Malignant gliomas: MR imaging spectrum of radiation therapy- and chemotherapy-induced necrosis of the brain after treatment

Quantitative multiparametric MRI assessment of glioma response to radiotherapy in a rat model

BACKGROUND

The inability of structural MRI to accurately measure tumor response to therapy complicates care management for patients with gliomas. The purpose of this study was to assess the potential of several noninvasive functional and molecular MRI biomarkers for the assessment of glioma response to radiotherapy.

METHODS

Fourteen U87 tumor-bearing rats were irradiated using a small-animal radiation research platform (40 or 20 Gy), and 6 rats were used as controls. MRI was performed on a 4.7 T animal scanner, preradiation treatment, as well as at 3, 6, 9, and 14 days postradiation. Image features of the tumors, as well as tumor volumes and animal survival, were quantitatively compared.

RESULTS

Structural MRI showed that all irradiated tumors still grew in size during the initial days postradiation. The apparent diffusion coefficient (ADC) values of tumors increased significantly postradiation (40 and 20 Gy), except at day 3 postradiation, compared with preradiation. The tumor blood flow decreased significantly postradiation (40 and 20 Gy), but the relative blood flow (tumor vs contralateral) did not show a significant change at most time points postradiation. The amide proton transfer weighted (APTw) signals of the tumor decreased significantly at all time points postradiation (40 Gy), and also at day 9 postradiation (20 Gy). The blood flow and APTw maps demonstrated tumor features that were similar to those seen on gadolinium-enhanced T1-weighted images.

CONCLUSIONS

Tumor ADC, blood flow, and APTw were all useful imaging biomarkers by which to predict glioma response to radiotherapy. The APTw signal was most promising for early response assessment in this model.

Perfusion MRI: the five most frequently asked clinical questions

OBJECTIVE

This article addresses questions that radiologists frequently ask when planning, performing, processing, and interpreting MRI perfusion studies in CNS imaging.

CONCLUSION

Perfusion MRI is a promising tool in assessing stroke, brain tumors, and neurodegenerative diseases. Most of the impediments that have limited the use of per-fusion MRI can be overcome to allow integration of these methods into modern neuroimaging protocols.

MRI patterns of T1 enhancing radiation necrosis versus tumour recurrence in high-grade gliomas

INTRODUCTION

Despite the emergence of new imaging technologies, the differentiation of treatment-related changes from recurrent tumour in patients with high-grade gliomas remains a difficult challenge. We evaluated whether specific MRI (magnetic resonance imaging) T1 post-contrast enhancement patterns can help to distinguish between radiation necrosis and tumour recurrence.

METHODS

This study was approved by local institutional review board. Fifty-one patients with World Health Organization grade III-IV glioma underwent reoperation after prior chemoradiation. The percentage of radiation necrosis versus recurrent tumour in reoperation specimens was estimated by an experienced neuropathologist. Enhancement patterns on T1 post-contrast sequences from the MRIs obtained prior to reoperation were evaluated according to pathology.

RESULTS

T1 contrast enhancement patterns correlating with recurrent tumour included focal solid nodules and solid uniform enhancement with distinct margins. Eighty-five per cent (17/20) of patients with ≥70% recurrent tumour at reoperation demonstrated one of these patterns on preoperative MRI. Enhancement patterns correlating with radiation necrosis included a hazy mesh-like diffuse enhancement and rim enhancement with feathery indistinct margins. Ninety-four per cent (17/18) of patients with ≥70% radiation necrosis demonstrated one of these two patterns. Thirteen cases had more mixed pathology (>30% of tumour/necrosis) and demonstrated patterns associated with recurrence and/or necrosis. Compared to MR spectroscopy performed in 10 patients, enhancement patterns on MRI were just as accurate in predicting pathologic diagnosis.

CONCLUSION

Identifying distinct patterns of contrast enhancement on MRI may help to differentiate between radiation necrosis and tumour recurrence in high-grade gliomas.

Invited review--neuroimaging response assessment criteria for brain tumors in veterinary patients

The evaluation of therapeutic response using cross-sectional imaging techniques, particularly gadolinium-enhanced MRI, is an integral part of the clinical management of brain tumors in veterinary patients. Spontaneous canine brain tumors are increasingly recognized and utilized as a translational model for the study of human brain tumors. However, no standardized neuroimaging response assessment criteria have been formulated for use in veterinary clinical trials. Previous studies have found that the pathophysiologic features inherent to brain tumors and the surrounding brain complicate the use of the response evaluation criteria in solid tumors (RECIST) assessment system. Objectives of this review are to describe strengths and limitations of published imaging-based brain tumor response criteria and propose a system for use in veterinary patients. The widely used human Macdonald and response assessment in neuro-oncology (RANO) criteria are reviewed and described as to how they can be applied to veterinary brain tumors. Discussion points will include current challenges associated with the interpretation of brain tumor therapeutic responses such as imaging pseudophenomena and treatment-induced necrosis, and how advancements in perfusion imaging, positron emission tomography, and magnetic resonance spectroscopy have shown promise in differentiating tumor progression from therapy-induced changes. Finally, although objective endpoints such as MR imaging and survival estimates will likely continue to comprise the foundations for outcome measures in veterinary brain tumor clinical trials, we propose that in order to provide a more relevant therapeutic response metric for veterinary patients, composite response systems should be formulated and validated that combine imaging and clinical assessment criteria.

