Experimental validation in a neutron exposure frame of the MINAS TIRITH for cell damage simulation.

In the domains of medicine and space exploration, refining risk assessment models for protecting healthy tissue from ionizing radiation is crucial. Understanding radiation-induced effects requires biological experimentations at the cellular population level and the cellular scale modeling using Monte Carlo track structure codes. We present MINAS TIRITH, a tool using Geant4-DNA Monte Carlo-generated databases to study DNA damage distribution at the cell population scale. It introduces a DNA damage location module and proposes a method to convert double-strand breaks (DSB) into DNA Damage Response foci. We evaluate damage location precision and DSB-foci conversion parameters. MINAS TIRITH's accuracy is validated againstγ-H2AX foci distribution from cell population exposed to monoenergetic neutron beams (2.5 or 15.1 MeV) under different configurations, yielding mixed radiation fields. Strong agreement between simulation and experimental results was found demonstrating MINAS TIRITH's predictive precision in radiation-induced DNA damage topology. Additionally, modeling intercellular damage variability within a population subjected to a specific macroscopic dose identifies subpopulations, enhancing realistic fate models. This approach advances our understanding of radiation-induced effects on cellular systems for risk assessment improvement.

MINAS TIRITH: a new tool for simulating radiation-induced DNA damage at the cell population level.

Objective. The mechanisms of radiation-induced DNA damage can be understood via the fundamental acquisition of knowledge through a combination of experiments and modeling. Currently, most biological experiments are performed by irradiating an entire cell population, whereas modeling of radiation-induced effects is usually performed via Monte Carlo simulations with track structure codes coupled to realistic DNA geometries of a single-cell nucleus. However, the difference in scale between the two methods hinders a direct comparison because the dose distribution in the cell population is not necessarily uniform owing to the stochastic nature of the energy deposition. Thus, this study proposed the MINAS TIRITH tool to model the distribution of radiation-induced DNA damage in a cell population.Approach. The proposed method is based on precomputed databases of microdosimetric parameters and DNA damage distributions generated using the Geant4-DNA Monte Carlo Toolkit. First, a specific energyzwas assigned to each cell of an irradiated population for a particular absorbed doseDabs,following microdosimetric formalism. Then, each cell was assigned a realistic number of DNA damage events according to the specific energyz,respecting the stochastic character of its occurrence.Main results. This study validated the MINAS TIRITH tool by comparing its results with those obtained using the Geant4-DNA track structure code and a Geant4-DNA based simulation chain for DNA damage calculation. The different elements of comparison indicated consistency between MINAS TIRITH and the Monte Carlo simulation in case of the dose distribution in the population and the calculation of the amount of DNA damage.Significance. MINAS TIRITH is a new approach for the calculation of radiation-induced DNA damage at the cell population level that facilitates reasonable simulation times compared to those obtained with track structure codes. Moreover, this tool enables a more direct comparison between modeling and biological experimentation.

Future development of biologically relevant dosimetry.

Proton and ion beams are radiotherapy modalities of increasing importance and interest. Because of the different biological dose response of these radiations as compared with high-energy photon beams, the current approach of treatment prescription is based on the product of the absorbed dose to water and a biological weighting factor, but this is found to be insufficient for providing a generic method to quantify the biological outcome of radiation. It is therefore suggested to define new dosimetric quantities that allow a transparent separation of the physical processes from the biological ones. Given the complexity of the initiation and occurrence of biological processes on various time and length scales, and given that neither microdosimetry nor nanodosimetry on their own can fully describe the biological effects as a function of the distribution of energy deposition or ionization, a multiscale approach is needed to lay the foundation for the aforementioned new physical quantities relating track structure to relative biological effectiveness in proton and ion beam therapy. This article reviews the state-of-the-art microdosimetry, nanodosimetry, track structure simulations, quantification of reactive species, reference radiobiological data, cross-section data and multiscale models of biological response in the context of realizing the new quantities. It also introduces the European metrology project, Biologically Weighted Quantities in Radiotherapy, which aims to investigate the feasibility of establishing a multiscale model as the basis of the new quantities. A tentative generic expression of how the weighting of physical quantities at different length scales could be carried out is presented.

