Effects of pulsed, spatially fractionated, microscopic synchrotron X-ray beams on normal and tumoral brain tissue.

Microbeam radiation therapy (MRT) uses highly collimated, quasi-parallel arrays of X-ray microbeams of 50-600keV, produced by third generation synchrotron sources, such as the European Synchrotron Radiation Facility (ESRF), in France. The main advantages of highly brilliant synchrotron sources are an extremely high dose rate and very small beam divergence. High dose rates are necessary to deliver therapeutic doses in microscopic volumes, to avoid spreading of the microbeams by cardiosynchronous movement of the tissues. The minimal beam divergence results in the advantage of steeper dose gradients delivered to a tumor target, thus achieving a higher dose deposition in the target volume in fractions of seconds, with a sharper penumbra than that produced in conventional radiotherapy. MRT research over the past 20 years has yielded many results from preclinical trials based on different animal models, including mice, rats, piglets and rabbits. Typically, MRT uses arrays of narrow ( approximately 25-100 microm wide) microplanar beams separated by wider (100-400 microm centre-to-centre) microplanar spaces. The height of these microbeams typically varies from 1 to 100 mm, depending on the target and the desired preselected field size to be irradiated. Peak entrance doses of several hundreds of Gy are surprisingly well tolerated by normal tissues, up to approximately 2 yr after irradiation, and at the same time show a preferential damage of malignant tumor tissues; these effects of MRT have now been extensively studied over nearly two decades. More recently, some biological in vivo effects of synchrotron X-ray beams in the millimeter range (0.68-0.95 mm, centre-to-centre distances 1.2-4 mm), which may differ to some extent from those of microscopic beams, have been followed up to approximately 7 months after irradiation. Comparisons between broad-beam irradiation and MRT indicate a higher tumor control for the same sparing of normal tissue in the latter, even if a substantial fraction of tumor cells are not receiving a radiotoxic level of radiation. The hypothesis of a selective radiovulnerability of the tumor vasculature versus normal blood vessels by MRT, and of the cellular and molecular mechanisms involved remains under investigation. The paper highlights the history of MRT including salient biological findings after microbeam irradiation with emphasis on the vascular components and the tolerance of the central nervous system. Details on experimental and theoretical dosimetry of microbeams, core issues and possible therapeutic applications of MRT are presented.

Survival of rats bearing advanced intracerebral F 98 tumors after glutathione depletion and microbeam radiation therapy: conclusions from a pilot project.

BACKGROUND: Resistance to radiotherapy is frequently encountered in patients with glioblastoma multiforme. It is caused at least partially by the high glutathione content in the tumour tissue. Therefore, the administration of the glutathione synthesis inhibitor Buthionine-SR-Sulfoximine (BSO) should increase survival time. METHODS: BSO was tested in combination with an experimental synchrotron-based treatment, microbeam radiation therapy (MRT), characterized by spatially and periodically alternating microscopic dose distribution. One hundred thousand F98 glioma cells were injected into the right cerebral hemisphere of adult male Fischer rats to generate an orthotopic small animal model of a highly malignant brain tumour in a very advanced stage. Therapy was scheduled for day 13 after tumour cell implantation. At this time, 12.5% of the animals had already died from their disease. The surviving 24 tumour-bearing animals were randomly distributed in three experimental groups: subjected to MRT alone (Group A), to MRT plus BSO (Group B) and tumour-bearing untreated controls (Group C). Thus, half of the irradiated animals received an injection of 100 µM BSO into the tumour two hours before radiotherapy. Additional tumour-free animals, mirroring the treatment of the tumour-bearing animals, were included in the experiment. MRT was administered in bi-directional mode with arrays of quasi-parallel beams crossing at the tumour location. The width of the microbeams was ≈28 µm with a center-to-center distance of ≈400 µm, a peak dose of 350 Gy, and a valley dose of 9 Gy in the normal tissue and 18 Gy at the tumour location; thus, the peak to valley dose ratio (PVDR) was 31. RESULTS: After tumour-cell implantation, otherwise untreated rats had a mean survival time of 15 days. Twenty days after implantation, 62.5% of the animals receiving MRT alone (group A) and 75% of the rats given MRT + BSO (group B) were still alive. Thirty days after implantation, survival was 12.5% in Group A and 62.5% in Group B. There were no survivors on or beyond day 35 in Group A, but 25% were still alive in Group B. Thus, rats which underwent MRT with adjuvant BSO injection experienced the largest survival gain. CONCLUSIONS: In this pilot project using an orthotopic small animal model of advanced malignant brain tumour, the injection of the glutathione inhibitor BSO with MRT significantly increased mean survival time.

