Chaos in free electron laser oscillators

The chaotic nature of a storage-ring Free Electron Laser (FEL) is investigated. The derivation of a low embedding dimension for the dynamics allows the low-dimensionality of this complex system to be observed, whereas its unpredictability is demonstrated, in some ranges of parameters, by a positive Lyapounov exponent. The route to chaos is then explored by tuning a single control parameter, and a period-doubling cascade is evidenced, as well as intermittence.Comment: Accepted in EPJ

Synchrotron radiation-based experimental determination of the optimal energy for cell radiotoxicity enhancement following photoelectric effect on stable iodinated compounds

This study was designed to experimentally evaluate the optimal X-ray energy for increasing the radiation energy absorbed in tumours loaded with iodinated compounds, using the photoelectric effect. SQ20B human cells were irradiated with synchrotron monochromatic beam tuned at 32.8, 33.5, 50 and 70 keV. Two cell treatments were compared to the control: cells suspended in 10 mg ml1 of iodine radiological contrast agent or cells pre-exposed with 10 mM of iodo-desoxyuridine (IUdR) for 48 h. Our radiobiological end point was clonogenic cell survival. Cells irradiated with both iodine compounds exhibited a radiation sensitisation enhancement. Moreover, it was energy dependent, with a maximum at 50 keV. At this energy, the sensitisation calculated at 10% survival was equal to 2.03 for cells suspended in iodinated contrast agent and 2.60 for IUdR. Cells pretreated with IUdR had higher sensitisation factors over the energy range than for those suspended in iodine contrast agent. Also, their survival curves presented no shoulder, suggesting complex lethal damages from Auger electrons. Our results confirm the existence of the 50 keV energy optimum for a binary therapeutic irradiation based on the presence of stable iodine in tumours and an external irradiation. Monochromatic synchrotron radiotherapy concept is hence proposed for increasing the differential effect between healthy and cancerous tissue irradiation

Towards in vivo dosimetry for contrast enhanced synchrotron stereotactic radiation therapy based on iodine x-ray spectroscopy

The first trial applications of Contrast-Enhanced Synchrotron Stereotactic Radiation Therapy (SSRT) is underway since June 2012 at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France). The phase I-II clinical trial is designed to test the feasibility and safety of SSRT through a dose escalation protocol. Contrast enhanced radiotherapy achieves localized dose enhancement due to higher photoelectric effect rate in the target. This increase is obtained through the preferential uptake of high-Z media (iodine) in the tumoral area combined with irradiations with medium energy synchrotron x-rays. In vivo dosimetry (i.e. experimental dosimetry in real time during the treatment) would be a serious added value to the project, in terms of online dose monitoring and quality control. It is challenging to perform in vivo dosimetry with the currently available conventional clinical techniques. In this work we investigated a method using x-ray fluorescence detection to derive the iodine concentration contained in a tumor during the treatment of a patient, as a first step towards in vivo dosimetry. A mean iodine concentration of 0.33 ± 0.22 mg/ml has been retrieved in the tumor of the patient compared to 2 mg/ml expected would correspond to 3% local dose enhancement in the tumor. Further work will be performed to improve the attenuation correction method. The expected amount of iodine should be 2 mg/ml in the tumor (20% dose enhancement). This method is suitable to detect iodine in the target but has some problem in quantifying the real amount of iodine present during the irradiation

Theoretical approach based on Monte-Carlo simulations to predict the cell survival following BNCT

International audienceWe present here a very preliminary work on BNCT Dosimetry. The approach is as follows:A full Monte Carlo calculation is used to separate all dose components and determine the corresponding physical dose fractions with a realistic clinical model.These dose fractions are then used as mixed fields to predict cell-survivals and RBE values for a specific cell-line, thanks to the radiobiological model NanOxTM

A Novel Intravital Method to Evaluate Cerebral Vasospasm in Rat Models of Subarachnoid Hemorrhage: A Study with Synchrotron Radiation Angiography

Precise in vivo evaluation of cerebral vasospasm caused by subarachnoid hemorrhage has remained a critical but unsolved issue in experimental small animal models. In this study, we used synchrotron radiation angiography to study the vasospasm of anterior circulation arteries in two subarachnoid hemorrhage models in rats. Synchrotron radiation angiography, laser Doppler flowmetry-cerebral blood flow measurement, [125I]N-isopropyl-p-iodoamphetamine cerebral blood flow measurement and terminal examinations were applied to evaluate the changes of anterior circulation arteries in two subarachnoid hemorrhage models made by blood injection into cisterna magna and prechiasmatic cistern. Using synchrotron radiation angiography technique, we detected cerebral vasospasm in subarachnoid hemorrhage rats compared to the controls (p<0.05). We also identified two interesting findings: 1) both middle cerebral artery and anterior cerebral artery shrunk the most at day 3 after subarachnoid hemorrhage; 2) the diameter of anterior cerebral artery in the prechiasmatic cistern injection group was smaller than that in the cisterna magna injection group (p<0.05), but not for middle cerebral artery. We concluded that synchrotron radiation angiography provided a novel technique, which could directly evaluate cerebral vasospasm in small animal experimental subarachnoid hemorrhage models. The courses of vasospasm in these two injection models are similar; however, the model produced by prechiasmatic cistern injection is more suitable for study of anterior circulation vasospasm

