating characteristic (ROC) curve analyses to differentiate between high-grade gliomas (HGGs) and low-grade gliomas (LGGs).

Results

Median T/N ratio of ¹⁸F-FAMT PET was 2.85, 4.65, and 4.09 for grade II, III, and IV gliomas, respectively, with significant differences between HGGs and LGGs (p = 0.006). Both T/N ratio (p = 0.016) and maximum standardized uptake value (p = 0.033) of ¹⁸F-FDG PET showed significant differences between HGGs and LGGs. ROC analysis yielded an optimal cut-off of 3.37 for the T/N ratio of ¹⁸F-FAMT PET to differentiate between HGGs and LGGs (sensitivity 81%, specificity 67%, accuracy 76%, area under the ROC curve 0.776). Positive predictive value was 84%, and negative predictive value was 62%. T/N ratio of ¹⁸F-FAMT PET was not correlated with MIB-1 labeling index in all gliomas, whereas T/N ratio of ¹⁸F-FDG PET was positively correlated (r_s = 0.400, p = 0.013). Significant positive correlation was observed between T/N ratios of ¹⁸F-FDG and ¹⁸F-FAMT (r_s = 0.454, p = 0.004), but median T/N ratio of ¹⁸F-FAMT PET was significantly higher than that of ¹⁸F-FDG PET in all grades of glioma.

Conclusions

The T/N ratio of ¹⁸F-FAMT uptake has high positive predictive value for detection of HGGs. ¹⁸F-FAMT PET had higher T/N ratio, with better tumor-normal brain contrast, compared to ¹⁸F-FDG PET in both LGGs and HGGs. Therefore, ¹⁸F-FAMT is a useful radiotracer for the preoperative visualization of gliomas.

Assessment of molecular markers demonstrates concordance between samples acquired via stereotactic biopsy and open craniotomy in both anaplastic astrocytomas and glioblastomas

The classification, treatment and prognosis of high-grade gliomas has been shown to correlate with the expression of molecular markers (e.g. MGMT promotor methylation and IDH1 mutations). Acquisition of tumor samples may be obtained via stereotactic biopsy or open craniotomy. Between the years 2009 and 2013, 22 patients initially diagnosed with HGGs via stereotactic biopsy, that ultimately underwent open craniotomy for resection of their tumor were prospectively included in an institutional glioma database. MGMT promotor analysis was performed using methylation-specific (MS)-PCR and IDH1R132H mutation analysis was performed using immunohistochemistry. Three patients (13.7%) exhibited IDH1R132H mutations in samples obtained via stereotactic biopsy. Tissue derived from stereotaxic biopsy was demonstrated to have MGMT promotor methylation in ten patients (45.5%), while a non-methylated MGMT promotor was demonstrated in ten patients (45.5%); inconclusive results were obtained for the remaining two patients (9%) within our cohort. The initial histologic grading, IDH1R132H mutation and MGMT promotor methylation results were confirmed using samples obtained during open craniotomy in all but one patient; here inconclusive MGMT promotor analysis was obtained in contrast to that which was obtained via stereotactic biopsy. Tumor samples acquired via stereotactic biopsy provide accurate information with regard to clinically relevant molecular markers that have been shown to impact patient care decisions. The profile of markers analyzed in our cohort was nearly concordant between those samples obtained via stereotactic biopsy or open craniotomy thereby suggesting that clinical decisions may be based on the molecular profile of the tumor samples obtained via stereotactic biopsy.

Advances in neuro-oncology imaging

Despite the fact that MRI has evolved to become the standard method for diagnosis and monitoring of patients with brain tumours, conventional MRI sequences have two key limitations: the inability to show the full extent of the tumour and the inability to differentiate neoplastic tissue from nonspecific, treatment-related changes after surgery, radiotherapy, chemotherapy or immunotherapy. In the past decade, PET involving the use of radiolabelled amino acids has developed into an important diagnostic tool to overcome some of the shortcomings of conventional MRI. The Response Assessment in Neuro-Oncology working group - an international effort to develop new standardized response criteria for clinical trials in brain tumours - has recommended the additional use of amino acid PET imaging for brain tumour management. Concurrently, a number of advanced MRI techniques such as magnetic resonance spectroscopic imaging and perfusion weighted imaging are under clinical evaluation to target the same diagnostic problems. This Review summarizes the clinical role of amino acid PET in relation to advanced MRI techniques for differential diagnosis of brain tumours; delineation of tumour extent for treatment planning and biopsy guidance; post-treatment differentiation between tumour progression or recurrence versus treatment-related changes; and monitoring response to therapy. An outlook for future developments in PET and MRI techniques is also presented.

