Early evaluation of tumour metabolic response using [18F]fluorodeoxyglucose and positron emission tomography: a pilot study following the phase II chemotherapy schedule for temozolomide in recurrent high-grade gliomas

PET-CT in Clinical Adult Oncology-V. Head and Neck and Neuro Oncology

Simple Summary

Positron emission tomography (PET), typically combined with computed tomography (CT) has become a critical advanced imaging technique in oncology. With PET-CT, a radioactive molecule (radiotracer) is injected in the bloodstream and localizes to sites of tumor because of specific cellular features of the tumor that accumulate the targeting radiotracer. The CT scan, performed at the same time, provides information to facilitate attenuation correction, so that radioactivity from deep or dense structures can be better visualized, but with head and neck malignancies it is critical to provide correlating detailed anatomic imaging. PET-CT has a variety of applications in oncology, including staging, therapeutic response assessment, restaging, and surveillance. This series of six review articles provides an overview of the value, applications, and imaging and interpretive strategies of PET-CT in the more common adult malignancies. The fifth report in this series provides a review of PET-CT imaging in head and neck and neuro oncology.

Abstract

PET-CT is an advanced imaging modality with many oncologic applications, including staging, assessment of response to therapy, restaging, and longitudinal surveillance for recurrence. The goal of this series of six review articles is to provide practical information to providers and imaging professionals regarding the best use of PET-CT for specific oncologic indications, and the potential pitfalls and nuances that characterize these applications. In addition, key tumor-specific clinical information and representative PET-CT images are provided to outline the role that PET-CT plays in the management of oncology patients. Hundreds of different types of tumors exist, both pediatric and adult. A discussion of the role of FDG PET for all of these is beyond the scope of this review. Rather, this series of articles focuses on the most common adult malignancies that may be encountered in clinical practice. It also focuses on FDA-approved and clinically available radiopharmaceuticals, rather than research tracers or those requiring a local cyclotron. The fifth review article in this series focuses on PET-CT imaging in head and neck tumors, as well as brain tumors. Common normal variants, key anatomic features, and benign mimics of these tumors are reviewed. The goal of this review article is to provide the imaging professional with guidance in the interpretation of PET-CT for the more common head and neck malignancies and neuro oncology, and to inform the referring providers so that they can have realistic expectations of the value and limitations of PET-CT for the specific type of tumor being addressed.

Correlation between FDG-PET uptake and survival in patients with primary brain tumors

This study evaluates F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) semi-quantitative analysis as biomarker of tumor aggressiveness and predictor of survival in patients with primary brain tumors. Semi-quantitative analyses (SUVmax, SUVmean) were derived from FDG PET images in 78 patients with suspected recurrence of primary brain tumors based on MRI. SUVmax and the ratio of lesion SUVmax to the SUVmean of contralateral white matter (SUVmax/WM) were measured. A one-way Analysis of Variance (ANOVA), Kaplan-Meier analyses and the log rank test for evaluating statistical significance were utilized. There was statistical significance for time between FDG-PET and patient death. There was a significant difference with respect to FDG-PET time to death between patients with glioblastoma and patients with anaplastic oligodendroglioma, oligodendroglioma, and other histological subtypes. There is significant correlation with SUVmax/WM and patient survival following FDG-PET when a cut-point ratio of 1.90 is used. A 1.90 cut-point ratio of SUVmax/WM was associated with a difference in survival. GBM was associated with a significant difference in terms of reduced survival following FDG PET compared to most other histological sub-types. These results may inform current treatment and counseling strategies for patients with primary brain tumors.

Imaging Glioblastoma Posttreatment: Progression, Pseudoprogression, Pseudoresponse, Radiation Necrosis

Radiographic monitoring of posttreatment glioblastoma is important for clinical trials and determining next steps in management. Evaluation for tumor progression is confounded by the presence of treatment-related radiographic changes, making a definitive determination less straight-forward. The purpose of this article was to describe imaging tools available for assessing treatment response in glioblastoma, as well as to highlight the definitions, pathophysiology, and imaging features typical of true progression, pseudoprogression, pseudoresponse, and radiation necrosis.

Imaging Glioblastoma Posttreatment: Progression, Pseudoprogression, Pseudoresponse, Radiation Necrosis

Radiographic monitoring of posttreatment glioblastoma is important for clinical trials and determining next steps in management. Evaluation for tumor progression is confounded by the presence of treatment-related radiographic changes, making a definitive determination less straight-forward. The purpose of this article was to describe imaging tools available for assessing treatment response in glioblastoma, as well as to highlight the definitions, pathophysiology, and imaging features typical of true progression, pseudoprogression, pseudoresponse, and radiation necrosis.

Dynamic susceptibility contrast and diffusion MR imaging identify oligodendroglioma as defined by the 2016 WHO classification for brain tumors: histogram analysis approach

PURPOSE

According to the revised World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS) of 2016, oligodendrogliomas are now defined primarily by a specific molecular signature (presence of IDH mutation and 1p19q codeletion). The purpose of our study was to assess the value of dynamic susceptibility contrast MR imaging (DSC-MRI) and diffusion-weighted imaging (DWI) to characterize oligodendrogliomas and to distinguish them from astrocytomas.

METHODS

Seventy-one adult patients with untreated WHO grade II and grade III diffuse infiltrating gliomas and known 1p/19q codeletion status were retrospectively identified and analyzed using relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) maps based on whole-tumor volume histograms. The Mann-Whitney U test and logistic regression were used to assess the ability of rCBV and ADC to differentiate between oligodendrogliomas and astrocytomas both independently, but also related to the WHO grade. Prediction performance was evaluated in leave-one-out cross-validation (LOOCV).

RESULTS

Oligodendrogliomas showed significantly higher microvascularity (higher rCBV_Mean ≥ 0.80, p = 0.013) and higher vascular heterogeneity (lower rCBV_Peak ≤ 0.044, p = 0.015) than astrocytomas. Diffuse gliomas with higher cellular density (lower ADC_Mean ≤ 1094 × 10^-6 mm²/s, p = 0.009) were more likely to be oligodendrogliomas than astrocytomas. Histogram analysis of rCBV and ADC was able to differentiate between diffuse astrocytomas (WHO grade II) and anaplastic astrocytomas (WHO grade III).

