Advanced MR Techniques for Preoperative Glioma Characterization: Part 1

Preoperative clinical magnetic resonance imaging (MRI) protocols for gliomas, brain tumors with dismal outcomes due to their infiltrative properties, still rely on conventional structural MRI, which does not deliver information on tumor genotype and is limited in the delineation of diffuse gliomas. The GliMR COST action wants to raise awareness about the state of the art of advanced MRI techniques in gliomas and their possible clinical translation or lack thereof. This review describes current methods, limits, and applications of advanced MRI for the preoperative assessment of glioma, summarizing the level of clinical validation of different techniques. In this first part, we discuss dynamic susceptibility contrast and dynamic contrast-enhanced MRI, arterial spin labeling, diffusion-weighted MRI, vessel imaging, and magnetic resonance fingerprinting. The second part of this review addresses magnetic resonance spectroscopy, chemical exchange saturation transfer, susceptibility-weighted imaging, MRI-PET, MR elastography, and MR-based radiomics applications. Evidence Level: 3 Technical Efficacy: Stage 2.

BIOM-44. MAGNETIC RESONANCE IMAGING MAPPING OF BRAIN TUMOR BURDEN TO EVALUATE RESPONSE TO PULSED LOW-DOSE-RATE RADIOTHERAPY FOLLOWING RESECTION OF GLIOBLASTOMA MULTIFORME: A 4-PATIENT CASE SERIES

BACKGROUND

Pulsed low-dose-rate radiotherapy (pLDR) is an accepted reirradiation technique for recurrent glioma, but its upfront use, concurrent with temozolomide (TMZ) following resection of high-grade glioma is currently under investigation. Evaluating the response to upfront radiation can be challenging and there is limited data on expected rates of pseudoprogression with pLDR. Standard magnetic resonance imaging (MRI) has limitations in differentiating pseudoprogression from tumor progression, sometimes necessitating surgery for pathologic confirmation. Advanced MRI can be used to create fractional tumor burden (FTB) maps that spatially distinguish active tumor from treatment-related effect (pseudoprogression), perhaps providing a more reliable imaging biomarker in the absence of additional surgery.

METHODS

We performed a retrospective chart review to report the responses of four patients with glioblastoma to upfront pLDR and TMZ following resection. Each patient received advanced surveillance MRI and redo surgery. Tumor pathology included IDH-wild type (n = 4) and O6-methylguanine-DNA methyltransferase (MGMT) methylated (n = 1) tumors.

RESULTS

The median age of patients was 57.5 years (range 55-60 years) and all were male. One patient experienced mortality and another was transitioned to hospice. In all four cases, there were concerns of tumor progression in postcontrast MRI. Pathologic diagnosis revealed either treatment effect (n = 2) or tumor (n = 2). FTB maps were predominantly indicative of lesion volumes being comprised of treatment effect (n = 3) and tumor (n = 1). From the three FTB maps in the former category, the median fraction of the enhancing tumor volume comprised of vascular tumor was 6.4% (range 1.8-6.8%).

CONCLUSION

This case series provides insight into response to upfront pLDR and TMZ following resection of glioblastoma and demonstrates the capacity for FTB mapping to spatially distinguish tumor progression from treatment effect in this patient population.

NIMG-12. DSC-MRI PERFUSION IMAGING IN UNTREATED BRAIN METASTASES USING THE CONSENSUS ACQUISITION PROTOCOL: A MULTI-SITE BENCHMARK STUDY

INTRODUCTION

DSC-MRI perfusion methods are commonly used to evaluate both primary and metastatic brain cancer with the creation of maps of relative cerebral blood volume (rCBV). Recently, guidelines were established to ensure a standard DSC-MRI acquisition protocol that reduces inter-site variability. The purpose of this study was to initiate the determination of rCBV benchmark values using the DSC-MRI consensus protocol in treatment-naïve brain metastases.

