Theoretical dose distributions for microbeam radiation therapy (MRT) are computed in this paper using the GEANT4 Monte Carlo (MC) simulation toolkit. MRT is an innovative experimental radiotherapy ...technique carried out using an array of parallel microbeams of synchrotron-wiggler-generated x rays. Although the biological mechanisms underlying the effects of microbeams are still largely unknown, the effectiveness of MRT can be traced back to the natural ability of normal tissues to rapidly repair small damages to the vasculature, and on the lack of a similar healing process in tumoral tissues. Contrary to conventional therapy, in which each beam is at least several millimeters wide, the narrowness of the microbeams allows a rapid regeneration of the blood vessels along the beams’ trajectories. For this reason the calculation of the “valley” dose is of crucial importance and the correct use of MC codes for such purposes must be understood. GEANT4 offers, in addition to the standard libraries, a specialized package specifically designed to deal with electromagnetic interactions of particles with matter for energies down to 250 eV. This package implements two different approaches for electron and photon transport, one based on evaluated data libraries, the other adopting analytical models. These features are exploited to cross-check theoretical computations for MRT. The lateral and depth dose profiles are studied for the irradiation of a 20 cm diameter, 20 cm long cylindrical phantom, with cylindrical sources of different size and energy. Microbeam arrays are simulated with the aid of superposition algorithms, and the ratios of peak-to-valley doses are computed for typical cases used in preclinical assays. Dose profiles obtained using the GEANT4 evaluated data libraries and analytical models are compared with simulation results previously obtained using the PENELOPE code. The results show that dose profiles computed with GEANT4’s analytical model are almost indistinguishable from those obtained with the PENELOPE code, but some noticeable differences appear when the evaluated data libraries are used.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A Monte Carlo code for the simulation of X-ray imaging and spectroscopy experiments in heterogeneous samples is presented. The energy spectrum, polarization and profile of the incident beam can be ...defined so that X-ray tube systems as well as synchrotron sources can be simulated. The sample is modeled as a 3D regular grid. The chemical composition and density is given at each point of the grid. Photoelectric absorption, fluorescent emission, elastic and inelastic scattering are included in the simulation. The core of the simulation is a fast routine for the calculation of the path lengths of the photon trajectory intersections with the grid voxels. The voxel representation is particularly useful for samples that cannot be well described by a small set of polyhedra. This is the case of most naturally occurring samples. In such cases, voxel-based simulations are much less expensive in terms of computational cost than simulations on a polygonal representation. The efficient scheme used for calculating the path lengths in the voxels and the use of variance reduction techniques make the code suitable for the detailed simulation of complex experiments on generic samples in a relatively short time. Examples of applications to X-ray imaging and spectroscopy experiments are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The aim of this research work is the development of a low-cost system for telemedicine based on the DVB-T technology. The diffusion of DVB-T standard and the low cost of DVB-T set-top boxes bring the ...vision of a capillary distribution of tele-home care monitoring systems with easy-to-use patient's interface.
Exploiting the potentiality of the DVB-T set-top box, we transformed it into an "on-demand tele-home care interface". The Xlet we developed is able to govern the functionality of an external microcontroller-based unit for the acquisition of the bio-signals of interest. The uplink connection is used to send the exam results to a remote care center.
The Xlet providing the patient interface on the set-top box is uploaded by a DVB-T broadcaster without any intervention in the patient's home. A prototypal low-cost base station for the acquisition of the patient's signals (1-lead ECG) has been developed. It is able to be connected to the set-top box via an infrared link. A smart-card-based system is in charge for the customization of the Xlet for every patient.
The proposed system, based on a currently widespread infrastructure, is able to allow the patients monitoring from home without any installation procedure. Even untrained (or elderly) people can easily use such system due to their practice with the basic DVB-T home-entertainment equipments.
We describe a portable readout system for an X-ray hybrid detector based on the Medipix2 pixel readout chip. The Medipix2 chip (256times256 square pixels with 55 mum pitch) is bump-bonded with a ...pixellated Silicon sensor 300-micron thick. The readout system consists of a simple small size electronic card based on a single powerful microcontroller and can be connected to a PC through the widespread Universal Serial Bus (USB) interface. The reduced size of the final card (3.8 cmtimes4.8 cm) makes it suitable for special applications like dental radiology
Medipix2 parallel readout system Fanti, V.; Marzeddu, R.; Randaccio, P.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2003, Volume:
509, Issue:
1-3
Journal Article
Peer reviewed
A fast parallel readout system based on a PCI board has been developed in the framework of the Medipix collaboration.11http://medipix.web.cern ch/MEDIPIX/
The readout electronics consists of two ...boards: the motherboard directly interfacing the Medipix2 chip, and the PCI board with digital I/O ports 32 bits wide. The device driver and readout software have been developed at low level in Assembler to allow fast data transfer and image reconstruction.
The parallel readout permits a transfer rate up to 64Mbytes/s.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Preclinical Microbeam Radiation Therapy (MRT) research programs are carried out at the European Synchrotron Radiation Facility (ESRF) and at a few other synchrotron facilities. MRT needs an accurate ...evaluation of the doses delivered to biological tissues for carrying out pre-clinical studies. This point is crucial for determining the effect induced by changing any of the physical irradiation parameters. The doses of interest in MRT are normally calculated using Monte Carlo (MC) methods. A few MC packages have been used in the last decade for MRT dose evaluations in independent studies. The aim of this investigation is to provide a preliminary basis to perform a systematic comparison of the dose results obtained, under identical irradiation conditions and for the same scoring geometries with the following five MC codes: EGS4, PENELOPE, GEANT4, EGSnrc, and MCNPX. Dose profiles have been calculated in an in-depth region of cylindrical phantoms made of water or PMMA. Beams in both cylindrical and planar geometry have been considered. This comparison shows an overall agreement among the different codes although minor differences occur, which need further investigations.
A fast readout system for the Medipix2 pixel chip has been developed for digital angiography applications to allow real time X-ray imaging of contrast media flowing in blood vessels. The readout ...system is designed to acquire data coming from the 32-bit Medipix2 parallel port of a maximum of eight chips at a rate of 25 frames per second. The readout electronics is peripheral component interconnect (PCI) bus-based and consists of two boards: the motherboard directly interfacing the chip for settings and data flow and the PCI board linking the motherboard to the bus. With parallel readout, a transfer rate of up to 64 MByte/s has been achieved.
A Simulator for X-ray images Fanti, V.; Marzeddu, R.; Massazza, G. ...
Radiation protection dosimetry,
01/2005, Volume:
114, Issue:
1-3
Journal Article
Peer reviewed
A simulator for X-ray images is presented based on a virtual X-ray source and a virtual human body obtained from tomographic slices. In the simulator it is possible to modify the tube potential, the ...anodic current, the exposure time, the filtration and some geometric parameters such as source–skin distance, orientation and field size. The virtual body consists of a three-dimensional voxel matrix in which CT numbers for each point of the body are stored. The interactions of X rays passing through the body are evaluated using the pencil beam technique. The image is obtained by computing the dose absorbed by the detector and converting it into optical density using a proper response function. The image spatial resolution is limited by the voxel size. The influence of each parameter on the image quality can be observed interactively. The dose absorbed in each point of the body is an important parameter obtained as output of the simulator.
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