Andrew Ceballos

Dielectric laser acceleration of sub-100 keV electrons with silicon dual-pillar grating structures

We present the demonstration of high gradient (370 MeV/m) laser acceleration and deflection of sub-relativistic electrons with silicon dual pillar grating structures using both evanescent inverse Smith-Purcell modes and coupled cosh-like modes.

Seeing the invisible: Direct visualization of therapeutic radiation beams using air scintillation

PURPOSE To assess whether air scintillation produced during standard radiation treatments can be visualized and used to monitor a beam in a nonperturbing manner. METHODS Air scintillation is caused by the excitation of nitrogen gas by ionizing radiation. This weak emission occurs predominantly in the 300-430 nm range. An electron-multiplication charge-coupled device camera, outfitted with an f/0.95 lens, was used to capture air scintillation produced by kilovoltage photon beams and megavoltage electron beams used in radiation therapy. The treatment rooms were prepared to block background light and a short-pass filter was utilized to block light above 440 nm. RESULTS Air scintillation from an orthovoltage unit (50 kVp, 30 mA) was visualized with a relatively short exposure time (10 s) and showed an inverse falloff (r(2) = 0.89). Electron beams were also imaged. For a fixed exposure time (100 s), air scintillation was proportional to dose rate (r(2) = 0.9998). As energy increased, the divergence of the electron beam decreased and the penumbra improved. By irradiating a transparent phantom, the authors also showed that Cherenkov luminescence did not interfere with the detection of air scintillation. In a final illustration of the capabilities of this new technique, the authors visualized air scintillation produced during a total skin irradiation treatment. CONCLUSIONS Air scintillation can be measured to monitor a radiation beam in an inexpensive and nonperturbing manner. This physical phenomenon could be useful for dosimetry of therapeutic radiation beams or for online detection of gross errors during fractionated treatments.

Electron beam position monitor for a dielectric microaccelerator

We report the fabrication and first demonstration of an electron beam position monitor for a dielectric microaccelerator. This device is fabricated on a fused silica substrate using standard optical lithography techniques and uses the radiated optical wavelength to measure the electron beam position with a resolution of 10 μm, or 7% of the electron beam spot size. This device also measures the electron beam spot size in one dimension.

Modular platform for low-light microscopy.

Cell imaging using low-light techniques such as bioluminescence, radioluminescence, and low-excitation fluorescence has received increased attention, particularly due to broad commercialization of highly sensitive detectors. However, the dim signals are still regarded as difficult to image using conventional microscopes, where the only low-light microscope in the market is primarily optimized for bioluminescence imaging. Here, we developed a novel modular microscope that is cost-effective and suitable for imaging different low-light luminescence modes. Results show that this microscope system features excellent aberration correction capabilities and enhanced image resolution, where bioluminescence, radioluminescence and epifluorescence images were captured and compared with the commercial bioluminescence microscope.

Design and fabrication of curved silicon image planes for miniature monocentric imagers

We introduce the design and fabrication of a segmented, hemispherical silicon image plane for 10 mm-diameter spherical monocentric lens. In order to conform to the spherical focal plane of the lens, we create flexible gore patterns consisting of spring-connected silicon hexagons. Mechanical functionality is demonstrated by assembling 20 μm-thick, patterned silicon gores into a curved test fixture. We have also fabricated and tested a photodiode array in a CMOS compatible process. The hemispherical imager will enable a compact 160° field-of-view camera with a fill factor over 80% using a single spherical lens.

Waveguide optical tweezers for selective cell lysis

Waveguide evanescent fields enable lysing of selected red blood cells. Cells are trapped on waveguides and are lysed by rapidly reducing the trapping forces. Red blood cells of different age require different levels of lysing power, allowing selective lysing of crenate cells.

TH-C-17A-09: Direct Visualization and Monitoring of Medical Radiation Beams in Air

PURPOSE Radiation therapy errors are rare but potentially catastrophic. Recent fatal incidents could have been avoided by utilizing real-time methods of monitoring delivery of radiation during treatment. However, few existing methods are practical enough to be used routinely. The study presents the first experimental demonstration of a novel non-perturbing method of monitoring radiation therapy through the phenomena of air scintillation. METHODS Monitoring of radiation delivery was devised by leveraging the phenomena of nitrogen excitation in air by ionizing radiation. The excitation induced weak luminescence in the 300-400 nm range, a process called air scintillation. An electron-multiplication charge-coupled device camera (f/0.95 lens; 440 nm shortpass) was set-up in a clinical treatment vault and was used to capture air scintillation images of kilovoltage and megavoltage beams. Monte Carlo simulations were performed to determine the correlation of radiation dose to air scintillation. RESULTS Megavoltage beams from a Varian Clinac 21EX and kilovoltage beams from an orthovoltage unit (50 kVp, 30 mA) were visualized with a relatively short exposure time (10 s). Cherenkov luminescence produced in a plastic transparent phantom did not interfere with detection of air scintillation. The image intensity displayed an inverse intensity falloff (r2 = 0.89) along the central axis and was proportional to dose rate (r2 = 0.9998). As beam energy increased, the divergence of the imaged beam decreased. Last, air scintillation was visualized during a simulated total skin irradiation electron treatment. CONCLUSION Air scintillation can be clinically detected to monitor a radiation beam in an inexpensive and non-perturbing manner. This new method is advantageous in monitoring for gross delivery and uniquely capable of wide area in a single acquisition, such as the case for online verification of total body / skin / lymphoid irradiation treatments.