CONCLUSION

Histogram-derived rCBV and ADC parameter may be used as biomarkers for identification of oligodendrogliomas and may help characterize diffuse gliomas based upon their genetic characteristics.

PET/CT in the Evaluation of Response to Treatment of Liver Metastases from Colorectal Cancer with Bevacizumab and Irinotecan

The present approach at our institution for the treatment of patients with colorectal (CRC) cancer and with liver metastases planned for metastasectomy is the neoadjuvant administration of Bevacizumab with Irinotecan based therapy. Metabolic imaging of tumor viability with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), and simultaneous anatomic localization provided by low-dose non-enhanced computed tomography (CT), can be obtained in a combined modality FDG-PET/CT scan. The purpose of this study was to evaluate the possible contribution of FDG-PET/CT as a surrogate marker to evaluate treatment response of liver metastases in vivo. This is a retrospective evaluation of 18F-FDG PET and CT findings in the first seven consecutive patients. FDG-PET/CT scans were performed before the start of the neoadjuvant and after four cycles of therapy, just prior to surgery. Results were compared to concurrent contrast-enhanced CT, when required, and pathology. Response to treatment was determined according to RECIST size criteria obtained from data from thin (3–5mm) slice CT, and changes in uptake of 18F-FDG uptake on PET.

A total of 20 liver lesions were evaluated in seven patients. Overall, 6/7 patients had favorable response to treatment, and only one had progression of disease. One patient was found to be inoperable at surgery. Biopsy was obtained in 1/4 lesions in this patient, while pathology was unable for the remaining three lesions. As such, pathologic validation of findings was available for 17/20 lesions. Complete response (CR) was evident on FDG-PET in 10/17 (58%) lesions, whereas only 4/17(23%) were deemed CR by CT. Similarly, only 1/17 (6%) lesion appeared stable by FDG-PET criteria, whereas three (18%) were termed stable disease (SD) according to size on CT.

FDG-PET findings correlated better than CT with pathology, and were more indicative of pathology. Overall PET/CT correctly predicted necrosis at pathology in 70% vs. 35% by CT. Our results suggest that 18F-FDG PET may be instrumental for predicting the pathologic response to Bevacizumab based therapy.

Role of [(11)C] methionine positron emission tomography in the diagnosis and prediction of survival in brain tumours

OBJECTIVE

[(11)C] methionine (MET) positron-emission tomography (PET) is a useful diagnostic and therapeutic tool in neuro-oncology. The aim of this study was to evaluate the relationship between MET uptake and the histopathological grade in both primary brain tumours and brain metastases. A secondary goal was to assess the relationship between MET uptake and patients' survival after surgery.

METHODS

We reviewed a consecutive series of 43 PET studies performed at our institution. Out of the 43 patients studied, 35 harboured primary brain tumours (3 grade I, 12 grade II, 7 grade III and 13 grade IV) and 8 patients had brain metastases. We measured the tumour/cortex ratio (T/C ratio) on each PET study and we investigated the correlations among the tracer uptake, tumour grade, tumour type, MRI parameters and outcome.

RESULTS

The mean T/C ratio was 1.8 ± 0.9 for benign lesions and low grade gliomas (grade I and II) and 2.7 ± 1 for high grade gliomas (grade III and IV). In brain metastases it was 2.5 ± 0.7, with a significant difference in MET uptake between low and high grades gliomas (P=0.03). There was no statistically significant difference among all different histologic types. We found that both contrast enhancement and perfusion studies correlate with MET uptake in brain tumours. Moreover, in Kaplan-Meier curves, the T/C ratio adversely affects long term survival in patients with brain tumours (P=0.01).

CONCLUSIONS

MET PET appears to be useful in diagnosis and evaluation of potential malignancy in brain tumours. MET uptake is also related with the overall survival in patients with brain tumours. Nevertheless, further studies are needed in order to define its possible clinical implications in identifying patients at high risk of tumour progression or resistance to therapy.

Emerging methods for disease monitoring in malignant gliomas

MRI remains the backbone of measuring disease burden and treatment response in individuals with malignant gliomas. Traditional radiographic approaches, however, are largely limited to depicting anatomic changes and are not a direct measure of disease burden. For example, contrast enhancement is related to blood-brain barrier integrity rather than actual tumor size. Without accurate measures of disease, common clinical dilemmas include 'pseudo-progression' (e.g., after chemoradiation) or 'pseudo-response' (e.g., with steroid treatment and antiangiogenic agents), which can lead to delays in therapy, premature discontinuation of successful treatments and to unnecessary surgical procedures. This overview focuses on novel, minimally invasive approaches in the area of imaging and blood-based biomarkers that aim to more accurately determine disease status and response to treatment in malignant brain tumors.

Spinal cord stimulation as adjuvant during chemotherapy and reirradiation treatment of recurrent high-grade gliomas

AIMS

Relapsed high-grade gliomas (HGGs) have poor prognoses and there is no standard treatment. HGGs have ischemia/hypoxia associated and, as such, drugs and oxygen have low access, with increased resistance to chemotherapy and radiotherapy. Tumor hypoxia modification can improve outcomes and overall survival in some patients with these tumors. In previous works, we have described that cervical spinal cord stimulation can modify tumor microenvironment in HGG by increasing tumor blood flow, oxygenation, and metabolism. The aim of this current, preliminary, nonrandomized, study was to assess the clinical effect of spinal cord stimulation during brain reirradiation and chemotherapy deployed for the treatment of recurrent HGG; the hypothesis being that an improvement in oxygenated blood supply would facilitate enhanced delivery of the scheduled therapy.

MATERIALS AND METHODS

Seven patients had spinal cord stimulation applied during the scheduled reirradiation and chemotherapy for the treatment of recurrent HGG (6 anaplastic gliomas and 1 glioblastoma). Median dose of previous irradiation was 60 Gy (range = 56-72 Gy) and median dose of reirradiation was 46 Gy (range = 40-46 Gy). Primary end point of the study was overall survival (OS) following confirmation of HGG relapse.

RESULTS

From the time of diagnosis of last tumor relapse before reirradiation, median OS was 39 months (95% CI = 0-93) for the overall study group: 39 months (95% CI = 9-69) for those with anaplastic gliomas and 16 months for the patient with glioblastoma. Posttreatment, doses of corticosteroids was significantly decreased (P = .026) and performance status significantly improved (P = .046).