Amino acid PET and MR perfusion imaging in brain tumours

Purpose

Despite the excellent capacity of the conventional MRI to image brain tumours, problems remain in answering a number of critical diagnostic questions. To overcome these diagnostic shortcomings, PET using radiolabeled amino acids and perfusion-weighted imaging (PWI) are currently under clinical evaluation. The role of amino acid PET and PWI in different diagnostic challenges in brain tumours is controversial.

Methods

Based on the literature and experience of our centres in correlative imaging with PWI and PET using O-(2-[¹⁸F]fluoroethyl)-l-tyrosine or 3,4-dihydroxy-6-[¹⁸F]-fluoro-l-phenylalanine, the current role and shortcomings of amino acid PET and PWI in different diagnostic challenges in brain tumours are reviewed. Literature searches were performed on PubMed, and additional literature was retrieved from the reference lists of identified articles. In particular, all studies in which amino acid PET was directly compared with PWI were included.

Results

PWI is more readily available, but requires substantial expertise and is more sensitive to artifacts than amino acid PET. At initial diagnosis, PWI and amino acid PET can help to define a site for biopsy but amino acid PET appears to be more powerful to define the tumor extent. Both methods are helpful to differentiate progression or recurrence from unspecific posttherapeutic changes. Assessment of therapeutic efficacy can be achieved especially with amino acid PET, while the data with PWI are sparse.

Conclusion

Both PWI and amino acid PET add valuable diagnostic information to the conventional MRI in the assessment of patients with brain tumours, but further studies are necessary to explore the complementary nature of these two methods.

Nuclear Medicine Imaging in Pediatric Neurology

Nuclear medicine imaging can provide important complementary information in the management of pediatric patients with neurological diseases. Pre-surgical localization of the epileptogenic focus in medically refractory epilepsy patients is the most common indication for nuclear medicine imaging in pediatric neurology. In patients with temporal lobe epilepsy, nuclear medicine imaging is particularly useful when magnetic resonance imaging findings are normal or its findings are discordant with electroencephalogram findings. In pediatric patients with brain tumors, nuclear medicine imaging can be clinically helpful in the diagnosis, directing biopsy, planning therapy, differentiating tumor recurrence from post-treatment sequelae, and assessment of response to therapy. Among other neurological diseases in which nuclear medicine has proved to be useful are patients with head trauma, inflammatory-infectious diseases and hypoxic-ischemic encephalopathy.

From the clinician's point of view - What is the status quo of positron emission tomography in patients with brain tumors?

The most common type of primary brain tumor is malignant glioma. Despite intensive therapeutic efforts, the majority of these neoplasms remain incurable. Imaging techniques are important for initial tumor detection and comprise indispensable tools for monitoring treatment. Structural imaging using contrast-enhanced MRI is the method of choice for brain tumor surveillance, but its capacity to differentiate tumor from nonspecific tissue changes can be limited, particularly with posttreatment gliomas. Metabolic imaging using positron-emission-tomography (PET) can provide relevant additional information, which may allow for better assessment of tumor burden in ambiguous cases. Specific PET tracers have addressed numerous molecular targets in the last decades, but only a few have achieved relevance in routine clinical practice. At present, PET studies using radiolabeled amino acids appear to improve clinical decision-making as these tracers can offer better delineation of tumor extent as well as improved targeting of biopsies, surgical interventions, and radiation therapy. Amino acid PET imaging also appears useful for distinguishing glioma recurrence or progression from postradiation treatment effects, particularly radiation necrosis and pseudoprogression, and provides information on histological grading and patient prognosis. In the last decade, the tracers O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) and 3,4-dihydroxy-6-[(18)F]-fluoro-L-phenylalanine (FDOPA) have been increasingly used for these indications. This review article focuses on these tracers and summarizes their recent applications for patients with brain tumors. Current uses of tracers other than FET and FDOPA are also discussed, and the most frequent practical questions regarding PET brain tumor imaging are reviewed.

Comparison of amino acid positron emission tomographic radiotracers for molecular imaging of primary and metastatic brain tumors

Positron emission tomography (PET) is an imaging technology that can detect and characterize tumors based on their molecular and biochemical properties, such as altered glucose, nucleoside, or amino acid metabolism. PET plays a significant role in the diagnosis, prognostication, and treatment of various cancers, including brain tumors. In this article, we compare uptake mechanisms and the clinical performance of the amino acid PET radiotracers (l-[methyl-11C]methionine [MET], 18F-fluoroethyl-tyrosine [FET], 18F-fluoro-l-dihydroxy-phenylalanine [FDOPA], and 11C-alpha-methyl-l-tryptophan [AMT]) most commonly used for brain tumor imaging. First, we discuss and compare the mechanisms of tumoral transport and accumulation, the basis of differential performance of these radioligands in clinical studies. Then we summarize studies that provided direct comparisons among these amino acid tracers and to clinically used 2-deoxy-2[18F]fluoro-d-glucose [FDG] PET imaging. We also discuss how tracer kinetic analysis can enhance the clinical information obtained from amino acid PET images. We discuss both similarities and differences in potential clinical value for each radioligand. This comparative review can guide which radiotracer to favor in future clinical trials aimed at defining the role of these molecular imaging modalities in the clinical management of brain tumor patients.