METHODS

Patients from three sites with treatment-naïve, contrast-enhancing brain metastases on MRI were considered for inclusion in this retrospective study. The MRIs included pre- and post-contrast T1w(T1+C) images obtained after administration of gadolinium-based contrast agent (GBCA) (0.1 mmol/kg), which serves as the recommended preload for the DSC-MRI data collection. A 2nd GBCA dose (0.1 mmol/kg) was administered 40-60sec after the collection of baseline GRE-EPI images using recommended settings (FA=60o, TE/TR=30ms/1100-1250ms) for 120s. Calibrated pre/post T1w difference maps (dT1) were used for delineation of enhancing lesion, and standardized (calibrated) rCBV (sRCBV) created. Mean sRCBV for metastases were compared to normal appearing white matter (NAWM) and treatment-naive glioblastoma (GBM) from a previous study. Pairwise comparisons were performed using the Mann-Whitney nonparametric test.

RESULTS

N=52 patients with primary histology of lung (n=27); breast (n=6); skin (n=7); gastrointestinal (GI: n=3) and genitourinary (GU: n=9) cancers were included in comparison to GBM (n=31). The mean sRCBV for all metastases (1.77+/-1.05) is significantly lower (p=0.0003) than for GBM (2.67+/-1.34) but with both statistically greater (p< 0.0001) than NAWM (0.706+/-0.163). Individually, lung (1.47+/- 0.61), breast (2.275+/-0.87), skin (2.10+/-1.22), GI (1.91+/- 0.64) and GU (2.01+/-0.63) mean sRCBV are statistically greater than for NAWM.

CONCLUSION

Using the consensus DSC-MRI acquisition protocol confirms use of sRCBV to identify biologically active, treatment-naive brain metastases setting benchmark values for future applications.

EXTH-16. THE ORAL IRON-MIMETIC GALLIUM MALTOLATE SUPPRESSES TREATMENT-RESISTANT GLIOBLASTOMA – IN VIVO VALIDATION

BACKGROUND

We previously reported on our in vitro and in vivo studies using the metallocompound gallium maltolate (GaM) to target glioblastoma (GBM). We demonstrated a profound cytotoxic effect in vitrov and in vivo. Additionally, our preliminary in vivo data suggested a substantial inhibitory effect on tumor growth, as well as a significant extension of disease-specific survival (OS). Here, we further validate the inhibitory effects of GaM in vivo.

METHODS

In vitro irradiated adult GBM U87-MG cells were stereotactically implanted into the right striatum of male and female athymic rats. Advanced MR imaging at 9.4T was carried out weekly starting two weeks after implantation. Daily oral GaM (50 mg/kg) or vehicle were provided on tumor confirmation. Longitudinal advanced MRI parameters were processed for enhancing tumor ROIs in OsiriX 8.5.1 (lite) with Imaging Biometrics Software (Imaging Biometrics LLC,). Statistical analyses included Kaplan-Meier survival plots, linear mixed model (LMM) comparisons, and t-statistic for slopes comparison (as indicator of tumor growth rate).

RESULTS

Median OS for the male pilot cohort (5 control, 5 GaM) was 28 and 51 days, respectively; 31 and 59 days for the male replication cohort (1 control, 3 GaM); 37 and 48 days for the female replication cohort (6 control, 7 GaM). GaM-treated xenograft tumors grew significantly slower than control tumors with sex and time dependent growth rates. No significant differences were seen between male and female cohorts in both control and treatment groups at all timepoints. Hence, subsequent analyses were performed on pooled data. Median OS was 30.5 days and 48 days for control and GaM groups, respectively (p < .001). A strong correlation between treatment and survival (Χ2 = 6.238187; p = .0125) and tumor growth suppression (LMM; p < .0001) was evident.

CONCLUSION

We have successfully validated the inhibitory effects of GaM on GBM growth in vivo.

NIMG-44. DSC-MRI FRACTIONAL TUMOR BURDEN VOLUME PREDICTS OVERALL SURVIVAL IN UNMETHYLATED NEWLY DIAGNOSED HIGH GRADE GLIOMA

OBJECTIVE

Image maps of Fractional Tumor Burden (FTB), derived from dynamic susceptibility contrast (DSC) perfusion MRI, provide clinically meaningful information for glioma treatment management. The goal of this study was to determine if presurgical FTB is predictive of overall survival (OS) in high-grade glioma (HGG) classified according to WHO 2016 criteria.

