Quantifying gadolinium-based nanoparticle uptake distributions in brain metastases via magnetic resonance imaging.

AGuIX, a novel gadolinium-based nanoparticle, has been deployed in a pioneering double-blinded Phase II clinical trial aiming to assess its efficacy in enhancing radiotherapy for tumor treatment. This paper moves towards this goal by analyzing AGuIX uptake patterns in 23 patients. A phantom was designed to establish the relationship between AGuIX concentration and longitudinal ( T 1 ) relaxation. A 3T MRI and MP2RAGE sequence were used to generate patient T 1 maps. AGuIX uptake in tumors was determined based on longitudinal relaxivity. AGuIX (or placebo) was administered to 23 patients intravenously at 100 mg/kg 1-5 hours pre-imaging. Each of 129 brain metastases across 23 patients were captured in T 1 maps and examined for AGuIX uptake and distribution. Inferred AGuIX recipients had average tumor uptakes between 0.012 and 0.17 mg/ml, with a mean of 0.055 mg/ml. Suspected placebo recipients appeared to have no appreciable uptake. Tumors presented with varying spatial AGuIX uptake distributions, suspected to be related to differences in accumulation time and patient-specific bioaccumulation factors. This research demonstrates AGuIX's ability to accumulate in brain metastases, with quantifiable uptake via T 1 mapping. Future analyses will extend these methods to complete clinical trial data (~ 134 patients) to evaluate the potential relationship between nanoparticle uptake and possible tumor response following radiotherapy.Clinical Trial Registration Number: NCT04899908.Clinical Trial Registration Date: 25/05/2021.

Phase I/II study testing the combination of AGuIX nanoparticles with radiochemotherapy and concomitant temozolomide in patients with newly diagnosed glioblastoma (NANO-GBM trial protocol).

BACKGROUND: Despite standard treatments including chemoradiotherapy with temozolomide (TMZ) (STUPP protocol), the prognosis of glioblastoma patients remains poor. AGuIX nanoparticles have a high radiosensitizing potential, a selective and long-lasting accumulation in tumors and a rapid renal elimination. Their therapeutic effect has been proven in vivo on several tumor models, including glioblastoma with a potential synergetic effect when combined with TMZ based chemoradiotherapy, and they are currently evaluated in 4 ongoing Phase Ib and II clinical trials in 4 indications (brain metastases, lung, pancreatic and cervix cancers) (> 100 patients received AGuIX). Thus, they could offer new perspectives for patients with newly diagnosed glioblastoma. The aim of this study is to determine the recommended dose of AGuIX as a radiosensitizer in combination with radiotherapy and TMZ during the concurrent radio-chemotherapy period for phase II (RP2D) and to estimate the efficacy of the combination. METHODS: NANO-GBM is a multicenter, phase I/II, randomized, open-label, non-comparative, therapeutic trial. According to a dose escalation scheme driven by a TITE-CRM design, 3 dose levels of AGuIX (50, 75 and 100 mg/kg) will be tested in phase I added to standard concomitant radio-chemotherapy. Patients with grade IV glioblastoma, not operated or partially operated, with a KPS ≥ 70% will be eligible for the study. The primary endpoints are i) for phase I, the RP2D of AGuIX, with DLT defined as any grade 3-4 NCI-CTCAE toxicity and ii) for phase II, the 6-month progression-free survival rate. The pharmacokinetics, distribution of nanoparticles, tolerance of the combination, neurological status, overall survival (median, 6-month and 12-month rates), response to treatment, and progression-free survival (median and 12-month rates) will be assessed as secondary objectives. Maximum sixty-six patients are expected to be recruited in the study from 6 sites. DISCUSSION: The use of AGuIX nanoparticles could allow to overpass the radioresistance to the reference treatment of newly diagnosed glioblastomas that have the poorest prognosis (incomplete resection or biopsy only). TRIAL REGISTRATION: Clinicaltrials.gov: NCT04881032 , registered on April 30, 2021. Identifier with the French National Agency for the Safety of Medicines and Health Products (ANSM): N°Eudra CT 2020-004552-15. PROTOCOL: version 3, 23 May 2022.

