Evaluation of the response of metastatic brain tumors to stereotactic radiosurgery by proton magnetic resonance spectroscopy, 201TlCl single-photon emission computerized tomography, and gadolinium-enhanced magnetic resonance imaging

Recognition and Management of the Long-term Effects of Cranial Radiation

OPINION STATEMENT

Cranial radiation is ubiquitous in the treatment of primary malignant and benign brain tumors as well as brain metastases. Improvement in radiotherapy targeting and delivery has led to prolongation of survival outcomes. As long-term survivorship improves, we also focus on prevention of permanent side effects of radiation and mitigating the impact when they do occur. Such chronic treatment-related morbidity is a major concern with significant negative impact on patient's and caregiver's respective quality of life. The actual mechanisms responsible for radiation-induced brain injury remain incompletely understood. Multiple interventions have been introduced to potentially prevent, minimize, or reverse the cognitive deterioration. Hippocampal-sparing intensity modulated radiotherapy and memantine represent effective interventions to avoid damage to regions of adult neurogenesis. Radiation necrosis frequently develops in the high radiation dose region encompassing the tumor and surrounding normal tissue. The radiographic findings in addition to the clinical course of the patients' symptoms are taken into consideration to differentiate between tissue necrosis and tumor recurrence. Radiation-induced neuroendocrine dysfunction becomes more pronounced when the hypothalamo-pituitary (HP) axis is included in the radiation treatment field. Baseline and post-treatment evaluation of hormonal profile is warranted. Radiation-induced injury of the cataract and optic system can develop when these structures receive an amount of radiation that exceeds their tolerance. Special attention should always be paid to avoid irradiation of these sensitive structures, if possible, or minimize their dose to the lowest limit.

Stereotactic radiotherapy for brain oligometastases

Brain metastases, the most common metastases in adults, will develop in up to 40% of cancer patients, accounting for more than one-half of all intracranial tumors. They are most associated with breast and lung cancer, melanoma and, less frequently, colorectal and kidney carcinoma.

Magnetic resonance imaging (MRI) is the gold standard for diagnosis. For the treatment plan, computed tomography (CT ) images are co-registered and fused with a gadolinium-enhanced T1-weighted MRI where tumor volume and organs at risk are contoured. Alternatively, plain and contrast-enhanced CT scans are co-registered. Single-fraction stereotactic radiotherapy (SRT ) is used to treat patients with good performance status and up to 4 lesions with a diameter of 30 mm or less that are distant from crucial brain function areas. Fractionated SRT (2–5 fractions) is used for larger lesions, in eloquent areas or in proximity to crucial or surgically inaccessible areas and to reduce treatment-related neurotoxicity. The single-fraction SRT dose, which depends on tumor diameter, impacts local control. Fractionated SRT may encompass different schedules. No randomized trial data compared the safety and efficacy of single and multiple fractions. Both single-fraction and fractionated SRT provide satisfactory local control rates, tolerance, a low risk of transient acute adverse events and of radiation necrosis the incidence of which correlated with the irradiated brain volume.

Consensus recommendations for a standardized brain tumor imaging protocol for clinical trials in brain metastases

A recent meeting was held on March 22, 2019, among the FDA, clinical scientists, pharmaceutical and biotech companies, clinical trials cooperative groups, and patient advocacy groups to discuss challenges and potential solutions for increasing development of therapeutics for central nervous system metastases. A key issue identified at this meeting was the need for consistent tumor measurement for reliable tumor response assessment, including the first step of standardized image acquisition with an MRI protocol that could be implemented in multicenter studies aimed at testing new therapeutics. This document builds upon previous consensus recommendations for a standardized brain tumor imaging protocol (BTIP) in high-grade gliomas and defines a protocol for brain metastases (BTIP-BM) that addresses unique challenges associated with assessment of CNS metastases. The "minimum standard" recommended pulse sequences include: (i) parameter matched pre- and post-contrast inversion recovery (IR)-prepared, isotropic 3D T1-weighted gradient echo (IR-GRE); (ii) axial 2D T2-weighted turbo spin echo acquired after injection of gadolinium-based contrast agent and before post-contrast 3D T1-weighted images; (iii) axial 2D or 3D T2-weighted fluid attenuated inversion recovery; (iv) axial 2D, 3-directional diffusion-weighted images; and (v) post-contrast 2D T1-weighted spin echo images for increased lesion conspicuity. Recommended sequence parameters are provided for both 1.5T and 3T MR systems. An "ideal" protocol is also provided, which replaces IR-GRE with 3D TSE T1-weighted imaging pre- and post-gadolinium, and is best performed at 3T, for which dynamic susceptibility contrast perfusion is included. Recommended perfusion parameters are given.