METHODS

Standardized relative cerebral blood volume (sRCBV) maps were created and co-registered with T1+C images using Horos (Version 4.0.0) and Imaging Biometrics software (Version 21.05) (Elm Grove, WI). Enhancing tumor volumes were determined from calibrated pre/post T1 difference (dT1) maps. Tissue-validated sRCBV thresholds were used to create FTB class maps within enhancing lesion with red regions (sRCBV > 1.556) indicating a high probability of vascular tumor, blue regions (sRCBV< 1.0) indicating avascular (non-tumor) tissue and yellow representing tissue with a lower probability of vascular tumor. FTB volume fractions (FTBv) for all vascular tumor (sRCBV >1.0) or the most vascular tumor (sRCBV > 1.566) were determined. Subjects were separated by MGMT methylation status. GraphPad Prism statistical software (Version 9.3.1) was used for Kaplan Meier survival analysis at 12 and 24 months with patients stratified by median FTBv.

RESULTS

Forty-one subjects (23 males, 18 females) with a median age of 59.45 years were included. Median 12-month and overall survival of unmethylated groups stratified by FTBv (rCBV > 1.0) of 8.33cc was 10.69 and 15.35 months (p=.0453; p=.0317). Unmethylated subjects stratified with FTBv (rCBV > 1.566) of 7.13cc had a median survival of 10.69 and 15.20 with short- and long-term survival distinguished at 12 months (p=0.0033), 24 months (p=0.0002) and overall (p=0.0002). No significant difference in survival was found between the methylated subgroups with FTBv (rCBV > 1.0) or FTBv (rCBV > 1.566) stratified analyses.

CONCLUSION

These results demonstrate that pre-surgical FTBv is predictive of OS in newly diagnosed unmethylated high-grade glioma.

NIMG-36. MR PERFUSION IS A BETTER PREDICTOR OF TUMOR RECURRENCE AND TREATMENT RESPONSE THAN STANDARD MRI IN SOME OLIGODENDROGLIOMA PATIENTS

Dynamic susceptibility contrast (DSC) perfusion MRI (pMRI) has proven efficacy in the evaluation of glioma grade, progression and response to therapy. While not currently integrated within RANO (Response Assessment in Neuro Oncology) criteria, pMRI is often assessed alongside standard imaging of astrocytic glioma. In contrast, evaluation of pMRI in oligodendroglioma, has been less well-studied despite its potential to evaluate the comparatively greater vascularity of its “chicken-wire” capillary networks. Moreover, standard imaging to evaluate oligodendroglioma course can be confounded by slow-growing enhancement that does not meet RANO threshold for progression, or disease control despite low or absent radiographic response, and radiation-induced leukoencephalopathy resembling hyperintense changes on T2w and FLAIR imaging. Consequently, there is a clinical need to understand the potential role of pMRI in the evaluation of oligodendroglioma. As an initial step, we present here a case study of a patient with oligodendroglioma for which pMRI bested standard imaging in evaluation throughout radiographic disease surveillance. A 32 y/o gentleman with oligodendroglioma WHO grade 2 (IDH mutant, 1p19q codeletion) completed standard treatment, including surgical resection, irradiation, and chemotherapy. During surveillance imaging, a region of hyperperfusion on pMRI developed. However, since standard imaging was stable, RANO criteria was not met and observation was continued without intervention. Subsequent standard imaging demonstrated clear radiographic progression, reflecting the radiographic findings of pMRI but with delayed manifestation. Systemic chemotherapy was resumed with successively stable standard MR imaging. In contrast, the previous region of hyperperfusion improved over serial pMRI, and more consistently mirrored the patient’s clinical course. This case illustrates the timely radiographic importance of pMRI in assessing stability of tumor as well as treatment response. Considerations for the inclusion of pMRI within RANO criteria should be explored further.