Thin-film designs by simulated annealing.

With the increasing power of computers, new methods in synthesis of optical multilayer systems have appeared. Among these, the simulated-annealing algorithm has proved its efficiency in several fields of physics. We propose to show its performances in the field of optical multilayer systems through different filter designs.

[Analysis of restraint of the femur head. Experimental study of allograft of cold bone and autoclaved bone to kill the HIV virus]. / Analyse des contraintes de l'extrémité supérieure du fémur. Etude expérimentale allogreffes os congelés - os autoclaves en vue de la destruction du virus H.I.V.

The retrovirus S.I.A.D. grown in marrow bone and iatrogenic infections may be possible after bone graft in following total hip arthroplasties. Previous investigators proposed several methods to kill the virus, but without bacteriological safety. They found 20 to 55% of loss on mechanical properties. The present study reports the response of autoclaved femoral heads compression testing on material machine Model 1026 Instron. The stress response of marrow bone to stains showed a classic peak and with linear regression study we saw a relationship between autoclaved bone and cold bone. The cortical bone resists to strains highly 12% of load.

Biomechanics of the hip: forces exerted during walking.

Since the work of Pauwels, the forces exerted on the coxofemoral joint during walking have been studied either in different spatial planes (frontal, sagittal and horizontal) or by three-dimensional spatial analysis. Starting from the findings of our own studies, our aim was to compare the two methods of analysis (two-dimensional and three-dimensional) in order to provide a better understanding of the benefits and limitations of each method. In pursuit of this aim, we studied the pressure forces exerted on the coxofemoral joint, using a geometric plane technique following a method similar to that of Pauwels [20], and with a three-dimensional modelling technique using the finite element method. The material, taken from the published literature, was the same in both our studies. The results are expressed in terms of the size and orientation of the pressure force exerted on the coxofemoral joint during the monopodal weightbearing phase of walking. A comparison of these two methods of analysis clearly demonstrates the simplicity of two-dimensional analysis (which must incorporate as a minimum the frontal plane and the sagittal plane) and the richness of the three-dimensional analysis. The latter method, by appropriate manipulation of the information obtained, provides a starting point for computer simulations performed with the aim of testing a biomechanical or therapeutic hypothesis.

[Comparative mechanic resistance of frozen and irradiated spongy bone]. / Résistance mécanique comparative de l'os spongieux congelé et irradié.

The mechanical properties of 20 frozen (-30 degrees C) femoral heads are determined. 10 were treated by gamma radiations. It is noted that the rate of weakness of cancellous bone is 20%.

[Stress and quantification of pressures borne by the hip in unilateral support in the sagittal plane. I]. / Etude des sollicitations et quantification des pressions subies par la hanche en appui monopodal dans le plan sagittal.

Thanks to the works of Pauwels, the pressures sustained by the hip during unilateral weightbearing in the frontal plane are now well known and have given rise to a number of surgical applications. Considered as negligible by Pauwels, the sagittal plane has been little studied; in fact, with Pauwels' methodology, but taking into account the muscular moments, it appears that the forces exerted in the sagittal plane are far from being negligible and vary, according to the phase of weightbearing, from once the weight of the body (weightbearing on the sole) to two and a half times the weight of the body (weightbearing on the heel).

[Changes in the pressure borne by the hip during the phase of unilateral support in locomotion. II]. / Variation des pressions subies par la hanche durant la phase d'appui monopodal de la marche.