Diagnostic value of alternative techniques to gadolinium-based contrast agents in MR neuroimaging-a comprehensive overview

Gadolinium-based contrast agents (GBCAs) increase lesion detection and improve disease characterization for many cerebral pathologies investigated with MRI. These agents, introduced in the late 1980s, are in wide use today. However, some non-ionic linear GBCAs have been associated with the development of nephrogenic systemic fibrosis in patients with kidney failure. Gadolinium deposition has also been found in deep brain structures, although it is of unclear clinical relevance. Hence, new guidelines from the International Society for Magnetic Resonance in Medicine advocate cautious use of GBCA in clinical and research practice. Some linear GBCAs were restricted from use by the European Medicines Agency (EMA) in 2017.

This review focuses on non-contrast-enhanced MRI techniques that can serve as alternatives for the use of GBCAs. Clinical studies on the diagnostic performance of non-contrast-enhanced as well as contrast-enhanced MRI methods, both well established and newly proposed, were included. Advantages and disadvantages together with the diagnostic performance of each method are detailed. Non-contrast-enhanced MRIs discussed in this review are arterial spin labeling (ASL), time of flight (TOF), phase contrast (PC), diffusion-weighted imaging (DWI), magnetic resonance spectroscopy (MRS), susceptibility weighted imaging (SWI), and amide proton transfer (APT) imaging.

Ten common diseases were identified for which studies reported comparisons of non-contrast-enhanced and contrast-enhanced MRI. These specific diseases include primary brain tumors, metastases, abscess, multiple sclerosis, and vascular conditions such as aneurysm, arteriovenous malformation, arteriovenous fistula, intracranial carotid artery occlusive disease, hemorrhagic, and ischemic stroke.

In general, non-contrast-enhanced techniques showed comparable diagnostic performance to contrast-enhanced MRI for specific diagnostic questions. However, some diagnoses still require contrast-enhanced imaging for a complete examination.

Aberrant interactions of peripheral measures and neurometabolites with lipids in complex regional pain syndrome using magnetic resonance spectroscopy: A pilot study

Background The aim of this study was to assess peripheral measures and central metabolites associated with lipids using magnetic resonance spectroscopy. Results Twelve patients with complex regional pain syndrome (CRPS) and 11 healthy controls participated. Using magnetic resonance spectroscopy, we measured the levels of lipid 13a (Lip13a) and lipid 09 (Lip09) relative to total creatine (tCr) levels in the right and left thalamus. We found negative correlations of Lip13a/tCr in the right thalamus with red blood cells or neutrophils, but a positive correlation between Lip13a/tCr and lymphocytes in the controls. We found negative correlations between Lip09/tCr and peripheral pH or platelets in the controls. There were positive correlations between Lip09a/tCr and myo-inositol/tCr, between Lip13a/tCr and N-acetylaspartate (NAA)/tCr, and between Lip09/tCr and NAA/tCr in healthy controls. On the other hand, there were positive correlations between Lip13a/tCr and Lip09/tCr and urine pH in CRPS patients. There were significant correlations between Lip13a/tCr or Lip09/tCr and different peripheral measures depending on the side of the thalamus (right or left) in CRPS patients. Conclusion This is the first report indicating that abnormal interactions of Lip13a and Lip09 in the thalamus with peripheral measures and central metabolites may mediate the complex pathophysiological mechanisms underlying CRPS.

Follow-up results of brain metastasis patients undergoing repeat Gamma Knife radiosurgery

OBJECTIVE

Stereotactic radiosurgery (SRS) without upfront whole-brain radiotherapy (WBRT) has influenced recent treatment recommendations for brain metastasis patients. However, in brain metastasis patients who undergo SRS alone, new brain metastases inevitably appear with relatively high incidences during post-SRS follow-up. However, little is known about the second SRS results. The treatment results of second SRS were retrospectively reviewed, mainly for newly developed or, uncommonly, for recurrent brain metastases in order to reappraise the efficacy of this treatment strategy with a special focus on the maintenance of neurological status and safety.

