Image-fusion of MR spectroscopic images for treatment planning of gliomas

The Utility of Spectroscopic MRI in Stereotactic Biopsy and Radiotherapy Guidance in Newly Diagnosed Glioblastoma

Current diagnostic and therapeutic approaches for gliomas have limitations hindering survival outcomes. We propose spectroscopic magnetic resonance imaging as an adjunct to standard MRI to bridge these gaps. Spectroscopic MRI is a volumetric MRI technique capable of identifying tumor infiltration based on its elevated choline (Cho) and decreased N-acetylaspartate (NAA). We present the clinical translatability of spectroscopic imaging with a Cho/NAA ≥ 5x threshold for delineating a biopsy target in a patient diagnosed with non-enhancing glioma. Then, we describe the relationship between the undertreated tumor detected with metabolite imaging and overall survival (OS) from a pilot study of newly diagnosed GBM patients treated with belinostat and chemoradiation. Each cohort (control and belinostat) were split into subgroups using the median difference between pre-radiotherapy Cho/NAA ≥ 2x and the treated T1-weighted contrast-enhanced (T1w-CE) volume. We used the Kaplan-Meier estimator to calculate median OS for each subgroup. The median OS was 14.4 months when the difference between Cho/NAA ≥ 2x and T1w-CE volumes was higher than the median compared with 34.3 months when this difference was lower than the median. The T1w-CE volumes were similar in both subgroups. We find that patients who had lower volumes of undertreated tumors detected via spectroscopy had better survival outcomes.

Prediction of IDH Status Through MRI Features and Enlightened Reflection on the Delineation of Target Volume in Low-Grade Gliomas

Isocitrate dehydrogenase mutational status defines distinct biologic behavior and clinical outcomes in low-grade gliomas. We sought to determine magnetic resonance imaging characteristics associated with isocitrate dehydrogenase mutational status to evaluate the predictive roles of magnetic resonance imaging features in isocitrate dehydrogenase mutational status and therefore their potential impact on the determination of clinical target volume in radiotherapy. Forty-eight isocitrate dehydrogenase-mutant and 28 isocitrate dehydrogenase–wild-type low-grade gliomas were studied. Isocitrate dehydrogenase mutation was related to more frequency of cortical involvement compared to isocitrate dehydrogenase–wild-type group (34/46 vs 6/24, P = .0001). Peritumoral edema was less frequent in isocitrate dehydrogenase–mutant tumors (32.6% vs 58.3% for isocitrate dehydrogenase–wild-type tumors, P = .0381). Isocitrate dehydrogenase–wild-type tumors were more likely to have a nondefinable border, while isocitrate dehydrogenase–mutant tumors had well-defined borders (66.7% vs 39.1%, P = .0287). Only 8 (17.4%) of 46 of the isocitrate dehydrogenase–mutant tumors demonstrated marked enhancement, while this was 66.7% in isocitrate–wild-type tumors (P < .0001). Choline–creatinine ratio for isocitrate dehydrogenase–wild-type tumors was significantly higher than that for isocitrate dehydrogenase–mutant tumors. In conclusion, frontal location, well-defined border, cortical involvement, less peritumoral edema, lack of enhancement, and low choline–creatinine ratio were predictive for the definition of isocitrate dehydrogenase–mutant low-grade gliomas. Magnetic resonance imaging can provide an advantage in the detection of isocitrate dehydrogenase status indirectly and indicate the need to explore new design for treatment planning in gliomas. Choline–creatinine ratio in magnetic resonance spectroscopy could be a potential more reasonable reference for the new design of delineation of target volume in low-grade gliomas.

Radiotherapy Advances in Pediatric Neuro-Oncology

Radiation therapy (RT) represents an integral component in the treatment of many pediatric brain tumors. Multiple advances have emerged within pediatric radiation oncology that aim to optimize the therapeutic ratio—improving disease control while limiting RT-related toxicity. These include innovations in treatment planning with magnetic resonance imaging (MRI) simulation, as well as increasingly sophisticated radiation delivery techniques. Advanced RT techniques, including photon-based RT such as intensity-modulated RT (IMRT) and volumetric-modulated arc therapy (VMAT), as well as particle beam therapy and stereotactic RT, have afforded an array of options to dramatically reduce radiation exposure of uninvolved normal tissues while treating target volumes. Along with advances in image guidance of radiation treatments, novel RT approaches are being implemented in ongoing and future prospective clinical trials. As the era of molecular risk stratification unfolds, personalization of radiation dose, target, and technique holds the promise to meaningfully improve outcomes for pediatric neuro-oncology patients.

