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

Effect of the NΔ interaction on observables of the πNN and γNN systems

Effects on the hadronic and electromagnetic properties of the two-nucleon system above pion threshold, arising from the interaction of the Δ isobar with nucleons, are investigated. The instantaneous nucleon-Δ potential is based on the meson exchange. Two-body reactions connecting channels with at most one pion and one photon are studied. Processes leading to a three-body pion-two-nucleon final state are considered in the restricted kinematic domain in which the pion forms the P33 resonance with one of the nucleons. The nucleon-Δ potential is seen to increase the relative importance of the inelastic strength of two-nucleon spin-triplet states with respect to spin-singlet states, correcting a deficiency common in most existing models. Theoretical predictions are compared with recent experimental data for the various reactions. In particular, the differential cross section and the proton beam asymmetry for pp→nΔ++ (pπ+) are calculated, the latter observable being especially sensitive to the nucleon-Δ interaction