METHODS

This was an institutional review board–approved, retrospective cohort study that used a prospectively accumulated database, including 3102 consecutive patients with brain metastases who underwent SRS between July 1998 and June 2015. Among these 3102 patients, 859 (376 female patients; median age 64 years; range 21–88 years) who underwent a second SRS without WBRT were studied with a focus on overall survival, neurological death, neurological deterioration, local recurrence, salvage SRS, and SRS-induced complications after the second SRS. Before the second SRS, the authors also investigated the clinical factors and radiosurgical parameters likely to influence these clinical outcomes. For the statistical analysis, the standard Kaplan-Meier method was used to determine post–second SRS survival and neurological death. A competing risk analysis was applied to estimate post–second SRS cumulative incidences of local recurrence, neurological deterioration, salvage SRS, and SRS-induced complications.

RESULTS

The post–second SRS median survival time was 7.4 months (95% CI 7.0–8.2 months). The actuarial survival rates were 58.2% and 34.7% at 6 and 12 months after the second SRS, respectively. Among 789 deceased patients, the causes of death could not be determined in 24 patients, but were confirmed in the remaining 765 patients to be nonbrain diseases in 654 (85.5%) patients and brain diseases in 111 (14.5%) patients. The actuarial neurological death–free survival rates were 94.4% and 86.6% at 6 and 12 months following the second SRS. Multivariable analysis revealed female sex, Karnofsky Performance Scale score of 80% or greater, better modified recursive partitioning analysis class, smaller tumor numbers, and higher peripheral dose to be significant predictive factors for longer survival. The cumulative incidences of local recurrence were 11.2% and 14.9% at 12 and 24 months after the second SRS. The crude incidence of neurological deterioration was 7.1%, and the respective cumulative incidences were 4.5%, 5.8%, 6.7%, 7.2%, and 7.5% at 12, 24, 36, 48, and 60 months after the second SRS. SRS-induced complications occurred in 25 patients (2.9%) after a median post–second SRS period of 16.8 months (range 0.6–95.0 months; interquartile range 5.6–29.3 months). The cumulative incidences of complications were 1.4%, 2.0%, 2.4%, 3.0%, and 3.0% at 12, 24, 36, 48, and 60 months after the second SRS, respectively.

CONCLUSIONS

Carefully selected patients with recurrent tumors—either new or locally recurrent—are favorable candidates for a second SRS, particularly in terms of neurological status maintenance and the safety of this treatment strategy.

[Imaging methods used in the differential diagnosis between brain tumour relapse and radiation necrosis after stereotactic radiosurgery of brain metastases: Literature review]

After stereotactic radiosurgery for a cerebral metastasis, one of the dreaded toxicities is radionecrosis. In the follow-up of these patients, it is impossible to distinguish radiation necrosis from tumour relapse either clinically or with MRI. In current practice, many imaging methods are designed such as special sequences of MRI (dynamic susceptibility contrast perfusion and susceptibility-weighted imaging, diffusion), proton magnetic resonance spectroscopy, positron emission tomography, or more seldom 201-thallium single-photon emission computerized tomography. This article is a required literature analysis in order to establish a decision tree with the analysis of retrospective and prospective data.

Cerebral Lipid Accumulation Detected by MRS in a Child with Carnitine Palmitoyltransferase 2 Deficiency: A Case Report and Review of the Literature on Genetic Etiologies of Lipid Peaks on MRS

The majority of lipids in the brain are located in the bilayer membranes. These lipids are not visible by magnetic resonance spectroscopy since they have restricted mobility. Only mobile lipids, such as cholesterol esters or triglycerides in neutral lipid droplets, have enough rotational freedom to generate a signal on spectroscopy. These signals are detected as peaks at 1.3 ppm, originating from the methylene groups in the fatty acid chain, and 0.9 ppm, originating from the distal methyl group. We review the literature on the different genetic conditions that have been found to show lipid peaks on brain spectroscopy and report the first patient with carnitine palmitoyltransferase 2 deficiency shown to have such lipid peaks, thus indicating brain fat accumulation.

