Practical quantitative measurement of graticule misalignment relative to collimator axis of rotation.

We design a practical procedure for measuring translational and rotational misalignment of graticule with collimator axis of rotation and collimator jaws, respectively. The procedure's quantitative results are accurate to less than 0.2 mm (at isocenter) and do not assume alignment of radiation focal spot with collimator axis of rotation. When provided with these quantitative results, the manufacturer can custom-adjust graticules to the purchaser's collimator head

A Millimeter-scale Single Charged Particle Dosimeter for Cancer Radiotherapy

This paper presents a millimeter-scale CMOS 64$\times$64 single charged particle radiation detector system for external beam cancer radiotherapy. A 1$\times$1 $\mu m^2$ diode measures energy deposition by a single charged particle in the depletion region, and the array design provides a large detection area of 512$\times$512 $\mu m^2$. Instead of sensing the voltage drop caused by radiation, the proposed system measures the pulse width, i.e., the time it takes for the voltage to return to its baseline. This obviates the need for using power-hungry and large analog-to-digital converters. A prototype ASIC is fabricated in TSMC 65 nm LP CMOS process and consumes the average static power of 0.535 mW under 1.2 V analog and digital power supply. The functionality of the whole system is successfully verified in a clinical 67.5 MeV proton beam setting. To our' knowledge, this is the first work to demonstrate single charged particle detection for implantable in-vivo dosimetry

Sensitivity analysis of an asymmetric Monte Carlo beam model of a Siemens PRIMUS accelerator

72 1024x768 Normal 0 false false false The assumption of cylindrical symmetry in radiotherapy accelerator models can pose a challenge for precise Monte Carlo modeling. This assumption makes it difficult to account for measured asymmetries in clinical dose distributions. We have performed a sensitivity study examining the effect of varying symmetric and asymmetric beam and geometric parameters of a Monte Carlo model for a Siemens PRIMUS accelerator. The accelerator and dose output were simulated using modified versions of BEAMnrc and DOSXYZnrc that allow lateral offsets of accelerator components and lateral and angular offsets for the incident electron beam. Dose distributions were studied for 40 × 40 cm2 fields. The resulting dose distributions were analyzed for changes in flatness, symmetry, and off-axis ratio (OAR). The electron beam parameters having the greatest effect on the resulting dose distributions were found to be electron energy and angle of incidence, as high as 5% for a 0.25° deflection. Electron spot size and lateral offset of the electron beam were found to have a smaller impact. Variations in photon target thickness were found to have a small effect. Small lateral offsets of the flattening filter caused significant variation to the OAR. In general, the greatest sensitivity to accelerator parameters could be observed for higher energies and off-axis ratios closer to the central axis. Lateral and angular offsets of beam and accelerator components have strong effects on dose distributions, and should be included in any high-accuracy beam model

Improvements in Monte Carlo Simulation of Large Electron Fields

Two Monte Carlo systems, EGSnrc and Geant4, were used to calculate dose distributions in large electron fields used in radiotherapy. Source and geometry parameters were adjusted to match calculated results with measurement. Both codes were capable of accurately reproducing the measured dose distributions of the 6 electron beams available on the accelerator. Depth penetration was matched to 0.1 cm. Depth dose curves generally agreed to 2% in the build-up region, although there is an additional 2-3% experimental uncertainty in this region. Dose profiles matched to 2% at the depth of maximum dose in the central region of the beam, out to the point of the profile where the dose begins to fall rapidly. A 3%/3mm match was obtained outside the central region except for the 6 MeV beam, where dose differences reached 5%. The discrepancy observed in the bremsstrahlung tail in published results that used EGS4 is no longer evident. The different systems required different source energies, incident beam angles, thicknesses of the exit window and primary foils, and distance between the primary and secondary foil. These results underscore the requirement for an experimental benchmark of electron scatter for beam energies and foils relevant to radiotherapy

The effect of misonidazole on cell survival at low doses of radiation

Since Puck and Marcus first measured the effect of ionizing radiation on mammalian cell survival in 1956 the 'Puck plating' assay has been widely used as an endpoint for radiobiology experiments. The assay has contributed greatly to our knowledge of the processes involved when radiation interacts with cells, tissues, and whole animals. Generally cell survival experiments are carried out at fairly high doses of radiation (5-30 Gray) where cell survival drops below 50% of the survival of un-irradiated cells. Very little data has been accumulated at lower doses. Most of our knowledge in this region has been extrapolated from measurements made at higher doses. This is in part due to the difficulty of obtaining accurate results at higher survival levels, a problem primarily due to the difficulty in accurately determining the number of cells plated for the assay. This statistical uncertainty becomes important at survival levels greater than 50%. The uncertainty can be significantly reduced at these survival levels by accurately counting the number of cells plated, using a microscope, a procedure which is very time consuming when performed manually. A method of automating the procedure with a computer controlled motor driven microscope stage is described in this thesis. With the automated procedure the assay time is reduced by a factor of three. In this thesis the effect of the radiosensitizer misonidazole on cell survival was measured at radiation doses as low as one Gray. The results show that the drug is a poor radiosensitizer at low doses for the experimental system used. The clinical and radiobiological significance of these observations is discussed. This experiment exemplifies the value of measuring cell survival at low doses.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Practical quantitative measurement of graticule misalignment relative to collimator axis of rotation.

We design a practical procedure for measuring translational and rotational misalignment of graticule with collimator axis of rotation and collimator jaws, respectively. The procedure's quantitative results are accurate to less than 0.2 mm (at isocenter) and do not assume alignment of radiation focal spot with collimator axis of rotation. When provided with these quantitative results, the manufacturer can custom-adjust graticules to the purchaser's collimator head

Treatment head disassembly to improve the accuracy of large electron field simulation

Purpose: The purposes of this study are to improve the accuracy of source and geometry parameters used in the simulation of large electron fields from a clinical linear accelerator and to evaluate improvement in the accuracy of the calculated dose distributions

Programas de Monitoramento Ambiental aplicados na Sub-Região Baixo Tapajós e Vale do Jamanxim, estado do Pará

The study area of this work includes two sub-regions covered by the BR-163 road, which is Baixo Tapajós and Vale do Jamanxim. This region was monitored from Environmental Monitoring Programs of the Federal Government. This study presents results of anthropism data from ProAE 2012 for Special Areas and deforestation data from PRODES / INPE 2011 applied to the remainder. After structuring the database, software R 2.13.2 was used to generate histogram of frequency of the investigated variables (anthropism, roads and drainage), from synchronization with the database created in Terra View 4.1.0. Non-Special Areas represents 43,7% of the investigated area, and according PRODES 2011 presents 1.212.693,00 hectares of deforestation accumulated, that is, 20,00% of total. Special Areas occupies 57,3% of the investigated territory, and ProAE 2012 identified 319.320,76 hectares of anthropism, which equates to 3,92%. The frequency histograms: percentage of anthropism, presence of roads and drainage, for Special and Non-Special Areas, pointed to the same pattern between anthropism and roads, rather than drainage. Despite anthropism rates are lower within the Special Areas, there is still a high human pressure therein, as it presents ProAE 2012 results. These protected areas are forest, mineral and biodiversity reserve, bringing the challenge consolidation of environmental management in this region.Pages: 6853-686