Beam Quality Measurements Research Articles

Beam quality measurement and image analysis of RF optical emission system

With the development of radio-over-fiber (ROF), beam quality is also an important parameter in evaluating ROF systems. Therefore, this paper selects the low-frequency to very high frequency (VHF) direct modulated optical emission system to verify its feasibility and excellent performance. It then analyzes the beam quality and image processing. In this paper, MATLAB is selected for the theoretical simulation, then CMOS is used to collect light spots, RayCiV2.5 is used to Gaussian fit the light field intensity distribution, and finally the ideal and actual light spot parameters are compared. Due to the influence of noise, this paper also preprocessed the image by brightness adjustment, filtering, edge fitting, etc. It proposed a fast two-sided filtering algorithm, which obtained a high peak signal-to-noise ratio (PSNR) and strong applicability. The results show that the edge-mode rejection ratio is as high as 33.6 dB, the beam quality is good, and it can be well applied in ROF. The M2 factor is 2.75, the optical field intensity Gaussian fit is 99.8 %, and the signal-to-noise ratio (SNR) is as high as 54.7 dB. Moreover, the image is robust after fast bilateral filtering.

Minimum phantom size for megavoltage photon beam reference dosimetry.

Water phantoms are required to perform reference dosimetry and beam quality measurements but there are no published studies about the size requirements for suchphantoms. To investigate, using Monte Carlo techniques, the size requirements for water phantoms used in reference dosimetry and/or to measure the beam quality specifiers and . The EGSnrc application DOSXYZnrc is used to calculate , the dose per incident fluence at 10cm depth in a water phantom irradiated by incident beams of or 6MV photons. The water phantom dimensions are varied from to and occasionally smaller. The and values are also calculated with care being taken to distinguish results when using Method A (changing depth of water in phantom) and Method B (moving entire phantom). Typical statistical uncertainties are 0.03%. Phantom dimensions have only minor effects for phantoms larger than . A table of corrections to the dose at 10cm depth in beams of or 6MV photons are provided and range from no correction to 0.75% for a beam incident on a phantom. There can be distinct differences in the values measured using Method A or Method B, especially for smaller phantoms. It is explicitly demonstrated that, within 0.15%, values for a phantom measured using Method A or B are independent of source detector distance between 40 and200cm. The phantom sizes recommended in the TG-51 and IAEA TRS-398 reference dosimetry protocols are adequate for accurate reference dosimetry and in some cases are even conservative. Correction factors are necessary for accurate measurement of the dose at 10cm depth in smaller phantoms and these factors are provided. Very accurate beam quality specifiers are not required for reference dosimetry itself, but for specifying beam stability and characteristics it is important to specify phantom sizes and also the method used for measurements.

Radiation doses received in the UK breast screening programmes 2019-2023.

To report the latest UK mammography dose survey results and to compare radiation doses from digital breast tomosynthesis (DBT) and full-field digital mammography (FFDM) in UK breast screening. Anonymized exposure factors were collected for 111 152 screening cases and 5113 assessment cases from 405 x-ray sets across the United Kingdom using an online submission system linked to a national database of mammography quality control data. Output and beam quality measurements from each set were combined with exposure data to estimate mean glandular doses (MGD). FFDM doses increased by ∼10% compared to the 2016-2019 national survey but compressed breast thicknesses (CBT) remained similar. DBT doses were 34%-40% higher than FFDM overall and 34% higher than FFDM for breasts 50-60mm thick. We found a possible overestimation of PMMA breast equivalent thicknesses at low CBTs, but the evidence was not conclusive. Recent changes to the mix of x-ray models in use in UK breast screening have resulted in higher FFDM breast doses. DBT doses in the NHSBSP are on average higher than FFDM by ∼34%-40%. This is the first national study to report DBT and FFDM MGDs in UK breast screening.

Simulation of attenuation and compression in beam quality measurement of high power laser

Simulation of attenuation and compression in beam quality measurement of high power laser

Experiment on attenuation and compression in beam quality measurement of high power laser

Experiment on attenuation and compression in beam quality measurement of high power laser

Analysis and Correction of Smeared Image From Interline-Transfer CCD in Beam Quality Measurement

The smear effect caused by light penetration of interline-transfer (IT) CCD in beam quality measurement (BQM) is detrimental and not analyzed pertinently. This report proposes a mathematical model and a correction method for the smeared image. The smear noise is fitted and subtracted through its correlation with the light signal obtained from the model and pre-calibration. The application in BQM is presented by measuring beam quality factor M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and power in the bucket (PIB). The results verify the validity of the method. An evaluation standard of the correction effect is also recommended.