CONCLUSIONS

Spinal cord stimulation during reirradiation and chemotherapy is feasible and well tolerated. In our study, spinal cord stimulation was associated with clinical improvement and longer survival than previously reported in recurrent anaplastic gliomas. Spinal cord stimulation as adjuvant during chemotherapy and reirradiation in relapsed HGGs merits further research.

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.

Conversion of arterial input functions for dual pharmacokinetic modeling using Gd-DTPA/MRI and 18F-FDG/PET

Reaching the full potential of magnetic resonance imaging (MRI)-positron emission tomography (PET) dual modality systems requires new methodologies in quantitative image analyses. In this study, methods are proposed to convert an arterial input function (AIF) derived from gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) in MRI, into a (18)F-fluorodeoxyglucose ((18)F-FDG) AIF in PET, and vice versa. The AIFs from both modalities were obtained from manual blood sampling in a F98-Fisher glioblastoma rat model. They were well fitted by a convolution of a rectangular function with a biexponential clearance function. The parameters of the biexponential AIF model were found statistically different between MRI and PET. Pharmacokinetic MRI parameters such as the volume transfer constant (K(trans)), the extravascular-extracellular volume fraction (ν(e)), and the blood volume fraction (ν(p)) calculated with the Gd-DTPA AIF and the Gd-DTPA AIF converted from (18)F-FDG AIF normalized with or without blood sample were not statistically different. Similarly, the tumor metabolic rates of glucose (TMRGlc) calculated with (18) F-FDG AIF and with (18) F-FDG AIF obtained from Gd-DTPA AIF were also found not statistically different. In conclusion, only one accurate AIF would be needed for dual MRI-PET pharmacokinetic modeling in small animal models.

Multimodality assessment of brain tumors and tumor recurrence

Neuroimaging plays a significant role in the diagnosis of intracranial tumors, especially brain gliomas, and must consist of an assessment of location and extent of the tumor and of its biologic activity. Therefore, morphologic imaging modalities and functional, metabolic, or molecular imaging modalities should be combined for primary diagnosis and for following the course and evaluating therapeutic effects. MRI is the gold standard for providing detailed morphologic information and can supply some additional insights into metabolism (MR spectroscopy) and perfusion (perfusion-weighted imaging) but still has limitations in identifying tumor grade, invasive growth into neighboring tissue, and treatment-induced changes, as well as recurrences. These insights can be obtained by various PET modalities, including imaging of glucose metabolism, amino acid uptake, nucleoside uptake, and hypoxia. Diagnostic accuracy can benefit from coregistration of PET results and MRI, combining the high-resolution morphologic images with the biologic information. These procedures are optimized by the newly developed combination of PET and MRI modalities, permitting the simultaneous assessment of morphologic, functional, metabolic, and molecular information on the human brain.

Modification of loco-regional microenvironment in brain tumors by spinal cord stimulation. Implications for radio-chemotherapy

The effectiveness of radiotherapy and chemotherapy in high grade gliomas (HGG) depends on tumor micro-environment. We summarize our experience of the influence of spinal cord stimulation (SCS) on this micro-environment. Patients with HGG (n = 26) were assessed pre- and post-SCS, using: (1) Doppler in middle cerebral arteries (MCA) and (2) in common carotid arteries (CCA); (3) tumor blood-flow using single photon emission computed tomography (SPECT); (4) tumor-pO(2) (mmHg) using polarographic probes (eight tumor areas from five patients); and (5) tumor glucose metabolism using (18)F-fluoro-2-deoxyglucose ((18)FDG) positron emission tomography ((18)FDG-PET). Pre-SCS: tumor blood-flow was lower (P < 0.001) than peri-tumor areas and healthy contra-lateral areas. Tumor-pO(2) was lower (P < 0.042) than healthy tissue. Tumor glucose metabolism was higher than peri-tumor areas (P = 0.017) and healthy contra-lateral areas (P = 0.048). Post-SCS: there were increases in: MCA blood-flow (P ≤ 0.002), CCA blood-flow (P ≤ 0.013), tumor blood-flow (P = 0.033), tumor glucose metabolism (P = 0.027) and tumor-pO(2) (P = 0.022). The percentage of hypoxic values decreased (P = 0.007). SCS can modify tumor micro-environment. The potential usefulness of SCS in improving the effectiveness of radio-chemotherapy in HGG needs to be evaluated.

[Clinical factors in glioblastoma and neuroradiology]

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

Can 18F-FDG-PET response during radiotherapy be used as a predictive factor for the outcome of head and neck cancer patients?

OBJECTIVES

We investigated if (18F) fluoro-2-deoxy-D-glucose positron emission tomography (F-FDG-PET) during radiotherapy or concurrent chemoradiotherapy adds information about the treatment outcome compared with an FDG-PET study before treatment.

METHODS

Forty-three patients with head and neck cancer were treated with helical tomotherapy. F-FDG-PET was performed at baseline and during the treatment after 47 Gy. Tracer accumulation at the tumor site was assessed visually and semiquantitatively using the maximal standardized uptake values (SUV(max)). With median SUV(max) of both the studies as cutoff, patients were categorized into low and high SUV(max) groups. For visual analysis, two independent observers classified patients as complete metabolic responders (CMR) or noncomplete metabolic responders (NCMR).

RESULTS

At baseline the median SUV(max) was 8.11 (2.41-15.13). The overall survival (OS) and disease-free survival (DFS) were 81 and 67% versus 50 and 40% for the low and high SUV(max), respectively. OS was significantly different (P=0.027). During therapy, median SUV(max) was 4.03 (1.94-7.58). OS and DFS were 82 and 63%, versus 47 and 42% for the low and high SUV(max) group, respectively. OS was significantly different (P=0.026). No significant differences between CMR versus NCMR in OS (72 vs. 60%), and DFS (56 vs. 49%) were found.

CONCLUSION

Categorizing patients on the basis of a semiquantitative approach resulted in significant differences in OS for both the scans before and during therapy. Future work on a larger number of patients is warranted to determine SUV(max) cutoff values which could be used for the early identification of patients with poor treatment outcome or perhaps other therapeutic approaches.