NIMG-54. LOW FRACTIONAL TUMOR BURDEN VOLUME OBTAINED FROM PERFUSION MRI REVEALS SIGNIFICANT SURVIVAL BENEFIT IN MGMT UNMETHYLATED GLIOBLASTOMA

INTRODUCTION

Standard imaging remains inadequate for the determination of GBM response within the first 3 months following upfront chemoradiation therapy (CRT). Since advanced diffusion and DSC perfusion (pMRI) MRI are currently not included in RANO criteria, greater reliance is placed on MGMT methylation status, with methylated tumors demonstrating survival benefit. While pMRI has demonstrated usefulness following CRT, a newer pMRI biomarker termed Fractional Tumor Burden (FTB) provides both spatial and quantifiable information. The purpose of this study was to evaluate whether advanced MRI including FTB informs a survival benefit beyond MGMT promoter methylation status in newly diagnosed GBM (nGBM).

METHODS

Consented subjects with nGBM, and known MGMT status who completed standard upfront therapy and had MRI within 6 weeks of CRT completion, were included. Known IDH-mutant tumors were excluded. DSC was collected with the consensus protocol and leakage-corrected relative cerebral blood volume (rCBV) generated. Apparent diffusion coefficient (ADC) was calculated from diffusion MRI (b-value: 0,1000 s/mm2). FTB-defined tumor volumes were calculated from rCBV and delta T1w enhancement. Kaplan-Meier 24-month overall survival (OS) was evaluated for MGMT status and stratified by cohort mean for rCBV (1.3 a.u.) and ADC (1300 x10-6mm2/s), and empirically for FTB (5 ml) (significance: P >.05).

RESULTS

A total of 43 subjects were included (male/female=21/22; age=57(23-74)). MRI was acquired an average of 29 (12-42) days following CRT. Significant OS differences were confirmed for MGMT methylation (OS=19.08 vs. 10.18 mo; P=.0129). No significant survival differences were found (P >.05) when stratified by rCBV or ADC. While FTB did not provide further OS distinctions in methylated GBM, those with unmethylated MGMT had significant OS benefit when FTB volume was < 5 ml (OS=16.15 vs 8.39 mo; P=.0054).

CONCLUSION

FTB further informs OS in MGMT promoter unmethylated GBM, where those with lower volume had survival approaching that of methylated subjects.

TMOD-25. IN VIVO MODEL OF TREATMENT-RESISTANT GLIOBLASTOMA HIGHLIGHTS SEX DIFFERENCES IN SURVIVAL

BACKGROUND

Sex differences independent from acute hormone action are evident in the incidence and tumorigenesis of several cancers, including glioblastoma (GBM). Malignant brain tumors with mesenchymal, proneural, and neural GBM subtypes occur twice as frequently in males than in females, implying a molecular basis for the sex disparities observed. Accordingly, response to therapy and overall survival, may also differ between male and female GBM patients. Further elucidation of these differences would benefit from a robust preclinical testing system, such as the one described here.

METHODS

Adult (U87-MG) GBM cells were exposed to a total radiation dose of 10 Gy, effecting an epithelial to mesenchymal transition. The resultant irradiated U87-10Gy cells were tested for cell viability and allowed to reach confluence prior to stereotactic implantation into the right striatum of male and female athymic rats. In vivo advanced MR imaging at 9.4T was carried out weekly starting two weeks after implantation. Advanced MRI parameters were processed for enhancing tumor ROIs in OsiriX 8.5.1 (lite) with Imaging Biometrics™ Software (IQ-AI, Ltd.).

RESULTS

Tumor take was 90% in males and 60% in females, indicating an ‘incidence’ ratio of 1.5. Overall survival was significantly higher in females (median = 48, range = 40-72 days) than in males (median = 28, range = 27-30 days) (p = 0.024). Immunohistochemical and imaging analyses are pending and will be discussed.

