No abstract available

[en] Cone beam CT is a powerful tool to ensure an optimum patient positioning in radiotherapy. When cone beam CT scan of a patient is acquired, scan data of the patient are compared and evaluated against a reference image set and patient position offset is calculated. Via the linac control system, the patient is moved to correct for position offset and treatment starts. This procedure requires a reliable system for movement of patient. In this work we present a new method to characterize the reproducibility, linearity and accuracy in table positioning. The method applies to all treatment tables used in radiotherapy. Material and methods. The table characteristics are investigated on our two recent Elekta Synergy Platforms equipped with Precise Table installed in a shallow pit concrete cavity. Remote positioning of the table uses the auto set-up (ASU) feature in the linac control system software Desktop Pro R6.1. The ASU is used clinically to correct for patient positioning offset calculated via cone beam CT (XVI)-software. High precision steel rulers and a USB-microscope has been used to detect the relative table position in vertical, lateral and longitudinal direction. The effect of patient is simulated by applying external load on the iBEAM table top. For each table position an image is exposed of the ruler and display values of actual table position in the linac control system is read out. The table is moved in full range in lateral direction (50 cm) and longitudinal direction (100 cm) while in vertical direction a limited range is used (40 cm). Results and discussion. Our results show a linear relation between linac control system read out and measured position. Effects of imperfect calibration are seen. A reproducibility within a standard deviation of 0.22 mm in lateral and longitudinal directions while within 0.43 mm in vertical direction has been observed. The usage of XVI requires knowledge of the characteristics of remote table positioning. It is our opinion that the method presented meets the requirements in high precision IGRT

[en] A method for estimating a beam centering error from a beam density distribution obtained by a single radial probe has been developed. Estimation of the centering error is based on an analysis of radial beam positions in the direction of the radial probe. Radial motion of a particle is described as betatron oscillation around an accelerated equilibrium orbit. By fitting the radial beam positions of several consecutive turns to an equation of the radial motion, not only amplitude of the centering error but also frequency of the radial betatron oscillation and energy gain per turn can be evaluated simultaneously. The estimated centering error amplitude was consistent with a result of an orbit simulation. This method was exceedingly helpful for minimizing the centering error of a 10 MeV proton beam during the early stages of acceleration. A well-centered beam was obtained by correcting the magnetic field with a first harmonic produced by two pairs of harmonic coils. In order to push back an orbit center to a magnet center, currents of the harmonic coils were optimized on the basis of the estimated centering error amplitude. (authors)

[en] The Quasi-Zenith Satellite System (QZSS) from Japan will supplement the global positioning system (GPS) for more accurate and stable positioning, navigation and timing services. However, QZSS and GPS measurements are not free of inter-system bias (ISB) for various receiver brands. After estimating and clustering the receiver ISB values of GPS and QZSS for all three overlapping frequencies L1, L2 and L5, we show that the code ISB of the receivers can have at least two groups and the firmware versions of the groups may overlap with each other, making the look-up-table calibration difficult. Therefore, we propose to discriminate one code ISB value from the other for a specific receiver by the observations of a few epochs so that precise calibration can be implemented within a short time. The phase fractional ISB (F-ISB) calibration of QZSS and GPS is easier as their magnitudes are receiver-type and firmware-version related. Experiments for the code positioning show that the QZSS and GPS integration with the ISB calibrated by the looked-up values has an obviously smaller 3D distance root mean square, i.e. the root mean square of the radial distances from the true position to the calculated positions. The empirical success rate of the ambiguity fixing in precise positioning is also improved with the looked-up phase F-ISB values. (paper)

[en] Published in summary form only

[en] Short communication

[en] We have shown that timing readout for triple charge division centroid finding method by using the ratio to time response of transmission line is possible. Attention must be drawn toward the threshold voltages of discriminators and the best results are taken when this voltage is one second of the summation of both sides' signals. This summation, for charge division readout, is almost constant. In future program, we will expand the TCD pattern toward long range position sensing and generalize the GCD readout method. (author)

[en] The dosimetric characteristics of a production pilot multi-leaf collimator (Elekta Beam ModulatorElekta Oncology Systems, Crawley, UK) having a 4 mm leaf width (at isocentre) have been investigated. Characteristics explored included leaf bank set-up, penumbra width (80-20%) as a function of leaf position, leaf positioning reproducibility, interleaf leakage and leaf transmission. The penumbra values for leaf ends were measured to be between 4.2 and 4.8 mm for various large rectangular fields studied using Kodak X-omat V film at isocentre (1.5 cm deep). Similar films were taken with a standard 1 cm width multi-leaf collimator (MLC) and the penumbra for leaf ends was found to range from 4.3 to 5.2 mm. Other results showed that the rounded leaf tip provided tight control of the penumbra across the leaves' full range of travel. The positioning of the leaves was within a 0.5 mm range when approaching from the same direction. The maximum interleaf leakage was found to be 1.7% and the average leaf transmission less than 1.0%. No major differences were observed in leakage and transmission with changing gantry angle

[en] The effects of inter-system biases (ISBs) in multi-global navigation satellite system (GNSS) combined positioning cannot be ignored in zero-differenced observations. Furthermore, for relative positioning of multi-GNSS from double-differenced observations, there also exists double-differenced ISB, and the influence on precise relative positioning cannot be ignored. The characteristics of double-differenced ISBs are analyzed by using a large volume of global positioning system (GPS) and BeiDou Navigation Satellite System (BDS) data for differential relative positioning. Different baselines result in different double-differenced ISBs; ISBs obtained from different days show consistency and periodicity for the same baseline. We propose a parameter estimation approach to realize consistency of relative positioning results for different GNSS systems, and thus improve their usability. The results show that the double-differenced ISBs are stable for the same period of time over consecutive days, and can be used for modeling and prediction. (paper)

[en] A new method for micro-beam XRF localization is presented. A laser beam along with an incident X-ray hits on the surface of a sample. The micro region on the sample that reached by X-ray beam can be localized by means of the visible spot of the laser beam. This method is suitable for X-ray microprobes using an X-ray tube or synchrotron radiation as excitation sources