Imaging biomarkers in primary brain tumours

We are getting used to referring to instrumentally detectable biological features in medical language as "imaging biomarkers". These two terms combined reflect the evolution of medical imaging during recent decades, and conceptually comprise the principle of noninvasive detection of internal processes that can become targets for supplementary therapeutic strategies. These targets in oncology include those biological pathways that are associated with several tumour features including independence from growth and growth-inhibitory signals, avoidance of apoptosis and immune system control, unlimited potential for replication, self-sufficiency in vascular supply and neoangiogenesis, acquired tissue invasiveness and metastatic diffusion. Concerning brain tumours, there have been major improvements in neurosurgical techniques and radiotherapy planning, and developments of novel target drugs, thus increasing the need for reproducible, noninvasive, quantitative imaging biomarkers. However, in this context, conventional radiological criteria may be inappropriate to determine the best therapeutic option and subsequently to assess response to therapy. Integration of molecular imaging for the evaluation of brain tumours has for this reason become necessary, and an important role in this setting is played by imaging biomarkers in PET and MRI. In the current review, we describe most relevant techniques and biomarkers used for imaging primary brain tumours in clinical practice, and discuss potential future developments from the experimental context.

Voxel-based clustered imaging by multiparameter diffusion tensor images for glioma grading

Gliomas are the most common intra-axial primary brain tumour; therefore, predicting glioma grade would influence therapeutic strategies. Although several methods based on single or multiple parameters from diagnostic images exist, a definitive method for pre-operatively determining glioma grade remains unknown. We aimed to develop an unsupervised method using multiple parameters from pre-operative diffusion tensor images for obtaining a clustered image that could enable visual grading of gliomas. Fourteen patients with low-grade gliomas and 19 with high-grade gliomas underwent diffusion tensor imaging and three-dimensional T1-weighted magnetic resonance imaging before tumour resection. Seven features including diffusion-weighted imaging, fractional anisotropy, first eigenvalue, second eigenvalue, third eigenvalue, mean diffusivity and raw T2 signal with no diffusion weighting, were extracted as multiple parameters from diffusion tensor imaging. We developed a two-level clustering approach for a self-organizing map followed by the K-means algorithm to enable unsupervised clustering of a large number of input vectors with the seven features for the whole brain. The vectors were grouped by the self-organizing map as protoclusters, which were classified into the smaller number of clusters by K-means to make a voxel-based diffusion tensor-based clustered image. Furthermore, we also determined if the diffusion tensor-based clustered image was really helpful for predicting pre-operative glioma grade in a supervised manner. The ratio of each class in the diffusion tensor-based clustered images was calculated from the regions of interest manually traced on the diffusion tensor imaging space, and the common logarithmic ratio scales were calculated. We then applied support vector machine as a classifier for distinguishing between low- and high-grade gliomas. Consequently, the sensitivity, specificity, accuracy and area under the curve of receiver operating characteristic curves from the 16-class diffusion tensor-based clustered images that showed the best performance for differentiating high- and low-grade gliomas were 0.848, 0.745, 0.804 and 0.912, respectively. Furthermore, the log-ratio value of each class of the 16-class diffusion tensor-based clustered images was compared between low- and high-grade gliomas, and the log-ratio values of classes 14, 15 and 16 in the high-grade gliomas were significantly higher than those in the low-grade gliomas (p < 0.005, p < 0.001 and p < 0.001, respectively). These classes comprised different patterns of the seven diffusion tensor imaging-based parameters. The results suggest that the multiple diffusion tensor imaging-based parameters from the voxel-based diffusion tensor-based clustered images can help differentiate between low- and high-grade gliomas.

•

We have developed a novel unsupervised method for voxel-based clustered imaging.

•

Each class ratio in clustered images differentiated high from low-grade gliomas.

•

The 16-class clustered images showed the best performance for the differentiation.

•

Each class comprised different patterns of the seven diffusion tensor-based features.

•

Multiple parameters from diffusion tensor images are useful for glioma grading.