Cerebral radiation necrosis

Cerebral radiation-induced injury ranges from acute reversible edema to late irreversible radiation necrosis (RN). Cerebral RN is poorly responsive to treatment, is associated with permanent neurological deficits and occasionally progresses to death. We review the literature regarding cerebral RN after radiotherapy for various brain and head and neck lesions and discuss its clinical features, imaging characteristics, pathophysiology and treatment. For new enhancing lesions on computed tomography or magnetic resonance imaging, apart from tumor progression or recurrence, RN needs to be considered in the differential diagnosis. Further studies are required to design chemoradiotherapy protocols that are effective in treating tumors while minimizing risk of RN. Current available treatments for RN, steroid and surgery, only relieve the mass effect. None of the experimental treatments to date have consistently been shown to reverse the pathologic process of RN.

Differentiation of true progression from pseudoprogression in glioblastoma treated with radiation therapy and concomitant temozolomide: comparison study of standard and high-b-value diffusion-weighted imaging

PURPOSE

To explore the role of histogram analysis of apparent diffusion coefficient (ADC) maps obtained at standard- and high-b-value (1000 and 3000 sec/mm(2), respectively) diffusion-weighted (DW) imaging in the differentiation of true progression from pseudoprogression in glioblastoma treated with radiation therapy and concomitant temozolomide.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board of Seoul National University Hospital, and informed consent requirement was waived. Thirty patients with histopathologically proved glioblastoma who had undergone concurrent chemotherapy and radiation therapy (CCRT) with temozolomide underwent diffusion-weighted MR imaging with b values of 1000 and 3000 sec/mm(2), and corresponding ADC maps were calculated from entire newly developed or enlarged enhancing lesions after completion of CCRT. Histogram parameters of each ADC map between true progression (n = 15) and pseudoprogression (n = 15) groups were compared by using the unpaired Student t test. Receiver operating characteristic analysis was used to determine the best cutoff values for predictors in the differentiation of true progression from pseudoprogression. Results were validated in an independent test set of nine patients by using the best cutoff value to predict differentiation of true progression from pseudoprogression. The accuracy of the selected best cutoff value in the independent test set was then calculated.

RESULTS

In terms of cumulative histograms, the fifth percentile of both ADC at b value of 1000 sec/mm(2) (ADC1000) and the ADC at b value of 3000 sec/mm(2) (ADC3000) were significantly lower in the true progression group than in the pseudoprogression group (P = .049 and P < .001, respectively). In contrast, neither the mean ADC1000 nor the mean ADC3000 was significantly different between the two groups. The diagnostic values of the parameters derived from ADC1000 and ADC3000 were compared, and a significant difference (0.224, P = .016) was found between the area under the receiver operating characteristic curve of the fifth percentile for ADC1000 and that for ADC3000. The accuracies were 66.7% (six of nine patients) and 88.9% (eight of nine patients) based on the fifth percentile of both ADC1000 and ADC3000 in the independent test set, respectively.

CONCLUSION

The fifth percentile of the cumulative ADC histogram obtained at a high b value was the most promising parameter in the differentiation of true progression from pseudoprogression of the newly developed or enlarged enhancing lesions after CCRT with temozolomide for glioblastoma treatment. Online supplemental material is available for this article.

Pseudoprogression after glioma therapy: a comprehensive review

Over the last decade, pseudoprogression as a clinically significant entity affecting both glioma patient management and the conduct of clinical trials has been recognized as a significant issue. The authors have summarized the literature relative to the incidence, chronological sequence, therapy-relatedness, impact of O-6-methylguanine-DNA methyltransferase methylation status and clinical features of pseudoprogression. Evidence regarding numerous neuroradiologic techniques to differentiate pseudoprogression from tumor recurrence is summarized. The implications of pseudoprogression on prognosis and clinical trial design are substantial, and are reviewed. Relative to this, the overlapping terms pseudoprogression and radiation necrosis are clarified to produce an appropriate basis for future consideration and research regarding this important biological phenomenon.

Identification of early and distinct glioblastoma response patterns treated by boron neutron capture therapy not predicted by standard radiographic assessment using functional diffusion map

Background

Radiologic response of brain tumors is traditionally assessed according to the Macdonald criteria 10 weeks from the start of therapy. Because glioblastoma (GB) responds in days rather than weeks after boron neutron capture therapy (BNCT) that is a form of tumor-selective particle radiation, it is inconvenient to use the Macdonald criteria to assess the therapeutic efficacy of BNCT by gadolinium-magnetic resonance imaging (Gd-MRI). Our study assessed the utility of functional diffusion map (fDM) for evaluating response patterns in GB treated by BNCT.

Methods

The fDM is an image assessment using time-dependent changes of apparent diffusion coefficient (ADC) in tumors on a voxel-by-voxel approach. Other than time-dependent changes of ADC, fDM can automatically assess minimum/maximum ADC, Response Evaluation Criteria In Solid Tumors (RECIST), and the volume of enhanced lesions on Gd-MRI over time. We assessed 17 GB patients treated by BNCT using fDM. Additionally, in order to verify our results, we performed a histopathological examination using F98 rat glioma models.

Results

Only the volume of tumor with decreased ADC by fDM at 2 days after BNCT was a good predictor for GB patients treated by BNCT (P value = 0.022 by log-rank test and 0.033 by wilcoxon test). In a histopathological examination, brain sections of F98 rat glioma models treated by BNCT showed cell swelling of both the nuclei and the cytoplasm compared with untreated rat glioma models.

Conclusions

The fDM could identify response patterns in BNCT-treated GB earlier than a standard radiographic assessment. Early detection of treatment failure can allow a change or supplementation before tumor progression and might lead to an improvement of GB patients’ prognosis.

Neuroimaging findings of the post-treatment effects of radiation and chemotherapy of malignant primary glial neoplasms

Post-treatment radiation and chemotherapy of malignant primary glial neoplasms present a wide spectrum of tumor appearances and treatment-related entities. Radiologic findings of these post-treatment effects overlap, making it difficult to distinguish treatment response and failure. The purposes of this article are to illustrate and contrast the imaging appearances of recurrent tumor from necrosis and to discuss other radiologic effects of cancer treatments. It is critical for radiologists to recognize these treatment-related effects to help direct clinical management.

