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Brynn Cropp
The head-scatter factors H were examined for four different linear accelerators and were found to be similar at field sizes larger than 3 x 3 cm2. Sharply reduced values for small collimator openings were observed for all the accelerators. It is concluded that the head-scatter (or collimator-scatter) factor has two major components. Scatter of photons in various structures in the beam path, especially the flattening filter, causes a slow (about 10%) increase with increased collimator opening. Insertion of a built-in wedge may double this number. When the collimators are closed, they ultimately block photons from the periphery of the source. This may cause a considerable reduction of the primary photon fluence and typically affects fields smaller than 3 x 3 cm2. The effect can be used to estimate the source size, with results that correlate with the design of the bending magnet.
Featured at The Vinoy Renaissance St. Petersburg Resort & Golf Club, the Scatter Brain Sculpture will make you think twice without a doubt. This anything but ordinary piece is made of an antique bronze cast iron and set on a beautiful white marble base. With butterflies surrounding the bust head, this sculpture will add a whimsical touch to your home decor.
Our objective in this study has been to investigate how head scatter varies with the off-axis position in a 6 MV x-ray beam. We define the head-scatter off-axis ratio, HOA, as the ratio of the kerma due to head-scatter photons at the off-axis position x to the kerma from direct primary photons on the central axis. "Direct primary" are those photons that come from the source without interactions in the intervening structures. We determined HOA from measurements with an ionization chamber in a miniphantom. Head-scatter and direct primary photons contribute to a measurement of the ionization per mu Q(x) at the off-axis position x in the open field cx x cy. The ionization per mu QP(x), measured in the same position but with the field collimated to the smallest possible opening (cx x 3 cm), is intended to include only direct primary photons. Head-scatter photons cannot be completely eliminated, and the errors due to remaining head scatter and radiation back-scattered by the movable collimators into the monitor were estimated. For normalization of the final results, ionization due to direct primary photons was also measured on the central axis, QP(0). HOA was derived from these three measurements as HOA(cx,cy,x)=(Q(cx,cy,x) - QP(cx,cy,x))/QP(cx,cy,0). On the central axis (x=y=0), HOA represents the "scatter-to-primary ratio" between head scatter and the direct primary dose. Monte Carlo simulations were made to help with the interpretation and evaluation of the results. HOA could be fitted to a Gaussian model with two components corresponding to sources of widths 1.8 and 14 cm, projected on a plane 5 cm below the x-ray source. The narrow Gaussian component is interpreted as the source of photons scattered in the flattening filter and the primary collimator. The broad component is attributed to photons scattered in the secondary (variable) collimators. Conventional head-scatter models (e.g., a single Gaussian source model) do not fit the measured HOA data for large collimator settings (c>20 cm) or outside beam collimation. The full width at half-maximum (FWHM) of HOA(x) across the field increased with the field width (cx) in the direction of the measurements in a manner consistent with the field of view of the two sources. It was not sensitive to the field measure in the orthogonal direction (cy). Head scatter outside the field also increased with field size, reflecting an increased contribution of photons scattered at large angles. It exceeds the leakage through the collimator 2 cm outside the edge for square fields c>10 cm. Monte Carlo calculations showed considerably less head scatter outside the field than measurements.
Automatic visibility and present weather sensors normally use the forward scattering of infrared light to estimate visibility and classify precipitation. Sensors produced by Biral emit a cone of modulated near infrared (850 nm) from the transmitter head, which is scattered by particles in the air. The intensity of scattering is not the same in all directions, since this is strongly dependent on the shape, size and composition of the particle.
Present weather sensors which do not have a back scatter receiver usually discriminate between rain and snow using only the forward scatter signal from an individual hydrometeor (raindrop or snowflake), often combined with air temperature.
An example of the relative difference between forward and back scattered infrared for different individual hydrometeors is presented in figure 3. These measurements were taken as rain turned to ice pellets then snow as a thunderstorm passed over a Bristol-based sensor on 2 March 2016. Classifications were based on human observation, with approximately three minutes between the different hydrometeor types. Air temperature remained above freezing throughout, at 6C during the rainfall and ice pellets, and 5C during the snowfall.