Applications of positron emission tomography in neuro-oncology: a clinical approach

The field of neuro-oncology is concerned with some of the most challenging and difficult to treat conditions in medicine. Despite modern therapies patients diagnosed with primary brain tumours often have a poor prognosis. Imaging can play an important role in evaluating the disease status of such patients. In addition to the structural information derived from MRI and CT scans, positron emission tomography (PET) provides important quantitative metabolic assessment of brain tumours. This review describes the use of PET with radiolabelled glucose and amino acid analogues to aid in the diagnosis of tumours, differentiate between recurrent tumour and radiation necrosis and guide biopsy or treatment. [(18)F]Fluorodeoxyglucose (FDG) is the tracer that has been used most widely because it has a 2 h half life and can be transported to imaging centres remote from the cyclotron and radiochemistry facilities which synthesise the tracers. The high uptake of FDG in normal grey matter however limits its use in some low grade tumours which may not be visualised. [(11)C] methionine (MET) is an amino acid tracer with low accumulation in normal brain which can detect low grade gliomas, but its short 20 min half life has limited its use to imaging sites with their own cyclotron. The emergence of new fluorinated amino acid tracers like [(18)F]Fluoroethyl-l-tyrosine (FET) will likely increase the availability and utility of PET for patients with primary brain tumours. PET can, further, characterise brain tumours by investigating other metabolic processes such as DNA synthesis or thymidine kinase activity, phospholipid membrane biosynthesis, hypoxia, receptor binding and oxygen metabolism and blood flow, which will be important in the future assessment of targeted therapy.

18 F-FDG PET standard uptake values of the normal pons in children: establishing a reference value for diffuse intrinsic pontine glioma

BACKGROUND

Positron emission tomography (PET) scanning with [18 F]fluorodeoxyglucose (18 F-FDG) is a useful diagnostic and prediction tool in brain tumors, but its value in childhood diffuse intrinsic pontine glioma (DIPG) is still unclear. For interpretation of 18 F-FDG PET results in DIPG, uptake values of the normal pons of children of increasing ages are mandatory. The aim of this study was to determine 18 F-FDG standard uptake value ratios (SUVr) of the normal pons and to compare these to those of DIPG.

METHODS

We studied 36 subjects with a normal, non-affected pons (aged 5 to 23 years) and 6 patients with DIPG (aged 4 to 17 years) who underwent 18 F-FDG PET scanning. Magnetic resonance imaging (MRI) was co-registered to define the regions of interest. SUVr and SUVrmax for the pons/cerebellum (SUVrp/c) and the pons/occipital lobe (SUVrp/o) were calculated. Independent-samples t tests and Mann-Whitney U tests were used to compare the mean SUVr and Pearson's test for correlations.

RESULTS

For the normal pons, mean SUVrp/c and SUVrp/o were 0.65 (±0.054) and 0.51 (±0.056), respectively. No significant correlations were found between the SUVr of the normal pons and sex, age, nor pontine volume. A modest but statistically significant correlation was found between SUVr and post-injection time acquisition timing. For DIPG, mean SUVrp/c and SUVrp/o were 0.74 (±0.20) and 0.65 (±0.30), respectively, while mean SUVrp(max)/c and SUVrp(max)/o were 1.95 (±0.48) and 1.81 (±0.20), respectively.

CONCLUSION

The SUVr of the unaffected pons are strikingly constant between children, irrespective of sex and age, and can therefore be well used as a reference value for 18 F-FDG PET studies in DIPG.

Present and potential future issues in glioblastoma treatment

The treatment of glioblastomas requires a multidisciplinary approach that takes the presently incurable nature of the disease into consideration. Treatments are multimodal and include surgery, radiotherapy and chemotherapy. Current recommendations are that patients with glioblastomas should undergo maximum surgical resection, followed by concurrent radiation and chemotherapy with the novel alkylating drug temozolomide. This is then to be followed by additional adjuvant temozolomide for a period of up to 6 months. Major advances in surgical and imaging technologies used to treat glioblastoma patients are described. These technologies include magnetic resonance imaging and metabolic data that are helpful in the diagnosis and guiding of surgical resection. However, glioblastomas almost invariably recur near their initial sites. Disease progression usually occurs within 6 months and leads rapidly to death. A number of signaling pathways can be activated constitutively in migrating glioma cells, thus rendering these cells resistant to proapoptotic insults, such as conventional chemotherapies. Therefore, the molecular and cellular therapies and local drug delivery that could be used to complement conventional treatments are described, and some of the currently ongoing clinical trials are reviewed, with respect to these new approaches.

Metabolic mapping of gliomas using hybrid MR-PET imaging: feasibility of the method and spatial distribution of metabolic changes

BACKGROUND AND PURPOSE

The most powerful adjunct to histopathology for the grading of gliomas seems to be the metabolic imaging using positron emission tomography and magnetic resonance spectroscopy (MRS). The purposes of this study were to examine the feasibility of simultaneous acquisition of both techniques for purposes of tumor grading in a newly launched hybrid magnetic resonance positron emission tomography (MR-PET) and to examine the spatial distributions of metabolic changes in gliomas.

