Early metabolic changes in metastatic brain tumors after Gamma Knife radiosurgery:1H-MRS study

Brain Metastases of Non-Small Cell Lung Cancer: Magnetic Resonance Spectroscopy for Clinical Outcome Assessment in Patients with Stereotactic Radiotherapy

Background

Brain metastases (BM) are severe incidents among patients with non-small cell lung cancer (NSCLC) and have been associated with significant morbidity and decreased survival; thus, new methods are required to improve clinical management. Magnetic resonance spectroscopy (MRS) allows noninvasive measurements of biochemical information from tumor tissue, providing clinically useful imaging biomarkers. The primary aim of this study was to explore the application of MRS in the assessment of tumor prognosis after stereotactic radiotherapy in NSCLC patients with BM.

Patients and Methods

MRS was performed on NSCLC patients attending Qingdao Center Hospital with suspected BM, and 68 patients were included in the survival analysis. The qualitative and quantitative parameters of MRS metabolites, such as choline (Cho), creatine (Cr), and N-acetyl-aspartate (NAA), were recorded. To select a cutoff for MRS metabolite parameters in the tumor and to distinguish patients who had recurrence, we performed an ROC curve analysis. Univariate and multivariate Cox regression analyses were used to assess the association between MRS metabolite parameters and clinical cancer prognosis.

Results

The average age was 56 years. A total of 68 NSCLC patients underwent metabolic evaluation with single voxel proton MRS and were selected for retrospective analysis. According to the area under the curve (AUC) to predict recurrence, the MRS metabolite parameters were determined as Cho (AUC=0.550), Cr (AUC=0.415), NAA (AUC=0.524), NAA/Cr (AUC=0.600), Cho/Cr (AUC=0.723), and Cho/NAA (AUC=0.543). Cho and Cr predicted poor survival while Cho/Cr and NAA/Cr predicted improved survival (P<0.05). In the multivariate model with adjustment to establish the potential role of MRS metabolite parameters, Cho/Cr showed a significant association with OS (P=0.009) and PFS (P=0.006) after stereotactic radiotherapy.

Conclusion

The positive results of this study indicate the predictive value of metabolic characteristics of BM detected with MRS for the outcome after stereotactic radiotherapy.

Potential of high field functional MRI in the neuroradiological diagnosis of brain tumours

Functional 3 tesla magnetic resonance imaging (MRI) techniques such as diffusion and perfusion imaging and MR spectroscopy (MRS) allow a more accurate diagnosis of central nervous system tumours. This retrospective study analysed the MRI scans of 121 consecutive patients with a diagnosis of glial brain tumours who underwent surgery and/or biopsy and whose histological reports were available. Our aim was to establish if and how functional MRI techniques had enhanced the diagnostic accuracy with respect to morphological examination. To quantify the diagnostic contribution of these techniques and their predictive value, a questionnaire was compiled by an observer blinded to the neuroradiological diagnosis and to the histological results after surgery/biopsy. Patients were divided into two groups based on the time of 3T MRI examination performed: before or after surgery/biopsy. In the group of non-operated patients low grade gliomas could be distinguished from high grade malignant tumours, whereas in the group of operated patients signs of tumour persistence or recurrence could be distinguished from the effects of previous treatments. Functional MRI techniques improved the accuracy of diagnosis with respect to morphological examination alone in both groups of patients: areas of increased cellularity, neoangiogenesis or metabolic changes were identified confirming diagnosis, whereas methodological errors were disclosed in cases of incorrect diagnosis.

Effects of gamma ray irradiation on energy metabolism in the rat brain: a 31P nuclear magnetic resonance spectroscopy study

OBJECT

Gamma Knife surgery (GKS) is performed to treat patients with functional neurological diseases, but the neurophysiological mechanisms of GKS's biological effects with subnecrotic doses remain largely undefined. The purpose of the present study was to investigate the effects of gamma irradiation on energy metabolism in the rat brain by using 31P nuclear magnetic resonance spectroscopy (31P-NMRS).

METHODS

The whole brains of Wistar rats were irradiated with a subnecrotic (60-Gy) dose of radiation. One week after the irradiation, brain slices (400 microm thick) were incubated in standard artificial cerebrospinal fluid to undergo 31P-NMRS investigation. Changes in high-energy phosphate, phosphocreatine (PCr), and gamma-ATP, as well as inorganic phosphate levels before, during, and after ischemic stress for 64 minutes were measured. Histological findings were also evaluated using light and electron microscopy. The decrease in the PCr level was significantly slower during ischemia and recovery after reperfusion was significantly faster and greater in the gamma-irradiated rats than in the control animals. The gamma-ATP level after ischemia was also higher in the gamma-irradiated rats than in the controls. Neither neuronal damage nor astrocytosis was observed in the irradiated cerebral cortices.

