Proton magnetic spectroscopic imaging of the child's brain: the response of tumors to treatment

Evolving Diagnostic and Treatment Strategies for Pediatric CNS Tumors: The Impact of Lipid Metabolism

Pediatric neurological tumors are a heterogeneous group of cancers, many of which carry a poor prognosis and lack a "standard of care" therapy. While they have similar anatomic locations, pediatric neurological tumors harbor specific molecular signatures that distinguish them from adult brain and other neurological cancers. Recent advances through the application of genetics and imaging tools have reshaped the molecular classification and treatment of pediatric neurological tumors, specifically considering the molecular alterations involved. A multidisciplinary effort is ongoing to develop new therapeutic strategies for these tumors, employing innovative and established approaches. Strikingly, there is increasing evidence that lipid metabolism is altered during the development of these types of tumors. Thus, in addition to targeted therapies focusing on classical oncogenes, new treatments are being developed based on a broad spectrum of strategies, ranging from vaccines to viral vectors, and melitherapy. This work reviews the current therapeutic landscape for pediatric brain tumors, considering new emerging treatments and ongoing clinical trials. In addition, the role of lipid metabolism in these neoplasms and its relevance for the development of novel therapies are discussed.

Magnetic resonance spectroscopy for the study of cns malignancies

Despite intensive research, brain tumors are amongst the malignancies with the worst prognosis; therefore, a prompt diagnosis and thoughtful assessment of the disease is required. The resistance of brain tumors to most forms of conventional therapy has led researchers to explore the underlying biology in search of new vulnerabilities and biomarkers. The unique metabolism of brain tumors represents one potential vulnerability and the basis for a system of classification. Profiling this aberrant metabolism requires a method to accurately measure and report differences in metabolite concentrations. Magnetic resonance-based techniques provide a framework for examining tumor tissue and the evolution of disease. Nuclear Magnetic Resonance (NMR) analysis of biofluids collected from patients suffering from brain cancer can provide biological information about disease status. In particular, urine and plasma can serve to monitor the evolution of disease through the changes observed in the metabolic profiles. Moreover, cerebrospinal fluid can be utilized as a direct reporter of cerebral activity since it carries the chemicals exchanged with the brain tissue and the tumor mass. Metabolic reprogramming has recently been included as one of the hallmarks of cancer. Accordingly, the metabolic rewiring experienced by these tumors to sustain rapid growth and proliferation can also serve as a potential therapeutic target. The combination of 13C tracing approaches with the utilization of different NMR spectral modalities has allowed investigations of the upregulation of glycolysis in the aggressive forms of brain tumors, including glioblastomas, and the discovery of the utilization of acetate as an alternative cellular fuel in brain metastasis and gliomas. One of the major contributions of magnetic resonance to the assessment of brain tumors has been the non-invasive determination of 2-hydroxyglutarate (2HG) in tumors harboring a mutation in isocitrate dehydrogenase 1 (IDH1). The mutational status of this enzyme already serves as a key feature in the clinical classification of brain neoplasia in routine clinical practice and pilot studies have established the use of in vivo magnetic resonance spectroscopy (MRS) for monitoring disease progression and treatment response in IDH mutant gliomas. However, the development of bespoke methods for 2HG detection by MRS has been required, and this has prevented the wider implementation of MRS methodology into the clinic. One of the main challenges for improving the management of the disease is to obtain an accurate insight into the response to treatment, so that the patient can be promptly diverted into a new therapy if resistant or maintained on the original therapy if responsive. The implementation of 13C hyperpolarized magnetic resonance spectroscopic imaging (MRSI) has allowed detection of changes in tumor metabolism associated with a treatment, and as such has been revealed as a remarkable tool for monitoring response to therapeutic strategies. In summary, the application of magnetic resonance-based methodologies to the diagnosis and management of brain tumor patients, in addition to its utilization in the investigation of its tumor-associated metabolic rewiring, is helping to unravel the biological basis of malignancies of the central nervous system.