Advanced MRI and PET imaging for assessment of treatment response in patients with gliomas

Imaging techniques are important for accurate diagnosis and follow-up of patients with gliomas. T1-weighted MRI, with or without gadolinium, is the gold standard method. However, this technique only reflects biological activity of the tumour indirectly by detecting the breakdown of the blood-brain barrier. Therefore, especially for low-grade glioma or after treatment, T1-weighted MRI enhanced with gadolinium has substantial limitations. Development of more advanced imaging methods to improve outcomes for individual patients is needed. New imaging methods based on MRI and PET can be employed in various stages of disease to target the biological activity of the tumour cells (eg, increased uptake of aminoacids or nucleoside analogues), the changes in diffusivity through the interstitial space (diffusion-weighted MRI), the tumour-induced neovascularisation (perfusion-weighted MRI or contrast-enhanced MRI, or increased uptake of aminoacids in endothelial wall), and the changes in concentrations of metabolites (magnetic resonance spectroscopy). These techniques have advantages and disadvantages, and should be used in conjunction to best help individual patients. Advanced imaging techniques need to be validated in clinical trials to ensure standardisation and evidence-based implementation in routine clinical practice.

PET in Brain Tumors

Evaluating gliomas, either at diagnosis or at recurrence, is among the historical indications of FDG positron emission tomography (PET) imaging. There is a clear relationship between the tumor grade, patient prognosis, and intensity of uptake. Yet the exact role of FDG PET imaging remains debated. PET and methionine labeled with the short-lived C11 also have been proposed, with the significant advantage of high tumor-to-cortex contrast and distinct bological properties that lead to specific indications. Clinical use of this tracer is hampered by the need for an on-site cyclotron, however. In recent years, the increased availability of fluorinated amino-acid analogs, in particular FET, has open the way to renewed scientific interest in the field of neuro-oncological PET and PET/CT. This article discusses FDG and alternative tracers for diagnosing and characterizing primary brain tumors, detecting their recurrences, helping to guide the radiation therapy, and for evaluating the response to treatments.

Effects of bevacizumab plus irinotecan on response and survival in patients with recurrent malignant glioma: a systematic review and survival-gain analysis

Background

The combination of bevacizumab and irinotecan is a new chemotherapy protocol increasingly used for recurrent malignant glioma. Results from phase II trials suggest this drug combination is beneficial to patients, but no conclusive comparisons between this and other treatment protocols have been published.

Methods

We performed a systematic review and survival gain analysis of phase II studies to evaluate the efficacy and safety of bevacizumab plus irinotecan treatment. To do this, we utilized a preexisting database from which the mean overall survival and response rate of patients could be predicted. Survival gain, which characterized the influence of treatment, was defined as the difference between observed and predicted mean overall survival. Response gain was calculated similarly.

Results

741 cohorts were enrolled in the database. Among them, 282 cohorts were based on recurrent adult HGG, mean reported median overall survival was 10.96 ± 8.4 months, and mean response rate was 18.9% ± 20.5. We found that compared with other treatment protocols, bevacizumab plus irinotecan largely improved response rates (P = 0.00002) and had a possible moderate effect on overall survival time (P = 0.024). Hemorrhage, thromboembolic complications, and gastrointestinal toxicities were the most frequently reported side effects.

Conclusion

The combination of bevacizumab and irinotecan might improve outcome in patients with recurrent malignant glioma. Randomized controlled trials are recommended to evaluate this treatment protocol and the additional value of irinotecan.

Evaluation of treatment-associated inflammatory response on diffusion-weighted magnetic resonance imaging and 2-[18F]-fluoro-2-deoxy-D-glucose-positron emission tomography imaging biomarkers

PURPOSE

Functional imaging biomarkers of cancer treatment response offer the potential for early determination of outcome through the assessment of biochemical, physiologic, and microenvironmental readouts. Cell death may result in an immunologic response, thus complicating the interpretation of biomarker readouts. This study evaluated the temporal effect of treatment-associated inflammatory activity on diffusion magnetic resonance imaging and 2-[(18)F]-fluoro-2-deoxy-D-glucose-positron emission tomography imaging (FDG-PET) biomarkers to delineate the effects of the inflammatory response on imaging readouts.

EXPERIMENTAL DESIGN

Rats with intracerebral 9L gliosarcomas were separated into four groups consisting of control, an immunosuppressive agent dexamethasone (Dex), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), and BCNU+Dex. Animals were imaged using diffusion-weighted magnetic resonance imaging and FDG-PET at 0, 3, and 7 days posttreatment.

RESULTS

In the BCNU- and BCNU+Dex-treated animal groups, diffusion values increased progressively over the 7-day study period to approximately 23% over baseline. The FDG percentage change of standard uptake value decreased at day 3 (-30.9%) but increased over baseline levels at day 7 (+20.1%). FDG-PET of BCNU+Dex-treated animals were found to have percentage of standard uptake value reductions of -31.4% and -24.7% at days 3 and 7, respectively, following treatment. Activated macrophages were observed on day 7 in the BCNU treatment group with much fewer found in the BCNU+Dex group.

CONCLUSIONS

Results revealed that treatment-associated inflammatory response following tumor therapy resulted in the accentuation of tumor diffusion response along with a corresponding increase in tumor FDG uptake due to the presence of glucose-consuming activated macrophages. The dynamics and magnitude of potential inflammatory response should be considered when interpreting imaging biomarker results.

Molecular imaging (PET) of brain tumors

Despite the recognized limitations of (18)Fluorodeoxyglucose positron emission tomography (FDG-PET) in brain tumor imaging due to the high background of normal gray matter, this imaging modality provides critical information for the management of patients with cerebral neoplasms with regard to the following aspects: (1) providing a global picture of the tumor and thus guiding the appropriate site for stereotactic biopsy, and thereby enhancing its accuracy and reducing the number of biopsy samples; and (2) prediction of biologic behavior and aggressiveness of the tumor, thereby aiding in prognosis. Another area, which has been investigated extensively, includes differentiating recurrent tumor from treatment-related changes (eg, radiation necrosis and postsurgical changes). Furthermore, FDG-PET has demonstrated its usefulness in differentiating lymphoma from toxoplasmosis in patients with acquired immune deficiency syndrome with great accuracy, and is used as the investigation of choice in this setting. Image coregistration with magnetic resonance imaging and delayed FDG-PET imaging are 2 maneuvers that substantially improve the accuracy of interpretation, and hence should be routinely employed in clinical settings. In recent years an increasing number of brain tumor PET studies has used other tracers (like labeled methionine, tyrosine, thymidine, choline, fluoromisonidazole, EF5, and so forth), of which positron-labeled amino acid analogues, nucleotide analogues, and the hypoxia imaging tracers are of special interest. The major advantage of these radiotracers over FDG is the markedly lower background activity in normal brain tissue, which allows detection of small lesions and low-grade tumors. The promise of the amino acid PET tracers has been emphasized due to their higher sensitivity in imaging recurrent tumors (particularly the low-grade ones) and better accuracy for differentiating between recurrent tumors and treatment-related changes compared with FDG. The newer PET tracers have also shown great potential to image important aspects of tumor biology and thereby demonstrate ability to forecast prognosis. The value of hypoxia imaging tracers (such as fluoromisonidazole or more recently EF5) is substantial in radiotherapy planning and predicting treatment response. In addition, they may play an important role in the future in directing and monitoring targeted hypoxic therapy for tumors with hypoxia. Development of optimal image segmentation strategy with novel PET tracers and multimodality imaging is an approach that deserves mention in the era of intensity modulated radiotherapy, and which is likely to have important clinical and research applications in radiotherapy planning in patients with brain tumor.