Radionecrosis of malignant glioma and cerebral metastasis: a diagnostic challenge in MRI

Detecting a new area of contrast-enhancement at MRI after irradiation of malignant brain tumor arises the problem of differential diagnosis between tumor recurrence and radiation necrosis induced by the treatment. The challenge for imaging is to distinguish the two diagnoses given: the prognostic and therapeutic issues. Various criteria have been proposed in the literature based on morphological, functional or metabolic MRI. The purpose of this study was to perform an analysis of these tools to identify MRI best criteria to differentiate radiation necrosis lesions from malignant gliomas and brain metastases recurrence. For gliomas, the morphology of the contrast-enhancement cannot guide the diagnosis and the use of perfusion techniques and spectroscopy (multivoxels if possible) are necessary. In the follow-up of metastasis, a transient increase and moderate lesion volume is possible with a good prognosis. Morphological characteristics (volume ratio T2/T1Gd) and perfusion analysis provide valuable tools for approaching the diagnosis of radionecrosis.

Differentiation of local tumor recurrence from radiation-induced changes after stereotactic radiosurgery for treatment of brain metastasis: case report and review of the literature

BACKGROUND

Structural follow-up magnetic resonance imaging (MRI) after stereotactic radiosurgery (SRS) for brain metastases frequently displays local changes in the area of applied irradiation, which are often difficult to interpret (e.g., local tumor recurrence, radiation-induced changes). The use of stereotactic biopsy for histological assessment of these changes has a high diagnostic accuracy and can be considered as method of choice. In order to solve this relevant clinical problem non-invasively, advanced MRI techniques and amino acid positron-emission-tomography (PET) are increasingly used.

CASE PRESENTATION

We report the long-term follow-up of a patient who had been treated with linear accelerator based SRS for cerebral metastases of a lung cancer. Fifty-eight months after SRS, the differentiation of local recurrent brain metastasis from radiation-induced changes using structural MRI was difficult. For further differentiation, perfusion-weighted MRI (PWI), proton magnetic resonance spectroscopy (MRS), and (11)C-methyl-L-methionine (MET) PET was performed. Due to artifacts and technical limitations, PWI MRI and MRS findings were not conclusive. In contrast, MET PET findings were suggestive for radiation-induced changes. Finally, a stereotactic biopsy for histological assessment of these changes demonstrated clearly a radiation-induced necrosis and the absence of vital tumor.

CONCLUSION

The use of stereotactic biopsy for histological assessment of indistinguishable lesions on structural MRI after SRS for treatment of brain metastasis represents a highly reliable method to differentiate local tumor recurrence from radiation-induced changes. In this field, results of studies with both advanced MRI techniques and amino acid PET suggest encouraging results. However, artifacts and technical limitations (e.g., lesion size) are still a problem and comparative studies are needed to investigate the relationship, diagnostic performance, and complementary character of advanced MRI techniques and amino acid PET.

Differentiation of tumor progression and radiation-induced effects after intracranial radiosurgery

A number of intracranial tumors demonstrate some degree of enlargement after stereotactic radiosurgery (SRS). It necessitates differentiation of their regrowth and various treatment-induced effects. Introduction of low-dose standards for SRS of benign neoplasms significantly decreased the risk of the radiation-induced necrosis after -management of schwannomas and meningiomas. Although in such cases a transient increase of the mass volume within several months after irradiation is rather common, it usually followed by spontaneous shrinkage. Nevertheless, distinguishing tumor recurrence from radiation injury is often required in cases of malignant parenchymal brain neoplasms, such as metastases and gliomas. The diagnosis is frequently complicated by histopathological heterogeneity of the lesion with coexistent viable tumor and treatment-related changes. Several neuroimaging modalities, namely structural magnetic resonance imaging (MRI), diffusion-weighted imaging, diffusion tensor imaging, perfusion computed tomography (CT) and MRI, single-voxel and multivoxel proton magnetic resonance spectroscopy as well as single photon emission CT and positron emission tomography with various radioisotope tracers, may provide valuable diagnostic information. Each of these methods has advantages and limitations that may influence its usefulness and accuracy. Therefore, use of a multimodal radiological approach seems reasonable. Addition of functional and metabolic neuroimaging to regular structural MRI investigations during follow-up after SRS of parenchymal brain neoplasms may permit detailed evaluation of the treatment effects and early prediction of the response. If tissue sampling of irradiated intracranial lesions is required, it is preferably performed with the use of metabolic guidance. In conclusion, differentiation of tumor progression and radiation-induced effects after intracranial SRS is challenging. It should be based on a complex evaluation of the multiple clinical, radiosurgical, and radiological factors.