Metabolomic signature of brain cancer

Despite advances in surgery and adjuvant therapy, brain tumors represent one of the leading causes of cancer-related mortality and morbidity in both adults and children. Gliomas constitute about 60% of all cerebral tumors, showing varying degrees of malignancy. They are difficult to treat due to dismal prognosis and limited therapeutics. Metabolomics is the untargeted and targeted analyses of endogenous and exogenous small molecules, which charact erizes the phenotype of an individual. This emerging "omics" science provides functional readouts of cellular activity that contribute greatly to the understanding of cancer biology including brain tumor biology. Metabolites are highly informative as a direct signature of biochemical activity; therefore, metabolite profiling has become a promising approach for clinical diagnostics and prognostics. The metabolic alterations are well-recognized as one of the key hallmarks in monitoring disease progression, therapy, and revealing new molecular targets for effective therapeutic intervention. Taking advantage of the latest high-throughput analytical technologies, that is, nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS), metabolomics is now a promising field for precision medicine and drug discovery. In the present report, we review the application of metabolomics and in vivo metabolic profiling in the context of adult gliomas and paediatric brain tumors. Analytical platforms such as high-resolution (HR) NMR, in vivo magnetic resonance spectroscopic imaging and high- and low-resolution MS are discussed. Moreover, the relevance of metabolic studies in the development of new therapeutic strategies for treatment of gliomas are reviewed.

Proton MRS imaging in pediatric brain tumors

Magnetic resonance (MR) techniques offer a noninvasive, non-irradiating yet sensitive approach to diagnosing and monitoring pediatric brain tumors. Proton MR spectroscopy (MRS), as an adjunct to MRI, is being more widely applied to monitor the metabolic aspects of brain cancer. In vivo MRS biomarkers represent a promising advance and may influence treatment choice at both initial diagnosis and follow-up, given the inherent difficulties of sequential biopsies to monitor therapeutic response. When combined with anatomical or other types of imaging, MRS provides unique information regarding biochemistry in inoperable brain tumors and can complement neuropathological data, guide biopsies and enhance insight into therapeutic options. The combination of noninvasively acquired prognostic information and the high-resolution anatomical imaging provided by conventional MRI is expected to surpass molecular analysis and DNA microarray gene profiling, both of which, although promising, depend on invasive biopsy. This review focuses on recent data in the field of MRS in children with brain tumors.

Early prediction of response to Vorinostat in an orthotopic rat glioma model

Glioblastoma is the most common primary brain tumor and is uniformly fatal despite aggressive surgical and adjuvant therapy. As survival is short, it is critical to determine the value of therapy early on in treatment. Improved early predictive assessment would allow neuro-oncologists to personalize and adjust or change treatment sooner to maximize the use of efficacious therapy. During carcinogenesis, tumor suppressor genes can be silenced by aberrant histone deacetylation. This epigenetic modification has become an important target for tumor therapy. Suberoylanilide hydroxamic acid (SAHA, Vorinostat, Zolinza) is an orally active, potent inhibitor of histone deacetylase (HDAC) activity. A major shortcoming of the use of HDAC inhibitors in the treatment of patients with brain tumors is the lack of reliable biomarkers to predict and determine response. Histological evaluation may reflect tumor viability following treatment, but is an invasive procedure and impractical for glioblastoma. Another problem is that response to SAHA therapy is associated with tumor redifferentiation and cytostasis rather than tumor size reduction, thus limiting the use of traditional imaging methods. A noninvasive method to assess drug delivery and efficacy is needed. Here, we investigated whether changes in (1)H MRS metabolites could render reliable biomarkers for an early response to SAHA treatment in an orthotopic animal model for glioma. Untreated tumors exhibited significantly elevated alanine and lactate levels and reduced inositol, N-acetylaspartate and creatine levels, typical changes reported in glioblastoma relative to normal brain tissues. The (1)H MRS-detectable metabolites of SAHA-treated tumors were restored to those of normal-like brain tissues. In addition, reduced inositol and N-acetylaspartate were found to be potential biomarkers for mood alteration and depression, which may also be alleviated with SAHA treatment. Our study suggests that (1)H MRS can provide reliable metabolic biomarkers at the earliest stage of SAHA treatment to predict the therapeutic response.