CONCLUSION

The outcomes noted in this pilot study mirror incidence and survival outcomes noted in GBM patients undergoing standard care. Our model of treatment-resistant glioma provides a robust testing system to study underlying sex differences in GBM biology and treatment response in parallel analyses of male and female data.

Magnolia extract is effective for the chemoprevention of oral cancer through its ability to inhibit mitochondrial respiration at complex I

Background

Magnolia extract (ME) is known to inhibit cancer growth and metastasis in several cell types in vitro and in animal models. However, there is no detailed study on the preventive efficacy of ME for oral cancer, and the key components in ME and their exact mechanisms of action are not clear. The overall goal of this study is to characterize ME preclinically as a potent oral cancer chemopreventive agent and to determine the key components and their molecular mechanism(s) that underlie its chemopreventive efficacy.

Methods

The antitumor efficacy of ME in oral cancer was investigated in a 4-nitroquinoline-1-oxide (4NQO)-induced mouse model and in two oral cancer orthotopic models. The effects of ME on mitochondrial electron transport chain activity and ROS production in mouse oral tumors was also investigated.

Results

ME did not cause detectable side effects indicating that it is a promising and safe chemopreventive agent for oral cancer. Three major key active compounds in ME (honokiol, magnolol and 4-O-methylhonokiol) contribute to its chemopreventive effects. ME inhibits mitochondrial respiration at complex I of the electron transport chain, oxidizes peroxiredoxins, activates AMPK, and inhibits STAT3 phosphorylation, resulting in inhibition of the growth and proliferation of oral cancer cells.

Conclusion

Our data using highly relevant preclinical oral cancer models, which share histopathological features seen in human oral carcinogenesis, suggest a novel signaling and regulatory role for mitochondria-generated superoxide and hydrogen peroxide in suppressing oral cancer cell proliferation, progression, and metastasis.

NIMG-28. VALIDATION OF SINGLE-DOSE DSC-MRI PROTOCOLS FOR ROBUST PERFUSION ASSESSMENT IN BRAIN TUMORS

Dynamic susceptibility contrast (DSC) MRI measures of brain tumor cerebral blood volume (CBV) are able to predict grade, overall survival and response to treatment. Wide-spread acceptance of DSC-MRI has been challenged by the need to balance contrast agent dose and CBV accuracy. The goal of this study was to identify and validate single-dose, BTIP compliant, DSC-MRI protocols. Using a validated, patient-based DRO, we evaluated CBV accuracy across a range of acquisition parameters (field strength, TR, TE, flip angle, multi-echo acquisitions, dosing protocols) and post-processing steps. To validate the optimal protocols, we next collected DSC-MRI data following ASFNR’s recommended “double – dose” approach, where a single-dose preload (to minimize T1 effects) is given prior to a second bolus injection (for DSC-MRI data acquisition). The single-dose DSC-MRI data was collected during the preload bolus injection. Consistency of the derived CBV data, visual agreement and data characteristics (e.g. CNR) was statistically evaluated. When using a single-dose and routine single-echo pulse sequence, the DRO analysis found that a low flip angle (LFA = 30o) and 30ms TE provided the highest CBV accuracy (concordance correlation coefficient (CCC) = 0.92) and precision (coefficient of variation (CV) = 8.2%)). For comparison, the maximum accuracy found with the DRO utilizes a double-dose injection protocol and yielded a CCC of 0.98 and CV of 6.8%. Single-dose, multi-echo acquisitions provided higher accuracy than the LFA data and matched that found with the double-dose approach. In patients (data collection ongoing), the agreement between single-dose LFA (n > 40) or multi-echo (n > 40) based CBV values and the reference double-dose approach was very high (CCC > 0.94) and were statistically equivalent. Optimized single-dose DSC-MRI protocols provide highly accurate CBV data, use lower doses of contrast agent, and simplify scan procedures, indicating their potential for robust use in clinical practice and trials.