Adopting the methodology that we have just described, our study completes that of Pauwels in that we take into consideration the pressures sustained by the hip not only in the frontal plane but also in the horizontal and sagittal planes during the phase of unilateral weightbearing when walking. Thanks to the work of Braune and Fischer (1) the forces exerted on the hip are now well known and are represented by the weight of the body, the muscular forces and the dynamic forces generated by walking. From these data, we have been able to quantify the pressures sustained by the hip in each plane during the different phases of unilateral weightbearing when walking (weightbearing on heel, sole and toes).

Anatomical and functional study on the musculus semimembranosus.

The dissection of 18 knees taken from fresh cadavers has led to a detailed description of the semimembranosus muscle (musculus semimembranosus). It is exclusively tibial with its three tendons rendering the muscle functional, whatever the position of the knee may be. There are other attachments, sometimes described are merely expansions extending to the menisco-tibial and menisco-femoral formations, from which this distal termination must be distinguished. Electromyography performed on 17 specimens confirms that this muscle serves more as a brake on outer rotation than an inner rotator muscle, especially when the hip is flexed and the knee stretched.

Reciprocal angulation of vertebral bodies in a sagittal plane: approach to references for the evaluation of kyphosis and lordosis.

In order to establish a sagittal plane curve reference table for standing subjects examined laterally, we determined an easily reproducible standard posture. A sample of 100 healthy subjects from 20 to 29 years of age, was chosen (43 women, 57 men). The reciprocal angulations of each vertebral body in relation to the others were fed into a digitalizer and studied by computer. The study particularly concerns maximum kyphosis, maximum lordosis, sacral base slopes, and the tilt of intermediate vertebral bodies. The dispersion of the results is remarkably wide and, within the extreme values, the distribution is irregular. Individual correlations of these values are often dispersed, but spinal morphotypology. For considerable lengths, average values cannot be used as norms, given the wide span of values. Only the extreme limits are useful for the appreciation of curves as excessive, insufficient, or inverted.

[Resistance to traction of the periarticular ligaments and tendons of the knee]. / De la résistance à la traction des ligaments et tendons péri-articulaires du genou.

The authors present a methodical study concerning traction strength of the ligaments and the periarticular tendons of the knee. The straining potential and the mechanical strength of these elements are made clear. This study permits applications in chronic laxities of the knee by giving the mechanical value of the different kinds of tendon reconstruction.

[Anterior strut grafting in kyphosis and kyphoscoliosis (author's transl)]. / Greffes antérieures en étai dans le traitement des cyphoses et cyphoscolioses.

The authors have reviewed 58 cases submitted to strut grafting in the concavity of the curve. There were 44 kyphoscolioses and 12 kyphoses. The average follow-up was more than two years and the average pre-operative deformity was 127 degrees. The average improvement was 38 degrees and the secondary loss was only 3 degrees. The results are analysed with regard to the surgical technique used. In some cases, posterior fixation was added and the graft was either from the tibia, the fibula or a rib. In 16 cases a secondary fracture of the graft was found. It appeared between the fourth and tenth post-operative months. During this period, reduction of the graft was seen. The graft was found to thicken later at about the eighteenth post-operative month. It is concluded that the technique is worthwhile provided it is associated with posterior internal fixation, and that an external brace is worn for at least eighteen months after operation.

[Fracture of the odontoid process (author's transl)]. / Fractures de l'apophyse odontoïde (dens) de l'axis. 102 cas dont 73 fractures récentes.

102 cases of fractures of the odontoid process have been seen by the author - 73 recent cases and 29 old ones. It was important to distinguish basal fractures (29 cases), which all united after conservative treatment by reduction and skull traction for six weeks followed by a plaster cast for six to eight weeks, and fractures of the body (44 cases). 41 body fractures were treated conservatively, of which 6 died and only 20 united. The authors consider that treatment by skull traction must always be tried. An eventual indication for surgery can be made at about the 20th day if displacement is found to be present in spite of treatment. Fusion in these cases must be limited to C1-C2. It is best obtained by a combination of wiring and grafting.