Short echo time single voxel 1H magnetic resonance spectroscopy in the diagnosis and characterisation of pineal tumours in children

BACKGROUND

Magnetic resonance spectroscopy (MRS) has been successful in characterising a range of brain tumours and is a useful aid to non-invasive diagnosis. The pineal region poses considerable surgical challenges and a major surgical resection is not required in the management of all tumours. Improved non-invasive assessment of pineal region tumours would be of considerable benefit.

METHODS

Single voxel MRS (TE 30 ms, TR 1500, 1.5 T) was performed on 15 pineal tumours: 5 germinomas, 1 non-germinomatous secreting germ cell tumour (GCT), 2 teratomas, 5 pineoblastomas, 1 pineal parenchymal tumour (PPT) of intermediate differentiation and 1 pineocytoma. Two germinomas outside the pineal gland were also studied. Metabolite, lipid and macromolecule concentrations were determined with LCModel™.

RESULTS

Germ cell tumours had significantly higher lipid and macromolecule concentrations than other tumours (t-test; P < 0.05). The teratomas had significantly lower total choline and creatine levels than germinomas (z test; P < 0.05). Taurine was convincingly detected in germinomas as well as PPTs.

CONCLUSIONS

Magnetic resonance spectroscopy is useful for characterising pineal region tumours, aiding the non-invasive diagnosis and giving additional biological insight.

[Proton magnetic resonance spectroscopic imaging and other types of metabolic imaging for radiotherapy planning in adult and pediatric high-grade gliomas]

Radiation therapy improves survival in high-grade gliomas but most patients relapse and usually within radiation fields. This may be due to uncertainties in target delineation and difficulties in identifying radioresistant regions for dose escalation. The use of T1 and T2-weighted magnetic resonance imaging (MRI) coregistration on the planning CT improves the target volume definition but magnetic resonance spectroscopic imaging (MRSI) and other types of metabolic and functional imaging (perfusion MRI, diffusion-weighted MRI, positron emission tomography (PET) imaging) may give useful additional information for target delineation. This article focuses on the potential of each imaging modality: assessment of response to treatment, detection of abnormalities not seen on MRI, predictive value for the site of local relapse. The incorporation of such techniques may improve target volume definition.

Imaging of central nervous system tumors in children: advances and limitations

Magnetic resonance technology is continually improving. Functional imaging techniques such as magnetic resonance spectroscopy, perfusion imaging, diffusion imaging, and diffusion tensor imaging are increasingly used in the diagnosis and treatment of brain tumors in children. However, estimate of tumor size remains the primary imaging endpoint in the evaluation of response to treatment, and validation across institutions and vendor platforms of magnetic resonance imaging functional parameters is necessary given the relatively uncommon occurrence of brain tumors in children. Pediatric neuroimaging can be challenging, and the optimal way to image children with tumors of the central nervous system is not uniformly applied across all centers. Application of proper scanning techniques and validation of functional imaging techniques should lead to improved care of children with central nervous system tumors.

Prospective serial proton MR spectroscopic assessment of response to tamoxifen for recurrent malignant glioma

OBJECTIVE

Early prediction of imminent failure during chemotherapy for malignant glioma has the potential to guide proactive alterations in treatment before frank tumor progression. We prospectively followed patients with recurrent malignant glioma receiving tamoxifen chemotherapy using proton magnetic resonance spectroscopic imaging ((1)H-MRSI) to identify intratumoral metabolic changes preceding clinical and radiological failure.

METHODS

We performed serial (1)H-MRSI examinations to assess intratumoral metabolite intensities in 16 patients receiving high-dose oral tamoxifen monotherapy for recurrent malignant glioma (WHO grade III or IV) as part of a phase II clinical trial. Patients were followed until treatment failure, death, or trial termination.