T1 Mapping From MPRAGE Acquisitions: Application to the Measurement of the Concentration of Nanoparticles in Tumors for Theranostic Use.

BACKGROUND: The measurement of the concentration of theranostic agents in vivo is essential for the assessment of their therapeutic efficacy and their safety regarding healthy tissue. To this end, there is a need for quantitative T1 measurements that can be obtained as part of a standard clinical imaging protocol applied to tumor patients. PURPOSE: To generate T1 maps from MR images obtained with the magnetization-prepared rapid gradient echo (MPRAGE) sequence. To evaluate the feasibility of the proposed approach on phantoms, animal and patients with brain metastases. STUDY TYPE: Pilot. PHANTOM/ANIMAL MODEL/POPULATION: Solutions containing contrast agents (chelated Gd3+ and iron nanoparticles), male rat of Wistar strain, three patients with brain metastases. FIELD STRENGTH/SEQUENCE: A 3-T and 7-T, saturation recovery (SR), and MPRAGE sequences. ASSESSMENT: The MPRAGE T1 measurement was compared to the reference SR method on phantoms and rat brain at 7-T. The robustness of the in vivo method was evaluated by studying the impact of misestimates of tissue proton density. Concentrations of Gd-based theranostic agents were measured at 3-T in gray matter and metastases in patients recruited in NanoRad clinical trial. STATISTICAL TESTS: A linear model was used to characterize the relation between T1 measurements from the MPRAGE and the SR acquisitions obtained in vitro at 7-T. RESULTS: The slope of the linear model was 0.966 (R2  = 0.9934). MPRAGE-based T1 values measured in the rat brain were 1723 msec in the thalamus. MPRAGE-based T1 values measured in patients in white matter and gray matter amounted to 747 msec and 1690 msec. Mean concentration values of Gd3+ in metastases were 61.47 µmol. DATA CONCLUSION: The T1 values obtained in vitro and in vivo support the validity of the proposed approach. The concentrations of Gd-based theranostic agents may be assessed in patients with metastases within a standard clinical imaging protocol using the MPRAGE sequence. EVIDENCE LEVEL: 2. TECHNICAL EFFICACY: Stage 1.

Meloxicam can Potentiate the Therapeutic Effects of Synchrotron Microbeam Radiation Therapy on High-Grade Glioma Bearing Rats.

The microbeam radiation therapy (MRT), a spatially micro-fractionated synchrotron radiotherapy, leads to better control of incurable high-grade glioma than that obtained upon homogeneous radiotherapy. We evaluated the effect of meloxicam, a non-steroidal anti-inflammatory drug (NSAID), to increase the MRT response. Survival of rats bearing intracranial 9L gliosarcoma treated with meloxicam and/or MRT (400 Gy, 50 µm-wide microbeams, 200 µm spacing) was monitored. Tumor growth was assessed on histological tissue sections and COX-2 transcriptomic expression was studied 1 to 25 days after radiotherapy. Meloxicam significantly extended the median survival of microbeam-irradiated rats (from +10.5 to +20 days). Dual treatment led to last survivors until D90 (D39 for the MRT group) and to tumor 9.5 times smaller than MRT alone. No significant modification of COX-2 expression was induced by MRT in normal and tumor tissues. The meloxicam reinforced the anti-tumor effect of MRT for glioma treatment. Although the mechanisms of interaction between meloxicam and MRT remain to be elucidated, the addition of this NSAID, easily implemented as a supplement to water for example, is a very favorable therapeutic regimen since it doubled the survival benefit compared to MRT alone.

3D Spatial Distribution of Nanoparticles in Mice Brain Metastases by X-ray Phase-Contrast Tomography.

Characterizing nanoparticles (NPs) distribution in multiple and complex metastases is of fundamental relevance for the development of radiological protocols based on NPs administration. In the literature, there have been advances in monitoring NPs in tissues. However, the lack of 3D information is still an issue. X-ray phase-contrast tomography (XPCT) is a 3D label-free, non-invasive and multi-scale approach allowing imaging anatomical details with high spatial and contrast resolutions. Here an XPCT qualitative study on NPs distribution in a mouse brain model of melanoma metastases injected with gadolinium-based NPs for theranostics is presented. For the first time, XPCT images show the NPs uptake at micrometer resolution over the full brain. Our results revealed a heterogeneous distribution of the NPs inside the melanoma metastases, bridging the gap in spatial resolution between magnetic resonance imaging and histology. Our findings demonstrated that XPCT is a reliable technique for NPs detection and can be considered as an emerging method for the study of NPs distribution in organs.