A comprehensive review of MR imaging changes following radiosurgery to 500 brain metastases

BACKGROUND AND PURPOSE

Stereotactic radiosurgery is known to control 85%-95% of intracranial metastatic lesions during a median survival of 6-8 months. However, with the advent of newer systemic cancer therapies, survival is improving; this change mandates a longitudinal quantitative analysis of the radiographic response of brain metastases to radiosurgery.

MATERIALS AND METHODS

MR imaging of 516 metastases in 120 patients treated with GK-SRS from June 2006 to December 2009 was retrospectively reviewed. Lesion volume at initial treatment and each follow-up was calculated by using the following formula: length × width × height / 2. Volume changes were correlated with patient demographics, histopathology, and radiation treatment variables.

RESULTS

Thirty-two percent of lesions increased in volume following radiosurgery. Clinically, this translated into 54% of patients having ≥1 of their lesions increase in size. This increase begins at 6 weeks and can last beyond 15 months' post-SRS. Male sex (P = .002), mean voxel dose <37 Gy (P = .009), and initial treatment volume >500 mm(3) (P < .001) are associated with posttreatment increases in tumor size. Median survival following radiosurgery was 9.5 months for patients with all lesions exhibiting stable/decreased volumes, >18.4 months for patients with all lesions exhibiting increased volumes, and 16.4 months for patients with mixed lesional responses.

CONCLUSIONS

Most metastatic lesions are stable or smaller in size during the first 36 months post-SRS. However, a transient increase in volume is seen in approximately one-third of lesions. Sex, treatment dose, initial lesion size, and histopathology all correlate with variations in lesion volume post-SRS. The longer the patient survives, the more likely an increase in lesion size will be seen on follow-up imaging.

MR-visible lipids and the tumor microenvironment

MR-visible lipids or mobile lipids are defined as lipids that are observable using proton MRS in cells and tissues. These MR-visible lipids are composed of triglycerides and cholesterol esters that accumulate in neutral lipid droplets, where their MR visibility is conferred as a result of the increased molecular motion available in this unique physical environment. This review discusses the factors that lead to the biogenesis of MR-visible lipids in cancer cells and in other cell types, such as immune cells and fibroblasts. We focus on the accumulations of mobile lipids that are inducible in cultured cells by a number of stresses, including culture conditions, and in response to activating stimuli or apoptotic cell death induced by anticancer drugs. This is compared with animal tumor models, where increases in mobile lipids are observed in response to chemo- and radiotherapy, and to human tumors, where mobile lipids are observed predominantly in high-grade brain tumors and in regions of necrosis. Conducive conditions for mobile lipid formation in the tumor microenvironment are discussed, including low pH, oxygen availability and the presence of inflammatory cells. It is concluded that MR-visible lipids appear in cancer cells and human tumors as a stress response. Mobile lipids stored as neutral lipid droplets may play a role in the detoxification of the cell or act as an alternative energy source, especially in cancer cells, which often grow in ischemic/hypoxic environments. The role of MR-visible lipids in cancer diagnosis and the assessment of the treatment response in both animal models of cancer and human brain tumors is also discussed. Although technical limitations exist in the accurate detection of intratumoral mobile lipids, early increases in mobile lipids after therapeutic interventions may be useful as a potential biomarker for the assessment of treatment response in cancer.

Observed magnetic resonance imaging changes in pediatric patients treated with stereotactic radiosurgery for intracranial tumors

PURPOSE

This study seeks to characterize magnetic resonance imaging (MRI) changes following stereotactic radiosurgery (SRS) of pediatric brain malignancies.

METHODS

Serial MRI evaluations were performed on 21 lesions treated with SRS for either medulloblastoma (n=12), juvenile pilocytic astrocytoma (n=4), ependymoma (n=2), atypical rhabdoid teratoid tumor (n=2), or pineocytoma (n=1). Prescription doses ranged from 14 to 30 Gy in one to five fractions. Tumor response was qualified as complete (CR), partial (PR), stable disease (SD), or progressive disease (PD) according to the RECIST v1.1. Median radiographic follow-up after SRS was 17 months.