The Impact of Arterial Input Function Determination Variations on Prostate Dynamic Contrast-Enhanced Magnetic Resonance Imaging Pharmacokinetic Modeling: A Multicenter Data Analysis Challenge, Part II

This multicenter study evaluated the effect of variations in arterial input function (AIF) determination on pharmacokinetic (PK) analysis of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) data using the shutter-speed model (SSM). Data acquired from eleven prostate cancer patients were shared among nine centers. Each center used a site-specific method to measure the individual AIF from each data set and submitted the results to the managing center. These AIFs, their reference tissue-adjusted variants, and a literature population-averaged AIF, were used by the managing center to perform SSM PK analysis to estimate K^trans (volume transfer rate constant), v_e (extravascular, extracellular volume fraction), k_ep (efflux rate constant), and τ_i (mean intracellular water lifetime). All other variables, including the definition of the tumor region of interest and precontrast T₁ values, were kept the same to evaluate parameter variations caused by variations in only the AIF. Considerable PK parameter variations were observed with within-subject coefficient of variation (wCV) values of 0.58, 0.27, 0.42, and 0.24 for K^trans, v_e, k_ep, and τ_i, respectively, using the unadjusted AIFs. Use of the reference tissue-adjusted AIFs reduced variations in K^trans and v_e (wCV = 0.50 and 0.10, respectively), but had smaller effects on k_ep and τ_i (wCV = 0.39 and 0.22, respectively). k_ep is less sensitive to AIF variation than K^trans, suggesting it may be a more robust imaging biomarker of prostate microvasculature. With low sensitivity to AIF uncertainty, the SSM-unique τ_i parameter may have advantages over the conventional PK parameters in a longitudinal study.

ACRIN 6684: Multicenter, phase II assessment of tumor hypoxia in newly diagnosed glioblastoma using magnetic resonance spectroscopy

A multi-center imaging trial by the American College of Radiology Imaging Network (ACRIN) "A Multicenter, phase II assessment of tumor hypoxia in glioblastoma using 18F Fluoromisonidazole (FMISO) with PET and MRI (ACRIN 6684)", was conducted to assess hypoxia in patients with glioblastoma (GBM). The aims of this study were to support the role of proton magnetic resonance spectroscopic imaging (1H MRSI) as a prognostic marker for brain tumor patients in multi-center clinical trials. Seventeen participants from four sites had analyzable 3D MRSI datasets acquired on Philips, GE or Siemens scanners at either 1.5T or 3T. MRSI data were analyzed using LCModel to quantify metabolites N-acetylaspartate (NAA), creatine (Cr), choline (Cho), and lactate (Lac). Receiver operating characteristic curves for NAA/Cho, Cho/Cr, lactate/Cr, and lactate/NAA were constructed for overall survival at 1-year (OS-1) and 6-month progression free survival (PFS-6). The OS-1 for the 17 evaluable patients was 59% (10/17). Receiver operating characteristic analyses found the NAA/Cho in tumor (AUC = 0.83, 95% CI: 0.61 to 1.00) and in peritumoral regions (AUC = 0.95, 95% CI 0.85 to 1.00) were predictive for survival at 1 year. PFS-6 was 65% (11/17). Neither NAA/Cho nor Cho/Cr was effective in predicting 6-month progression free survival. Lac/Cr in tumor was a significant negative predictor of PFS-6, indicating that higher lactate/Cr levels are associated with poorer outcome. (AUC = 0.79, 95% CI: 0.54 to 1.00). In conclusion, despite the small sample size in the setting of a multi-center trial comprising different vendors, field strengths, and varying levels of expertise at data acquisition, MRS markers NAA/Cho, Lac/Cr and Lac/NAA predicted overall survival at 1 year and 6-month progression free survival. This study validates that MRSI may be useful in evaluating the prognosis in glioblastoma and should be considered for incorporating into multi-center clinical trials.