Theranostic AGuIX nanoparticles as radiosensitizer: A phase I, dose-escalation study in patients with multiple brain metastases (NANO-RAD trial).

BACKGROUND AND PURPOSE: Brain metastasis impacts greatly on patients' quality of life and survival. The phase I NANO-RAD trial assessed the safety and maximum tolerated dose of systemic administration of a novel gadolinium-based nanoparticle, AGuIX, in combination with whole brain radiotherapy in patients with multiple brain metastases not suitable for stereotactic radiotherapy. MATERIALS AND METHODS: Patients with measurable brain metastases received escalating doses of AGuIX nanoparticles (15, 30, 50, 75, or 100 mg/kg intravenously) on the day of initiation of WBRT (30 Gy in 10 fractions) in 5 cohorts of 3 patients each. Toxicity was assessed using NCI Common Terminology Criteria for Adverse Events v4.03. RESULTS: Fifteen patients with 354 metastases were included. No dose-limiting toxic effects were observed up to AGuIX 100 mg/kg. Plasma elimination half-life of AGuIX was similar for all groups (mean 1.3 h; range 0.8-3 h). Efficient targeting of metastases (T1 MRI enhancement, tumor selectivity) and persistence of AGuIX contrast enhancement were observed in metastases from patients with primary melanoma, lung, breast, and colon cancers. The concentration of AGuIX in metastases after administration was proportional to the injected dose. Thirteen of 14 evaluable patients had a clinical benefit, with either stabilization or reduction of tumor volume. MRI analysis showed significant correlation between contrast enhancement and tumor response, thus supporting a radiosensitizing effect. CONCLUSION: Combining AGuIX with radiotherapy for patients with brain metastases is safe and feasible. AGuIX specifically targets brain metastases and is retained within tumors for up to 1 week; ongoing phase II studies will more definitively assess efficacy.

Non-conventional Ultra-High Dose Rate (FLASH) Microbeam Radiotherapy Provides Superior Normal Tissue Sparing in Rat Lung Compared to Non-conventional Ultra-High Dose Rate (FLASH) Radiotherapy.

Conventional radiotherapy is a widely used non-invasive form of treatment for many types of cancer. However, due to a low threshold in the lung for radiation-induced normal tissue damage, it is of less utility in treating lung cancer. For this reason, surgery is the preferred treatment for lung cancer, which has the detriment of being highly invasive. Non-conventional ultra-high dose rate (FLASH) radiotherapy is currently of great interest in the radiotherapy community due to demonstrations of reduced normal tissue toxicity in lung and other anatomy. This study investigates the effects of FLASH microbeam radiotherapy, which in addition to ultra-high dose rate incorporates a spatial segmentation of the radiation field, on the normal lung tissue of rats. With a focus on fibrotic damage, this work demonstrates that FLASH microbeam radiotherapy provides an order of magnitude increase in normal tissue radio-resistance compared to FLASH radiotherapy. This result suggests FLASH microbeam radiotherapy holds promise for much improved non-invasive control of lung cancer.

Targeting brain metastases with ultrasmall theranostic nanoparticles, a first-in-human trial from an MRI perspective.

The use of radiosensitizing nanoparticles with both imaging and therapeutic properties on the same nano-object is regarded as a major and promising approach to improve the effectiveness of radiotherapy. Here, we report the MRI findings of a phase 1 clinical trial with a single intravenous administration of Gd-based AGuIX nanoparticles, conducted in 15 patients with four types of brain metastases (melanoma, lung, colon, and breast). The nanoparticles were found to accumulate and to increase image contrast in all types of brain metastases with MRI enhancements equivalent to that of a clinically used contrast agent. The presence of nanoparticles in metastases was monitored and quantified with MRI and was noticed up to 1 week after their administration. To take advantage of the radiosensitizing property of the nanoparticles, patients underwent radiotherapy sessions following their administration. This protocol has been extended to a multicentric phase 2 clinical trial including 100 patients.