Inhibition of submandibular and lacrimal gland infiltration in nonobese diabetic mice by transgenic expression of soluble TNF-receptor p55.

Besides a prominent mononuclear cell infiltration of the islets of Langerhans, nonobese diabetic (NOD) mice also show massive cellular infiltrates of the submandibular and lacrimal glands concomitant with histological signs of tissue damage. To obtain insights into the mechanisms operative during the initiation and progression of tissue damage, we followed by in situ hybridization the appearance of cells containing mRNA of the gene encoding the proinflammatory cytokine TNF-alpha in the cellular infiltrates. Cells expressing TNF-alpha are mainly located in infiltrates, are absent in nonaffected glands, and are preferentially found among CD4 T cells. Secretion of TNF-alpha by gland-infiltrating cells was confirmed by an ELISPOT procedure. Direct evidence for an instrumental role of TNF-alpha in initiation and progression of submandibular and lacrimal gland infiltration is provided by the observed significant reduction in the extent of infiltration in nonobese diabetic mice transgenic for a soluble TNF receptor p55 fused to the Fc part of human IgG3. This protection from infiltration is paralleled by decreased expression of the adhesion molecules ICAM-1 and VCAM-1 in submandibular and lacrimal glands. These data suggest a central role of TNF-alpha in the initiation and progression of autoimmune tissue destruction of salivary glands and indicate beneficial effects of soluble TNF receptors in the treatment of organ-specific autoimmune diseases.

BCA-1 is highly expressed in Helicobacter pylori-induced mucosa-associated lymphoid tissue and gastric lymphoma.

Infection with Helicobacter pylori (Hp) induces the formation of lymphoid tissue in the stomach and the occasional development of primary gastric B-cell lymphomas. We have studied the expression of 2 chemokines that attract B lymphocytes, BCA-1 and SLC, in gastric tissue samples obtained from patients with chronic gastritis induced by Hp infection or nonsteroidal anti-inflammatory drugs, as well as from patients with Hp-associated low-grade and high-grade gastric lymphomas. High-level expression of BCA-1 and its receptor, CXCR5, was observed in all mucosal lymphoid aggregates and in the mantle zone of all secondary lymphoid follicles in Hp-induced gastric mucosa-associated lymphoid tissue (MALT). Follicular dendritic cells and B lymphocytes are possible sources of BCA-1, which is not expressed by T lymphocytes, macrophages, or CD1a(+) dendritic cells. Strong expression of BCA-1 and CXCR5 was also detected in the transformed B cells of gastric MALT lymphomas. By contrast, SLC was confined almost exclusively to endothelial cells in and outside the lymphoid tissue. Only scant, occasional SLC expression was observed in the marginal zone of MALT follicles. Our findings indicate that BCA-1, which functions as a homing chemokine in normal lymphoid tissue, is induced in chronic Hp gastritis and is involved in the formation of lymphoid follicles and gastric lymphomas of the MALT type.

Computational modelling of the cerebral cortical microvasculature: effect of x-ray microbeams versus broad beam irradiation.

Microbeam Radiation Therapy is an innovative pre-clinical strategy which uses arrays of parallel, tens of micrometres wide kilo-voltage photon beams to treat tumours. These x-ray beams are typically generated on a synchrotron source. It was shown that these beam geometries allow exceptional normal tissue sparing from radiation damage while still being effective in tumour ablation. A final biological explanation for this enhanced therapeutic ratio has still not been found, some experimental data support an important role of the vasculature. In this work, the effect of microbeams on a normal microvascular network of the cerebral cortex was assessed in computer simulations and compared to the effect of homogeneous, seamless exposures at equal energy absorption. The anatomy of a cerebral microvascular network and the inflicted radiation damage were simulated to closely mimic experimental data using a novel probabilistic model of radiation damage to blood vessels. It was found that the spatial dose fractionation by microbeam arrays significantly decreased the vascular damage. The higher the peak-to-valley dose ratio, the more pronounced the sparing effect. Simulations of the radiation damage as a function of morphological parameters of the vascular network demonstrated that the distribution of blood vessel radii is a key parameter determining both the overall radiation damage of the vasculature and the dose-dependent differential effect of microbeam irradiation.

Radiosurgical palliation of aggressive murine SCCVII squamous cell carcinomas using synchrotron-generated X-ray microbeams.