MATERIALS AND METHODS

Twenty-eight consecutive patients with gliomas underwent simultaneous methionine (Met) MR-PET imaging for detection of the most malignant tumor part before surgical sampling. After coregistration and fusion of MR-PET and MRS data, tumor to normal brain (T/N) Met uptake ratios and the corresponding metabolites peaks (choline [Cho], creatine [Cr], and N-acetylaspartate [NAA]) in MRS were recorded. The patients were divided into 4 types on the basis of the relation between the Met uptake area and the increased metabolite ratios: type I, the increased Met uptake area had at least 50% overlap or was completely within the area of increased Cho/NAA ratio; type II, the increased Met uptake site had less than 50% overlap of increased Cho/NAA ratio site; type III, the increased Met uptake region had no spatial relationship with the "hot" lesions in the MRS maps; and type IV, there was no pathologically increased Met uptake. The surgical sampling was performed in the tumor part with the highest Met uptake and, in the absence of increased Met accumulation, in the site with the highest Cho/NAA ratio. All surgical samples were referred to the neuropathology division for histological grading.

RESULTS

A total of 16 low-grade gliomas (World Health Organization grade II) and 12 high-grade gliomas (World Health Organization grade III) were included. Three lesions (10%) of type I were identified. Four lesions (14%) were classified as type II and 6 lesions (21%) were classified as type 3, where the increased Met uptake region had no spatial relationship with the hot lesions in the MRS maps. In 15 of the 28 patients (54%), there was no increased Met accumulation (type 4 lesions). Maps of Cho/NAA and Cr/NAA showed a close spatial relationship in most of the patients. Median T/N Met uptake ratio in the pooled surgically sampled tumor sites was 1.6 (range, 1-3), and median Cho/NAA and Cho/Cr ratios were 2.1 (range, 0.9-5.8) and 1.5 (range, 0.5-8.3), respectively. Spearman rank correlations of the metabolic markers in the low-grade gliomas showed significant correlations between Met uptake and Cr/NAA ratio (ρ = 0.59; P = 0.015) as well as between Cho/NAA and Cr/NAA ratios (ρ = 0.79; P = 0.0002). The normalized tumor creatine was significantly higher in anaplastic tumors compared with the low-grade gliomas (P = 0.001). A tendency for a significant positive correlation was found between normalized tumor creatine and Met uptake in the anaplastic tumors.

CONCLUSIONS

Metabolic mapping before histological sampling is feasible using simultaneous MR-PET imaging. High T/N Met uptake ratio reflecting high expression of amino-acid membrane transporters, which is indicative of proliferating tumor cell populations, does not always spatially correlate with neuronal cell loss and cell membrane proliferation (Cho/NAA) seen in MRS. Increased Cr/NAA is associated with increased methionine uptake in low-grade gliomas, whereas normalized creatine in tumor tends to correlate with methionine accumulation, which indicates a possible coupling of these metabolic indices in anaplastic tumors. Thus, spatial distribution differences in gliomas should be taken into account when planning surgical sampling.

Brain tumors

This review addresses the specific contributions of nuclear medicine techniques, and especially positron emission tomography (PET), for diagnosis and management of brain tumors. (18)F-Fluorodeoxyglucose PET has particular strengths in predicting prognosis and differentiating cerebral lymphoma from nonmalignant lesions. Amino acid tracers including (11)C-methionine, (18)F-fluoroethyltyrosine, and (18)F-L-3,4-dihydroxyphenylalanine provide high sensitivity, which is most useful for detecting recurrent or residual gliomas, including most low-grade gliomas. They also play an increasing role for planning and monitoring of therapy. (18)F-fluorothymidine can only be used in tumors with absent or broken blood-brain barrier and has potential for tumor grading and monitoring of therapy. Ligands for somatostatin receptors are of particular interest in pituitary adenomas and meningiomas. Tracers to image neovascularization, hypoxia, and phospholipid synthesis are under investigation for potential clinical use. All methods provide the maximum of information when used with image registration and fusion display with contrast-enhanced magnetic resonance imaging scans. Integration of PET and magnetic resonance imaging with stereotactic neuronavigation systems allows the targeting of stereotactic biopsies to obtain a more accurate histologic diagnosis and better planning of conformal and stereotactic radiotherapy.