Ultrasmall theranostic gadolinium-based nanoparticles improve high-grade rat glioma survival.

We formulated an ultra-small, gadolinium-based nanoparticle (AGuIX) with theranostic properties to simultaneously enhance MRI tumor delineation and radiosensitization in a glioma model. The 9L glioma cells were orthotopically implanted in 10-week-old Fischer rats. The intra-tumoral accumulation of AGuIX was quantified using MRI T1-maps. Rats randomized to intervention cohorts were subsequently treated with daily temozolomide for five consecutive days before radiotherapy treatment. Collectively, a series of 32 rats were divided into untreated (n = 7), temozolomide-only (n = 7), temozolomide and MRT (n = 9), AGuIX and MRT (n = 7), and triple therapy (temozolomide, AGuIX NPs, and MRT; n = 9) cohorts. AGuIX nanoparticles achieved a maximum intra-tumoral concentration (expressed as concentration of Gd3+) at 1 h after intravenous injection, reaching a mean of 227.9 ±â€¯60 µM. This was compared to concentrations of 10.5 ±â€¯9.2 µM and 62.9 ±â€¯24.7 µM in the contralateral hemisphere and cheek, respectively. There was a slower washout in the intra-tumor region, with sustained tumor-to-contralateral ratio of AGuIX, up to 14-fold, for each time point. The combination of AGuIX or temozolomide with MRT improved the median survival time (40 days) compared to the MeST of control rats (25 days) (p < 0.002). There was a trend towards further increased survival when the three treatments were combined (MeST of 46 days). This study demonstrated the selective accumulation of AGuIX in high grade glioma, as well as the potential survival benefits when combined with chemoradiation.

Treatment of multiple brain metastases using gadolinium nanoparticles and radiotherapy: NANO-RAD, a phase I study protocol.

INTRODUCTION: Occurrence of multiple brain metastases is a critical evolution of many cancers with significant neurological and overall survival consequences, despite new targeted therapy and standard whole brain radiotherapy (WBRT). A gadolinium-based nanoparticle, AGuIX, has recently demonstrated its effectiveness as theranostic and radiosensitiser agent in preclinical studies. The favourable toxicity profile in animals and its administration as a simple intravenous injection has motivated its use in patients with this first in human study. METHODS AND ANALYSIS: The NANO-RAD study is a phase I, first in human injection, monocentric, open-label, dose-escalation study to investigate the safety, the tolerability and the spectrum of side effects of AGuIX in combination with WBRT (30 Gy, 10 fractions of 3 Gy) for patients with multiple brain metastases. Five dose escalation cohorts are planned: 15, 30, 50, 75 and 100 mg/kg. A total of 15-18 patients will be recruited into this trial. The primary objective is to determine the maximum-tolerated dose of AGuIX nanoparticles combined with WBRT for the treatment of multiple brain metastases. Toxicity will be assessed using the National Cancer Institute Common Toxicity Criteria V.4.03. Secondary objectives are pharmacokinetic profile, distribution of AGuIX in metastases and surrounding healthy tissue visualised by MRI, intracranial progression-free survival and overall survival. Intracranial response will be determined according to Response Evaluation Criteria in Solid Tumour Criteria V.1.1 comparing MRI performed prior to treatment and at each follow-up visits. ETHICS AND DISSEMINATION: Approval was obtained from the ethics committee Sud Est V, France (Reference number 15-CHUG-48). The study was approved by the French National Agency for the Safety of Medicines and Health Products (ANSM) (Reference number 151519A-12). The results will be published in peer-reviewed journals or disseminated through national and international conferences. TRIAL REGISTRATION NUMBER: NCT02820454; Pre-results.

AGuIX® from bench to bedside-Transfer of an ultrasmall theranostic gadolinium-based nanoparticle to clinical medicine.