Microbeam radiosurgery (MBRS), also referred to as microbeam radiation therapy (MRT), was tested at the European Synchrotron Radiation Facility (ESRF). The left tibiofibular thigh of a mouse bearing a subcutaneously (sc) implanted mouse model (SCCVII) of aggressive human squamous-cell carcinoma was irradiated in two orthogonal exposures with or without a 16 mm aluminium filter through a multislit collimator (MSC) by arrays of nearly parallel microbeams spaced 200 microm on centre (oc). The peak skin-entrance dose from each exposure was 442 Gy, 625 Gy, or 884 Gy from 35 microm wide beams or 442 Gy from 70 microm wide beams. The 442/35, 625/35, 884/35 and 442/70 MBRSs yielded 25 day, 29 day, 37 day and 35 day median survival times (MST) (post-irradiation), respectively, exceeding the 20 day MST from 35 Gy-irradiation of SCCVIIs with a seamless 100 kVp X-ray beam.

Survival of tumor-bearing mice exposed to heavy water or heavy water plus methotrexate.

Moderate body deuteration combined with a cytostatic drug [methotrexate (MTX)] significantly increases the survival time of young adult DBA/2 mice bearing transplantable P815. L5178Y, or L1210 tumors. Neoplastic cells were grown in vitro from tumor stock and injected i.p. into mice from two groups, one drinking tap water, and other drinking 30% heavy water in tap water. One-half of the animals in each of these two groups was given a single injection of MTX (4 mg/kg body weight) on 3 consecutive days per week. At death, extension of primary and metastatic tumors was examined and was found to be macro- and microscopically comparable in the corresponding groups. The mean survival time of untreated mice drinking tap water was about 2 weeks following injection of the fast-growing P815, L5178Y, or L1210 (V) tumors and approximately 5 weeks after injection of cells from a slower-growing L1210 subline. Body deuteration alone roughly doubled the survival time solely of mice bearing this L1210 subline. Treatment with MTX approximately doubled the mean survival time of hosts bearing one of the fast-growing tumors. Combined treatment with heavy water and MTX increased the mean survival time of the mice in all groups by 15 to 125% as compared to control values. The reasons for this effect are unknown. However, heavy water has been shown to exert antimitotic activity and to depress the incorporation of radioactive precursors into DNA of proliferating mammalian cells. The depression of antibody formation following antigenic stimulation and the reduction in numbers of nonneoplastic lymphoid cells of mice following moderate body deuteration may have contributed to the enhancement of MTX activity in addition to other effects of deuterium.

Somatostatin and vasoactive intestinal peptide receptors in human mesenchymal tumors: in vitro identification.

Somatostatin and vasoactive intestinal peptide (VIP) have been shown to be of diagnostic and therapeutic interest in several types of human epithelial tumors expressing the respective receptor. The present study evaluates the presence of somatostatin and VIP receptors in 64 primary or metastatic human mesenchymal tumors. In vitro receptor autoradiography on cryostat sections was performed using 125I-labeled [Tyr3]-octreotide as well as 125I-labeled [Leu8,D-Trp22,Try25]-somatostatin-28 as radioligands for somatostatin receptors and 125I-labeled VIP as radioligand for VIP receptors. Somatostatin receptors were identified in bone and vascular/perivascular tumors (3 of 3 osteosarcomas, 1 of 1 giant cell tumor, 2 of 2 angiosarcomas, and 4 of 4 hemangiopericytomas), in 2 of 2 synovial sarcomas, in 2 of 5 histiocytomas, and in several muscle cell tumors (1 of 2 leiomyomas, 2 of 4 leiomyosarcomas, and 3 of 5 rhabdomyosarcomas) but were absent in 4 liposarcomas, 3 mesotheliomas, 3 chondrosarcomas, 10 Ewing sarcomas, 11 schwannomas, and 5 Wilms' tumors. VIP receptors were identified in 3 of 3 differentiated liposarcomas, 2 of 2 angiosarcomas, 4 of 4 hemangiopericytomas, 2 of 2 synovial sarcomas, 3 of 3 mesotheliomas, 5 of 5 Wilms tumors, as well as in 2 of 5 histiocytomas, 1 of 2 leiomyomas, 2 of 4 leiomyosarcomas, 3 of 3 intermediately differentiated rhabdomyosarcomas, and 1 of 3 osteosarcomas but not in chondrosarcomas, Ewing sarcomas, schwannomas, or undifferentiated rhabdomyosarcomas. The receptors were located on neoplastic cells. The somatostatin receptors were of high affinity and of high specificity for biologically active somatostatin analogues with high affinity for somatostatin-14 and somatostatin-28 as well as for octreotide, thus representing the sst2 subtype; in a few cases of tumors having somatostatin receptors with low affinity for octreotide, in situ hybridization techniques identified preferentially sst1 mRNA. These data suggest that human mesenchymal tumors may be targets for somatostatin and/or VIP receptor in vivo imaging; they may also be potential targets for somatostatin or VIP analogue therapy.

