Spectral and spatial shaping of a laser-produced ion beam for radiation-biology experiments

International audience; The study of radiation biology on laser-based accelerators is most interesting due to the unique irradiation conditions they can produce, in terms of peak current and duration of the irradiation. In this paper we present the implementation of a beam transport system to transport and shape the proton beam generated by laser-target interaction for in vitro irradiation of biological samples. A set of four permanent magnet quadrupoles is used to transport and focus the beam, efficiently shaping the spectrum and providing a large and relatively uniform irradiation surface. Real time, absolutely calibrated, dosimetry is installed on the beam line, to enable shot-to-shot control of dose deposition in the irradiated volume. Preliminary results of cell sample irradiation are presented to validate the robustness of the full system

Monte Carlo simulation of a CPO beam line: modelling the nuclear interactions

The Proton Therapy Center in Orsay (CPO) and CEA/DAPNIA launched the joint project on Monte Carlo modeling of a CPO beam line with the aim to achieve a prediction of dose distribution in all the calibration configurations (depth and the shape of the tumor) better than 2%. The calculation module is intended to be used for the absolute dosimetry of the clinical beam (patient Quality Assurance - QA), and in a second stage for predicting the dose distribution on a voxelized phantom constructed from the Computer Tomography (CT) patient's data. The MCNPX code was used as a basic Monte Carlo simulation tool in this study. All the elements of a CPO beam line were modelled with sub-millimetric precision. To speed up the calculations of modulated dose profiles in water phantom, a routine simulating rotation of modulator wheel was created to save phase space of particle tracks crossing the modulator. The modeling of nuclear interactions, which contribute noticeably into the total absorbed dose in water phantom at the prescribed proton energy (average raw beam energy 201 MeV), was improved by means of creation and implementation of the two new evaluated proton-induced nuclear data files up to 200 MeV for 1H and 16O. Thus, the simulations of 3D dose profiles in water show excellent agreement with measured data allowing to move forward to the absolute dose calibrations

Monte Carlo modeling of a protontherapy beam line dedicated to ophthalmologic treatments

A Monte Carlo modeling tool was applied at the Institut-Curie Centre de Protonthérapie d'Orsay, France, to simulate the passively scattered beam line used for treatment of ocular melanoma. The primary aim of this study is to validate the model for subsequent calculation of patient doses due to secondary neutrons. The Monte Carlo code MCNPX is used here to model the geometry of the beam line. The beam parameters at the entrance of the ophthalmologic beam line are not well known (beam emittance, lateral distribution, and energy spread). Hence, to accurately implement the beam source in the model, we need to calculate and measure these parameters in the first step of this study. Then, we perform comparisons between calculated and measured proton absorbed dose profiles under various scattering conditions. Comparisons between calculated and measured depth versus dose profiles show discrepancies <0.6 mm (range) and <1.1 mm (beam size and penumbra) for the lateral dose profiles. Hence, calculated relative dose profiles are considered to be correctly described by the Monte Carlo model. Some improvements are still needed to reproduce absolute dose profiles. This study should lead to the use of the numerical model for radiation protection applications

Mechanisms of phosphene generation in ocular proton therapy as related to space radiation exposure

International audienceParticle therapy provides an opportunity to study the human response to space radiation in ground-based facilities. On this basis, a study of light flashes analogous to astronauts’ phosphenes reported by patients undergoing ocular proton therapy has been undertaken. The influence of treatment parameters on phosphene generation was investigated for 430 patients treated for a choroidal melanoma at the proton therapy centre of the Institut Curie (ICPO) in Orsay, France, between 2008 and 2011. 60% of them report light flashes, which are predominantly (74%) blue. An analysis of variables describing the patient’s physiology, properties of the tumour and dose distribution shows that two groups of tumour and beam variables are correlated with phosphene occurrence. Physiology is found to have no influence on flash triggering. Detailed correlation study eventually suggests a possible twofold mechanism of phosphene generation based on (i) indirect Cerenkov light in the bulk of the eye due to nuclear interactions and radioactive decay and (ii) direct excitation of the nerve fibres in the back of the eye and/or radical excess near the retina

Dosimetric characteristics of four PTW microDiamond detectors in high-energy proton beams

International audienceSmall diamond detectors are useful for the dosimetry of high-energy proton beams. However, linear energy transfer (LET) dependence has been observed in the literature with such solid state detectors. A novel synthetic diamond detector has recently become commercially available from the manufacturer PTW-Freiburg (PTW microDiamond type 60019). This study was designed to thoroughly characterize four microDiamond detectors in clinical proton beams, in order to investigate their response and their reproducibility in high LET regions. Very good dosimetric characteristics were observed for two of them, with good stability of their response (deviation less than 0.4% after a pre-irradiation dose of approximately 12 Gy), good repeatability (coefficient of variation of 0.06%) and a sensitivity of approximately 0.85 nC Gy(-1). A negligible dose rate dependence was also observed for these two microDiamonds with a deviation of the sensitivity less than 0.7% with respect to the one measured at the reference dose rate of 2.17 Gy min(-1), in the investigated dose rate range from 1.01 Gy min(-1) to 5.52 Gy min(-1). Lateral dose profile measurements showed the high spatial resolution of the microDiamond oriented with its stem perpendicular to the beam axis and with its small sensitive thickness of about 1 mu m in the scanning profile direction. Finally, no significant LET dependence was found with these two diamond dosimeters in comparison to a reference ionization chamber (model IBA PPC05). These good results were in accordance to the literature. However, this study showed also a non reproducibility between the devices in terms of stability, sensitivity and LET dependence, since the two other microDiamonds characterized in this work showed different dosimetric characteristics making them not suitable for proton beam dosimetry with a maximum difference of the peak-to-plateau ratio of 6.7% relative to the reference ionization chamber in a clinical 138 MeV proton beam

Spatial fractionation of the dose in proton therapy: Proton minibeam radiation therapy

International audienceIn radiation therapy, a renewed interest is emerging for the study of spatially fractionated irradiation. In this article, a few applications using spatial fractionation of the dose will be discussed with a focus on proton minibeam radiation therapy. Examples of calculated dose (1D profiles and 2D dose distributions) and biological evidence obtained so far will be presented for various spatially fractionated techniques GRID, micro- and minibeam radiation therapy. Recent results demonstrating that proton minibeam radiation therapy leads to an increase in normal tissues sparing will be discussed, which opens the door to a dose escalation in the tumour and a possibly efficient treatment of very radioresistant tumours

Secondary neutron doses in proton therapy treatments of ocular melanoma and craniopharyngioma

International audienceMonte Carlo simulations were used to assess secondary neutron doses received by patients treated with proton therapy for ocular melanoma and craniopharyngioma. MCNPX calculations of out-of-field doses were done for ∼20 different organs considering realistic treatment plans and using computational phantoms representative of an adult male individual. Simulations showed higher secondary neutron doses for intracranial treatments, ∼14 mGy to the salivary glands, when compared with ocular treatments, ∼0.6 mGy to the non-treated eye. This secondary dose increase is mainly due to the higher proton beam energy (178 vs. 75 MeV) as well as to the impact of the different beam parameters (modulation, collimation, field size etc.). Moreover, when compared with published data, the assessed secondary neutron doses showed similar trends, but sometimes with sensitive differences. This confirms secondary neutrons to be directly dependent on beam energy, modulation technique, treatment configuration and methodology