Reverse-Taper Mid-Infrared Quantum Cascade Lasers for Coherent Power Scaling

We present a reverse-taper quantum cascade laser (QCL) emitting at 4.6 μm, a novel-geometry device that can scale the output power while maintaining good beam quality. Buried-ridge waveguides with tapered and straight regions were formed by ICP etching and HVPE regrowth – the tapered region scales the output power, while the emitting facet is located at the narrow-end taper section, which provides mode filtering by suppressing high-order spatial modes. Beam profiles were observed under quasi-continuous-wave (QCW)/CW operation and beam quality (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) measurements along with beam-stability measurements were performed – a small degree of collimated-beam centroid movement (<0.46 mrad, peak-to-peak) was observed, along with M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> values close to 1 up to ∼1 W QCW power. Devices of shorter cavity lengths were also investigated, indicating that the output power scales with the core-region volume but results in a small increase in angular deviation.

Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit.

Relative dosimetry measurements are required to fully commission kilovoltage X-ray units for superficial and orthovoltage X-ray therapy. Validation of these relative dosimetry measurements with Monte Carlo methods is advantageous being independent of the measurement process. In this study use is made of the X-ray spectrum generating program SpekPy along with the EGSnrc Monte Carlo code to calculate depth doses and explore the dosimetry effect of changes in backscatter. These calculations are compared with previously reported measurements for the Pantak SXT 150 X-ray therapy unit. SpekPy can also be used to generate half value layer (HVL) values and these are also compared to previously reported HVL measurements for the same X-ray therapy unit. It was found that agreements of the order of 5% in HVL, 3% in depth dose and 1% in backscatter doses were found between Monte Carlo calculations and the previously published measured data. Exit doses in conditions of lack of full backscatter were explored with Monte Carlo calculations demonstrating reduced exit dose up to 20% in these conditions. It is concluded that SpekPy with Monte Carlo codes such as EGSnrc provides a straightforward approach to validating various relative dosimetry measurements in kilovoltage X-ray dosimetry.

Crosstalk correction of array fibers applied to beam quality measurement

Crosstalk correction of array fibers applied to beam quality measurement

Limitations of the S2 (spatially and spectrally resolved) imaging technique

Spatially and spectrally resolved imaging (S2 imaging) is a technique that was developed as an alternative to beam quality (M2) measurements to characterize the modal content of large mode area (LMA) fibers. While it is known that the success of S2 imaging is highly dependent on the broadband source and the launch conditions into the fiber, the information resulting from this method is more limited than may appear at first glance. Experiments and numerical simulations are used to show that (a) the accuracy of the reconstructed LP01 mode profile varies greatly depending on launch conditions, and (b) there are always errors in the reconstructed LP11 mode profile. Not only do these findings reveal that the reconstructed mode areas cannot be accurately determined, but it also shows that the relative modal intensities can only be determined accurately under nearly perfect conditions of fundamental mode launch and propagation through the fiber. Despite these findings, the S2 technique can still be used under nearly ideal launch and propagation conditions to identify the modes and their group delays, and accurately reconstruct only the fundamental mode.

Investigation of single-shot beam quality measurements using state of the art solid-state dosimeters for routine quality assurance applications in mammography

<h2>Abstract</h2><h3>Purpose</h3> To assess if single shot acquisitions with solid-state dosimeters as well as Robson's method could replace ionization chambers for tube output and HVL measurements, saving medical physicists time. <h3>Material and methods</h3> The energy responses of 4 solid-state dosimeters with automatic calculation of HVL were compared to ionization chamber measurements. Five anode/filter combinations were tested: Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag, from 24kVp to 35kVp. Tube output was measured free in air. HVL was measured using the solid-state dosimeters (single-shot acquisition), then manually with aluminum sheets and finally using the parametrization method of Robson. <h3>Results</h3> Deviations in tube output and HVL related to energy response in SSD were small in the 25–32 kVp range, and for tube output typically within 3%. Extrapolation using the Robson parametrization was within 5%, except for one device and for all W/Rh. Deviations of the HVL using the single shot approach were within 10% of the gold standard data. Larger deviations were found at the extreme tube voltages of 24kVp and 35kVp (maximum of 24%). <h3>Conclusion</h3> With the assumption that deviations in tube output of 5% and for HVL of 10% are acceptable, all tested solid state dosimeters met this criterion in the tube voltage range of 26kVp to 32kVp. Robson's method worked well for the spectra for which the method was developed, making both alternative approaches trustworthy for routine quality assurance purposes.

Passively Q-switched 914 nm microchip laser for lidar systems.