RESULTS

Patients were officially classified as responders (7 patients) or non-responders (9 patients) 8 weeks into treatment. At 8 weeks, responders and non-responders had different intratumoral intensities across all measured metabolites except choline. Beyond 8 weeks, metabolite intensities remained stable in all responders, but changed again with approaching disease progression. Choline, lipid, choline/NAA, and lactate/NAA were significantly elevated (P < 0.02), while creatine (P < 0.04) was significantly reduced, compared to stabilized levels on average 4 weeks prior to failure. Lactate was significantly elevated (P = 0.036) fully 8 weeks prior to failure. In one patient who was still responding to tamoxifen at the conclusion of the trial, metabolite intensities never deviated from 8-week levels for the duration of follow-up.

CONCLUSIONS

Characteristic global intratumoral metabolic changes, detectable on serial (1)H-MRSI studies, occur in response to chemotherapy for malignant glioma and may predict imminent treatment failure before actual clinical and radiological disease progression.

Improving spatial signal homogeneity in MR 2D chemical shift imaging using outer volume saturation bands

Many endeavors of improving chemical shift imaging (CSI) techniques have been made during last two decades. Good examples of two-dimensional CSI and three-dimensional CSI can be found in the literature. However, clinical CSI using available sequences is still not satisfactory. The purpose of this study was to assess the effect of outer volume saturation bands on signal homogeneity in MR 2D chemical shift imaging. The 2D CSI scans were acquired using a point resolved spectroscopy (PRESS) CSI sequence on a phantom filled with brain metabolites. A single PRESS volume of interest was prescribed graphically. The acquisition matrix was 18x18 phase encodings over a 24-cm FOV. Identical acquisitions were obtained with and without outer-volume saturation bands. After initial acquisition was obtained, four more acquisitions were repeated for both studies with and without saturation bands. Identical five groups of voxels were compared for both studies. Standard deviations of metabolite ratios were calculated in each group for both studies. Spectra obtained without outer-volume saturation bands showed signal to noise gradient with higher concentration of signal within voxels at the center of the volume of interest. Outer volume saturation bands reduced this gradient. In general, standard deviations of metabolite ratios with saturation bands were smaller than those without saturation bands. Improved spatial homogeneity of spectra in voxels of CSI with saturation bands was obtained. Outer-volume saturation bands improve spatial signal homogeneity of chemical shift imaging.

A metabolomics perspective of human brain tumours

During the past decade or so, a wealth of information about metabolites in various human brain tumour preparations (cultured cells, tissue specimens, tumours in vivo) has been accumulated by global profiling tools. Such holistic approaches to cellular biochemistry have been termed metabolomics. Inherent and specific metabolic profiles of major brain tumour cell types, as determined by proton nuclear magnetic resonance spectroscopy ((1)H MRS), have also been used to define metabolite phenotypes in tumours in vivo. This minireview examines the recent advances in the field of human brain tumour metabolomics research, including advances in MRS and mass spectrometry technologies, and data analysis.

Optimal classification of long echo time in vivo magnetic resonance spectra in the detection of recurrent brain tumors

We describe the optimal high-level postprocessing of single-voxel (1)H magnetic resonance spectra and assess the benefits and limitations of automated methods as diagnostic aids in the detection of recurrent brain tumor. In a previous clinical study, 90 long-echo-time single-voxel spectra were obtained from 52 patients and classified during follow-up (30/28/32 normal/non-progressive tumor/tumor). Based on these data, a large number of evaluation strategies, including both standard resonance line quantification and algorithms from pattern recognition and machine learning, were compared in a quantitative evaluation. Results from linear and non-linear feature extraction, including ICA, PCA and wavelet transformations, and also the data from resonance line quantification were combined systematically with different classifiers such as LDA, chemometric methods (PLS, PCR), support vector machines and ensemble methods. Classification accuracy was assessed using a leave-one-out cross-validation scheme and the area under the curve (AUC) of the receiver operator characteristic (ROC). A regularized linear regression on spectra with binned channels reached 91% classification accuracy compared with 83% from quantification. Interpreting the loadings of these regressions, we find that lipid and lactate signals are too unreliable to be used in a simple machine rule. Choline and NAA are the main source of relevant information. Overall, we find that fully automated pattern recognition algorithms perform as well as, or slightly better than, a manually controlled and optimized resonance line quantification.