Vasoactive intestinal peptide/pituitary adenylate cyclase-activating peptide receptor subtypes in human tumors and their tissues of origin.

The evaluation of peptide receptors in man is needed not only to discover the physiological target tissues of a given peptide but also to identify diseases with a sufficient receptor overexpression for diagnostic or therapeutic interventions. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) receptors have been evaluated in human tumors and in their tissues of origin using in vitro receptor autoradiography with 125I-VIP or 125I-acetyl-PACAP-27 in tissue sections. The VIP/PACAP receptor subtypes VPAC1, VPAC2, and PAC1 were evaluated in these tissues by determining the rank order of potencies of VIP and PACAP as well as VPAC1- and VPAC2-selective analogues. The VIP/PACAP receptors expressed in the great majority of the most frequently occurring human tumors, including breast (100% receptor incidence), prostate (100%), pancreas (65%), lung (58%), colon (96%), stomach (54%), liver (49%), and urinary bladder (100%) carcinomas as well as lymphomas (58%) and meningiomas (100%), are predominantly of the VPAC1 type. Their cells or tissues of origin, i.e., hepatocytes, breast lobules and ducts, urothelium, prostate glands, pancreatic ducts, lung acini, gastrointestinal mucosa, and lymphocytes, also predominantly express VPAC1. Leiomyomas predominantly express VPAC2 receptors, whereas paragangliomas, pheochromocytomas, and endometrial carcinomas preferentially express PAC1 receptors. Conversely, VPAC2 receptors are found mainly in smooth muscle (i.e., stomach), in vessels, and in stroma (e.g., of the prostate), whereas PAC1 receptors are present in the adrenal medulla and in some uterine glands. Whereas the very wide distribution of VIP/PACAP receptors in the normal human body is indicative of a key role of these peptides in human physiology, the high VIP/PACAP receptor expression in tumors may represent the molecular basis for clinical applications of VIP/PACAP such as in vivo scintigraphy and radiotherapy of tumors as well as VIP/PACAP analogue treatment for tumor growth inhibition.

Effects of single cyclophosphamide doses on the kinetics of thoracic duct lymph and blood leukocytes in calves.

After 5 or 20 mg cyclophosphamide per kg body weight, given once i.v., the output in thoracic duct lymph of small and large lymphoid cells, cells incorporating [3H]lymidine in vitro, mitotic cells, pyknotic cells, and/or the number of lymphocytes and neutrophils in peripheral blood were measured in six calves. The median grain count of labeled cells and the DNA content of pyknotic nucleic were determined. After both doses there was an exponential decrease and subsequent recovery of the median grain count. The larger dose caused a temporary cessation of lymphoid cell division, reduced the output of nondividing small lymphoid cells, and probably imparied proliferation of neutrophil precursors. The results suggest that increased cell production during recovery was due to changes in the growth fraction and that feedback mechanisms acting on G0-G1 cells controled the proliferation of lymphoid cells.

Expression of hypoxia-inducible factor-1alpha: a novel predictive and prognostic parameter in the radiotherapy of oropharyngeal cancer.

Hypoxia has long been recognized as detrimental to the successful treatment of malignant tumors with ionizing radiation. Because hypoxia-inducible factor (HIF)-1alpha plays an essential role in oxygen homeostasis in vitro, we explored the predictive potential of this factor in a cohort of 98 patients with squamous cell cancer of the oropharynx, who were treated by curative radiation therapy. Ninety-four % of the primary tumors showed overexpression of HIF-1alpha, relative to the surrounding tissue, as determined by immunohistochemistry. The degree of HIF-1alpha immunoreactivity correlated inversely with both the rate of complete remission of the primary tumor (odds ratio, 0.33; P = 0.03) and lymph node metastases (odds ratio, 0.34; P = 0.02) as well as with local failure-free survival (risk ratio, 2.15; P = 0.006), disease-free survival (risk ratio, 2.01; P = 0.008), and overall survival (risk ratio, 2.17; P = 0.002). The multivariate analysis revealed the predictive power of HIF-1alpha to be independent of other covariables. We conclude that HIF-1alpha is overexpressed in the vast majority of patients with squamous cell cancer of the oropharynx and that the degree of expression has predictive and prognostic significance in individuals undergoing curative radiation therapy.