Central nervous system lymphoma initially diagnosed as tumefactive multiple sclerosis after brain biopsy

A 72-year-old man was admitted with left homonymous hemianopsia and hemiparesis. Magnetic resonance imaging revealed a heterogeneously enhanced lesion in the right parietal lobe. A brain biopsy showed acute demyelination without malignancy, which led to a diagnosis of tumefactive multiple sclerosis (MS). The patient received corticosteroid therapy and experienced clinical and radiological improvement. Six months later, new lesions appeared, and a second biopsy revealed proliferation of dysplastic lymphocytes. This led to a revised diagnosis of primary central nervous system lymphoma (PCNSL). Because PCNSL mimics MS both clinically and radiologically, PCNSL is difficult to diagnose. Performing repeated brain biopsies may therefore be required when PCNSL is strongly suspected.

Clinical value of [¹¹C]methionine PET for stereotactic radiation therapy with intensity modulated radiation therapy to metastatic brain tumors

PURPOSE

This study investigated the clinical impact of (11)C-labeled methionine-positron emission tomography (MET-PET) for stereotactic radiation therapy with intensity modulated radiation therapy (SRT-IMRT) in metastatic brain tumors.

METHODS AND MATERIALS

Forty-two metastatic brain tumors were examined. All tumors were treated with SRT-IMRT using a helical tomotherapy system. Gross tumor volume (GTV) was defined and drawn on the stereotactic magnetic resonance (MR) image, taking into account the respective contributions of MR imaging and MET-PET. Planning target volume (PTV) encompassed the GTV-PET plus a 2-mm margin. SRT-IMRT was performed, keeping the dose for PTV at 25-35 Gy in 5 fractions. The ratio of the mean value of MET uptake to the contralateral normal brain (L/N ratio) was plotted for the PTV prior to SRT-IMRT, at 3 months following SRT-IMRT, and at 6 months following SRT-IMRT. Tumor characteristic changes of MET uptake before and after SRT-IMRT were evaluated quantitatively, comparing them with MRI examination.

RESULTS

Mean ± SD L/N ratios were 1.95 ± 0.83, 1.18 ± 0.21, and 1.12 ± 0.25 in the pre-SRT-IMRT group, in the 3 months post-SRT-IMRT group, and in the 6 months post-SRT-IMRT group, respectively. Differences in the mean L/N ratio between the pre-SRT-IMRT group and the 3-month post-SRT-IMRT group and between the pre-SRT-IMRT group and the 6 month post-SRT-IMRT group were statistically significant, irrespective of MRI examination.

CONCLUSIONS

We showed examples of metastatic lesions demonstrating significant decreases in MET uptake following SRT-IMRT. MET-PET seems to have a potential role in providing additional information, although MRI remains the gold standard for diagnosis and follow-up after SRT-IMRT. The present study is a preliminary approach, but to more clearly define the impact of PET-based radiosurgical assessment, further experimental and clinical analyses are required.

Use of positron emission tomography in the evaluation of diffuse intrinsic brainstem gliomas in children

BACKGROUND

Diffuse intrinsic brainstem gliomas (DIBSGs) in children remain difficult tumors to treat and have a very poor prognosis. Intensifying both chemotherapy and radiation programs have been attempted without success. Positron emission tomography (PET) has been used to differentiate benign from malignant tumors and may predict outcome.

OBJECTIVES

To determine whether PET can characterize a specific metabolic pattern of DIBSGs and correlate this with patient survival.

METHODS

We conducted a retrospective review of patients with DIBSGs and PET scans at diagnosis. Data for ¹⁸[F] fluorodeoxyglucose (FDG) and ¹¹C-methionine (CMET) PET scans were collected. Treatment and survival were reviewed.

RESULTS

We identified 30 patients with DIBSGs, 25 of whom had FDG and/or CMET PET scans. Scans showed both focal and generalized metabolic activity, and the patterns showed no correlation with survival. Patients with both FDG and CMET positive scans had a mean survival of 380 days, whereas those negative for both isotopes had a mean survival of 446 days.

CONCLUSIONS

There was no specific PET pattern identified in this DIBSG cohort but a trend toward improved survival was noted with absence of FDG and CMET metabolism. Metabolically active areas may suggest potential sites for biopsy. We believe that biopsy is essential for improving therapy for this patient population.

[Clinical factors in glioblastoma and neuroradiology]

Glioblastoma is found preferentially in men (1.5/1), nearing age 60, but all ages can be concerned. Clinical symptoms are intracranial mass without specificity, intracranial hypertension and localization signs. From the clinical history, the essential prognosis factors are: age, Karnofsky score and cognitive dysfunction. Conventional MRI sequences, including T1-FSE with and without contrast injection and T2-FSE or Flair-weighted sequences, provide the diagnosis in most cases, showing an intraparenchymal mass with a heterogeneous, irregularly enhanced signal. Other sequences define the tumor more precisely. Diffusion sequences provide the differential diagnosis with an abscess or a highly cellular tumor such as lymphoma. Perfusion sequences allow appreciation of tumor microvascularization outlining the tumor's most active areas. Magnetic resonance spectroscopy (SRM) sequences allow noninvasive exploration of tumor metabolism. Beyond its diagnostic role, imagery assists the surgical procedure itself, particularly with functional MRI, allowing a precise preoperative mapping of functional cortical areas. Biopsy can also be guided toward the most active areas of the tumor. In the postoperative period, MRI completes the surgeon's impression on whether or not there is residual tumor. Finally, this exam has become essential in follow-up to diagnose recurrence, radionecrosis, or pseudoprogression.