The ThomX project status

Work supported by the French Agence Nationale de la recherche as part of the program EQUIPEX under reference ANR-10-EQPX-51, the Ile de France region, CNRS-IN2P3 and Université Paris Sud XI - http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/wepro052.pdfA collaboration of seven research institutes and an industry has been set up for the ThomX project, a compact Compton Backscattering Source (CBS) based in Orsay - France. After a period of study and definition of the machine performance, a full description of all the systems has been provided. The infrastructure work has been started and the main systems are in the call for tender phase. In this paper we will illustrate the definitive machine parameters and components characteristics. We will also update the results of the different technical and experimental activities on optical resonators, RF power supplies and on the electron gun

Heavy-atom enhanced synchrotron stereotactic radiotherapy of brain tumors: from DNA to preclinical studies

Gliomas are the most frequent primary brain tumors in adults. Despite multimodality treatment strategies that combine surgery, chemotherapy and radiotherapy, high grade gliomas are almost uniformly fatal. Heavy-atom-enhanced synchrotron stereotactic radiotherapy (SSR) is a novel therapeutic modality proposed to increase the toxicity to the tumor while protecting the surrounding healthy tissue. It consists in selective accumulation of high-Z elements in tumor followed by stereotactic irradiation, in tomography mode, with monochromatic X-rays from a synchrotron source, tuned at an optimal energy. Two complimentary SSR approaches have been successfully developed in the past 5 years, and may be promising in high-grade glioma management: iodine-enhanced SSR , with an iodinated contrast agent; and Pt-enhanced SSR , , a concomitant radio-chemotherapy treatment with locoregional injection of platinated chemotherapy drugs. Several in vitro and in vivo experiments have been carried out at the European Synchrotron Radiation Facility, either with iodine or platinum. In vivo experiments are performed on F98 glioma-bearing rats. The F98 glioma model simulates several characteristics of human glioblastoma including lethality following treatment with a variety of therapeutic modalities. Recently, we have shown that a significant increase in survival time is obtained when the platinated drug (cisplatin or carboplatin) is infused intratumoraly followed by X-rays irradiation. Furthermore, a significant percent of animals are cured. To optimise the treatment, work is in progress in order to determine and increase the incorporation of heavy-atoms in tumoral cells and also to improve the intracerebral drug distribution by developing new injection methods and using different chemotherapeutic drugs including oxaliplatin, chlorotertpyridineplatinum and 5-iodo-2-deoxyuridine. In addition, efforts will be made to have a better understanding of the biological consequences at the molecular and cellular level of the SSR treatment. 1 - Adam JF et al, International Journal of Radiation Oncology, Biology, Physics 2006; 64:603-611. 2 Biston MC et al, Cancer Research 2004; 64:2317-2323. 3 Rousseau J et al, Clinical Cancer Research 2007;13:5195-5201

In vivo dosimetry for Synchrotron Stereotactic Radiation Therapy

International audienceThe first clinical study of therapeutic applications of Contrast-Enhanced Synchrotron Stereotactic Radiation Therapy (SSRT) is underway since June 2012 at the European Synchrotron Radiation Facility (ESRF). The phase I-II clinical trial is designed to test the feasibility and safety of SSRTthrough a dose escalation protocol. So far, 10 patients suffering from brain metastasis of medium to small volume have already been treated using this modality. A localized dose enhancement is obtained due to higher photoelectric effect rate in the target and is directly related to the amount iodine located in a given voxel of tissue (about 10% per mg/mL of iodine). The 3D iodine content in a given patient is derived from the 3D CT acquisition obtained during the dosimetry CT procedure and associated treatment planning [1] . In vivo dosimetry (i.e., experimental dosimetry in real time during the treatment) would be a serious added value to the project, in terms of online dose monitoring and quality assurance. It is challenging to perform in vivo dosimetry with the currently available conventional clinical techniques [2] . Entrance measurements using semiconductor detectors lead tosignificant incoming beam perturbations (medium energy x-rays) whereas it’s complicated to set-up portal imaging techniques, as the iodine content is not taken into account. The idea is to measure the iodine fluorescence X-rays yield emitted from the target during the irradiation. This can be achieved using spectrometry techniques and iodine Kα peaks analysis. Our first approach consists in developing a 0D model with a CZT detector pointing on the irradiation isocenter to characterize the relationship between peak contents and average iodine concentration obtained in the tumor during irradiation [3]. Fluorescence from iodine tubes of different concentrations (0.5 to 20 mg/mL) were acquired in air and inserted into an anthropomorphic radiosurgery phantom. The same setup has been recently used on the last patient treated in SSRT at the ESRF. The detector was pointing the isocentre and the spectra were recorded during the three irradiation incidences. The iodine concentration was plotted versus the number of counts in the fluorescence channel for the tubes in air. We notice a non-linearity in the curve due to self-absorption [4]. Concerning the signalobtained in patients, it should be furthered analyzed in order to retrieve the concentration. For this purpose, simulations should be used, using a priori information from the dosimetry CT scans.. A potential improvement of the technique would be its transfer to a 3D modality using a pixelatedspectrometric detector.References[1] L. Obeid,et al. J. Cereb. Blood Flow Metab., vol. 34, no. 4, pp. 638–45, Apr. 2014.[2] B. Mijnheer,et al. Med. Phys., vol. 40, no. 7, p. 070903, Jul. 2013.[3] A. M. Rene Van Grieken, “Handbook of X-Ray Spectrometry, Second Edition,.” [Online].[4] C. Hall, J. Instrum., vol. 8, no. 06, pp. C06007–C06007, 2013