AGuIX® are sub-5 nm nanoparticles made of a polysiloxane matrix and gadolinium chelates. This nanoparticle has been recently accepted in clinical trials in association with radiotherapy. This review will summarize the principal preclinical results that have led to first in man administration. No evidence of toxicity has been observed during regulatory toxicity tests on two animal species (rodents and monkeys). Biodistributions on different animal models have shown passive uptake in tumours due to enhanced permeability and retention effect combined with renal elimination of the nanoparticles after intravenous administration. High radiosensitizing effect has been observed with different types of irradiations in vitro and in vivo on a large number of cancer types (brain, lung, melanoma, head and neck…). The review concludes with the second generation of AGuIX nanoparticles and the first preliminary results on human.

Micro-imaging of Brain Cancer Radiation Therapy Using Phase-contrast Computed Tomography.

PURPOSE: Experimental neuroimaging provides a wide range of methods for the visualization of brain anatomic morphology down to subcellular detail. Still, each technique-specific detection mechanism presents compromises among the achievable field-of-view size, spatial resolution, and nervous tissue sensitivity, leading to partial sample coverage, unresolved morphologic structures, or sparse labeling of neuronal populations and often also to obligatory sample dissection or other sample invasive manipulations. X-ray phase-contrast imaging computed tomography (PCI-CT) is an experimental imaging method that simultaneously provides micrometric spatial resolution, high soft-tissue sensitivity, and ex vivo full organ rodent brain coverage without any need for sample dissection, staining or labeling, or contrast agent injection. In the present study, we explored the benefits and limitations of PCI-CT use for in vitro imaging of normal and cancerous brain neuromorphology after in vivo treatment with synchrotron-generated x-ray microbeam radiation therapy (MRT), a spatially fractionated experimental high-dose radiosurgery. The goals were visualization of the MRT effects on nervous tissue and a qualitative comparison of the results to the histologic and high-field magnetic resonance imaging findings. METHODS AND MATERIALS: MRT was administered in vivo to the brain of both healthy and cancer-bearing rats. At 45 days after treatment, the brain was dissected out and imaged ex vivo using propagation-based PCI-CT. RESULTS: PCI-CT visualizes the brain anatomy and microvasculature in 3 dimensions and distinguishes cancerous tissue morphology, necrosis, and intratumor accumulation of iron and calcium deposits. Moreover, PCI-CT detects the effects of MRT throughout the treatment target areas (eg, the formation of micrometer-thick radiation-induced tissue ablation). The observed neurostructures were confirmed by histologic and immunohistochemistry examination and related to the micro-magnetic resonance imaging data. CONCLUSIONS: PCI-CT enabled a unique 3D neuroimaging approach for ex vivo studies on small animal models in that it concurrently delivers high-resolution insight of local brain tissue morphology in both normal and cancerous micro-milieu, localizes radiosurgical damage, and highlights the deep microvasculature. This method could assist experimental small animal neurology studies in the postmortem evaluation of neuropathology or treatment effects.

Synchrotron-generated microbeams induce hippocampal transections in rats.

Synchrotron-generated microplanar beams (microbeams) provide the most stereo-selective irradiation modality known today. This novel irradiation modality has been shown to control seizures originating from eloquent cortex causing no neurological deficit in experimental animals. To test the hypothesis that application of microbeams in the hippocampus, the most common source of refractory seizures, is safe and does not induce severe side effects, we used microbeams to induce transections to the hippocampus of healthy rats. An array of parallel microbeams carrying an incident dose of 600 Gy was delivered to the rat hippocampus. Immunohistochemistry of phosphorylated γ-H2AX showed cell death along the microbeam irradiation paths in rats 48 hours after irradiation. No evident behavioral or neurological deficits were observed during the 3-month period of observation. MR imaging showed no signs of radio-induced edema or radionecrosis 3 months after irradiation. Histological analysis showed a very well preserved hippocampal cytoarchitecture and confirmed the presence of clear-cut microscopic transections across the hippocampus. These data support the use of synchrotron-generated microbeams as a novel tool to slice the hippocampus of living rats in a minimally invasive way, providing (i) a novel experimental model to study hippocampal function and (ii) a new treatment tool for patients affected by refractory epilepsy induced by mesial temporal sclerosis.

Rat sensorimotor cortex tolerance to parallel transections induced by synchrotron-generated X-ray microbeams.