RESULTS

A total of 80 follow-up MRI scans were reviewed with a median of eight per patient. During serial MRI evaluation, eight lesions met criteria for PD at a median of 6 months. However, of these, three (37%) represented transient tumor edema with two lesions later developing a CR at a median of 15 months and one persisting as SD at 12 months. The remaining five lesions were true local failures. Of the 13 lesions that did not show evidence of PD, a CR was obtained in 11 lesions at a median of 3 months (range, 2-6), and SD was seen in the remaining two tumors at last follow-up.

CONCLUSION

Lesion enlargement following SRS for pediatric intracranial tumors is common, and a proportion of patients meeting requirements for PD at early radiographic follow-up may later develop complete resolution of their lesions. Physicians should be aware of these radiographic changes to avoid unwarranted medical and surgical interventions.

Evaluation of magnetic resonance diffusion and spectroscopy measurements as predictive biomarkers in stage 1 cervical cancer

OBJECTIVE

To establish whether ADC and total choline were significantly different between cervical tumors with different histological characteristics (type, degree of differentiation, presence or absence of lymphovascular invasion, lymph-node involvement) in order to establish their role as predictive biomarkers.

METHODS

62 patients with stage 1 cervical cancer were scanned at 1.5 T. T2-weighted imaging (TR/TE=4500/80 ms), to identify tumor and normal cervix, was followed by diffusion-weighted imaging (TR/TE=2500/69 ms; 5 b-values 0, 100, 300, 500 and 800 s/mm(2)) and MR spectroscopic imaging (15 mm slice, 7.5 mm in-plane resolution, TR=888 ms). Regions of interest in normal cervix and tumor were drawn on apparent diffusion coefficient (ADC) maps by an expert observer with reference to the T2-weighted images. ADCs were calculated using a monoexponential fit of data from all b-values. MR spectra in voxels designated as tumor (>30% tumor) or non-tumor were quantified using LCModel and referenced to tissue water.

RESULTS

There was a statistically significant difference between the ADC of tumor regions (1117+/-183x10(-6) mm(2)/s) and of selected normal regions (1724+/-198x10(-6) mm(2)/s; p<0.001), and between tumors that were well/moderately differentiated (1196+/-181x10(-6) mm(2)/s) compared with those that were poorly differentiated (1038+/-153x10(-6) mm(2)/s; p=0.016). There was no significant difference between the ADCs of the tumors when separated by other characteristics (tumor type, lymphovascular invasion, lymph-node metastases), or between measured total choline in any of the groups.

CONCLUSION

ADCs are lower in cancer compared to normal cervical tissue, with degree of tumor differentiation contributing to this difference.

MR imaging of late radiation therapy- and chemotherapy-induced injury: a pictorial essay

Radiation to the brain and adjuvant chemotherapy may produce late delayed changes from several months to years after treatment of intracranial malignancies with a reported prevalence of 5-24%. The pattern of treatment-related injury may vary from diffuse periventricular white matter lesions to focal or multifocal lesions. Differentiation of treatment-related injury from tumor progression/recurrence may be difficult with conventional MR imaging (MRI). With both disease processes, the characteristic but nonspecific imaging features are vasogenic edema, contrast enhancement, and mass effect. This pictorial essay presents MRI spectra of late therapy-induced injuries in the brain with a particular emphasis on radiation necrosis, the most common and severe form. Novel MRI techniques, such as diffusion-weighted imaging (DWI), proton MR spectroscopy (MRS), and perfusion MRI, improve the possibilities of better characterization of treatment-related changes. Advanced MRI techniques allow for the assessment of metabolism and physiology and may increase specificity for therapy-induced changes.

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.