Passively Q-switched microchip lasers enable great potential for sophisticated lidar systems due to their compact overall system design, excellent beam quality, and scalable pulse energies. However, many near-infrared solid-state lasers operate at >1000 nm which are not compatible with state-of-the-art silicon detectors. Here we demonstrate a passively Q-switched microchip laser operating at 914 nm. The microchip laser consists of a 3 mm long Nd3+:YVO4 crystal as a gain medium while Cr4+:YAG with an initial transmission of 98% is used as a saturable absorber. Quasi-continuous pumping enables single pulse operation and low duty cycles ensure low overall heat generation and power consumption. Thus, thermally induced instabilities are minimized and operation without active cooling is possible while ambient temperature changes are compensated by adjustment of the pump laser current only. Single-emitter diode pumping at 808 nm leads to a compact overall system design and robust setup. Utilization of a microchip cavity approach ensures single-longitudinal mode operation with spectral bandwidths in the picometer regime and results in short laser pulses with pulse durations below 10 ns. Furthermore, beam quality measurements show that the laser beam is nearly diffraction-limited. A 7% output coupler transmittivity is used to generate pulses with energies in the microjoule regime and peak powers of more than 600 W. Long-term pulse duration, pulse energy, and spectral wavelength measurements emphasize excellent system stability and facilitate the utilization of this laser in the context of a lidar system.

Beam quality measurement of high power laser by using an involute pinhole array.

A novel method for power-in-the-bucket (PIB) measurement of high power laser beams is proposed. The laser beam spot was first sampled by a rotating involute pinhole array and then collected by using a photodetector placed behind the pinholes. The spatial-temporal distribution and calibrated PIB curve of the laser beam can be obtained. The spatial and temporal resolution is 20 µm and 5ms, respectively. Compared with conventional methods, the proposed measurement method is simple, convenient, and accurate, which is suitable for high power laser beams with jitter.

Dose-area product ratio in external small-beam radiotherapy: beam shape, size and energy dependencies in clinical photon beams

In small-field radiotherapy (RT), a significant challenge is to define the amount of radiation dose absorbed in the patient where the quality of the beam has to be measured with high accuracy. The properties of a proposed new beam quality specifier, namely the dose-area-product ratio at 20 and 10 cm depths in water or DAPR20,10, were studied to yield more information on its feasibility over the conventional quality specifier tissue-phantom ratio or TPR20,10. The DAPR20,10 may be measured with a large-area ionization chamber (LAC) instead of small volume chambers or semi-conductors where detector, beam and water phantom positioning and beam perturbations introduce uncertainties. The effects of beam shape, size and energy on the DAPR20,10 were studied and it was shown that the DAPR20,10 increases with increasing beam energy similarly to TPR20,10 but in contrast exhibits a small beam size and shape dependence. The beam profile outside the beam limiting devices has been shown to have a large contribution to the DAPR20,10. There is potential in large area chambers to be used in DAPR measurement and its use in dosimetry of small-beam RT for beam quality measurements.

Beam stability of buried-heterostructure quantum cascade lasers employing HVPE regrowth

Measurements of beam stability for mid-infrared (IR)-emitting quantum cascade lasers (QCLs) are important for applications that require the beam to travel through air to remote targets, such as free-space communication links. We report beam-quality measurement results of narrow-ridge, 4.6 µm-emitting buried-heterostructure (BH) QCLs fabricated using ICP etching and HVPE regrowth. Beam-quality measurements under QCW operation exhibit M2 < 1.2 up to 1 W for ∼5 µm-wide ridges. 5 µm-wide devices display some small degree of centroid motion with increasing output power (< 0.125 mrad), which corresponds to a targeting error of ∼1.25 cm over a distance of 100 m.

Dosimetry audits in Taiwan radiotherapy departments

Objectives:This study examines the practice of the regulation of Standards for Medical Exposure Quality Assurance (SMEQA) in Taiwan based on on-site quality audit for radiation therapy systems from 2016 to 2019.Methods:81 radiation therapy departments, 141 linacs, 9 γ knife systems, 34 high dose rate brachytherapy systems, 20 Tomotherapys, and 6 Cyberknives were audited yearly. Data collection and analysis for each institute’s documents including QA procedure, ion chamber and electrometer calibration reports, and a questionnaire relating to machine type and staffing, were requested first and reviewed by auditors. On-site SMEQA core item measurements, including beam output, beam profile and energy constancy for external beam therapy systems, and the source strength, positioning, and timer accuracy for brachytherapy systems were audited second. More than 300 photon beams and more than 400 electron beams were measured each year.Results:There were approximately 8.9 radiotherapy units per million population, and 1.2 medical physicists per unit in Taiwan. For the output measurements, more than 78 and 75% of the photon beams and electron beams, respectively, from linacs were with deviations within ±1.0%. Photon beams have lower beam quality measurement deviations than electron beams. Including in-plane and cross-plane measurements, more than 90 and 85% photon and electron beams, respectively, were with flatness consistency within 1.0%. All audit measurements were within the SMEQA acceptance criteria.Conclusions:According to SMEQA regulations on-site QA audits were successfully carried out from 2016 to 2019 for all Taiwan radiotherapy units. The measurement results showed high quality machine performance in Taiwan.Advances in knowledge:Dosimetry audits with directly acquired measurement readings have lower uncertainties; allow immediate feedback, discussion, and adjustment in a timely manner. In addition to regulation system establishment and education and training implementation, the machine quality is closely related to machine maintenance implementation.