Microbeam radiation therapy is a novel preclinical technique, which uses synchrotron-generated X-rays for the treatment of brain tumours and drug-resistant epilepsies. In order to safely translate this approach to humans, a more in-depth knowledge of the long-term radiobiology of microbeams in healthy tissues is required. We report here the result of the characterization of the rat sensorimotor cortex tolerance to microradiosurgical parallel transections. Healthy adult male Wistar rats underwent irradiation with arrays of parallel microbeams. Beam thickness, spacing and incident dose were 100 or 600 µm, 400 or 1200 µm and 360 or 150 Gy, respectively. Motor performance was carried over a 3-month period. Three months after irradiation rats were sacrificed to evaluate the effects of irradiation on brain tissues by histology and immunohistochemistry. Microbeam irradiation of sensorimotor cortex did not affect weight gain and motor performance. No gross signs of paralysis or paresis were also observed. The cortical architecture was not altered, despite the presence of cell death along the irradiation path. Reactive gliosis was evident in the microbeam path of rats irradiated with 150 Gy, whereas no increase was observed in rats irradiated with 360 Gy.

MRI-guided clinical 6-MV radiosensitization of glioma using a unique gadolinium-based nanoparticles injection.

AIM: This study reports the use of gadolinium-based AGuIX nanoparticles (NPs) as a theranostic tool for both image-guided radiation therapy and radiosensitization of brain tumors. MATERIALS & METHODS: Pharmacokinetics and regulatory toxicology investigations were performed on rodents. The AGuIX NPs' tumor accumulation was studied by MRI before 6-MV irradiation. RESULTS: AGuIX NPs exhibited a great safety profile. A single intravenous administration enabled the tumor delineation by MRI with a T1 tumor contrast enhancement up to 24 h, and the tumor volume reduction when combined with a clinical 6-MV radiotherapy. CONCLUSION: This study demonstrates the efficacy and the potential of AGuIX NPs for image-guided radiation therapy, promising properties that will be assessed in the upcoming Phase I clinical trial.

The High Radiosensitizing Efficiency of a Trace of Gadolinium-Based Nanoparticles in Tumors.

We recently developed the synthesis of ultrasmall gadolinium-based nanoparticles (GBN), (hydrodynamic diameter <5 nm) characterized by a safe behavior after intravenous injection (renal clearance, preferential accumulation in tumors). Owing to the presence of gadolinium ions, GBN can be used as contrast agents for magnetic resonance imaging (MRI) and as radiosensitizers. The attempt to determine the most opportune delay between the intravenous injection of GBN and the irradiation showed that a very low content of radiosensitizing nanoparticles in the tumor area is sufficient (0.1 µg/g of particles, i.e. 15 ppb of gadolinium) for an important increase of the therapeutic effect of irradiation. Such a promising and unexpected result is assigned to a suited distribution of GBN within the tumor, as revealed by the X-ray fluorescence (XRF) maps.

Better Efficacy of Synchrotron Spatially Microfractionated Radiation Therapy Than Uniform Radiation Therapy on Glioma.

PURPOSE: Synchrotron microbeam radiation therapy (MRT) is based on the spatial fractionation of the incident, highly focused synchrotron beam into arrays of parallel microbeams, typically a few tens of microns wide and depositing several hundred grays. This irradiation modality was shown to have a high therapeutic impact on tumors, especially in intracranial locations. However, mechanisms responsible for such a property are not fully understood. METHODS AND MATERIALS: Thanks to recent progress in dosimetry, we compared the effect of MRT and synchrotron broad beam (BB) radiation therapy delivered at comparable doses (equivalent to MRT valley dose) on tumor growth control and on classical radiobiological functions by histologic evaluation and/or transcriptomic analysis. RESULTS: MRT significantly improved survival of rats bearing 9L intracranial glioma compared with BB radiation therapy delivered at a comparable dose (P<.001); the efficacy of MRT and BB radiation therapy was similar when the MRT dose was half that of BB. The greater efficacy of MRT was not correlated with a difference in cell proliferation (Mki67 and proliferating cell nuclear antigen) or in transcriptomic stimulation of angiogenesis (vascular endothelial growth factor A or tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 2) but was correlated with a higher cell death rate (factor for apoptosis signals) and higher recruitment of macrophages (tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 1 and CD68 transcripts) a few days after MRT. CONCLUSIONS: These results show the superiority of MRT over BB radiation therapy when applied at comparable doses, suggesting that spatial fractionation is responsible for a specific and particularly efficient tissue response. The higher induction of cell death and immune cell activation in brain tumors treated by MRT may be involved in such responses.