Metastatic hormone-refractory prostatic adenocarcinoma expresses somatostatin receptors and is visualized in vivo by [111In]-labeled DTPA-D-[Phe1]-octreotide scintigraphy.

Thirty-one patients with metastatic hormone-refractory prostatic adenocarcinoma were investigated scintigraphically with the 111In-labeled somatostatin analogue [DTPA-D-Phe1]-octreotide (OctreoScan) and with 99mTc-labeled HDP. In vitro somatostatin receptor autoradiography was performed on biopsies obtained from eight patients with hormone-refractory prostatic adenocarcinoma. In 30 of 31 patients (94%), at least one metastasis was positive at OctreoScan scintigraphy. Of the 346 lesions detected with 99mTc-labeled HDP bone scintigraphy, 128 were visualized with the OctreoScan technique, thus accounting for a 37% detection rate. Two uptakes on OctreoScan could not be identified on bone scintigraphy and were, thus, assessed as false positive. The biopsies of the eight patients disclosed a low density of receptors, localized on the tumor cells, as demonstrated with receptor autoradiography. Two patients with untreated metastatic prostatic adenocarcinoma were investigated in vivo before the start of endocrine therapy. However, none of the lesions detected by bone scintigraphy in these patients could be visualized with the OctreoScan technique. Positron emission tomography using [11C] methionine showed a decreased uptake in a metastatic index lesion in a patient treated with octreotide. It is concluded that hormone-refractory prostatic adenocarcinoma expresses somatostain receptors both in vitro and in vivo. The results obtained form the basis for the development of a new tool for in vivo characterization and of a new treatment strategy in patients with hormone-refractory prostatic adenocarcinoma.

Synchrotron X-ray microtransections: a non invasive approach for epileptic seizures arising from eloquent cortical areas.

Synchrotron-generated X-ray (SRX) microbeams deposit high radiation doses to submillimetric targets whilst minimizing irradiation of neighboring healthy tissue. We developed a new radiosurgical method which demonstrably transects cortical brain tissue without affecting adjacent regions. We made such image-guided SRX microtransections in the left somatosensory cortex in a rat model of generalized epilepsy using high radiation doses (820 Gy) in thin (200 µm) parallel slices of tissue. This procedure, targeting the brain volume from which seizures arose, altered the abnormal neuronal activities for at least 9 weeks, as evidenced by a decrease of seizure power and coherence between tissue slices in comparison to the contralateral cortex. The brain tissue located between transections stayed histologically normal, while the irradiated micro-slices remained devoid of myelin and neurons two months after irradiation. This pre-clinical proof of concept highlights the translational potential of non-invasive SRX transections for treating epilepsies that are not eligible for resective surgery.

Multiple actions of somatostatin in neoplastic disease.

The role played by the neuropeptide somatostatin, also known as somatotropin release inhibitory factor (SRIF), in human cancer is not well understood. Recent investigations involving somatostatin receptors in normal and neoplastic human tissues suggest that the action is complex and involves both direct and indirect mechanisms. In this article, Jean-Claude Reubi and Jean Laissue describe the variety of biological mechanisms involved in neoplasia that are associated with somatostatin, and illustrate the therapeutic potential and present limitations of somatostatin analogues.

New irradiation geometry for microbeam radiation therapy.

Microbeam radiation therapy (MRT) has the potential to treat infantile brain tumours when other kinds of radiotherapy would be excessively toxic to the developing normal brain. MRT uses extraordinarily high doses of x-rays but provides unusual resistance to radioneurotoxicity, presumably from the migration of endothelial cells from 'valleys' into 'peaks', i.e., into directly irradiated microslices of tissues. We present a novel irradiation geometry which results in a tolerable valley dose for the normal tissue and a decreased peak-to-valley dose ratio (PVDR) in the tumour area by applying an innovative cross-firing technique. We propose an MRT technique to orthogonally crossfire two arrays of parallel, nonintersecting, mutually interspersed microbeams that produces tumouricidal doses with small PVDRs where the arrays meet and tolerable radiation doses to normal tissues between the microbeams proximal and distal to the tumour in the paths of the arrays.

Predominance of granulocytopoiesis in bone marrow grafts in the omenta of mice treated with erythropoietin.