Recurrent glioblastoma: optimum area under the curve method derived from dynamic contrast-enhanced T1-weighted perfusion MR imaging

PURPOSE

To determine whether the ratio of the initial area under the time-signal intensity curve (AUC) (IAUC) to the final AUC--or AUCR--derived from dynamic contrast material-enhanced magnetic resonance (MR) imaging can be an imaging biomarker for distinguishing recurrent glioblastoma multiforme (GBM) from radiation necrosis and to compare the diagnostic accuracy of the AUCR with commonly used model-free dynamic contrast-enhanced MR imaging parameters.

MATERIALS AND METHODS

The institutional review board approved this retrospective study and waived the informed consent requirement. Fifty-seven consecutive patients with pathologically confirmed recurrent GBM (n = 32) or radiation necrosis (n = 25) underwent dynamic contrast-enhanced MR imaging. Histogram parameters of the IAUC at 30, 60, and 120 seconds and the AUCR, which included the mean value at the higher curve of the bimodal histogram (mAUCR(H)), as well as 90th percentile cumulative histogram cutoffs, were calculated and were correlated with final pathologic findings. The best predictor for differentiating recurrent GBM from radiation necrosis was determined by means of receiver operating characteristic (ROC) curve analysis.

RESULTS

The demographic data were not significantly different between the two patient groups. There were statistically significant differences in all of the IAUC and AUCR parameters between the recurrent GBM and the radiation necrosis patient groups (P < .05 for each). ROC curve analyses showed mAUCR(H) to be the best single predictor of recurrent GBM (mAUCR(H) for recurrent GBM = 0.35 ± 0.11 [standard deviation], vs 0.19 ± 0.17 for radiation necrosis; P < .0001; optimum cutoff, 0.23), with a sensitivity of 93.8% and a specificity of 88.0%.

CONCLUSION

A bimodal histogram analysis of AUCR derived from dynamic contrast-enhanced MR imaging can be a potential noninvasive imaging biomarker for differentiating recurrent GBM from radiation necrosis.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13130016/-/DC1.

Early assessment of the efficacy of temozolomide chemotherapy in experimental glioblastoma using [18F]FLT-PET imaging

Addition of temozolomide (TMZ) to radiation therapy is the standard treatment for patients with glioblastoma (GBM). However, there is uncertainty regarding the effectiveness of TMZ. Considering the rapid evolution of the disease, methods to assess TMZ efficacy early during treatment would be of great benefit. Our aim was to monitor early effects of TMZ in a mouse model of GBM using positron emission tomography (PET) with 3′-deoxy-3′-[¹⁸F]fluorothymidine ([¹⁸F]FLT).

Methods

Human glioma cells sensitive to TMZ (Gli36dEGFR-1) were treated with sub-lethal doses of TMZ to obtain cells with lower sensitivity to TMZ (Gli36dEGFR-2), as measured by growth and clonogenic assays. Gli36dEGFR-1 and Gli36dEGFR-2 cells were subcutaneously (s.c.) or intracranially (i.c.) xenografted into nude mice. Mice were treated for 7 days with daily injection of 25 or 50 mg/kg TMZ. Treatment efficacy was measured using [¹⁸F]FLT-PET before treatment and after 2 days. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) were used to determine tumor volumes before treatment and after 7 days.

Results

A significant difference was observed between TMZ and DMSO treated tumors in terms of variations of [¹⁸F]FLT T/B ratio as soon as day 2 in the i.c. as well as in the s.c. mouse model. Variations of [¹⁸F]FLT T/B uptake ratio between days 0 and 2 correlated with variations of tumor size between days 0 and 7 (s.c. model: n_tumor = 17 in n_mice = 11, P<0.01; i.c. model: n_tumor/mice = 9, P<0.01).

Conclusions

Our results indicate that [¹⁸F]FLT-PET may be useful for an early evaluation of the response of GBM to TMZ chemotherapy in patients with glioma.

Bevacizumab as a treatment for radiation necrosis of brain metastases post stereotactic radiosurgery

BACKGROUND

Cerebral radiation necrosis (RN) is a difficult to treat complication of stereotactic radiosurgery (SRS) that can result in progressive neurologic decline. Currently, steroids are the standard of care treatment for brain RN despite their adverse effect profile and limited efficacy. The purpose of this study was to evaluate the treatment efficacy of cerebral RN to bevacizumab in patients with brain metastases previously treated with SRS.

METHODS

We retrospectively reviewed 14 lesions in 11 patients treated with bevacizumab for brain RN secondary to SRS for their brain metastases. Steroid dosing, RN-associated symptoms, and magnetic resonance imaging (MRI) scans were examined before, during, and after bevacizumab administration.

RESULTS

Of the 11 patients included, 6 had metastatic non-small cell lung cancer, and 5 had metastatic breast cancer. The mean percentage decrease in RN volume seen on T1 post-Gadolinium and fluid-attenuated inversion recovery (FLAIR) MRI at first follow-up, at a mean of 26 days (range, 15-43 days), was 64.4% and 64.3%, respectively. MRI changes were sustained on follow-up MRI scans, obtained at a mean of 33 days (range, 7-58 days) after bevacizumab discontinuation. After bevacizumab treatment, all patients initially receiving steroids had a reduction in steroid requirement, and all but one had an improvement in or stability of RN-associated symptoms. No patients experienced intratumoral bleeds or other adverse effects related to their bevacizumab treatment.

CONCLUSIONS

Bevacizumab is effective and safe for the treatment of RN after SRS for brain metastasis. In this context, bevacizumab offers symptomatic relief, a reduction in steroid requirement, and a dramatic radiographic response.