Proton magnetic resonance spectroscopic imaging to differentiate between nonneoplastic lesions and brain tumors in children

PURPOSE

To investigate whether in vivo proton magnetic resonance spectroscopic imaging (MRSI) can differentiate between 1) tumors and nonneoplastic brain lesions, and 2) high- and low-grade tumors in children.

MATERIALS AND METHODS

Thirty-two children (20 males and 12 females, mean age = 10 +/- 5 years) with primary brain lesions were evaluated retrospectively. Nineteen patients had a neuropathologically confirmed brain tumor, and 13 patients had a benign lesion. Multislice proton MRSI was performed at TE = 280 msec. Ratios of N-acetyl aspartate/choline (NAA/Cho), NAA/creatine (Cr), and Cho/Cr were evaluated in the lesion and the contralateral hemisphere. Normalized lesion peak areas (Cho(norm), Cr(norm), and NAA(norm)) expressed relative to the contralateral hemisphere were also calculated. Discriminant function analysis was used for statistical evaluation.

RESULTS

Considering all possible combinations of metabolite ratios, the best discriminant function to differentiate between nonneoplastic lesions and brain tumors was found to include only the ratio of Cho/Cr (Wilks' lambda, P = 0.012; 78.1% of original grouped cases correctly classified). The best discriminant function to differentiate between high- and low-grade tumors included the ratios of NAA/Cr and Cho(norm) (Wilks' lambda, P = 0.001; 89.5% of original grouped cases correctly classified). Cr levels in low-grade tumors were slightly lower than or comparable to control regions and ranged from 53% to 165% of the control values in high-grade tumors.

CONCLUSION

Proton MRSI may have a promising role in differentiating pediatric brain lesions, and an important diagnostic value, particularly for inoperable or inaccessible lesions.

Multisection 1H magnetic resonance spectroscopic imaging assessment of glioma response to chemotherapy

This study evaluated the role of proton magnetic resonance spectroscopic imaging (1H MRSI) in assessing the response of low-grade brain tumors to a chemotherapy-only treatment regimen. Specifically, it was of interest to assess if 1H MRSI could detect early tumor response to therapy prior to magnetic resonance imaging (MRI) changes, and to establish which spectral markers were sensitive to regional changes within and around a heterogeneous tumor mass. A total of 14 patients with lower-grade gliomas were evaluated by multislice 1H MRSI, MRI and clinical examination. Changes associated with chemotherapy were assessed by longitudinal comparisons of regional levels of choline (Cho), N-acetyl-L-aspartate (NAA), and lactate (Lac) relative to total creatine. These changes were, in turn, compared to changes on pre- and post-contrast MR images and to each patient's clinical status. In enhancing tumor regions, there was a significant association between an increase in Lac/Cr during treatment and decreased progression-free survival time. At baseline, a low NAA/Cr in normal-appearing brain tissue adjacent to non-enhancing tumor was associated with decreased progression-free survival time, as was an increase in Cho/Cr during chemotherapy. An increase in Cho/Cr and Lac/Cr in normal-appearing brain regions next to non-enhancing tumor in one patient was noted 2 months before MRI showed progressive disease. These results suggest that 1H MRSI can be a powerful adjunct to MRI in the assessment of tumor response to chemotherapy, and that Cho/Cr and Lac/Cr appear to be the most reliable markers of tumor progression and may predict response prior to MRI changes.

Correlation between choline and MIB-1 index in human gliomas. A quantitative in proton MR spectroscopy study

BACKGROUND

Choline (Cho) containing compounds are usually evaluated using magnetic resonance spectroscopy (MRS) by relative ratios such as Cho/N-acetylaspartate (NAA) and Cho/creatine (Cre) ratios. To clarify the significance of Cho level in gliomas, we evaluated the quantified Cho level using MRS and compared it with the proliferation activity as determined by MIB-1 immunoreactivity in the histological specimen.

METHODS

There were seven benign and seven malignant gliomas. MRS was obtained using a single-voxel proton regional imaging of metabolites (PRIME) sequence with three different TE for T2 compensation. Quantified Cho level was compared with the number of MIB-1 immunopositive positive cells and cell density in surgical specimens.