CONCLUSIONS

Gamma irradiation with a subnecrotic dose may have neuroprotective effects that maintain a more stable cellular phosphorylation potential after ischemic stress. Such effects of GKS on energy metabolism coupled with neurotransmission (glutamate-glutamine cycling between neurons and astrocytes) may play a role in the treatment of neurological disease.

Dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain tissue after stereotactic radiosurgery: a serial proton magnetic resonance spectroscopy study

The present study evaluated the dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain after stereotactic radiosurgery (SRS). Forty neoplasms were evaluated with single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) both before and after treatment. From one to six examinations (median, 3) were done in each individual case during follow-up. At the time of each investigation additional (1)H-MRS was obtained from the normal-appearing brain distant from the radiosurgical target. Investigated metabolites included N-acetylaspartate (NAA), choline-containing compounds (Cho), creatine (Cr), and mobile lipids (Lip). Within the first month after SRS responded tumors showed a statistically significant increase in NAA/Cho ratio, and decrease of Cho content and Lip-to-normal brain Cr (nCr) ratio. By contrast, statistically significant metabolic alterations were not detected in stabilized tumors. Statistically significant volumetric and metabolic changes were not marked between three and 12 months after treatment in non-progressing lesions. Alternatively, decrease of NAA/Cho ratio, NAA content and Cr content, and increase in Lip/nCr ratio and Cho content were evident in progressive neoplasms, and subtle metabolic alterations could be revealed even before the increase in the lesion volume. Metabolic characteristics of normal-appearing brain distant from the radiosurgical target did not show statistically significant changes within the first year after treatment. In conclusion, additional use of serial (1)H-MRS during follow-up after SRS for intracranial metastases permits detailed evaluation of the metabolic tumor response and may be potentially helpful for early prediction of recurrence.

Quantitative in vivo proton MR spectroscopic evaluation of the irradiated rat brain

PURPOSE

To investigate if in vivo localized proton magnetic resonance spectroscopy (MRS) can detect putative metabolic changes in the irradiated rat brain and quantitatively measure brain metabolite changes in this model.

MATERIALS AND METHODS

A total of 20 adult male Fischer 344 rats were exposed to a fractionated regimen of whole brain irradiation (WBI) (total 45 Gy, given as five Gy fractions, twice per week for 4.5 weeks); 10 control rats received sham irradiation. A total of 52 weeks after WBI, all animals were subjected to high-resolution MRI and in vivo proton MRS to determine structural and brain metabolite changes. Brain metabolites were measured by using single-voxel MRS. Quantitative analysis of detectable metabolites was performed by using the spectral analysis method, LCModel.

RESULTS

Significant differences in brain metabolite concentrations were detected in rat brains irradiated with a clinically relevant fractionated radiotherapy regimen in 52 weeks, in comparison to age-matched sham-irradiated rats.

CONCLUSION

These findings indicate that quantitative in vivo MRS may serve as a sensitive imaging tool to noninvasively detect neurochemical changes in the irradiated brain.

Applications of magnetic resonance spectroscopy in radiotherapy treatment planning

Following advances in conformal radiotherapy, a key problem now facing radiation oncologists is target definition. While MRI and CT provide images of excellent spatial resolution, they do not always provide sufficient contrast to identify tumour extent or to identify regions of high cellular activity that might be targeted with boost doses. Magnetic resonance spectroscopy (MRS) is an alternative approach that holds great promise for aiding target definition for radiotherapy treatment planning, and for evaluation of response and recurrence. MRS is able to detect signals from low molecular weight metabolites such as choline and creatine that are present at concentrations of a few mM in tissue. Spectra may be acquired from single voxels, or from a 2D or 3D array of voxels using spectroscopic imaging. The current state of the art achieves a spatial resolution of 6-10 mm in a scan time of about 10-15 min. Co-registered MR images are acquired in the same examination. The method is currently under evaluation, in particular in brain (where MRS has been shown to differentiate between many tumour types and grades) and in prostate (where cancer may be distinguished from normal tissue and benign prostatic hypertrophy). The contrast achieved with MRS, based on tissue biochemistry, therefore provides a promising alternative for identifying tumour extent and regions of high metabolic activity. It is anticipated that MRS will become an essential tool for treatment planning where other modalities lack the necessary contrast.

Long-term normal-appearing brain tissue monitoring after irradiation using proton magnetic resonance spectroscopy in vivo: statistical analysis of a large group of patients

PURPOSE

The aim of this study was to detect the non-neoplastic white-matter changes vs. time after irradiation using 1H nuclear magnetic resonance (NMR) spectroscopy in vivo.

METHODS AND MATERIALS

A total of 394 1H MR spectra were acquired from 100 patients (age 19-74 years; mean and median age, 43 years) before and during 2 years after radiation therapy (the mean absorbed doses calculated for the averaged spectroscopy voxels are similar and close to 20 Gy).

