Measurement and Calculation of Electron Contamination for Radiotherapy Photon Mode

Context: This study was done to review the electron contamination sources and measurement based on dosimetry and simulation techniques for radiotherapy and also investigate factors affecting electron contamination reduction. Methods: We systematically searched five major indexing databases, including PubMed, Scopus, Embase, ISI web of science, and Cochrane central, using keywords of electron contamination, electron contamination AND measurement, electron contamination AND simulation, and electron contamination AND reduction until Dec 2020. Results: Overall, 35 studies were reviewed, including articles reporting the theory of electron contamination, papers on dosimetry methods to measure electron contamination, studies about simulation methods to assess electron contamination, and articles about reducing electron contamination. The results indicated an increase in electron contamination using a flattering filter, an increase in field size, the presence of prosthesis in the patient's body, and a rise in photon energy. Conclusions: It can be concluded that the excessive delivered doses by electron contamination can cause skin complications, such as erythema, desquamation, and telangiectasia inside or outside the photon field. The amount of electron contamination depends on factors, such as radiation field size, beam energy, and materials placed in the photon path. Electron contamination can be decreased by increasing the source distance to the point of measurement by the dosimeter, applying a lead foil, magnetic deflector, or replacing a portion of air column between patient and radiotherapy system head by helium gas, and also limiting the treatment field.

Explanation of Photon Navigation in the Mach-Zehnder Interferometer

Photons in interferometers manifest the functional ability to simultaneously navigate both paths through the device, but eventually appear at only one outlet. How this relates to the physical behaviour of the particle is still ambiguous, even though mathematical representation of the problem is adequate. This paper applies a non-local hidden-variable (NLHV) solution, in the form of the Cordus theory, to explain photon path dilemmas in the Mach–Zehnder (MZ) interferometer. The findings suggest that the partial mirrors direct the two reactive ends of the Cordus photon structures to different legs of the apparatus, depending on the energisation state of the photon. Explanations are provided for a single photon in the interferometer in the default, open-path, and sample modes. The apparent intelligence in the system is not because the photon knows which path to take, but rather because the MZ interferometer is a finely-tuned photon-sorting device that auto-corrects for randomness in the frequency phase to direct the photon to a specific detector. The principles also explain other tunnelling phenomena involving barriers. Thus, navigation dilemmas in the MZ interferometer may be explained in terms of physical realism after all.

Metalens-array–based high-dimensional and multiphoton quantum source

The development of two-dimensional metasurfaces has shown great potential in quantum-optical technologies because of the excellent flexibility in light-field manipulation. By integrating a metalens array with a nonlinear crystal, we demonstrate a 100-path spontaneous parametric down-conversion photon-pair source in a 10 × 10 array, which shows promise for high-dimensional entanglement and multiphoton-state generation. We demonstrate two-, three- and four-dimensional two-photon path entanglement with different phases encoded by metalenses with fidelities of 98.4, 96.6, and 95.0%, respectively. Furthermore, four-photon and six-photon generation is observed with high indistinguishability of photons generated from different metalenses. Our metalens-array–based quantum photon source is compact, stable, and controllable, indicating a new platform for integrated quantum devices.

Evaluation of simulated clear sky O2 A-band measurements from GOSAT over different surfaces - a sensitivity study

<p>We present a follow-up study on previous investigations of photon path lengths distributions in cloudy atmospheres using O<sub>2</sub> A-band measurements from the GOSAT TANSO-FTS satellite instrument (Kremmling, B., Investigation of photon path length distributions derived from oxygen A-band measurements of the GOSAT satellite instrument, PhD thesis, 2018). The original study used TANSO-FTS measurements of high spectral resolution over cloud covered ocean areas and compared them to radiative transfer simulations using the Monte Carlo model McArtim. The comparison is based on a fitting process, allowing spectral alignment as well as an adjustment of the simulated O<sub>2</sub> absorption. A systematic overestimation of 5-10% of the simulated O<sub>2</sub> absorption was found for the considered case studies. Despite the investigation of different sensitivity studies, the cause of this overestimation remained unresolved.</p><p>The consequence of these finding was the thorough investigation of clear sky measurements from TANSO-FTS between 2009 and 2015. The analysis includes the retrieval of the surface albedos and their comparison to those included in the TANSO-FTS data products as well as the subsequent fitting results of the simulated spectra. The analysis is applied to two datasets, both consisting of measurements passing different clear sky and quality criteria. Dataset 1 additionally has information from independent lidar measurements of CALIOP (CALIPSO) and is limited to the northern hemisphere due to the spatial and temporal collocation criteria. Dataset 2 has no independent collocation measurements but a more uniform distribution in space and time.</p><p>While the retrieved surface albedos compare well, an overestimation of the simulated O<sub>2</sub> absorption by about 5% is found for measurements over ocean. Good agreement is found for the land cases.</p><p>In order to better understand these observations, different sensitivity studies as well as fit settings are investigated. The sensitivity studies include parameters such as SZA, surface albedo, NDVI values as well as the polarization of the TANSO-FTS radiances. The presentation shows the outcome of these studies.</p>

Hyperspectral A-band retrievals of cloud droplet number concentration from OCO-2

<p>NASA’s Orbiting Carbon Observatory-2 (OCO-2) includes a hyperspectral (Dl~0.02 nm) oxygen A-band sensor, and the depth of its absorption features is related to the photon path length. Photon path length increases above a cloud if it is lower (i.e. higher P<sub>top</sub>), and within a cloud if its droplets are farther apart (i.e. lower N­<sub>d</sub>). This is a novel approach for retrieving N<sub>d</sub> that is independent of MODIS-like retrievals, which take an a priori vertical cloud structure and assume that non-adiabatic processes such as precipitation or entrainment affect clouds uniformly. Our last product, OCO2CLD-LIDAR-AUX, used CALIPSO P<sub>top</sub> to help separate the above- and within-cloud path length. Here we show progress in an updated OCO-2 only retrieval of marine boundary layer clouds, including using neural networks for cloud identification and phase classification, additional retrieval of r<sub>e</sub>, and how cloud vertical structure can bias retrieved P<sub>top</sub> and N<sub>d</sub>. Successfully addressing this bias would provide a new and independent N<sub>d</sub> retrieval that should capture changes due to non-adiabatic processes, and therefore provide a new test of aerosol cloud effects.</p>