Dosimetric Effects of Magnetic Resonance Imaging-assisted Radiotherapy Planning: Dose Optimization for Target Volumes at High Risk and Analytic Radiobiological Dose Evaluation

Based on the assumption that apparent diffusion coefficients (ADCs) define high-risk clinical target volume (aCTVHR) in high-grade glioma in a cellularity-dependent manner, the dosimetric effects of aCTVHR-targeted dose optimization were evaluated in two intensity-modulated radiation therapy (IMRT) plans. Diffusion-weighted magnetic resonance (MR) images and ADC maps were analyzed qualitatively and quantitatively to determine aCTVHR in a high-grade glioma with high cellularity. After confirming tumor malignancy using the average and minimum ADCs and ADC ratios, the aCTVHR with double- or triple-restricted water diffusion was defined on computed tomography images through image registration. Doses to the aCTVHR and CTV defined on T1-weighted MR images were optimized using a simultaneous integrated boost technique. The dosimetric benefits for CTVs and organs at risk (OARs) were compared using dose volume histograms and various biophysical indices in an ADC map-based IMRT (IMRTADC) plan and a conventional IMRT (IMRTconv) plan. The IMRTADC plan improved dose conformity up to 15 times, compared to the IMRTconv plan. It reduced the equivalent uniform doses in the visual system and brain stem by more than 10% and 16%, respectively. The ADC-based target differentiation and dose optimization may facilitate conformal dose distribution to the aCTVHR and OAR sparing in an IMRT plan.

SIVIC: Open-Source, Standards-Based Software for DICOM MR Spectroscopy Workflows

Quantitative analysis of magnetic resonance spectroscopic imaging (MRSI) data provides maps of metabolic parameters that show promise for improving medical diagnosis and therapeutic monitoring. While anatomical images are routinely reconstructed on the scanner, formatted using the DICOM standard, and interpreted using PACS workstations, this is not the case for MRSI data. The evaluation of MRSI data is made more complex because files are typically encoded with vendor-specific file formats and there is a lack of standardized tools for reconstruction, processing, and visualization. SIVIC is a flexible open-source software framework and application suite that enables a complete scanner-to-PACS workflow for evaluation and interpretation of MRSI data. It supports conversion of vendor-specific formats into the DICOM MR spectroscopy (MRS) standard, provides modular and extensible reconstruction and analysis pipelines, and provides tools to support the unique visualization requirements associated with such data. Workflows are presented which demonstrate the routine use of SIVIC to support the acquisition, analysis, and delivery to PACS of clinical ¹H MRSI datasets at UCSF.

The potential for an enhanced role for MRI in radiation-therapy treatment planning

The exquisite soft-tissue contrast of magnetic resonance imaging (MRI) has meant that the technique is having an increasing role in contouring the gross tumor volume (GTV) and organs at risk (OAR) in radiation therapy treatment planning systems (TPS). MRI-planning scans from diagnostic MRI scanners are currently incorporated into the planning process by being registered to CT data. The soft-tissue data from the MRI provides target outline guidance and the CT provides a solid geometric and electron density map for accurate dose calculation on the TPS computer. There is increasing interest in MRI machine placement in radiotherapy clinics as an adjunct to CT simulators. Most vendors now offer 70 cm bores with flat couch inserts and specialised RF coil designs. We would refer to these devices as MR-simulators. There is also research into the future application of MR-simulators independent of CT and as in-room image-guidance devices. It is within the background of this increased interest in the utility of MRI in radiotherapy treatment planning that this paper is couched. The paper outlines publications that deal with standard MRI sequences used in current clinical practice. It then discusses the potential for using processed functional diffusion maps (fDM) derived from diffusion weighted image sequences in tracking tumor activity and tumor recurrence. Next, this paper reviews publications that describe the use of MRI in patient-management applications that may, in turn, be relevant to radiotherapy treatment planning. The review briefly discusses the concepts behind functional techniques such as dynamic contrast enhanced (DCE), diffusion-weighted (DW) MRI sequences and magnetic resonance spectroscopic imaging (MRSI). Significant applications of MR are discussed in terms of the following treatment sites: brain, head and neck, breast, lung, prostate and cervix. While not yet routine, the use of apparent diffusion coefficient (ADC) map analysis indicates an exciting future application for functional MRI. Although DW-MRI has not yet been routinely used in boost adaptive techniques, it is being assessed in cohort studies for sub-volume boosting in prostate tumors.