Radiological progression of cerebral metastases after radiosurgery: assessment of perfusion MRI for differentiating between necrosis and recurrence

To assess the capability of perfusion MRI to differentiate between necrosis and tumor recurrence in patients showing radiological progression of cerebral metastases treated with stereotactic radiosurgery (SRS). From 2004 to 2006 dynamic susceptibility-weighted contrast-enhanced perfusion MRI scans were performed on patients with cerebral metastasis showing radiological progression after SRS during follow-up. Several perfusion MRI characteristics were examined: a subjective visual score of the relative cerebral blood volume (rCBV) map and quantitative rCBV measurements of the contrast-enhanced areas of maximal perfusion. For a total of 34 lesions in 31 patients a perfusion MRI was performed. Diagnoses were based on histology, definite radiological decrease or a combination of radiological and clinical follow-up. The diagnosis of tumor recurrence was obtained in 20 of 34 lesions, and tumor necrosis in 14 of 34. Regression analyses for all measures proved statistically significant (χ² = 11.6–21.6, P < 0.001–0.0001). Visual inspection of the rCBV map yielded a sensitivity and specificity of 70.0 respectively 92.9%. The optimal cutoff point for maximal tumor rCBV relative to white matter was 2.00 (improving the sensibility to 85.0%) and 1.85 relative to grey matter (GM), improving the specificity to 100%, with a corresponding sensitivity of 70.0%. Perfusion MRI seems to be a useful tool in the differentiation of necrosis and tumor recurrence after SRS. For the patients displaying a rCBV-GM greater than 1.85, the diagnosis of necrosis was excluded. Salvage treatment can be initiated for these patients in an attempt to prolong survival.

Radiographic and histopathologic observations after combined EGFR inhibition and hypofractionated stereotactic radiosurgery in patients with recurrent malignant gliomas

PURPOSE

To describe the radiographic and histopathologic changes after stereotactic radiosurgery (SRS) and epidermal growth factor receptor inhibition in patients with recurrent malignant gliomas.

METHODS AND MATERIALS

A total of 15 patients with recurrent high-grade gliomas were treated on a prospective Phase I trial combining SRS and gefitinib. The SRS dose was escalated from 18 to 36 Gy in three fractions. The planning target volume was the T(1)-weighted contrast-enhancing (T(1)C) lesion plus 2 mm. Gefitinib was given at 250 mg daily. Serial brain magnetic resonance imaging scans were analyzed to characterize the volumetric changes in the T(1)C and T(2) abnormalities after treatment. Two patients underwent resection for suspected recurrence.

RESULTS

The median pretreatment magnetic resonance imaging T(1)C and T(2) volume was 40.9 and 184.1 cm(3), respectively. The median post-SRS percentage of increases in the T(1)C volume at 1, 2-4, and 5-7 months was 8.9%, 41.3%, and 99.6%, respectively. The median percentage increase in the T(2) volume likewise showed a trend upward after SRS, from 18.0% at 1 month to 37.8% at 5-7 months. For the 2 patients who underwent resection after SRS for an increasing T(1)C volume, the histopathologic analysis revealed therapy-induced vascular injury and necrosis. One patient with an asymptomatic increase in the T(1)C volume after SRS was treated conservatively. After a peak T(1)C volume increase at 9 months, the T(1)C volume had declined to 50% of the maximal volume at 15 months. The patients with the most dramatic increase in T(1)C volume experienced the longest overall survival.

CONCLUSION

Patients experienced a notable increase in magnetic resonance imaging T(1)C and T(2) volumes after the combination of SRS and epidermal growth factor receptor inhibition. The tissue changes were consistent with a potent treatment effect.

Imaging techniques to evaluate the response to treatment in oncology: current standards and perspectives

Response evaluation in solid tumours currently uses radiological imaging techniques to measure changes under treatment. Imaging requires a well-defined anatomical lesion to be viewed and relies on the measurement of a reduction in tumour size during treatment as the basis for presumed clinical benefit. However, with the development of anti-angiogenesis agents, anatomical imaging has became inappropriate as certain tumours would not reduce in size. Functional studies are therefore necessary and dynamic contrast enhanced magnetic resonance imaging (DCE-MRI), DCE-computed tomography (CT) and DCE-ultrasonography (US) are currently being evaluated for monitoring treatments. Diffusion-weighted MR imaging (DW-MRI) and magnetic resonance spectroscopy (MRS) are also capable of detecting changes in cell density and metabolite content within tumours. In this article, we review anatomical and functional criteria currently used for monitoring therapy. We review the published data on DCE-MRI, DCE-CT, DCE-US, DW-MRI and MRS. This literature review covers the following area: basic principles of the technique, clinical studies, reproducibility and repeatability, limits and perspectives in monitoring therapy. Anatomical criteria such as response evaluation criteria in solid tumours (RECIST) will require adaptation to employ not only new tools but also different complementary techniques such as functional imaging in order to monitor therapeutic effects of conventional and new anti-cancer agents.