[Second surgery for glioblastoma. A 4-year retrospective study conducted in both the Montpellier and Nice Departments of Neurosurgery. A literature review]

BACKGROUND AND PURPOSE

Glioblastoma, the most common malignant primary brain tumor in adults, is usually rapidly fatal. The current care standards for newly diagnosed glioblastoma consist, when feasible, in surgical resection, radiotherapy, and chemotherapy, as described in the Stupp protocol. Despite optimal treatment, nearly all malignant gliomas recur. If the tumor is symptomatic for mass effect, repeated surgery may be proposed.

METHODS

We retrospectively analyzed the survival of patients with histologically confirmed primary glioblastoma (WHO grade 4) who were operated in two centers between January 2004 and December 2007. All patients who underwent a second resection for recurrent glioblastoma were included.

RESULTS

During this period, 320 patients were operated in the two centers, with 240 surgical resections and 80 surgical biopsies. In the surgical resection group, 8.3% (20 patients) underwent a second surgical resection for glioblastoma. The mean age was 52 years. At the end of the study, seven patients were alive. The median survival was 24 months and progression-free survival was 7.5 months.

CONCLUSIONS

The effect of resection of recurrent glioblastoma on survival has not been extensively studied. No randomized trials have been conducted. Our data were globally identical to other retrospective studies. Selected patients with recurrent glioblastoma may be candidates for repeated surgery when the situation appears favorable based on assessment of the individual patient's factors. Factors such medical history, neurological status, location of the tumor, and progression-free survival have been proven in retrospective studies to give better results.

Quantitative imaging biomarkers in neuro-oncology

Conventional structural imaging provides limited information on tumor characterization and prognosis. Advances in neurosurgical techniques, radiotherapy planning and novel drug treatments for brain tumors have generated increasing need for reproducible, noninvasive, quantitative imaging biomarkers. This Review considers the role of physiological MRI and PET molecular imaging in understanding metabolic processes associated with tumor growth, blood flow and ultrastructure. We address the utility of various techniques in distinguishing between tumors and non-neoplastic processes, in tumor grading, in defining anatomical relationships between tumor and eloquent brain regions and in determining the biological substrates of treatment response. Much of the evidence is derived from limited case series in individual centers. Despite their 'added value', the effect of these techniques as an adjunct to structural imaging in clinical research and practice remains limited.

A new model for prediction of drug distribution in tumor and normal tissues: pharmacokinetics of temozolomide in glioma patients

Difficulties in direct measurement of drug concentrations in human tissues have hampered the understanding of drug accumulation in tumors and normal tissues. We propose a new system analysis modeling approach to characterize drug distribution in tissues based on human positron emission tomography (PET) data. The PET system analysis method was applied to temozolomide, an important alkylating agent used in the treatment of brain tumors, as part of standard temozolomide treatment regimens in patients. The system analysis technique, embodied in the convolution integral, generated an impulse response function that, when convolved with temozolomide plasma concentration input functions, yielded predicted normal brain and brain tumor temozolomide concentration profiles for different temozolomide dosing regimens (75-200 mg/m(2)/d). Predicted peak concentrations of temozolomide ranged from 2.9 to 6.7 microg/mL in human glioma tumors and from 1.8 to 3.7 microg/mL in normal brain, with the total drug exposure, as indicated by the tissue/plasma area under the curve ratio, being about 1.3 in tumor compared with 0.9 in normal brain. The higher temozolomide exposures in brain tumor relative to normal brain were attributed to breakdown of the blood-brain barrier and possibly secondary to increased intratumoral angiogenesis. Overall, the method is considered a robust tool to analyze and predict tissue drug concentrations to help select the most rational dosing schedules.

99mTc-MIBI brain SPECT as an indicator of the chemotherapy response of recurrent, primary brain tumors

BACKGROUND

Malignant brain tumors carry a pejorative prognosis and necessitate aggressive therapy. Chemotherapy can be used in cases of tumor recurrence. With limited response rate and potential toxicity to chemotherapeutic treatment in patients with recurrent glioma, reliable response assessment is essential.

AIM

To define the place of 99mTc hexakis 2-methoxyisobutylisonitrile (99mTc-MIBI) Single Positron Emission Computed Tomography (SPECT) in monitoring chemotherapy response in recurrent primary brain tumors.

METHODS

In a retrospective analysis, thirty patients were investigated with MIBI SPECT. Imaging was performed 1h after the intravenous injection of 555 MBq of 99mTc-MIBI using a dedicated SPECT system. A MIBI uptake index (UI) was computed as the ratio of counts in the lesion to those in contralateral region. For all patients, we compared changes over time in UI with MRI and clinical data.

RESULTS

The changes in UI agreed well with the clinical and MRI-based assessments in 97% of cases. In 44% of these cases, the scintigraphic response appeared before the MRI response. In instances of treatment failure or rebound, the concordance between scintigraphy and MRI was 52%, and the scintigraphic response appeared before the MRI response in 48% of cases.

CONCLUSION

This study confirms our previous results obtained on a short series of patients with recurrent glioma, concerning the usefulness of MIBI SPECT in prediction of chemotherapy response. Moreover, in cases of tumor progression, we show that MIBI SPECT is an earlier indicator of escape from chemotherapy, an average 4 months before MRI changes.

