No abstract

Cherenkov radiation is induced when charged particles travel through dielectric media (such as biological tissue) faster than the speed of light through that medium. Detection of this radiation or excited luminescence during megavoltage external beam radiotherapy (EBRT) can allow emergence of a new approach to superficial dose estimation, functional imaging, and quality assurance for radiation therapy dosimetry. In this letter, the first in vivo Cherenkov images of a real-time Cherenkoscopy during EBRT are presented. The imaging system consisted of a time-gated intensified charge coupled device (ICCD) coupled with a commercial lens. The ICCD was synchronized to the linear accelerator to detect Cherenkov photons only during the 3.25-μs radiation bursts. Images of a tissue phantom under irradiation show that the intensity of Cherenkov emission is directly proportional to radiation dose, and images can be acquired at 4.7 frames/s with SNR>30. Cherenkoscopy was obtained from the superficial regions of a canine oral tumor during planned, Institutional Animal Care and Use Committee approved, conventional (therapeutically appropriate) EBRT irradiation. Coregistration between photography and Cherenkoscopy validated that Cherenkov photons were detected from the planned treatment region. Real-time images correctly monitored the beam field changes corresponding to the planned dynamic wedge movement, with accurate extent of overall beam field, and expected cold and hot regions.

We extend the Wigner current vector field (Wigner current) construct to single bosonic mode quantum systems interacting with an environment. In terms of the Wigner function quasiprobability density and associated Wigner current, the open system quantum dynamics can be concisely expressed as a continuity equation. Through the consideration of the harmonic oscillator and additively driven Duffing oscillator in the bistable regime as illustrative system examples, we show how the evolving Wigner current vector field on the system phase space yields useful geometric insights concerning how quantum states decohere away due to interactions with the environment, as well as how they may be stabilized through the counteracting effects of the system anharmonicity (i.e., nonlinearity).

We describe the design, simulation, and measured performance of concentrators designed to couple submillimeter wavelength radiation from free space into highly overmoded, rectangular, WR-10 waveguide. They consist of a combination of a Winston cone (also called a compound parabolic concentrator or CPC) with an adiabatic circular to rectangular transition. They are intended for use as adapters, between instruments using overmoded WR-10 waveguide as input or output and sources propagating through free space. Unlike conventional waveguide-coupled antennas, a geometric optics analysis is more appropriate than a mode-by-mode electromagnetic calculation of impedance and far-field pattern. Six separate designs were studied, with input diameters from 5 to 16 mm, and "throat" diameters (i.e., diameters at the circular interface between cone and transition sections) of 1 to 4 mm. Measurements at 394 m wavelength (760 GHz) using a far-IR waveguide laser beam indicate efficiencies of 40%-55%. The angular response is primarily determined by the Winston cone, and is well predicted by geometric optics theory, i.e., approximately constant out to an angle determined by the ratio of input to throat diameters. The efficiencies are primarily determined by the transition section, and for all concentrators are consistent with an average reflectance of 94% from the gold-plated, electroformed, interior surfaces. For each individual concentrator, efficiency variations with polarization, angular orientation and beamsize are below the measurement uncertainty.