Comparison of F-18 FET-PET with F-18 FDG-PET for biopsy planning of non-contrast-enhancing gliomas

OBJECTIVE

The management of non-contrast-enhancing brain tumours largely depends on biopsy, which allows a differentiation of low-grade gliomas (LGG) from high-grade gliomas (HGG). The aim of this study was to compare positron emission tomography using 2-[(18)F]-fluoro-2-deoxy-D: -glucose (FDG-PET) and O-(2-[(18)F]-fluoroethyl)-L: -tyrosine (FET-PET) in terms of providing target regions for biopsies.

MATERIALS AND METHODS

Fifteen consecutive patients with newly diagnosed brain tumours (n = 11) or suspected recurrence of a known LGG (n = 4), in whom MRI demonstrated no contrast enhancement, were studied by both FET-PET and FDG-PET. FET-PET, FDG-PET and MRI data were fused, and then transferred to the neurosurgical navigation system, prior to neurosurgical interventions.

RESULTS

Histology showed HGG (WHO grade III) in 6/15 and LGG (WHO grade II) in 9/15 patients. FET-PET revealed an increased intratumoural tracer uptake in 8/9 LGG and in 5/6 HGG. FDG-PET depicted hypermetabolic spots in 2/9 LGG and in 4/6 HGG. In 6 patients we observed an increased intratumoural uptake of both tracers. In 4 of them, the area of highest FET accumulation in the tumour corresponded to the focus of increased FDG uptake.

CONCLUSIONS

FET-PET appears to be superior to FDG-PET for biopsy planning in non-contrast-enhancing brain tumours. FDG-PET does not provide any additional information in this issue.

Switching on the lights for real-time multimodality tumor neuroimaging: The integrated positron-emission tomography/MR imaging system

A recent report of the feasibility of simultaneous PET/MR imaging of the healthy human brain has sparked excitement in the field of neuroimaging because of its potential influence and utility in clinical neuroscience research. The aim of this communication is to discuss the benefits and current drawbacks of the hybrid imaging system and to highlight some perspectives of the new technique for brain neoplasms.

Advances in imaging low-grade gliomas

Imaging plays a key role in the management of low-grade gliomas. The traditional view of these tumours as non-enhancing areas of increased signal on T2-weighted imaging is now accepted as being incorrect. Using new MR and PET techniques that can probe the pathological changes with in these tumours by assessing vascularity (perfusion MR), cellularity and infiltration (diffusion weighted and diffusion tensor MR), metabolism (MR spectroscopy and FDG PET) and proliferation (MR spectroscopy, methionine PET and 18F-fluorothymidine FLT PET). These tools will allow improvements in tumour grading, biopsy/therapy guidance and earlier assessment of the response to therapy.

Clinical impact of (11)C-methionine PET on expected management of patients with brain neoplasm

PURPOSE

We retrospectively examined the clinical efficacy of (11)C-methionine positron emission tomography ((11)C-MET PET) in patients with brain neoplasm, especially whether the (11)C-MET PET changed the clinical management and whether the change was beneficial or detrimental.

METHODS

This study reviewed 89 (11)C-MET PET scans for 80 patients (20 scans for initial diagnosis of brain tumor and 69 scans for differentiating tumor recurrence from radiation necrosis). Final diagnosis and the effect on the intended management were obtained from the questionnaire to the referring physicians or directly from the medical records. The diagnostic sensitivity, specificity, and accuracy for the (11)C-MET PET were evaluated. Regarding the management impact, the rate of scans that caused changes in intended management was also evaluated. Moreover, the occurrence of scans having detrimental diagnostic impact (DDI) and beneficial diagnostic impact (BDI) were evaluated.

RESULTS

Sensitivity, specificity, and accuracy of (11)C-MET PET was 87.8, 80.0, and 85.9%. The intended management was changed in 50.0% of the scans. DDI and BDI were observed in 4.3 and 36.2% of the total relevant scans, respectively.

CONCLUSION

(11)C-MET PET can provide useful information in initial diagnosis and differentiating tumor recurrence from radiation necrosis. The intended management was changed in half of the scans. Since a few cases did not receive the requisite treatment due to false-negative results of (11)C-MET PET, management decision should be made carefully, especially in the case of a negative scan.