Toward uniform implementation of parametric map Digital Imaging and Communication in Medicine standard in multisite quantitative diffusion imaging studies

This paper reports on results of a multisite collaborative project launched by the MRI subgroup of Quantitative Imaging Network to assess current capability and provide future guidelines for generating a standard parametric diffusion map Digital Imaging and Communication in Medicine (DICOM) in clinical trials that utilize quantitative diffusion-weighted imaging (DWI). Participating sites used a multivendor DWI DICOM dataset of a single phantom to generate parametric maps (PMs) of the apparent diffusion coefficient (ADC) based on two models. The results were evaluated for numerical consistency among models and true phantom ADC values, as well as for consistency of metadata with attributes required by the DICOM standards. This analysis identified missing metadata descriptive of the sources for detected numerical discrepancies among ADC models. Instead of the DICOM PM object, all sites stored ADC maps as DICOM MR objects, generally lacking designated attributes and coded terms for quantitative DWI modeling. Source-image reference, model parameters, ADC units and scale, deemed important for numerical consistency, were either missing or stored using nonstandard conventions. Guided by the identified limitations, the DICOM PM standard has been amended to include coded terms for the relevant diffusion models. Open-source software has been developed to support conversion of site-specific formats into the standard representation.

The Impact of Arterial Input Function Determination Variations on Prostate Dynamic Contrast-Enhanced Magnetic Resonance Imaging Pharmacokinetic Modeling: A Multicenter Data Analysis Challenge

Dynamic contrast-enhanced MRI (DCE-MRI) has been widely used in tumor detection and therapy response evaluation. Pharmacokinetic analysis of DCE-MRI time-course data allows estimation of quantitative imaging biomarkers such as K^trans(rate constant for plasma/interstitium contrast reagent (CR) transfer) and v_e (extravascular and extracellular volume fraction). However, the use of quantitative DCE-MRI in clinical prostate imaging islimited, with uncertainty in arterial input function (AIF, i.e., the time rate of change of the concentration of CR in the blood plasma) determination being one of the primary reasons. In this multicenter data analysis challenge to assess the effects of variations in AIF quantification on estimation of DCE-MRI parameters, prostate DCE-MRI data acquired at one center from 11 prostate cancer patients were shared among nine centers. Each center used its site-specific method to determine the individual AIF from each data set and submitted the results to the managing center. Along with a literature population averaged AIF, these AIFs and their reference-tissue-adjusted variants were used by the managing center to perform pharmacokinetic analysis of the DCE-MRI data sets using the Tofts model (TM). All other variables including tumor region of interest (ROI) definition and pre-contrast T₁ were kept the same to evaluate parameter variations caused by AIF variations only. Considerable pharmacokinetic parameter variations were observed with the within-subject coefficient of variation (wCV) of K^trans obtained with unadjusted AIFs as high as 0.74. AIF-caused variations were larger in K^trans than v_e and both were reduced when reference-tissue-adjusted AIFs were used. The parameter variations were largely systematic, resulting in nearly unchanged parametric map patterns. The CR intravasation rate constant, k_ep (= K^trans/v_e), was less sensitive to AIF variation than K^trans (wCV for unadjusted AIFs: 0.45 for k_epvs. 0.74 for K^trans), suggesting that it might be a more robust imaging biomarker of prostate microvasculature than K^trans.

Abstract 5606: Gallium maltolate inhibits brain tumor volume and blood volume in xenograft model