Beam Quality Measurement and Verification in Radiation Therapy

The aim of all radiotherapy treatment is to precisely deliver a prescribed dose of radiation to a tumour volume while simultaneously sparing the organs at risk (OARs) surrounding this tumour. Radiation therapy has evolved and the method of radiation generation varies, ranging from the controlled emission of gamma rays from a Cobalt 60 source to the production of particles such as; photons, electrons and protons produced in linear accelerators. The high energy photons employed during tumour treatment can interact with components of the gantry such as lead jaws, and produce particles that may contaminate the treatment beam. These contaminants are produced through various interactions with the photons and the absorbing medium such as; Compton Interaction, Photoelectric Effect and Pair Production. Photons have more penetrating power than charged particles of similar energy, and as they traverse a medium there is energy transformation to electron energy(1). The prospect of an interaction per unit distance travelled is denoted by the principle N= N_0 e^(-μx), where μ is dependent on the energy of the photon and the materials through which it travels(2). The aim of this paper is to conduct beam quality measurements and verification for treatment plan quality assurance in radiation therapy. An IBA Pharma type ion chamber (FC65-G) and electrometer (IBA Dose 2) were used to obtain ionization charges for an 18MV and a 6MV photon beam from a C-Series linear accelerator. These measurements were taken using a 1D water phantom, dimensions 40cm* 35cm*34.5 cm at a source to detector distance (SDD) of 100cm with the chamber 10cm beneath the water surface. The “K” (quality conversion factor) was calculated using the TPR20, 10 method. Two sets of measurements were taken at a depth of 20 cm and 10 cm beneath the water surface at a source to detector distance of 100cm. Three measurements were taken for both photon energies at polarities of +300, -300 and +100 on the electrometer. Ka values were calculated using the TPR20, 10 principles outlined in the TRS 135 protocol. The Ka value for the 6MV photon was determined to be 0.996 Gy while that for the 18MV was 0.973 Gy. These Ka values were then used to determine the tabulated percentage depth dose (PDD) for the photon energies. The tabulated PDD’s were 0.665 and 0.788 for the 6MV and 18MV beam respectively. From equation 2, Dw (10cm) for 6MV photon was calculated to be 0.68 Gy and that for the 18 MV photon was 0.81 Gy. The absorbed dose of the treatment unit at Dmax (Eq. 3) was calculated to be; (18MV) 1.03 Gy and (6MV) 1.03 Gy

Measurement of X-ray Beam Quality and Patient Dose Information from Analog Mammography

Measurement of X-ray beam quality and patient dose information from analog mammography have been studied by using an X-ray multimeter from 2016-2018. Parameters in the study are voltage accuracy, reproducibility test, radiation output linearity, radiation beam quality test, and patient dose information. The patient dose information using PMMA phantom with a thickness 4 cm in the Mean Glandular Dose (MGD) obtained dose values in 2016, 2017, 2018 are 0.982 mGy, 0.982 mGy, 0.953mGy, respectively. This study aims to determine the feasibility of mammography, while patient doses are compared with the standars set by the IAEA. The results showed that the suitability test of X-ray beam quality and patient dose information still comply the requirements recommended by the IAEA.

Improvement to beam quality of optically pumped terahertz gas lasers with hole-coupling resonators

The hole-coupling method, which is commonly used in the optically pumped THz gas laser, will reduce the beam quality due to the hard-edge diffraction. It is shown that by optimizing the parameters of the resonator a diffraction-limited output beam can be obtained. A method is proposed for the selection of a higher order waveguide mode, whose first zero point along the radial direction coincides with the edge of the output hole coupler and the effect of hard edge diffraction is depressed. Measurements of beam quality are taken on an experimental prototype whose optical setup is designed by this method. A quasi-Gaussian beam output is obtained, and the beam quality M2 factor is about 1.15

基于激光光场非等距双向传播的光束质量测量

基于激光光场非等距双向传播的光束质量测量