Clinical observation of peripheral nerve injury in 2 patients with cancer after radiotherapy

Aim of the study

This study aims to analyze the clinical manifestations and sequelae of peripheral nerve radiation damage of two cases of cancer patients after radiotherapy at the corresponding sites in clinical practice and to summarize experiences and lesions in order to provide a reference for future tumor radiotherapy.

Material and methods

Some data of two cases of patients, such as doses of radiotherapy, clinical manifestations and damage occurrence time, were collected and examinations were conducted to define diagnosis. Afterwards, therapies and follow-up were conducted.

Results

Case 1 (rectal cancer) was diagnosed as mild left lower extremity nerve damage. After the symptomatic treatment, the disease condition was improved, and there was no tumor recurrence sign. Case 2 (breast cancer) was diagnosed as left brachial plexus damage, and left upper extremity movement function was lost completely. While the analgesic treatment was conducted, anti-tumor relevant treatments were being carried out.

Conclusions

Radiotherapy can cause different extents of radioactive nerve damage. In practice, it is necessary to constantly improve the radiotherapy technology level and actively prevent the occurrence of complications. Once symptoms appear, the diagnosis and treatment should be conducted as early as possible in order to avoid aggravating damage to cause dysfunction and cause lifetime pain to patients.

Advanced MR imaging of gliomas: an update

Recent advances in the treatment of cerebral gliomas have increased the demands on noninvasive neuroimaging for the diagnosis, therapeutic planning, tumor monitoring, and patient outcome prediction. In the meantime, improved magnetic resonance (MR) imaging techniques have shown much potentials in evaluating the key pathological features of the gliomas, including cellularity, invasiveness, mitotic activity, angiogenesis, and necrosis, hence, further shedding light on glioma grading before treatment. In this paper, an update of advanced MR imaging techniques is reviewed, and their potential roles as biomarkers of tumor grading are discussed.

Outcomes for patients with anaplastic astrocytoma treated with chemoradiation, radiation therapy alone or radiation therapy followed by chemotherapy: a retrospective review within the era of temozolomide

Treatment for anaplastic astrocytoma (AA) is controversial. To assess three primary treatment approaches, patients from a single institution were retrospectively evaluated. To represent modern treatment selection, patients diagnosed with AA from December 2003 to December 2009 were selected. Those with insufficient data, incomplete pathology, and transformation or reclassification to glioblastoma in fewer than 6 months were excluded. A total of 163 patients were included in the final analyses. Median follow-up time was 4.2 years (range 0.5-7.8 years). Median age and Karnofsky performance status at diagnosis were 39.2 years and 90, respectively. 23.6 % of patients underwent biopsy, and 72.2 % underwent resection. Approximately 31 % received concurrent chemoradiation (CRT), 26.1 % had radiation therapy alone (RT), 38.2 % had radiation therapy followed by chemotherapy (RT-C), and 3 % were treated only with chemotherapy. Temozolomide was used almost exclusively during CRT (94.2 %) and adjuvantly. A median of 9.5 cycles of adjuvant chemotherapy was given. The combination of radiation and chemotherapy, either concurrent or sequential trended toward a higher rate of radiation necrosis. Median progression free survival (PFS) favored RT (not reached) over CRT (1.5 years) and RT-C (3.6 years) adjusted for pairwise comparison (p = 0.033, p = 0.050). Median overall survival (OS) was 5.7 years, and did not differ significantly by treatment group. OS for patients with AA did not vary by initial treatment selection. Although the longer PFS in those receiving RT versus CRT may be confounded by pseudoprogression, the equivalent OS among groups supports RT.

Bevacizumab in high-grade gliomas: a review of its uses, toxicity assessment, and future treatment challenges

High-grade gliomas continue to have dismal prognosis despite advances made in understanding the molecular genetics, signaling pathways, cytoskeletal dynamics, and the role of stem cells in gliomagenesis. Conventional treatment approaches, including surgery, radiotherapy, and cytotoxic chemotherapy, have been used with limited success. Therapeutic advances using molecular targeted therapy, immunotherapy, and others such as dietary treatments have not been able to halt tumor progression and disease-related death. High-grade gliomas (World Health Organization grades III/IV) are histologically characterized by cellular and nuclear atypia, neoangiogenesis, and necrosis. The expression of vascular endothelial growth factor, a molecular mediator, plays a key role in vascular proliferation and tumor survival. Targeting vascular endothelial growth factor has demonstrated promising results, with improved quality of life and progression-free survival. Bevacizumab, a humanized monoclonal antibody to vascular endothelial growth factor, is approved by the Food and Drug Administration as a single agent in recurrent glioblastoma and is associated with manageable toxicity. This review discusses the efficacy, practical aspects, and response assessment challenges with the use of bevacizumab in the treatment of high-grade gliomas.

Posttreatment evaluation of central nervous system gliomas

Although conventional contrast-enhanced MR imaging remains the standard-of-care imaging method in the posttreatment evaluation of gliomas, recent developments in therapeutic options such as chemoradiation and antiangiogenic agents have caused the neuro-oncology community to rethink traditional imaging criteria. This article highlights the latest recommendations. These recommendations should be viewed as works in progress. As more is learned about the pathophysiology of glioma treatment response, quantitative imaging biomarkers will be validated within this context. There will likely be further refinements to glioma response criteria, although the lack of technical standardization in image acquisition, postprocessing, and interpretation also need to be addressed.