RESULT

A positive correlation was observed between Cho and MIB-1 in benign gliomas, whereas there was a trend to an inverse correlation in malignant gliomas. This inverse correlation became a positive correlation when the necrotic area of the tumor (on the T1-weighted gadolinium enhanced images) was excluded from the voxel of interest (VOI) for MRS, but this correlation did not reach statistical significance.

CONCLUSIONS

The quantification data clarified the behavior of Cho in malignant gliomas. The quantification method has the advantage of limiting the influence of other metabolites on Cho determination. In particular, the levels of other commonly measured metabolites, including Cre, may also be altered in glioma, making ratios between metabolites misleading. Heterogeneity in the MRS VOI should be considered when evaluating the proliferative activity of malignant glioma by MRS.

Proton magnetic resonance spectroscopy in immunocompetent patients with primary central nervous system lymphoma

BACKGROUND

Magnetic resonance spectroscopy imaging (MRSI) non-invasively evaluates the metabolic profile of normal and abnormal brain tissue. Primary central nervous system lymphoma (PCNSL) is a highly aggressive tumor responsive to high-dose methotrexate based regimens. Patients often have complete responses but relapses are common. We characterized the MR spectra of PCNSL patients, correlated MRSI with MRI and evaluated whether early recurrence could be detected by MRSI.

METHODS

Patients with PCNSL had multi-voxel MRSI before, during, and after treatment. The region of interest was defined using axial FLAIR images. Metabolites assessed were N-acetyl-aspartate (NAA), choline (Cho), creatine (Cr), lipid, and lactate. Ratios of Cho/Cr, NAA/Cho, and NAA/Cr were calculated and correlated with MRI. Overall survival (OS), progression free survival (PFS), and relative risks of each of the ratios were determined.

RESULTS

MRSI was performed on 11 men and seven women; median age of 59. Sixty-seven MRSI studies were performed, 17 baseline and 48 follow-up studies. Median ratios in 16 pretreated patients were Cho/Cr-1.90, NAA/Cho-0.39, and NAA/Cr-1.27. Two patients had lipid at baseline, five had lactate and two had both. MRSI correlated with tumor response or progression on MRI; in three patients MRSI suggested disease progression prior to changes on MRI. Univariate analysis of metabolite ratios, lipid, and lactate revealed that none significantly affected PFS or OS. Kaplan-Meier analysis of the presence or absence of lipid, lactate or both revealed a trend for increased PFS.

CONCLUSION

MRSI and MRI correlate with tumor response or progression and may allow early detection of disease recurrence. The presence or absence of lipid and/or lactate may have prognostic significance. Further research using MRSI needs to be done to validate our findings and determine the role of MRSI in PCNSL.

NMR spectroscopy and pediatric brain tumors

Proton nuclear magnetic resonance spectroscopy ((1)H-NMRS) is a noninvasive in vivo technique that utilizes conventional MR imaging hardware to obtain biochemical information from a discrete volume of tissue after suppression of the water signal. MR spectroscopy coupled with conventional MR imaging allows correlation of structural changes with biochemical processes in tissues by measuring specific metabolites present in brain tissue. NMRS is commonly used in the evaluation of patients with brain tumors. This article reviews the basic principles of spectroscopy and its use in evaluating pediatric patients with brain tumors.

Identification of MRI and 1H MRSI parameters that may predict survival for patients with malignant gliomas