[Brain magnetic resonance spectroscopy]

MR spectroscopy (MRS) sequences allow noninvasive exploration of brain metabolism during a MRI examination. Their day-to-day use in a clinical setting has recently been improved by simple programming of sequences and automated quantification of metabolites. However, a few simple rules should be observed in the choice of sequences and the location of the voxels so as to obtain an informative, high-quality examination. The research applications of MR spectroscopy, where use of this examination seeks to better understand the pathophysiology of the disease, must be distinguished from its clinical indications, where MRS provides information that can be used directly in patient management. The most significant of the clinical uses are imaging intracranial tumors (positive and differential diagnosis, extension, treatment follow-up), diffuse brain injury, encephalopathies (especially hepatic and HIV-related), and the diagnosis of metabolic disorders.

[Indications for cerebral MR proton spectroscopy in 2007]

Magnetic resonance spectroscopy (MRS) is being increasingly performed alongside the more conventional MRI sequences in the exploration of neurological disorders. It is however important to clearly differentiate its clinical applications aiming at improving the differential diagnosis or the prognostic evaluation of the patient, from the research protocols, when MRS can contribute to a better understanding of the pathophysiology of the disease or to the evaluation of new treatments. The most important applications in clinical practice are intracranial space occupying lesions (especially the positive diagnosis of intracranial abscesses and gliomatosis cerebri and the differential diagnosis between edema and tumor infiltration), alcoholic, hepatic, and HIV-related encephalopathies and the exploration of metabolic diseases. Among the research applications, MRS is widely used in multiple sclerosis, ischemia and brain injury, epilepsy and neuro degenerative diseases.

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.

Proton magnetic resonance spectroscopy (MRS) of metastatic brain tumors: variations of metabolic profile

BACKGROUND

Spectroscopic imaging can be helpful for the noninvasive identification of parenchymal brain tumors. The objective of the present study was the characterization of the metabolic profile of intracranial metastases, based on proton magnetic resonance spectroscopy (MRS).

METHODS

One hundred and four metastatic brain tumors were evaluated by long-echo (TR, 2000 ms; TE, 136 ms) single-voxel volume-selected proton MRS. In 83 patients the tumor fraction within the MRS voxel constituted more than 50%.

RESULTS

Compared to normal brain, the tumors showed statistically significant decreases of N-acetylaspartate (P < 0.0001), creatine (P < 0.0001), and the [NAA]/choline-containing compounds ratio (P < 0.0001), increases of [Cho] (P < 0.0001) and the mobile lipids/[Cr] ratio (P < 0.0001) and the lactate/[Cr] ratio (P < 0.05), and the more frequent presence of [Lip] (P < 0.0001) and [Lac] (P < 0.0001) resonances. However, the majority of these differences were lost when data for patients whose tumor fraction within the MRS voxel constituted less than 50% were analyzed separately. Determination of the predominant metabolite peak on the MR spectrum [NAA, Cho, Lip] permitted us to define three general metabolic patterns of brain metastases, which, showed statistically significant associations with the size of the neoplasm (P < 0.001), type of its contrast enhancement (P < 0.01), and the extent of perilesional edema (P < 0.05).

CONCLUSION

Proton MRS can define metabolically different subsets of metastatic brain tumors, and these characteristics should be taken into consideration during the differential diagnosis of parenchymal brain lesions.

Spectroscopie par résonance magnétique des tumeurs cérébrales

MR spectroscopy (MRS) can complement MRI in the evaluation of intracranial tumors. Before treatment, MRS can contribute to the differential diagnosis between tumor and non tumoral lesion (especially intracranial abscesses), to assess the aggressiveness of a glial tumor or to determine its extension to better delineate the surgical removal or the target volume of radiotherapy. During treatment follow-up, MRS helps differentiate recurrent tumor from radionecrosis or physiological post-surgical contrast enhancement. The current studies are trying to determine if the indications of MRS, alone or in association with other MR sequences can further be extended in the study of brain tumors, in particular the follow-up of lesions undergoing chemo or radiotherapy.

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.