The effects of erythropoietin on the differentiation of murine bone marrow injected into the omenta of x-irradiated mice were investigated. Experimental hosts were injected with 2.5 units of erythropoietin on days 0-7 and sacrificed on day 10. Control hosts were injected with saline or sheep serum. After 10 days the grafts were greater than 95% granulocytic regardless of host treatment. Since these grafts contain multipotent hematopoietic stem cells and the experimental hosts were exposed to large doses of erythropoietin, the results of this experiment indicate that a specialized microenvironment is required for murine erythropoiesis in vivo.

Protection of mice from whole body gamma irradiation by deuteration of drinking water: hematologic findings.

Partial deuteration of mice by ingestion of 29% heavy water for 12 days prior to irradiation lessened their susceptibility to lethal doses of whole body gamma irradiation from a 60Co source. Deuteration alone slightly reduced the number of nucleated bone marrow cells, blood leukocytes, and platelets. After exposure to 8.5 Gy, all mice drank tap water. Radiation-induced destruction of hemopoietic and lymphoid tissues was of equal degree in deuterated and control animals. Conversely, nucleated bone marrow cells, blood leukocytes and platelets, endogenous spleen colonies, and thymus of deuterated mice displayed signs of an accelerated and/or enhanced regeneration. The cytokinetic changes observed in deuterated animals were consistent with a protective effect for pluripotent stem cells at the time of irradiation.

Hemopoietic effects in mice of a transplanted, granulocytosis-inducing tumor.

A transplanted tumor that induces granulocytosis and produces colony stimulating factor (CSF) was studied in mice during several passages. The sequence of events leading to granulocytosis was characterized. Band granulocytes were increased 3 days after tumor inoculation, while simultaneously CFU-s and CFU-c in bone marrow and spleen were transitorily low. This was followed by rapid accumulation of CFU-c and CFU-s in spleen, and by successive waves of increased mitotable and non-mitotable granulocytes in spleen and marrow. In contrast, marrow CFU-c and CFU-s remained normal or slightly decreased.

Microbeam radiation therapy: Clinical perspectives.

Microbeam radiation therapy (MRT), a novel form of spatially fractionated radiotherapy (RT), uses arrays of synchrotron-generated X-ray microbeams (MB). MRT has been identified as a promising treatment concept that might be applied to patients with malignant central nervous system (CNS) tumours for whom, at the current stage of development, no satisfactory therapy is available yet. Preclinical experimental studies have shown that the CNS of healthy rodents and piglets can tolerate much higher radiation doses delivered by spatially separated MBs than those delivered by a single, uninterrupted, macroscopically wide beam. High-dose, high-precision radiotherapies such as MRT with reduced probabilities of normal tissue complications offer prospects of improved therapeutic ratios, as extensively demonstrated by results of experiments published by many international groups in the last two decades. The significance of developing MRT as a new RT approach cannot be understated. Up to 50% of cancer patients receive conventional RT, and any new treatment that provides better tumour control whilst preserving healthy tissue is likely to significantly improve patient outcomes.

Synchrotron X-ray microbeams: A promising tool for drug-resistant epilepsy treatment.

Epilepsy is one of the most important neurological diseases. It concerns about 1% of the population worldwide. Despite the discovery of new molecules, one third of epileptic patients are resistant to anti-epileptic drugs and among them only a few can benefit from resective surgery. In this context, radiotherapy is an interesting alternative to the other treatments and several clinical devices exist (e.g., Gamma Knife(®)). The European Synchrotron Radiation Facility offers the possibility to develop new methods of radiosurgery and to study their antiepileptic effects. Here, we discuss several studies that we performed recently to test and try to understand the antiepileptic effects of X-ray synchrotron microbeams in different animal models of epilepsy. We showed a decrease of seizures after Interlaced Microbeam Radiotherapy (IntMRT) of the somatosensory cortex, known as the seizure generator, in a genetic model of absence epilepsy. These antiepileptic effects were stable over 4 months and with low tissular and functional side-effects. The irradiated pyramidal neurons still displayed their physiological activity but did not synchronize anymore. We also obtained a lasting suppression of seizures after IntMRT of the dorsal hippocampus in a mouse model of mesiotemporal lobe epilepsy. However, an important variability of antiepileptic efficiency was observed probably due to the small size of the targeted structure. Despite these encouraging proofs-of-concepts, there is now a need to adapt IntMRT to other models of epilepsy in rodents which are close to refractory forms of epilepsy in human patients and to implement this approach to non-human primates, before moving to clinical trials.