Although MR imaging (MRI) and MR spectroscopic imaging (MRSI) have been applied in the diagnosis and treatment planning for brain tumors, their prognostic significance has not yet been determined. The goal of this study was to identify pre-treatment MRI and MRSI parameters for patients with malignant glioma that may be useful in predicting survival. Two populations of patients with newly-diagnosed malignant glioma were examined with MRI and three-dimensional proton ((1)H) MRSI. Thirty-nine patients (22 grade 3 and 17 glioblastoma multiforme, GBM) were studied prior to surgery, and 33 GBM patients were studied after surgery but prior to treatment with radiation and chemotherapy. Signal intensities of choline (Cho), creatine (Cr), N-acetyl aspartate (NAA), and lactate/lipid (LL) were estimated from the spectra. Recursive partitioning methods were applied to parameters that included age, histological grade, MRI and MRSI variables to generate survival trees. Patients were grouped into high and low risk categories and the corresponding Kaplan-Meier curves were plotted for comparison between groups. The parameters that were selected by recursive partitioning as being predictive of poor outcome were older age, larger contrast enhancement, higher Cho-to-Cr, higher Cho-to-NAA, higher LL and lower Cr-to-NAA abnormalities. The survival functions were significantly different between the sub-groups of patients obtained from the survival tree for both pre-surgery and post-surgery data. The results of this study suggest that pre-treatment MRI and three-dimensional (1)H-MRSI provide information that predicts outcome for patients with malignant gliomas and have drawn attention to variables that should be examined prospectively in future studies using these techniques.

Pediatric brain tumors

Brain tumors in children vary with regard to histology, location, gender distribution, and age of onset. The past several decades have witnessed substantial improvements in the diagnosis and treatment. As a result, the number of long-term survivors also has increased continuously. Recent advances in neuroimaging facilitate tumor localization and mapping of brain function by noninvasive techniques and are becoming important in preoperative assessment for brain tumors. Surgery remains the mainstay of treatment of many tumor types. A role for chemotherapy is emerging, particularly for nonresectable tumors and in infants, for whom the adverse effects of radiation therapy are severe. Despite the improved treatments and prognostic data, however, many long-term survivors experience significant neurocognitive and developmental deficits.

Novel techniques in the delivery of radiation in pediatric oncology

The field of radiation oncology continues to develop at a rapid pace, due to concurrent progress in high speed computing, improved sensitivity in diagnostic imaging (both anatomic and physiologic), and the introduction of rational new therapeutics built on solid radiobiologic principles. These innovations will become critically important in the field of pediatric oncology, as they will allow for an increased therapeutic ratio in the developing child. Maximizing the benefit of lower dose radiation through the use of radiation modifiers (hypoxic cell sensitizers, signal transduction pathway inhibitors, concurrent chemotherapy), increasing the tolerance of normal tissues (radioprotectors) and tailoring the target area more closely to the desired critical tissues (IMRT, functional simulation with PET and MRS, radiolabeled monoclonal antibodies) will lessen the short and long term toxicity of radiation and increase its effectiveness.

The potential of proton magnetic resonance spectroscopy ((1)H-MRS) in the diagnosis and management of patients with brain tumors

Proton ((1)H) magnetic resonance spectroscopy (MRS) is a noninvasive method that can monitor the metabolic changes in most brain diseases. This technique is now available on current 1.5 Tesla magnetic resonance units and does not require sophisticated software or time-consuming post-processing techniques. Previous studies using single-voxel techniques showed the usefulness of MRS for the diagnosis of brain tumor despite some technical issues, including spatial resolution and volume coverage. Recent advances have been made through the use of multivoxel techniques and metabolite maps, which allow assessment of both the entire volume of the lesion and the surrounding normal-appearing brain tissue. Recent studies suggest the potential of this technique to guide biopsies, to define radiotherapy targets, and to monitor patients after treatment. Some persistent drawbacks, including measurement time and spectral resolution, will probably be overcome in the near future.

Clinical applications of proton MR spectroscopy in oncology

Proton magnetic resonance spectroscopy (H1-MRS) has been increasingly receiving more attention from radiologists, neurosurgeons, radiation and medical oncologists in the "in situ" clinical evaluation of human tumors. The utilization of H1-MRS, especially in human brain tumors, coupled to both routine magnetic resonance imaging (MRI) and functional MRI techniques provides greater information concerning tumor grading and extension and characterization of the normal surrounding tissue than what is possible with any other imaging technique alone. In this paper, we will review the current status of proton MR spectroscopy with emphasis on its clinical utility to diagnose tumors, its utility in planning surgical and radiation therapy interventions, and in its use in monitoring tumor treatment.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.