Cerebral radiation necrosis: a review of the pathobiology, diagnosis and management considerations

Radiation therapy forms one of the building blocks of the multi-disciplinary management of patients with brain tumors. Improved survival following radiation therapy may come with a cost, including the potential complication of radiation necrosis. Radiation necrosis impacts the quality of life in cancer survivors, and it is essential to detect and effectively treat this entity as early as possible. Significant progress in neuro-radiology and molecular pathology facilitate more straightforward diagnosis and characterization of cerebral radiation necrosis. Several therapeutic interventions, both medical and surgical, may halt the progression of radiation necrosis and diminish or abrogate its clinical manifestations, but there are still no definitive guidelines to follow explicitly that guide treatment of radiation necrosis. We discuss the pathobiology, clinical features, diagnosis, available treatment modalities, and outcomes in the management of patients with intracranial radiation necrosis that follows radiation used to treat brain tumors.

Discriminating radiation necrosis from tumor progression in gliomas: a systematic review what is the best imaging modality?

Differentiating post radiation necrosis from progression of glioma and pseudoprogression poses a diagnostic conundrum for many clinicians. As radiation therapy and temozolomide chemotherapy have become the mainstay of treatment for higher-grade gliomas, radiation necrosis and post treatment changes such as pseudoprogression have become a more relevant clinical problem for neurosurgeons and neurooncologists. Due to their radiological similarity to tumor progression, accurate recognition of these findings remains paramount given their vastly different treatment regimens and prognoses. However, no consensus has been reached on the optimal technique to discriminate between these two lesions. In order to clarify the types of imaging modalities for recurrent enhancing lesions, we conducted a systematic review of case reports, case series, and prospective studies to increase our current understanding of the imaging options for these common lesions and their efficacy. In particular, we were interested in distinguishing radiation necrosis from true tumor progression. A PubMed search was performed to include all relevant studies where the imaging was used to differentiate between radiation necrosis and recurrent gliomas with post-radiation enhancing lesions. After screening for certain parameters in our study, seventeen articles with 435 patients were included in our analysis including 10 retrospective and 7 prospective studies. The average time from the end of radiation therapy to the onset of a recurrent enhancing lesion was 13.2 months. The most sensitive and specific imaging modality was SPECT with a sensitivity of 87.6 % and specificity of 97.8 %. Based on our review, we conclude that certain imaging modalities may be preferred over other less sensitive/specific techniques. Overall, tests such as SPECT may be preferable in differentiating TP (tumor progression) from RN (radiation necrosis) due to its high specificity, while nonspecific imaging such as conventional MRI is not ideal.

Differentiating tumor recurrence from treatment necrosis: a review of neuro-oncologic imaging strategies

Differentiating treatment-induced necrosis from tumor recurrence is a central challenge in neuro-oncology. These 2 very different outcomes after brain tumor treatment often appear similarly on routine follow-up imaging studies. They may even manifest with similar clinical symptoms, further confounding an already difficult process for physicians attempting to characterize a new contrast-enhancing lesion appearing on a patient's follow-up imaging. Distinguishing treatment necrosis from tumor recurrence is crucial for diagnosis and treatment planning, and therefore, much effort has been put forth to develop noninvasive methods to differentiate between these disparate outcomes. In this article, we review the latest developments and key findings from research studies exploring the efficacy of structural and functional imaging modalities for differentiating treatment necrosis from tumor recurrence. We discuss the possibility of computational approaches to investigate the usefulness of fine-grained imaging characteristics that are difficult to observe through visual inspection of images. We also propose a flexible treatment-planning algorithm that incorporates advanced functional imaging techniques when indicated by the patient's routine follow-up images and clinical condition.

Radiation-induced imaging changes following Gamma Knife surgery for cerebral arteriovenous malformations

Object

The objective of this study was to evaluate the incidence, severity, clinical manifestations, and risk factors of radiation-induced imaging changes (RIICs) following Gamma Knife surgery (GKS) for cerebral arteriovenous malformations (AVMs).

Methods

A total of 1426 GKS procedures performed for AVMs with imaging follow-up available were analyzed. Radiation-induced imaging changes were defined as newly developed increased T2 signal surrounding the treated AVM nidi. A grading system was developed to categorize the severity of RIICs. Grade I RIICs were mild imaging changes imposing no mass effect on the surrounding brain. Grade II RIICs were moderate changes causing effacement of the sulci or compression of the ventricles. Grade III RIICs were severe changes causing midline shift of the brain. Univariate and multivariate logistic regression analyses were applied to test factors potentially affecting the occurrence, severity, and associated symptoms of RIICs.

Results

A total of 482 nidi (33.8%) developed RIICs following GKS, with 281 classified as Grade I, 164 as Grade II, and 37 as Grade III. The median duration from GKS to the development of RIICs was 13 months (range 2–124 months). The imaging changes disappeared completely within 2–128 months (median 22 months) following the development of RIICs. The RIICs were symptomatic in 122 patients, yielding an overall incidence of symptomatic RIICs of 8.6%. Twenty-six patients (1.8%) with RIICs had permanent deficits. A negative history of prior surgery, no prior hemorrhage, large nidus, and a single draining vein were associated with a higher risk of RIICs.

Conclusions

Radiation-induced imaging changes are the most common adverse effects following GKS. Fortunately, few of the RIICs are symptomatic and most of the symptoms are reversible. Patients with a relatively healthy brain and nidi that are large, or with a single draining vein, are more likely to develop RIICs.

Contrast-enhanced MR imaging in neuroimaging

MR imaging without and with gadolinium-based contrast agents (GBCAs) is an important imaging tool for defining normal anatomy and characteristics of lesions. GBCAs have been used in contrast-enhanced MR imaging in defining and characterizing lesions of the central nervous system for more than 20 years. The combination of unenhanced and GBCA-enhanced MR imaging is the clinical gold standard for the noninvasive detection and delineation of most intracranial and spinal lesions. MR imaging has a high predictive value that rules out neoplasm and most inflammatory and demyelinating processes of the central nervous system.