Comparing the risks of frameless stereotactic biopsy in eloquent and noneloquent regions of the brain: a retrospective review of 284 cases

Object

Frameless stereotactic biopsy has been shown in multiple studies to be a safe and effective tool for the diagnosis of brain lesions. However, no study has directly evaluated its safety in lesions located in eloquent regions in comparison with noneloquent locations. In this study, the authors determine whether an increased risk of neurological decline is associated with biopsy of lesions in eloquent regions of the brain.

Methods

Medical records, including imaging studies, were reviewed for 284 cases in which frameless stereotactic biopsy procedures were performed by 19 neurosurgeons at 7 institutions between January 2000 and December 2006. Lesion location was classified as eloquent or noneloquent in each patient. The incidence of neurological decline was calculated for each group.

Results

During the study period, 160 of the 284 biopsies predominately involved eloquent regions of the brain. In evaluation of the complication rate with respect to biopsy site, neurological decline occurred in 9 (5.6%) of 160 biopsies in eloquent brain areas and 10 (8.1%) of 124 biopsies in noneloquent regions; this difference was not statistically significant (p = 0.416). A higher number of needle passes was associated with the presence of a postoperative hemorrhage at the biopsy site, although not with a change in the result of neurological examination.

Conclusions

Frameless stereotactic biopsy of lesions located in eloquent brain regions is as safe and effective as biopsy of lesions in noneloquent regions. Therefore, with careful planning, frameless stereotactic biopsy remains a valuable and safe tool for diagnosis of brain lesions, independent of lesion location.

POSITRON EMISSION TOMOGRAPHY-GUIDED VOLUMETRIC RESECTION OF SUPRATENTORIAL HIGH-GRADE GLIOMAS

OBJECTIVE

Integrating positron emission tomographic (PET) images into the image-guided resection of high-grade gliomas (HGG) has shown that metabolic information on tumor heterogeneity and distribution are useful for planning surgery, improve tumor delineation, and provide a final target contour different from that obtained with magnetic resonance imaging (MRI) alone in about 80% of the procedures. Moreover, PET guidance helps to increase the amount of tumor removed and to target image-guided resection to anaplastic tissue areas. The present study aims to evaluate whether PET-guided volumetric resection (VR) in supratentorial HGG might add benefit to the patient's outcome.

METHODS

PET images using [18F]fluorodeoxyglucose (n=23) and [11C]methionine (n=43) were combined with MRI scans in the planning of VR procedures performed at the initial stage in 66 consecutive patients (43 M/23 F) with supratentorial HGG according to the technique previously described. In all cases (35 anaplastic gliomas [20 astrocytomas, 10 oligoastrocytomas, 5 oligodendrogliomas] and 31 glioblastomas [GBM]), level and distribution of PET tracer uptake were analyzed to define a PET contour projected on MRI scans to define a final target contour for VR. Maximal tumor resection was accomplished in each case, with the intention to remove the entire abnormal metabolic area comprised in the surgical planning. Early postoperative MRI and PET assessed tumor resection. Survival analysis was performed separately in anaplastic gliomas and glioblastoma multiforme according to the presence or absence of residual tracer uptake on postoperative PET and according to the presence or absence of residual contrast enhancement on postoperative MRI.

RESULTS

Preoperatively, metabolic information helped the surgical planning. In all procedures, PET contributed to define a final target contour different from that obtained with MRI alone. Postoperatively, 46 of 66 patients had no residual PET tracer uptake (total PET resection), 23 of 66 had no residual MRI contrast enhancement. No additional neurological morbidity due to the technique was reported. A total PET tracer uptake resection was associated with a significantly longer survival in anaplastic gliomas (P = 0.0071) and in glioblastoma multiforme (P = 0.0001), respectively. A total MRI contrast enhancement resection was not correlated with a significantly better survival, neither in anaplastic gliomas (P = 0.6089) nor in glioblastoma multiforme (P = 0.6806).

CONCLUSIONS

Complete resection of the increased PET tracer uptake prolongs the survival of HGG patients. Because PET information represents a more specific marker than MRI enhancement for detecting anaplastic tumor tissue, PET-guidance increases the amount of anaplastic tissue removed in HGG.

Tumor cell metabolism imaging

Molecular imaging of tumor metabolism has gained considerable interest, since preclinical studies have indicated a close relationship between the activation of various oncogenes and alterations of cellular metabolism. Furthermore, several clinical trials have shown that metabolic imaging can significantly impact patient management by improving tumor staging, restaging, radiation treatment planning, and monitoring of tumor response to therapy. In this review, we summarize recent data on the molecular mechanisms underlying the increased metabolic activity of cancer cells and discuss imaging techniques for studies of tumor glucose, lipid, and amino acid metabolism.