Molecular imaging-guided gene therapy of gliomas

Gene therapy of patients with glioblastoma using viral and non-viral vectors, which are applied by direct injection or convection-enhanced delivery (CED), appear to be satisfactorily safe. Up to date, only single patients show a significant therapeutic benefit as deduced from single long-term survivors. Non-invasive imaging by PET for the identification of viable target tissue and for assessment of transduction efficiency shall help to identify patients which might benefit from gene therapy, while non-invasive follow-up on treatment responses allows early and dynamic adaptations of treatment options. Therefore, molecular imaging has a critical impact on the development of standardised gene therapy protocols and on efficient and safe vector applications in humans.

Metabolic and molecular imaging in neuro-oncology

Techniques for human brain imaging have undergone rapid developments in recent years. Technological progress has enabled the assessment of many physiological parameters in vivo that are highly relevant for tumour grading, tissue characterisation, definition of the extent and infiltration of tumours, and planning and monitoring of therapy. In this review, we provide a brief overview of advanced MRI and molecular-tracer techniques that have many potential clinical uses. A broad range of techniques, including dynamic MRI, PET, and single photon emission computed tomography, provide measurements of various features of tumour blood flow and microvasculature. Using PET to measure glucose consumption enables visualisation of tumour metabolism, and magnetic resonance spectroscopy techniques provide complementary information on energy metabolism. Changes in protein and DNA synthesis can be assessed through uptake of labelled amino acids and nucleosides. Advanced imaging techniques can be used to assess tumour malignancy, extent, and infiltration, and might provide diagnostic clues to distinguish between lesion types and between recurrent tumour and necrosis. Stereotactic biopsies should be taken from the most malignant part of tumours, which can be identified by changes in microvascular structure and metabolic activity. Functional and metabolic imaging can improve the planning and monitoring of radiation and chemotherapy and contribute to the development of new therapies.

Nuclear Medicine in Pediatric Neurology and Neurosurgery: Epilepsy and Brain Tumors

In pediatric drug-resistant epilepsy, nuclear medicine can provide important additional information in the presurgical localization of the epileptogenic focus. The main modalities used are interictal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and ictal regional cerebral perfusion study with single-photon emission computed tomography (SPECT). Nuclear medicine techniques have a sensitivity of approximately 85% to 90% in the localization of an epileptogenic focus in temporal lobe epilepsy; however, in this clinical setting, they are not always clinically indicated because other techniques (eg, icterictal and ictal electroencephalogram, video telemetry, magnetic resonance imaging [MRI]) may be successful in the identification of the epileptogenic focus. Nuclear medicine is very useful when MRI is negative and/or when electroencephalogram and MRI are discordant. A good technique to identify the epileptogenic focus is especially needed in the setting of extra-temporal lobe epilepsy; however, in this context, identification of the epileptogenic focus is more difficult for all techniques and the sensitivity of the isotope techniques is only 50% to 60%. This review article discusses the clinical value of the different techniques in the clinical context; it also gives practical suggestions on how to acquire good ictal SPECT and interictal FDG-PET scans. Nuclear medicine in pediatric brain tumors can help in differentiating tumor recurrence from post-treatment sequelae, in assessing the response to treatment, in directing biopsy, and in planning therapy. Both PET and SPECT tracers can be used. In this review, we discuss the use of the different tracers available in this still very new, but promising, application of radioisotope techniques.

The role of spinal cord stimulation in the management of patients with brain tumors

High grade gliomas (HGG) have decreased blood flow resulting in hypoxia, limited access by chemotherapeutic agents, and reduced radiation-sensitivity. Spinal cord stimulation (SCS) has been used successfully in the treatment of pain and ischemic syndromes. The present article summarizes our investigations into the effects of SCS in patients with HGG. Before their scheduled radio-chemotherapy, 23 patients with HGG were assessed pre- and post-SCS using several evaluation techniques: (1) transcranial Doppler (TCD) for middle cerebral artery blood flow; (2) color Doppler for common carotid artery blood flow; (3) single photon emission computed tomography (SPECT) for tumor blood flow; (4) polarographic probe technique for tumor pO2 measurement; (5) positron emission tomography (PET) for tumor glucose metabolism. Pre-SCS, the tumors were more ischemic and more hypoxic than healthy tissues. Post-SCS, there was significant: (1) increase in blood flow measured by TCD (> or =18%), color Doppler (> or =61%) and SPECT (15%), (2) increase in oxygenation and decrease (> or =45%) in percentage of hypoxic values <10 mmHg and <5 mmHg, and (3) increase (43%) in glucose metabolism. Our studies show that SCS can modify loco-regional blood flow and oxygen supply, as well as glucose-metabolism in HGG. This suggests that SCS could prove useful as an adjuvant treatment to radio-chemotherapy. These data merit further confirmatory studies.

The role of PET scanning in determining pharmacoselective doses in oncology drug development

Molecular imaging is the most sensitive and specific method for measuring in vivo molecular pathways in man. Its use in oncology has developed significantly over the last 5-10 years. Molecules can be labelled with positron emitting isotopes and the emitted radiation is detected using sensitive positron emission tomography (PET) cameras. It is now possible to measure in vivo and normal tissue pharmacokinetics of anti-cancer drugs and investigate their mechanism of action. Radiolabelling of tracers can be used to measure specific pharmacodynamic endpoints and target identification. Increasing evidence shows how these technologies, when added to early drug development, can rapidly reduce the time for entry into man and early identification of mechanisms of action. With the move towards more segmented markets and identification of specific subgroups, PET's use for noninvasive biomarkers will become in- creasingly important. However, much international effort between academia and industry is required with prioritisation of development of this technology.