Specific biomarkers of receptors, pathways of inhibition and targeted therapies: clinical applications

A deeper understanding of the role of specific genes, proteins, pathways and networks in health and disease, coupled with the development of technologies to assay these molecules and pathways in patients, promises to revolutionise the practice of clinical medicine. In particular, the discovery and development of novel drugs targeted to disease-specific alterations could benefit significantly from non-invasive imaging techniques assessing the dynamics of specific disease-related parameters. Here we review the application of imaging biomarkers in the management of patients with brain tumours, especially malignant glioma. This first part of the review focuses on imaging biomarkers of general biochemical and physiological processes related to tumour growth such as energy, protein, DNA and membrane metabolism, vascular function, hypoxia and cell death. These imaging biomarkers are an integral part of current clinical practice in the management of primary brain tumours. The second article of the review discusses the use of imaging biomarkers of specific disease-related molecular genetic alterations such as apoptosis, angiogenesis, cell membrane receptors and signalling pathways. Current applications of these biomarkers are mostly confined to experimental small animal research to develop and validate these novel imaging strategies with future extrapolation in the clinical setting as the primary objective.

Pseudoprogression after high-dose busulfan-thiotepa with autologous stem cell transplantation and radiation therapy in children with brain tumors: Impact on survival

Children with a brain tumor treated with high-dose busulfan-thiotepa with autologous stem cell transplantation (ASCT) and radiation therapy (RT) often experience radiographic changes during follow-up. The purpose of the study was to identify the incidence, time course, risk factors, and clinical outcome of this complication. From May 1988 through May 2007, 110 patients (median age, 3.6 years; range, 1 month to 15.3 years) with a brain tumor had received 1 course of high-dose busulfan-thiotepa with stem cell rescue, followed or preceded by RT as part of their treatment. All MRI follow-up examinations were systematically reviewed. Twenty-three patients (21%) developed neuroradiological abnormalities at a median time of 9.2 months (range, 5.6-17.3 months) after ASCT. All contrast-enhancing lesions appeared in patients who had received RT after ASCT and were localized inside the 50-55Gy isodoses. They disappeared in 14 of 23 patients after a median time of 8 months (range, 3-17 months), leaving microcalcifications in some cases. The presence of MRI abnormalities was an independent prognostic factor for overall survival in the multivariate analysis (hazard ratio, 0.12; 95% confidence interval [CI], 0.04-0.33), with a 5-year overall survival rate of 84% among patients with MRI abnormalities (95% CI, 62-94), compared with 27% (95% CI, 19-37) among those without lesions. MRI-detectable pseudoprogression is a common early finding in children treated with high-dose busulfan-thiotepa followed by radiation therapy and is correlated with a better outcome.

Radiation necrosis of the pons after radiotherapy for nasopharyngeal carcinoma: diagnosis and treatment

We report a case of radiation necrosis in an unusual location, the pons, in a patient who had received chemoradiation for nasopharyngeal carcinoma (NPC) over one year prior to presentation. This patient presented with subacute onset of ataxic hemiparesis and slurred speech. Initial magnetic resonance imaging (MRI) studies showed two 1-2 cm peripherally contrast-enhancing lesions in the pons with extensive surrounding edema. Proton magnetic resonance spectroscopy (MRS) played a key role in narrowing the differential diagnosis to radiation necrosis. The patient underwent biweekly bevacizumab therapy and has remained clinically stable with radiologic improvement of his lesion. In addition to this case, we present an overview of the use of advanced neuroimaging in distinguishing radiation necrosis of the central nervous system (CNS) from other entities as well as the role of bevacizumab in treatment.

Accurate differentiation of recurrent gliomas from radiation injury by kinetic analysis of α-11C-methyl-L-tryptophan PET

PET of amino acid transport and metabolism may be more accurate than conventional neuroimaging in differentiating recurrent gliomas from radiation-induced tissue changes. α-(11)C-methyl-l-tryptophan ((11)C-AMT) is an amino acid PET tracer that is not incorporated into proteins but accumulates in gliomas, mainly because of tumoral transport and metabolism via the immunomodulatory kynurenine pathway. The aim of this study was to evaluate the usefulness of (11)C-AMT PET supplemented by tracer kinetic analysis for distinguishing recurrent gliomas from radiation injury.

METHODS

Twenty-two (11)C-AMT PET scans were obtained in adult patients who presented with a lesion suggestive of tumor recurrence on conventional MRI 1-6 y (mean, 3 y) after resection and postsurgical radiation of a World Health Organization grade II-IV glioma. Lesional standardized uptake values were calculated, as well as lesion-to-contralateral cortex ratios and 2 kinetic (11)C-AMT PET parameters (volume of distribution [VD], characterizing tracer transport, and unidirectional uptake rate [K]). Tumor was differentiated from radiation-injured tissue by histopathology (n = 13) or 1-y clinical and MRI follow-up (n = 9). Accuracy of tumor detection by PET variables was assessed by receiver-operating-characteristic analysis.

RESULTS

All (11)C-AMT PET parameters were higher in tumors (n = 12) than in radiation injury (n = 10) (P ≤ 0.012 in all comparisons). The lesion-to-cortex K-ratio most accurately identified tumor recurrence, with highly significant differences both in the whole group (P < 0.0001) and in lesions with histologic verification (P = 0.006); the area under the receiver-operating-characteristic curve was 0.99. A lesion-to-cortex K-ratio threshold of 1.39 (i.e., a 39% increase) correctly differentiated tumors from radiation injury in all but 1 case (100% sensitivity and 91% specificity). In tumors that were high-grade initially (n = 15), a higher lesion-to-cortex K-ratio threshold completely separated recurrent tumors (all K-ratios ≥ 1.70) from radiation injury (all K-ratios < 1.50) (100% sensitivity and specificity).