Magnetic resonance spectroscopy imaging in radiotherapy planning for recurrent glioma

PURPOSE

The purpose of this study was to investigate how incorporation of magnetic resonance spectroscopy imaging (MRSI) into radiotherapy planning would increase the target volume for patients with recurrent glioma.

METHODS

After prior standard radiotherapy, 25 patients with recurrent glioma were treated with bevacizumab and concurrent hypofractionated stereotactic radiotherapy (HFSRT), delivering 30 Gy in five fractions. MRSI were acquired for 12 patients. Areas with markedly higher choline levels relative to the levels of total creatine and N-acetylaspartate were identified and referred to as MRSI voxels with elevated metabolite ratios (EMR). Gross tumor volume (GTV) consisted of contrast-enhancing tumor on T1-weighted magnetic resonance images (MRI) and computed tomography. Clinical target volume (CTV) was GTV + 5 mm margin and MRSI voxels with EMR. Overall survival (OS) and 6-month progression free survival (PFS) for these patients were reported in a prior publication [Gutin et al., Int. J. Radiat. Oncol., Biol., Phys. 75(1), 156-163 (2009)], and the outcome was correlated with the GTV and the volume of MRSI voxels with EMR in this study.

RESULTS

Seven of the 12 patients had MRSI voxels with EMR. If none of the MRSI voxels with EMR were included, the CTV would range from 9.2 to 73.0 cm3 with a median of 31.0 cm3, whereas if all voxels were included, the CTV would range from 27.4 to 74.4 cm3 with a median of 35.0 cm3. For three of the seven patients, including the voxels with EMR, would have increased the CTV by 14%-23%. For one patient, where the MRSI voxels with EMR did not overlap the GTV, including these voxels would increase the CTV by 198%. No correlation could be found between the OS and PFS and the GTV or the volume of MRSI voxels with EMR.

CONCLUSIONS

Seven of 12 patients with recurrent glioma had MRSI voxels with EMR. For four of these seven patients, including the MRSI voxels with EMR, significantly increased the CTV. This study does not have statistical power to conclude on the importance of including areas with MRSI-suspect disease into the radiation target volume.

Functional MRI for Radiotherapy of Gliomas

In this paper, we review the applications of functional magnetic resonance imaging (MRI) for target delineation and critical organ avoidance for brain radiotherapy. In this article we distinguish functional MRI from brain functional MRI (fMRI). Functional MRI includes magnetic resonance spectroscopic imaging (MRSI), perfusion MRI, diffusion tensor imaging (DTI) and brain fMRI. These functional MRI modalities can provide unique metabolic, pathological and physiological information that are not available in anatomic MRI and can potentially improve the treatment outcomes of brain tumors. For example, both choline (Cho) to N-acetylaspartate (NAA) and Cho to creatine (Cr) ratios from MRSI increase with increasing tumor malignancy and can be used to grade gliomas. Relative cerebral blood volume (rCBV) measurements from dynamic susceptibility contrast perfusion magnetic resonance imaging (DSC MRI) are superior to conventional contrast-enhanced MRI in predicting tumor biology and may be even superior to pathologic assessment in predicting patient clinical outcomes. Brain fMRI can help identify and avoid functionally critical areas when constructing treatment plans for brain radiotherapy. In the past, functional MRI measurements have not been routinely used in a clinical arena due to the experimental nature of these imaging modalities. As these methods become more commonly used and effective image co-registration algorithms become available, integration of functional MRI into the treatment process of brain radiotherapy now appears to be clinically feasible, at least in major medical centers.