The back scatter receiver is unique to the Biral present weather sensors and provides reliable discrimination between rain and snow. This is demonstrated by reports of excellent snow detection and discrimination capability from our customers and field trials with trained meteorological observers.
Back scatter receivers form part of our SWS 200 and 250 series and VPF 730 and 750 series. The Biral VPF-750 represents our most advanced visibility and present weather sensor, with the addition of external temperature and relative humidity sensors to aid discrimination between fog and non-liquid particles which lower the visibility, such as smoke, wind-blown sand, and dust. An integrated freezing rain detector allows reporting of all forms of freezing precipitation, providing a comprehensive and reliable account of present weather for all environments.
I'm using Recharts and I have a composed chart with Scatter inside. I'm using the line prop to connect the scatters, but I would like the lines to indicate the direction of the line like the lines were arrows or something like that. How can I do it? Here is my scatter:
Yeah, it is very easy to do this. Supposing you have same amount of heads and tails data.Probably there is a more efficient way of coding this, but hey, it works. I encourage anyone with a better coding skills than me to improve it ;)
Purpose: To construct and test a semi-analytical model describing the effects on Monitor Unit (MU) verification caused by scattering in the treatment head. The implementation of the model should be accomplished using a small set of experimental data. Furthermore, the model should include a geometry dependent estimation of the resulting uncertainty.
Material and methods: The input required by the created model consists of basic treatment head geometry and 10 measured output factors in air (OFair) for square fields. It considers primary energy fluence, scattered radiation from an extra-focal source and from secondary collimators, as well as backscatter to the monitor chamber. Measurements and calculations were performed in open symmetric and asymmetric fields at points located both on and off the collimator axis, as well as at arbitrary treatment distances. The model has been verified for 19 photon beams in the range from 4 up to 50 MV, provided by nine different treatment units from six manufacturers.
Results: The presented model provided results with errors smaller than 1% (2 S.D.) in typical clinical situations for all beams tested. In more exceptional situations, i.e. combinations of unconventional treatment head designs, very elongated fields, and dosimetry points far away from the isocenter, the total uncertainty increased to approximately 2%. The spread in the results was further analysed in order to create a method for predicting the uncertainties under different treatment conditions.
Conclusions: A general head scatter model that is easy to implement has been developed and can be used as the basis for computerised MU verification. The model handles all commercially available treatment units adequately and also includes an estimation of the resulting uncertainty.
Purpose: T his s tudy a imed t o i nvestigate t he a ccuracy o f h ead s catter f actor ( Sc) by applying a developed multi-leaf collimator (MLC) scatter source model for an unflattened photon beam.
Methods: Sets of Sc values were measured for various jaw-defined square and rectangular fields and MLC-defined square fields for developing dual-source model (DSM) and MLC scatter model. A 6 MV unflattened photon beam has been used. Measurements were performed using a 0.125 cm3 cylindrical ionization chamber and a mini phantom. Then, the parameters of both models have been optimized, and Sc has been calculated. The DSM and MLC scatter models have been verified by comparing the calculated values to the three Sc set measurement values of the jaw-defined field and the two Sc set measurement values of MLC-defined fields used in the existing modeling, respectively.
Results: For jaw-defined fields, the calculated Sc using the DSM was consistent with the measured Sc value. This demonstrates that the DSM was properly optimized and modeled for the measured values. For the MLC-defined fields, the accuracy between the calculated and measured Sc values with the addition of the MLC scatter source appeared to be high, but the only use of the DSM resulted in a significantly bigger differences.
Conclusions: Both the DSM and MLC models could also be applied to an unflattened beam. When considering scattered radiation from the MLC by adding an MLC scatter source model, it showed a higher degree of agreement with the actual measured Sc value than when using only DSM in the same way as in previous studies.