CONCLUSION

Kinetic analysis of dynamic (11)C-AMT PET images may accurately differentiate between recurrent World Health Organization grade II-IV infiltrating gliomas and radiation injury. Separation of unidirectional uptake rates from transport can enhance the differentiating accuracy of (11)C-AMT PET. Applying the same approach to other amino acid PET tracers might also improve their ability to differentiate recurrent gliomas from radiation injury.

Assessment of treatment response in patients with glioblastoma using O-(2-18F-fluoroethyl)-L-tyrosine PET in comparison to MRI

The assessment of treatment response in glioblastoma is difficult with MRI because reactive blood-brain barrier alterations with contrast enhancement can mimic tumor progression. In this study, we investigated the predictive value of PET using O-(2-(18)F-fluoroethyl)-l-tyrosine ((18)F-FET PET) during treatment.

METHODS

In a prospective study, 25 patients with glioblastoma were investigated by MRI and (18)F-FET PET after surgery (MRI-/FET-1), early (7-10 d) after completion of radiochemotherapy with temozolomide (RCX) (MRI-/FET-2), and 6-8 wk later (MRI-/FET-3). Maximum and mean tumor-to-brain ratios (TBR(max) and TBR(mean), respectively) were determined by region-of-interest analyses. Furthermore, gadolinium contrast-enhancement volumes on MRI (Gd-volume) and tumor volumes in (18)F-FET PET images with a tumor-to-brain ratio greater than 1.6 (T(vol 1.6)) were calculated using threshold-based volume-of-interest analyses. The patients were grouped into responders and nonresponders according to the changes of these parameters at different cutoffs, and the influence on progression-free survival and overall survival was tested using univariate and multivariate survival analyses and by receiver-operating-characteristic analyses.

RESULTS

Early after completion of RCX, a decrease of both TBR(max) and TBR(mean) was a highly significant and independent statistical predictor for progression-free survival and overall survival. Receiver-operating-characteristic analysis showed that a decrease of the TBR(max) between FET-1 and FET-2 of more than 20% predicted favorable survival [corrected], with a sensitivity of 83% and a specificity of 67% (area under the curve, 0.75). Six to eight weeks later, the predictive value of TBR(max) and TBR(mean) was less significant, but an association between a decrease of T(vol 1.6) and PFS was noted. In contrast, Gd-volume changes had no significant predictive value for survival.

CONCLUSION

In contrast to Gd-volumes on MRI, changes in (18)F-FET PET may be a valuable parameter to assess treatment response in glioblastoma and to predict survival time.

CT-based quantitative SPECT for the radionuclide ²⁰¹Tl: experimental validation and a standardized uptake value for brain tumour patients

We have previously reported on a method for reconstructing quantitative data from 99mTc single photon emission computed tomography (SPECT) images based on corrections derived from X-ray computed tomography, producing accurate results in both experimental and clinical studies. This has been extended for use with the radionuclide ²⁰¹Tl. Accuracy was evaluated with experimental phantom studies, including corrections for partial volume effects where necessary. The quantitative technique was used to derive standardized uptake values (SUVs) for ²⁰¹Tl evaluation of brain tumours. A preliminary study was performed on 26 patients using ²⁰¹Tl SPECT scans to assess residual tumor after surgery and then to monitor response to treatment, with a follow-up time of 18 months. Measures of SUVmax were made following quantitative processing of the data and using a threshold grown volume of interest around the tumour. Phantom studies resulted in the calculation of concentration values consistently within 4% of true values. No continuous relation was found between SUVmax (post-resection) and patient survival. Choosing an SUVmax cut-off of 1.5 demonstrated a difference in survival between the 2 groups of patients after surgery. Patients with an SUVmax<1.5 had a 70% survival rate over the first 10 months, compared with a 47% survival rate for those with SUVmax>1.5. This difference did not achieve significance, most likely due to the small study numbers. By 18 months follow-up this difference had reduced, with corresponding survival rates of 40% and 27%, respectively. Although this study involves only a small cohort, it has succeeded in demonstrating the possibility of an SUV measure for SPECT to help monitor response to treatment of brain tumours and predict survival.

[Visualization of radiation effects on the central nervous system]

Therapy-related side effects, which are detectable with magnetic resonance imaging (MRI) at high sensitivity, are one of the most frequent causes of morbidity in cancer patients. They can be observed in the treatment of central nervous system (CNS) diseases as well as in systemic therapy, including whole brain irradiation and chemotherapy and are more often seen due to the better overall survival. This review describes the most frequent acute and chronic therapy-related changes in the CNS and the imaging findings. Acute changes are often reversible while chronic changes can be observed up to several years after treatment.The differentiation of treatment-related from tumor-related changes might be very difficult, although modern imaging modalities such as MR spectroscopy or MR perfusion measurements supply helpful differential diagnostic information.

Assessment of MRI parameters as imaging biomarkers for radiation necrosis in the rat brain

PURPOSE

Radiation necrosis is a major complication of radiation therapy. We explore the features of radiation-induced brain necrosis in the rat, using multiple MRI approaches, including T(1), T(2), apparent diffusion constant (ADC), cerebral blood flow (CBF), magnetization transfer ratio (MTR), and amide proton transfer (APT) of endogenous mobile proteins and peptides.

METHODS AND MATERIALS

Adult rats (Fischer 344; n = 15) were irradiated with a single, well-collimated X-ray beam (40 Gy; 10 × 10 mm(2)) in the left brain hemisphere. MRI was acquired on a 4.7-T animal scanner at ~25 weeks' postradiation. The MRI signals of necrotic cores and perinecrotic regions were assessed with a one-way analysis of variance. Histological evaluation was accomplished with hematoxylin and eosin staining.