Role of stereotactic radiosurgery and fractionated stereotactic radiotherapy for the treatment of recurrent glioblastoma multiforme

Glioblastoma multiforme (GBM) is a devastating malignant brain tumor characterized by resistance to available therapeutic approaches and relentless malignant progression that includes widespread intracranial invasion, destruction of normal brain tissue, progressive disability, and death. Stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (fSRT) are increasingly used in patients with recurrent GBM to complement traditional treatments such as resection, conventional external beam radiotherapy, and chemotherapy. Both SRS and fSRT are powerful noninvasive therapeutic modalities well suited to treat focal neoplastic lesions through the delivery of precise, highdose radiation. Although no randomized clinical trials have been performed, a variety of retrospective studies have been focused on the use of SRS and fSRT for recurrent GBMs. In addition, state-of-the-art neuroimaging techniques, such as MR spectroscopic imaging, diffusion tensor tractography, and nuclear medicine imaging, have enhanced treatment planning methods leading to potentially improved clinical outcomes. In this paper the authors reviewed the current applications and efficacy of SRS and fSRT in the treatment of GBM, highlighting the value of these therapies for recurrent focal disease.

In vivo lactate signal enhancement using binomial spectral-selective pulses in selective MQ coherence (SS-SelMQC) spectroscopy

Tumor vasculature and tissue oxygen pressure can influence tumor growth, metastases, and patient survival. Elevated levels of lactate may be observed during the process of aggressive tumor development accompanied by angiogenesis (the evolution of the microenvironment). The noninvasive MR detection of lactate in tumor tissues as a potential biomarker is difficult due to the presence of co-resonating lipids that are present at high concentrations. Methods were previously reported for lactate editing using the SELective Multiple Quantum Coherence (SelMQC) method. Here we report a sequence "SS-SelMQC," Spectral-Selective SelMQC, which is a modified version of SelMQC using binomial pulses. Binomial pulses were employed in this editing sequence for frequency excitation or inversion of selective lactate resonances. Lactate detection has been demonstrated using SS-SelMQC, both in vitro (30 mM lactate/H(2)O doped with 25 microM Gd-DTPA) and in vivo (Dunning R3337-AT prostate tumors), and compared to similar measurements made with SelMQC. Lactate areas were measured from nonlocalized spectra, one-dimensional (1D) localized spectra, and two-dimensional chemical shift images (CSI) of the localized slice. In data from whole phantoms, the modified pulse sequence yielded enhancement of the lactate signal of 2.4 +/- 0.40 times compared to SelMQC. Similar in vivo lactate signal enhancement of 2.3 +/- 0.24 times was observed in 1D slice-localized experiment.

Imaging of the cerebrum

The history of the development of cerebral imaging is a complex combination of the forces of innovation at both the individual and industrial levels. Principal paradigms of neuroimaging shifted as a result of technological breakthroughs, beginning with the discovery of x-rays and continuing with the development of computerized imaging to the latest imaging paradigm, nuclear magnetic resonance imaging. We discuss these landmarks in neuroimaging in historical context, with emphasis on the particularly rapid development of imaging technology during the past 30 to 40 years, including the most recent emerging technologies.

Present trend in the primary treatment of aggressive malignant glioma: glioblastoma multiforme

The standard treatment for glioblastoma multiforme is surgery, radiation, and chemotherapy. Yet this aggressive therapy has only a modest effect on survival with most patients surviving less than 1 year after diagnosis. This poor prognosis has lead scientists to seek alternative molecular approaches for the treatment of glioblastoma multiforme. Among these, gene therapy, vaccine therapy, and immunotherapy are all approaches that are currently being investigated. While these molecular approaches may not herald an immediate change in the prognosis of these aggressive tumors, combining them with existing approaches may bring some progress in the standard of care. This paper reviews current treatments and several newer therapies in preclinical and early clinical studies.

Open low-field magnetic resonance imaging for target definition, dose calculations and set-up verification during three-dimensional CRT for glioblastoma multiforme

AIMS

To assess the effect on target delineation of using magnetic resonance simulation for planning of glioblastoma multiforme (GBM). Dose calculations derived from computed tomography- and magnetic resonance-derived plans were computed. The accuracy of set-up verification using magnetic resonance imaging (MRI)-based digital reconstructed radiographs (DRRs) was assessed.

MATERIALS AND METHODS

Ten patients with GBM were simulated using computed tomography and MRI. MRI was acquired with a low-field (0.23 T) MRI unit (SimMRI). Gross tumour volumes (GTVs) were delineated by two radiation oncologists on computed tomography and MRI. In total, 30 plans were generated using both the computed tomography, with (planbathoCT) and without (planCT) heterogeneity correction, and MRI data sets (planSimMRI). The minimum dose delivered (Dmin) to the GTV between computed tomography- and MRI-based plans was compared. The accuracy of set-up positioning using MRI DRRs was assessed by four radiation oncologists.