Purpose: There are limited treatment options for glioblastomas (GBM). Tumor cells have a high requirement for iron; the latter is taken up by cells through transferrin receptor-mediated endocytosis of transferrin-iron. These receptors are highly expressed on GBM cells, which makes them an attractive target for transferrin receptor-directed therapies. Gallium is a group IIIa metal that can function as an iron mimetic by avidly binding to transferrin and incorporating into cells through the transferrin receptor. No studies have been performed to determine the efficacy of gallium-based therapies in brain tumors. Consequently, the goal of this study was to evaluate gallium maltolate in the treatment of a U87 xenograft brain tumor model. Methods: Athymc rats bearing U87 human grade IV astrocytoma cells were studied. Gallium maltolate (50 mg/kg/day, n=5) or saline (n=3) was given intravenously. via an alzet mini pump in the jugular vein. Magnetic resonance imaging (MRI) was performed on days 8 and 18 on a Bruker 9.4 T scanner. Enhancing tumor volumes were determined from the post-contrast T1w images, in all slices showing enhancing tumor. The spin and gradient echo relaxation rate changes were then determined giving estimates of microvascular and total blood volume. ((CBVmicro≈R2=R2MION-R*pre-MION CBVTotal≈ R2* = R2*MION-R2*pre-MION). Results: Gallium maltolate inhibited tumor growth (377132%), as measured by enhancing tumor volume, compared to saline controls (863481%). Treatment shows decrease of CBV micro and CBVTotal compared to the controls. The ratio of R2* /R2, which is a measure of mean vessel diameter, increased in saline treated controls but remained unchanged for the gallium maltolate treated rats. To our knowledge this is the first study performed that uses physiologic MRI measurements to investigate the effects of gallium maltolate on brain tumor xenografts. The differences shown are not statistically significant a result likely due to the small sample sizes, which is being remedied by ongoing additional studies. For the imaging studies included here tissue markers of proliferation (Ki67), hypoxia (HIF1) transferrin receptors, and vascular density (vWF) are being analyzed to provide additional information regarding mechanism of action. In general these results demonstrate, for the first time, that the novel gallium maltolate treatment holds promise for the treatment of malignant brain tumors.

Citation Format: Kimberly R. Pechman, Andrew Lozen, Mona Al-Gizawiy, Kathleen Schmainda, Christopher R. Chitambar. Gallium maltolate inhibits brain tumor volume and blood volume in xenograft model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5606. doi:10.1158/1538-7445.AM2013-5606

Abstract 2654: A prospective study of the effects of adjuvant chemotherapy (CT) on cognition and brain function in breast cancer patients

There is an accumulating body of literature reporting that cognitive deficits, possibly long lasting, including lack of concentration, short-term memory loss and difficulties in multitasking are observed in patients receiving chemotherapy (CT) (“chemobrain”). We have used functional magnetic resonance imaging (fMRI) to determine the nature of the changes in brain function that underlie the cognitive deficits that can result from CT. This research was carried out prospectively in women being treated with adjuvant CT for early-stage breast cancer (BC). Methods: Seven healthy aged-matched control subjects (No CT) and six subjects with BC took part in this study undergoing functional fMRI scanning on a 3.0T scanner prior to initiating CT and after receiving their fourth cycle of anthracycline-based CT. Task activation (n-back) and resting-state functional connectivity (fC) scans were carried out. The N-back letter task is a continuous performance task having 3 levels of increasing cognitive load designed to probe regions of the brain activated by attention and working memory. Resting-state fC measures spontaneous low frequency oscillations in MR signal in brain and is used to create maps of fC among brain regions. Results: There were no significant differences in n-back task performance between the CT group and controls. However, significant differences (p≤0.05) in task activation and fC between the two subjects groups were observed. N-back task activation was significantly greater in the BC group compared with controls in right inferior frontal gyrus and right cerebellum. There were significant interactions between subject group and cognitive load within right inferior parietal and left inferior occipital cortex. The default mode network consists of interconnected regions of the brain that are active while the subjects are at rest and reduce activity when subjects perform specific tasks. Within this network, the BC group has significantly less deactivation during task compared to controls. There were also differences between the groups in resting-state fC. Using the left amygdala as a seed region, changes in fC were seen in the pre-chemo scans of the BC group compared to the controls. The BC subjects showed a 185% increase in intraregional fC and increased fC with the superior temporal gyrus, an area along with the amygdala that is activated by emotional stimuli. These changes in fC may be due to increased stress response in BC subjects. After four sessions of CT the BC group showed significant decreases in fC between the amygdala and the parahippocampal gyrus, an area involved in encoding and retrieving memories. This decrease in functional connectivity along with alterations in brain activation by cognitive tasks may play a part in the memory and other cognitive complaints associated with cancer and CT and may inform the search for strategies to reduce CT associated cognitive dysfunction.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2654. doi:1538-7445.AM2012-2654