SPECTRAL SHIFTS IN THE NEAR ZONE OF A PARTIALLY COHERENT FIELD AFTER PASSING THROUGH A CIRCULAR APERTURE

Abstract In this paper, we investigate theoretically the spectral shifts in the near zone of a partially coherent field after passing through a circular aperture. The numerical results are presented for Lorentzian and Gaussian profiles of the original spectrum of the source. Various factors which have influenced on the spectral characteristics are also analyzed

Effect of Microstructure on Fatigue Properties of Several Ti-Alloys for Aerospace Application

A wide range of available Ti-alloys is used at Liebherr-Aerospace Lindenberg GmbH for several aeronautical applications in flight controls and landing gear systems. For these applications, the mechanical properties of conventionally manufactured Ti-alloys (α+β, near β) as well as additive manufactured Ti-alloy were optimized. Modification of the heat treatment parameters of a near-β titanium alloy leads to optimization of the hardening process of large cross-sections. This modification allows the adjustment of an optimum volume fraction of the primary α-phase resulting in enhancing of the elongation, fracture toughness and fatigue properties. For a fatigue critical forging part from (α+β)-alloy a slight modification of the chemical composition combined with an additional heat treatment step during the forging process was performed. The adjusted microstructure of the modified process exhibits better fatigue behavior when compared to the conventional microstructure. Ti6Al4V parts produced by Additive Manufacturing, printed with optimized parameters and followed by heat treatment will result in reasonable fatigue properties in all printing directions, reducing the anisotropy of the printed parts. These improvements bring Liebherr-Aerospace Lindenberg GmbH in the position to adapt the used titanium alloys for the needs in a wide range. For the evaluation of the microstructure, light and scanning electron microscopes were used. Furthermore a model described in the “Metallic Materials Properties Development and Standardization” (MMPDS) was modified and used for the evaluation of the fatigue results

A comparative evaluation of the performances of three built-in-storage-type solar water heaters

Three built-in-storage-type solar water heaters of equal volume were tested under identical conditions for performance evaluation. One of these water heaters was rectangular and the other two were triangular. One of the triangular water heaters had a baffle plate and the other did not. The triangular water heater with baffle plate was found to be not superior to the rectangular one in efficiency during the heating period. However, it was more efficient during the cooling period. The triangular water heater without the baffle plate was found to be the most efficient one during both the heating and the cooling periods

Evaluation of the size of micrometric/nanometric dosimeters for use in radiotherapy and medical physics

International audienceWhen treating tumors with radiotherapy, it is of utmost importance to ensure that the prescribed dose is accurately delivered to the target volumes. In that sense, in-vivo dosimetry in real time was recently implemented in radiotherapy departments. Dosimeter performance depends necessarily on physical and geometrical parameters (e.g. beam energy and distance from source to skin), which implies the use of correction factors. Implantable dosimeters are corrections. They should be as small as possible, but still they should provide reliable measurements to comply with the requirements of clinical practice in routine radiotherapy. The state-of-the-art of these kind of dosimeters was the subject of a review elsewhere (1), which reported that implantable detectors of submillimetric size are currently available. The purpose of this study is to assess by Monte- Carlo simulations how much the size of such dosimeters can be decreased without jeopardizing their performance in a clinical environment. First, the interaction of photons from a 60Co source with water was simulated with a Monte-Carlo tool (2). The calculations were performed for 0.3, 0.1, 1, 3 and 10 Gy. Then, the distributions of specific energy were obtained for volumes representing dosimeters at nanometric and micrometric scales. Cylinders with equal radii of 0.3, 0.1, 1, 3 and 10 μm were used for this purpose. The mean specific energy was calculated for each case. To evaluate how the dosimeter size would impact its performance in a clinical scenario, the probability p that a dosimeter measurement falls outside a given interval defined around was estimated. Intervals were defined as [-γ ; +γ] with γ equal to 3%, 5% and 10%. The pattern of the distributions of specific energy evolves with dosimeter size and irradiation dose. Fixing the irradiation dose and decreasing the dosimeter radius or fixing the radius and decreasing the irradiation dose strongly widened the range in measured values of specific energy, but also increased the probability of yielding a non-null measurement. In turn, for higher doses and radii, distributions tend to Gaussian curves.Concerning the probability of obtaining a measurement outside the defined interval, the larger the interval, the irradiation dose, and the dosimeter radius, the smaller this probability became (see figure above). The simulation results showed that dosimeters at a nanometric scale are not able to yield statisticallyreproducible measurements and are therefore unfit for use in clinical practice. Increasing the size to micrometric scale led to a decrease in the statistical fluctuations. Nevertheless, to have enough accuracy at routine clinical doses (approximately 2 Gy in the tumor volume), a dosimeter radius of at least 10 μm is required