Genetic and metabolic predictors of chemosensitivity in oligodendroglial neoplasms

The −1p/−19q genotype predicts chemosensitivity in oligodendroglial neoplasms, but some with intact 1p/19q also respond and not all with 1p/19q loss derive durable benefit from chemotherapy. We have evaluated the predictive and prognostic significance of pretherapy ²⁰¹Tl and ¹⁸F-FDG SPECT and genotype in 38 primary and 10 recurrent oligodendroglial neoplasms following PCV chemotherapy. 1p/19q loss was seen in 8/15 OII, 6/15 OAII, 7/7 OIII, 3/11 OAIII and was associated with response (Fisher-Exact: P=0.000) and prolonged progression-free (log-rank: P=0.002) and overall survival (OS) (log-rank: P=0.0048). Response was unrelated to metabolism, with tumours with high or low metabolism showing response. Increased ¹⁸F-FDG or ²⁰¹Tl uptake predicted shorter progression-free survival (PFS) in the series (log-rank: ²⁰¹Tl P=0.0097, ¹⁸F-FDG P=0.0170) and in cases with or without the −1p/−19q genotype. Elevated metabolism was associated with shorter OS in cases with intact 1p/19q (log-rank: ¹⁸F-FDG P=0.0077; ²⁰¹Tl P=0.0004) and shorter PFS in responders (log-rank: ¹⁸F-FDG P=0.005; ²⁰¹Tl P=0.0132). ²⁰¹Tl uptake and 1p/19q loss were independent predictors of survival in multivariate analysis. In this initial study, ²⁰¹Tl and ¹⁸F-FDG uptake did not predict response to PCV, but may be associated with poor survival following therapy irrespective of genotype. This may be clinically useful warranting further study.

[11C]methionine PET, histopathology, and survival in primary brain tumors and recurrence

BACKGROUND AND PURPOSE

[(11)C]Methionine (MET) PET imaging is a sensitive technique for visualizing primary brain tumors and recurrence/progression after therapy. The aim of this study was to evaluate the relationship between the uptake of MET and histopathologic grading and to investigate the prognostic value of the tracer, in both settings.

METHODS

Cerebral uptake of MET was determined in 52 patients: in 26 patients for primary staging (group A) and 26 patients with suspected brain tumor recurrence/progression after therapy (group B). Semiquantitative methionine uptake indices (UI) defined by the tumor (maximum)-to-background ratio was correlated with tumor grade and final outcome.

RESULTS

Overall median survival was 34.9 months. MET showed pathologically increased uptake in 41 of 52 scans. Although a weak linear correlation between MET uptake and grading was observed (R = 0.38, P = .028), analysis of variance showed no significant differences in MET UI between tumor grades for either group A or B. Benign and grade I lesions showed significant difference in MET uptake in comparison with higher grade lesions (P = .006). Using Kaplan-Meier survival analysis, no thresholds could be found at which MET was predictive for survival. Proportional hazard regression showed that only WHO grading class (low versus high) was predictive of survival (P = .015).

CONCLUSION

Interindividual MET uptake variability does not allow noninvasive grading on an individual patient basis. Moreover, there is no significant prognostic value in studying maximal methionine UI in brain tumors. The clinical use of MET should therefore be primarily focused on questions such as detection of recurrence, biopsy guidance, and radiation therapy target volume delineation.

Early change in glucose metabolic rate measured using FDG-PET in patients with high-grade glioma predicts response to temozolomide but not temozolomide plus radiotherapy

PURPOSE

To compare the ability of positron emission tomography (PET) to predict response to temozolomide vs. temozolomide plus radiotherapy.

METHODS AND MATERIALS

Nineteen patients with high-grade glioma (HGG) were studied. Patients with recurrent glioma received temozolomide 75 mg/m2 daily for 7 weeks (n=8). Newly diagnosed patients received temozolomide 75 mg/m2 daily plus radiotherapy 60 Gy/30 fractions over 6 weeks, followed by six cycles of adjuvant temozolomide 200 mg/m2/day (Days 1-5 q28) starting 1 month after radiotherapy (n=11). [18F]Fluorodeoxyglucose ([18F]FDG) PET scan and magnetic resonance imaging (MRI) were performed at baseline, and 7 and 19 weeks after initiation of temozolomide administration. Changes in glucose metabolic rate (MRGlu) and MRI response were correlated with patient survival.

RESULTS

In the temozolomide-alone group, patients who survived>26 vs. <or=26 weeks showed a greater reduction in MRGlu measured at 7 weeks with median changes of -34% and -4%, respectively (p=0.02). PET responders, defined as a reduction in MRGlu>or=25%, survived longer than nonresponders with mean survival times of 75 weeks (95% CI, 34-115 vs. 20 weeks (95% CI, 14-26) (p=0.0067). In the small group of patients studied, there was no relationship between MRI response and survival (p=0.52). For patients receiving temozolomide plus radiotherapy, there was no difference in survival between PET responders and nonresponders (p=0.32).

CONCLUSIONS

Early changes in MRGlu predict response to temozolomide, but not temozolomide plus radiotherapy.

A prospective PET study of patients with glioblastoma multiforme

OBJECTIVE

To study the post-surgical metabolic and structural cerebral changes in patients with glioblastoma multiforme (GBM).

MATERIALS AND METHODS

We examined ten patients prospectively with newly diagnosed GBM. All patients were primarily treated with surgery, followed by chemotherapy (carmustine, cisplatine and etoposide) and radiotherapy. Positron emission tomography (PET) was used to measure tumor- and cerebral metabolism. CT or MRI was used to estimate tumor volume by measurements of tumor area.

RESULTS

Tumor metabolism was not increased during chemotherapy (P = 0.71), but increased during radiotherapy (P = 0.01). CT/MRI showed similar results with no increase in tumor area during chemotherapy (P = 0.33) but increase during radiotherapy (P = 0.002). During the entire study, tumor metabolism and area increased evenly (P = 0.01).

CONCLUSIONS

Our study did not show a gain of PET compared with structural imaging in the prospective evaluation of GBM. We found a difference in metabolic increase and tumor growth between the two treatment regimens, although this finding has limited relevance due to the design of the study.

Modification of glucose metabolism in brain tumors by using cervical spinal cord stimulation

OBJECT

In previous studies the authors have shown potential increases in locoregional blood flow and oxygenation in tumors by using electrical cervical spinal cord stimulation (SCS). In the present report they demonstrate the effect of cervical SCS on brain tumor metabolism, as assessed using [18F]fluorodeoxyglucose-positron emission tomography (FDG-PET).

METHODS

Cervical devices were inserted in 11 patients who had high-grade gliomas, six of which had recurred. While the SCS device was deactivated, each patient underwent an initial FDG-PET study to clarify the clinical status. A second FDG-PET study was performed later the same day while the stimulation device was activated to determine the effect of cervical SCS on glucose metabolism. All 11 patients were invaluable for this PET study. Basal glucose metabolism was higher in the tumor than in the peritumoral areas (p = 0.048). There was a significant increase in glucose uptake during cervical SCS in both the tumor (p = 0.035) and the peritumoral (p = 0.001) areas, with measured increases of 43 and 38%, respectively. The estimated potential maximal residual activity of the first FDG dose's contribution to the activity on the second scan was 18.5 +/- 1% or less.