RESULTS

Oscillations were observed in choline-containing compounds (Cho)/creatine and phosphocreatine (Cr), Cho/N-acetylaspartate (NAA), and center of gravity (CG) of the lipid band in the range of 0.7-1.5 ppm changes over time reveal oscillations. The parameters have the same 8-month cycle period; however the CG changes precede the other by 2 months.

CONCLUSIONS

The results indicate the oscillative nature of the brain response to irradiation, which may be caused by the blood-brain barrier disruption and repair processes. These oscillations may influence the NMR results, depending on the cycle phase in which the NMR measurements are performed in. The earliest manifestation of radiation injury detected by magnetic resonance spectroscopy is the CG shift.

Diffusion Changes in a Tumor and Peritumoral Tissue After Stereotactic Irradiation for Brain Tumors

OBJECTIVE

Changes in apparent diffusion coefficient (ADC) in a tumor and peritumoral tissue after stereotactic irradiation (STI) were evaluated, and then the therapeutic efficacy of ADC measurement was assessed.

METHODS

In 20 tumors, diffusion-weighted imaging within 1 week before and 2-4 weeks after STI was performed. The normalized ADC (nADC) was measured. The nADCs in the tumor and peritumoral region before STI were compared with those after STI and the change in tumor nADC compared with the change in tumor size.

RESULTS

The nADC of the tumors was significantly higher 2-4 weeks after STI compared with that before STI. The nADC of the peritumoral regions 2-4 weeks after STI did not differ significantly from that before STI. A significant difference in the nADC at 2-4 weeks after STI was observed between the responder and nonresponder groups.

CONCLUSIONS

Changes in nADC as measured by diffusion-weighted imaging can predict response to STI.

Optimization of semi-quantification in metabolic PET studies with 18F-fluorodeoxyglucose and 11C-methionine in the determination of malignancy of gliomas

The treatment of the glioma patient depends on the nature of the lesion and on the aggressiveness of the tumor. The management of gliomas continues to be a challenging task, because morphological neuroimaging techniques do not always differentiate them from nontumoral lesions or high grade tumors from low grade lesions. Positron Emission Tomography (PET) offers the possibility of the in vivo quantitative characterization of brain tumors. Despite decades of useful application of PET in the clinical monitoring of gliomas, no consensus has been reached on the most effective image analysis approach for providing the best diagnostic performance under heavy-duty clinical diagnostic circumstances. The main objective of the present study was to find and validate optimal semi-quantitative search strategies for metabolic PET studies on gliomas, with special regard to the optimization of those metabolic tracer uptake ratios most sensitive in predicting histologic grade and prognosis. 11C-Methionine (11C-Met, n = 50) and/or 18F-Fluorodeoxyglucose (18F-FDG, n = 33) PET measurements were performed in 59 patients with primary and recurrent brain gliomas (22 high grade and 37 low grade tumors) in order to correlate the biological behavior and 11C-Met/18F-FDG uptake of tumors. Data were analyzed by region-of-interests (ROI) methods using standard uptake value calculation. Different ROI defining strategies were then compared with each other for two of the most commonly used metabolic radiotracers, 18F-FDG and 11C-Met, in order to determine their usefulness in grading gliomas. The results were compared to histological data in all patients. Both ANOVA and receiver operating characteristic (ROC) analysis indicated that the performance of 18F-FDG was superior to that of 11C-Met for most of the ratios. 18F-FDG is therefore suggested as the tracer of choice for noninvasive semi-quantitative indicator of histologic grade of gliomas. 11C-Methionine has been suggested as a complimentary tracer, useful in delineating the extent of the tumor. The best diagnostic performance was obtained by calculating the ratio of the peak 18F-FDG uptake of the tumor to that of white matter (p < 0.001; ANOVA). This metabolic tracer uptake ratio is therefore suggested as an easily obtained semi-quantitative PET indicator of malignancy and histological grade in gliomas.

Indications for resection and radiosurgery for brain metastases

PURPOSE OF REVIEW

This review is focused on indications for resection, stereotactic radiosurgery, and fractionated radiotherapy for patients with single or multiple brain metastases. Our purpose is to summarize the indications and effect of these management approaches.

RECENT FINDINGS

Brain metastases are a frequent challenge in patients with extracranial solid cancers. More than 40% of patients with cancer will develop metastases to the brain. While some patients present with large lesions and symptoms related to mass effect, many are diagnosed when asymptomatic tumors are found on screening studies. The main options for patients with brain metastases are whole brain radiation therapy, surgical resection, and stereotactic radiosurgery. Much information regarding outcomes, survival, management morbidity, and quality of life is available. Randomized, class III clinical trials demonstrate that multimodal therapy is important for both life quality and extended survival. A better understanding of the current therapeutic options should result in improvements in patient care.

SUMMARY

This is a review of the literature from May 2004 to June 2005 with special attention on publications related to effect on quality of life with different procedures and therapies.