RESULTS

ADC and CBF MRI could separate perinecrotic and contralateral normal brain tissue (p < 0.01 and < 0.05, respectively), whereas T(1), T(2), MTR, and APT could not. MRI signal intensities were significantly lower in the necrotic core than in normal brain for CBF (p < 0.001) and APT (p < 0.01) and insignificantly higher or lower for T(1), T(2), MTR, and ADC. Histological results demonstrated coagulative necrosis within the necrotic core and reactive astrogliosis and vascular damage within the perinecrotic region.

CONCLUSION

ADC and CBF are promising imaging biomarkers for identifying perinecrotic regions, whereas CBF and APT are promising for identifying necrotic cores.

Development of a novel animal model to differentiate radiation necrosis from tumor recurrence

Distinguishing tumor progression from radiation necrosis after treatment in patients with brain tumors presents a clinical dilemma. A well-characterized, orthotopic rodent model of radiation-induced brain necrosis including a tumor is not currently available The objective of the study was to create focal radiation necrosis in rat brain bearing human glioblastoma (GBM) using stereotactic radiosurgery and confirm it by immuno-histological analysis. Nude rats implanted with primary GBM cells were irradiated using a stereotactic setup (n = 3) or received no radiation (n = 3). Ten weeks after the implantation, growth of the tumor was confirmed by magnetic resonance imaging (MRI). For each animal, MRI and contrast-enhanced CT images were obtained and fused using registration software. The tumor was identified and delineated using the fused CT/MR images. A treatment plan was generated using a 4 mm radiosurgery cone such that one portion of the tumor receives 100% dose of 60 Gy sufficient to cause necrosis, whereas the tumor edge at depth receives only 50% or less dose, allowing for regrowth of the tumor. The brains were collected 10 weeks after irradiation and immuno-histological analysis was performed. Hematoxylin and eosin staining showed central liquefaction necrosis in the high dose region consistent with necrosis and viable tumor in the peripheral low dose region. Ki-67 staining showed highly proliferative tumor cells surrounding the necrotic parts of the tumor. Luxol fast blue and lectin staining showed demyelination and vascular injury in brain tissue consistent with radiation necrosis. We have developed a novel model of radiation necrosis in rats bearing glioma.

Pseudoprogression and treatment effect

The standard of care for newly diagnosed malignant glioblastoma entails postoperative radiotherapy and adjuvant chemotherapy with temozolomide. There has been an increase in the incidence of enhancing and progressive lesions seen on magnetic resonance imaging (MRI) following treatment. Conventional MRI with gadolinium contrast is unable to distinguish between the effects of treatment and actual tumor recurrence. New modalities have provided additional information for distinguishing treatment effects from tumor progression but are not 100% sensitive or specific in diagnosing progression. Novel radiographic or nonradiographic biomarkers with sensitivity and specificity verified in large randomized clinical trials are needed to detect progression.

Radiation necrosis following treatment of high grade glioma--a review of the literature and current understanding

Radiation therapy is an integral part of the standard treatment paradigm for malignant gliomas, with proven efficacy in randomized control trials. Radiation treatment is not without risk however, and radiation injury occurs in a certain proportion of patients. Difficulties in differentiating recurrence from radiation injury complicate the treatment course and can compromise care. These complexities are compounded by the recent distinction of two types of radiation injury: pseudoprogression and radiation necrosis, which are likely the result of radiation injury to the tumor and normal tissue, respectively. A thorough understanding of radiation-induced injury offers insights to guide further therapies. We detail the current knowledge of the mechanisms of radiation injury, along with potential targets for therapeutic intervention. Various diagnostic modalities are also described, in addition to the multiple options for treatment within the context of their pathophysiology and clinical efficacy. Radiation therapy is an integral part of the multidisciplinary management of gliomas, and the optimal diagnosis and management of radiation injury is paramount to improving patient outcomes.

Late temporal lobe necrosis after conventional radiotherapy for carcinoma of maxillary sinus

Cerebral radiation necrosis is a serious late complication after conventional radiotherapy that can present with focal neurologic deficits or with more generalized signs and symptoms of increased intracranial pressure, depending on the location. The incidence and severity of radionecrosis are dose-volume dependent. We report a case of cerebral radiation necrosis 5 years after radiotherapy for a maxillary sinus carcinoma.

Spurious progression in pediatric brain tumors

In this study, we sought to characterize post-therapy MRI changes mimicking progression, which we refer to as "spurious progression" (SP) in children with brain tumors. We analyzed whether SP is associated with particular tumor types or therapeutic modalities. Between 2000 and 2009, we identified 181 consecutive children <21 years of age at our center who were treated for brain tumors and had at least three MRI scans within a year after completing therapy. SP was defined as MRI abnormalities characterized by increase in size, enhancement, edema, or cystic changes within 12 months following therapy, and stabilization or improvement on subsequent imaging. One-hundred forty-one patients with brain tumors were evaluable. Fifty-six (40%) had imaging abnormalities initially suggestive of disease progression; of these, 34 (24%) had true disease progression (TP). The remaining 22 (16%) had SP based on either stability, decrease in enhancement, edema, size, or disappearance of these cystic or non-cystic abnormalities. SP occurred in patients with low grade (n = 20) and high grade lesions (n = 2). Median time to SP was 2.4 months (range, 0.7-8.3 months), with time to stability, decrease, or disappearance at a median of 4 months (range 1.4-7.7 months). Five patients were clinically symptomatic from SP and were treated with steroids, cyst drainage, and/or surgery. Therefore, SP occurs more commonly in children with low grade tumors, but can also occur with high grade brain tumors, regardless of therapeutic approach.