CONCLUSIONS

This PET study is the first in which is described the effect of cervical SCS on glucose metabolism in brain tumors and supports previous study data indicating a modification of locoregional blood flow and oxygenation by cervical SCS. These results open up new approaches to modifying the effect of radiochemotherapy in the treatment of malignant brain tumors.

Imaging vascular physiology to monitor cancer treatment

The primary physiological function of the vasculature is to support perfusion, the nutritive flow of blood through the tissues. Vascular physiology can be studied non-invasively in human subjects using imaging methods such as positron emission tomography (PET), magnetic resonance imaging (MRI), X-ray computed tomography (CT), and Doppler ultrasound (DU). We describe the physiological rationale for imaging vascular physiology with these methods. We review the published data on repeatability. We review the literature on 'before-and-after' studies using these methods to monitor response to treatment in human subjects, in five broad clinical settings: (1) antiangiogenic agents, (2) vascular disruptive agents, (3) conventional cytotoxic drugs, (4) radiation treatment, and (5) agents affecting drug delivery. We argue that imaging of vascular physiology offers an attractive 'functional endpoint' for clinical trials of anticancer treatment. More conventional measures of tumour response, such as size criteria and the uptake of fluorodeoxyglucose, may be insensitive to therapeutically important changes in vascular function.

Use of 11C-methionine PET to monitor the effects of temozolomide chemotherapy in malignant gliomas

PURPOSE

The purpose of this study was to monitor the metabolic effects of temozolomide (TMZ) chemotherapy in malignant gliomas by means of repeated positron emission tomography (PET) with [(11)C]methionine (MET).

METHODS

Fifteen patients with histologically proven malignant glioma were treated by TMZ chemotherapy. MET-PET studies were performed before and after the third cycle of TMZ chemotherapy in all patients, and in 12 patients also after the sixth cycle. Gadolinium-enhanced MRI studies were performed in 12 patients before the first and after the sixth cycle. Clinical status was assessed by the modified Rankin scale. Long-term outcome was assessed by calculating the time to progression (TTP) in months.

RESULTS

Decline in MET uptake during therapy corresponded to a stable clinical status. The median TTP was significantly longer in patients with decline in MET uptake than in those with increasing MET uptake (23 vs 3.5 months; p=0.01, log rank test). There was no significant correlation between change in MET uptake and change in contrast enhancement during treatment for all patients.

CONCLUSION

The present data demonstrate that clinical stability, which is often achieved under TMZ chemotherapy of malignant glioma, corresponds to a decline in or stability of tumour amino acid metabolism. Tumour responses can already be demonstrated with MET-PET after three cycles of chemotherapy, and absence of progression at that time indicates a high probability of further stability during the next three cycles. A reduction in MET uptake during TMZ treatment predicts a favourable clinical outcome. Molecular imaging of amino acid uptake by MET-PET offers a new method of measurement of the biological activity of recurrent glioma.

Imaging in neurooncology

Imaging in patients with brain tumors aims toward the determination of the localization, extend, type, and malignancy of the tumor. Imaging is being used for primary diagnosis, planning of treatment including placement of stereotaxic biopsy, resection, radiation, guided application of experimental therapeutics, and delineation of tumor from functionally important neuronal tissue. After treatment, imaging is being used to quantify the treatment response and the extent of residual tumor. At follow-up, imaging helps to determine tumor progression and to differentiate recurrent tumor growth from treatment-induced tissue changes, such as radiation necrosis. A variety of complementary imaging methods are currently being used to obtain all the information necessary to achieve the above mentioned goals. Computed tomography and magnetic resonance imaging (MRI) reveal mostly anatomical information on the tumor, whereas magnetic resonance spectroscopy and positron emission tomography (PET) give important information on the metabolic state and molecular events within the tumor. Functional MRI and functional PET, in combination with electrophysiological methods like transcranial magnetic stimulation, are being used to delineate functionally important neuronal tissue, which has to be preserved from treatment-induced damage, as well as to gather information on tumor-induced brain plasticity. In addition, optical imaging devices have been implemented in the past few years for the development of new therapeutics, especially in experimental glioma models. In summary, imaging in patients with brain tumors plays a central role in the management of the disease and in the development of improved imaging-guided therapies.

2-[11C]Thymidine Positron Emission Tomography Reproducibility in Humans

PURPOSE

To evaluate the reproducibility of 2-[11C]thymidine positron emission tomography (PET) scanning in patients with advanced intra-abdominal malignancies.

PATIENTS AND METHODS

The reproducibility of 2-[11C]thymidine PET was studied by comparing interpatient and intrapatient variability (coefficient of variability, COV) of both blood and tissue data. Arterial plasma metabolite levels were measured using on-line sampling and high-pressure liquid chromatography. 2-[11C]Thymidine retention in tissue was measured as the standardized uptake value at the end of the scan (SUV(end)), the area under the time-activity curve (AUC(0-1 hour)), and the fractional retention of thymidine (FRT). A group of seven patients were scanned 1 week apart with no intervening anticancer therapy.

RESULTS

There was interpatient variability in the levels of 2-[11C]thymidine and its main metabolite, 11CO2, in plasma. Variability in 2-[11C]thymidine PET data was greater between (COV: SUV(end) = 38%, AUC(0-1 hour) = 32%, FRT = 47%) than within (COV: SUV(end) = 8%, AUC(0-1 hour) = 2%, FRT = 9%) patients. There was a borderline significant difference between the paired tumor data for SUV(end) (P = 0.041), but not for AUC(0-1 hour) (P = 0.81) or FRT (P = 0.90). There was a good correlation between paired data for SUV(end) (r = 0.98), AUC(0-1 hour) (r = 0.99), and FRT (r = 0.95).

CONCLUSIONS

This is the first report showing that 2-[11C]thymidine PET scanning is reproducible in humans. Repeat scanning of tumor proliferation using 2-[11C]thymidine PET is feasible to perform in human intra-abdominal malignancies and should aid the future rapid assessment of antiproliferative tumor agents.