In vivo pink-beam imaging and fast alignment procedure for rat brain tumor radiation therapy.

A fast positioning method for brain tumor microbeam irradiations for preclinical studies at third-generation X-ray sources is described. The three-dimensional alignment of the animals relative to the X-ray beam was based on the X-ray tomography multi-slices after iodine infusion. This method used pink-beam imaging produced by the ID17 wiggler. A graphical user interface has been developed in order to define the irradiation parameters: field width, height, number of angles and X-ray dose. This study is the first reporting an image guided method for soft tissue synchrotron radiotherapy. It allowed microbeam radiation therapy irradiation fields to be reduced by a factor of ∼20 compared with previous studies. It permitted more targeted, more efficient brain tumor microbeam treatments and reduces normal brain toxicity of the radiation treatment.

Tolerance to Dose Escalation in Minibeam Radiation Therapy Applied to Normal Rat Brain: Long-Term Clinical, Radiological and Histopathological Analysis.

The major limitation to reaching a curative radiation dose in radioresistant tumors such as malignant gliomas is the high sensitivity to radiation and subsequent damage of the surrounding normal tissues. Novel dose delivery methods such as minibeam radiation therapy (MBRT) may help to overcome this limitation. MBRT utilizes a combination of spatial fractionation of the dose and submillimetric (600 µm) field sizes with an array ("comb") of parallel thin beams ("teeth"). The dose profiles in MBRT consist of peaks and valleys. In contrast, the seamless irradiations of the several squared centimeter field sizes employed in standard radiotherapy result in homogeneous dose distributions (and consequently, flat dose profiles). The innovative dose delivery methods employed in MBRT, unlike standard radiation therapy, have demonstrated remarkable normal tissue sparing. In this pilot work, we investigated the tolerance of the rat brain after whole-brain MBRT irradiation. A dose escalation was used to study the tissue response as a function of dose, so that a threshold could be established: doses as high as 100 Gy in one fraction were still well tolerated by the rat brain. This finding suggests that MBRT may be used to deliver higher and potentially curative radiation doses in clinical practice.

Multiparametric MRI as an early biomarker of individual therapy effects during concomitant treatment of brain tumours.

The aim of this study was to determine the ability of multiparametric MRI to identify the early effects of individual treatment, during combined chemo-radiotherapy on brain tumours. Eighty male rats bearing 9L gliosarcomas were randomized into four groups: untreated, anti-angiogenic therapy (SORA group), microbeam radiation therapy (MRT group) and both treatments (MRT+SORA group). Multiparametric MRI (tumour volume, diffusion-weighted MR imaging (ADC), blood volume fraction (BVf), microvessel index (VSI), vessel wall integrity (AUC(P846)) and tissue oxygen saturation (StO2)) was performed 1 day before and 2, 5 and 8 days after treatment initiation. Unpaired t-tests and one-way ANOVA were used for statistical analyses. Each MR parameter measured in our protocol was revealed to be sensitive to tumour changes induced by any of the therapies used (individually or combined). When compared with untreated tumours, SORA induced a decrease in BVf, VSI, StO2 and AUC(P846), MRT generated an increase in ADC and AUC(P846) and combined therapies yielded mixed effects: an increase in ADC and AUC(P846) and a decrease in BVf, StO2 and AUC(P846). MRT and MRT+SORA significantly slowed tumour growth. Despite these two groups presenting with similar tumour sizes, the information yielded from MR multiparameter assessment indicated that, when used concomitantly, each therapy induced distinguishable and appreciable physiological changes in the tumour. Our results suggest that multiparametric MRI can monitor the effects of individual treatments, used concomitantly, on brain tumours. Such monitoring would be useful for the detection of tumour resistance to drug/radiotherapy in patients undergoing concomitant therapies.