RESULTS

The mean GTVs delineated on computed tomography were significantly (P<0.001) larger than those contoured on MRI. The mean (+/-standard deviation) Dmin difference percentage was 0.3+/-0.8, 0.1+/-0.6 and -0.2+/-1.0% for the planCT/planbathoCT-, planCT/planSimMRI- and planbathoCT/planSimMRI-derived plans, respectively. The set-up differences observed with the computed tomography and MRI DRRs ranged from 1.0 to 4.0 mm (mean 1.5 mm; standard deviation+/-1.4).

CONCLUSIONS

GTVs defined on computed tomography were significantly larger than those delineated on MRI. Compared with computed tomography-derived plans, MRI-based dose calculations were accurate. The precision of set-up verifications based on computed tomography- and MRI-derived DRRs seemed similar. The use of MRI only for the planning of GBM should be further assessed.

Use of MR spectroscopy and functional imaging in the treatment planning of gliomas

Routine anatomical imaging with CT and MRI does not reliably indicate the true extent or the most malignant areas of gliomas and cannot identify the functionally critical parts of the brain. The aim of the study was to see if the use of MR spectroscopic imaging (MRSI) along with functional MRI (fMRI) can better define both the target and the critical structures to be avoided to improve radiation delivery in gliomas. 12 patients with gliomas underwent multivoxel MRS and functional imaging using GE processing software. The choline to creatine ratio (Cho:Cr), which represents the degree of abnormality for each individual voxel on MRSI, was derived, converted into a grayscale grading system, fused to the MRI images and then transferred to the planning CT images. An intensity-modulated radiation therapy (IMRT) plan was developed using the dose constraints based on both the anatomical and the functionally critical regions. Cho:Cr consistently identified the gross tumour volume (GTV) within the microscopic disease (clinical target volume, CTV) and allowed dose painting using IMRT. No correlation between MRSI based Cho:Cr > or =2 and MR defined CTV nor their location was noted. However, MRSI defined Cho:Cr > or =3 was smaller by 40% compared with post-contrast T1 weighted MRI defined GTV volumes. fMRI helped in optimizing the orientation of the beams. In conclusion, both MRSI and fMRI provide additional information to conventional imaging that may guide dose painting in treatment planning of gliomas. A Phase I IMRT dose intensification trial in gliomas using this information is planned.

Intensity modulated radiation therapy versus three-dimensional conformal radiation therapy for the treatment of high grade glioma: a dosimetric comparison

The present study compared the dosimetry of intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D-CRT) techniques in patients treated for high-grade glioma. A total of 20 patients underwent computed tomography treatment planning in conjunction with magnetic resonance imaging fusion. Prescription dose and normal-tissue constraints were identical for the 3D-CRT and IMRT plans. The prescribed dose was 59.4 Gy delivered at 1.8 Gy per fraction using 4-10 MV photons. Normal-tissue dose constraints were 50-54 Gy for the optic chiasm and nerves, and 55-60 Gy for the brainstem. The IMRT plan yielded superior target coverage as compared with the 3D-CRT plan. Specifically, minimum and mean planning target volume cone down doses were 54.52 Gy and 61.74 Gy for IMRT and 50.56 Gy and 60.06 Gy for 3D-CRT (p < or = 0.01). The IMRT plan reduced the percent volume of brainstem receiving a dose greater than 45 Gy by 31% (p = 0.004) and the percent volume of brain receiving a dose greater than 18 Gy, 24 Gy, and 45 Gy by 10% (p = 0.059), 14% (p = 0.015), and 40% (p < or = 0.0001) respectively. With IMRT, the percent volume of optic chiasm receiving more than 45 Gy was also reduced by 30.40% (p = 0.047). As compared with 3D-CRT, IMRT significantly increased the tumor control probability (p < or = 0.005) and lowered the normal-tissue complication probability for brain and brainstem (p < 0.033). Intensity-modulated radiation therapy improved target coverage and reduced radiation dose to the brain, brainstem, and optic chiasm. With the availability of new cancer imaging tools and more effective systemic agents, IMRT may be used to intensify tumor doses while minimizing toxicity, therefore potentially improving outcomes in patients with high-grade glioma.