Construction des modèles radiobiologiques de type TCP (tumor control probability) et NTCP (normal tissue complication probability) : de la dose à la prédiction des effets cliniques

International audienceLa prescription de la dose en radiothérapie est actuellement basée sur des abaques qui ne prennent pas en compte la complexité de la relation patient/dose/effet. Leurs performances prédictives tant sur l’efficacité anti-tumorale que sur la toxicité peuvent être améliorées par l’utilisation de modèles radiobiologiques. C’est dans cette optique qu’ont été développés les modèles de calculs TCP (Tumor Control Probability) et NTCP (Normal Tissue Complication Probability). Leur construction comporte plusieurs étapes importantes utiles à comprendre. La première étape est basée sur les modèles radiobiologiques permettant de définir de manière plus ou moins complexe des taux de cellules survivantes après irradiation. Deux étapes supplémentaires sont nécessaires pour convertir la dose physique en dose biologique équivalente, notamment en dose biologique équivalente à 2 Gy (EQD2) ; d’une part, pour prendre en compte l’effet du fractionnement de la dose, tant pour le volume cible que les organes à risque, et d’autre part, pour réaliser sa conversion en une dose uniforme qui permet de modéliser l’effet produit par une dose hétérogène sur un organe (dose uniforme équivalente généralisée (gEUD) de Niemierko). Enfin, les modèles radiobiologiques de prédiction des effets cliniques transforment les doses en probabilités de contrôle tumoral (TCP) ou de toxicité (NTCP) en recourant aux paramètres qui rendent compte des caractéristiques radiobiologiques des tissus en question. L’utilisation de ces modèles est encore limitée en pratique courante mais comme les logiciels de radiothérapie en propose l’utilisation, il est important d’en connaître les conditions d’application

Fiber background rejection and crystal over-response compensation for GaN based in vivo dosimetry

International audienceFor dosimetric measurements using an implantable optical fiber probe with GaN (Gallium Nitride) scintillator as radioluminescence (RL) transducer, a bi-channel method is proposed to reject the background contribution of the irradiated fiber segment. It is based on spectral differences between the narrow-band light emission from GaN and the large-band background from the irradiated optical fiber. Experimental validation of this method using 6 MV photon beam has shown that the remaining background contribution after subtraction is below 1.2% for square field sizes ranging from 3 cm to 20 cm. Furthermore, a compensation method for the over-response of GaN is also proposed, since GaN is not tissue equivalent. The over-response factor of GaN exhibits a linear increase with square field aperture and depends on depth from phantom surface. This behaviour is modelled to allow compensation in specific conditions. The proposed method has been evaluated and has shown a maximum deviation of 3% for a 6 MV photon beam and 1% for an 18 MV photon beam at a depth beyond the build-up region

Dosimetry systems based on Gallium Nitride probe for radiotherapy, brachytherapy and interventional radiology

International audienceOur studies focus on dedicated dosimetry systems based on the Gallium Nitride (GaN) probe for Quality Assurance and patient safety in radiotherapy, brachytherapy and interventional radiology. The small size GaN transducer in the probe has high radioluminescence (RL) yield and rapid RL signal response for real time measurements. Preliminary prototypes of dedicated systems were tested in clinical conditions for external beam radiotherapy, brachytherapy and interventional radiology. The obtained pre-clinical results appear favorable and encouraging: in radiotherapy, GaN RL response has not significant dependence on the main influence parameters, excepted for the field size. In brachytherapy, using an instrumented phantom with integration of GaN probes allows real time verification of planned treatments. In interventional radiology, skin dose measurements using GaN probe based dosimeters show consistent results with those from a reference dosimeter