W. Robert Binns

A METHOD TO ANALYZE 2-DIMENSIONAL DAILY RADIOTHERAPY PORTAL IMAGES FROM AN ON-LINE FIBER-OPTIC IMAGING SYSTEM

On-line radiotherapy imaging systems allow convenient treatment verification and generate a wealth of data. Quantitative analysis of data will provide important information about the nature of treatment variations. Using an inhouse fiber-optic imaging system to acquire daily portal images for five patients, we have developed a method to analyze the cumulative positional variation of blocks in the 2-dimensional images. For each beam arrangement used to treat a particular patient, a reference portal image was established. All other images for that patient were registered with respect to the anatomical landmarks visible on the reference image. Two-dimensional frequency distributions describing the overlap of the blocks during the course of treatment were then calculated and superimposed on the reference image. Results of the analysis show positional and quantitative information about the daily variation in block placement, and appeared to be site-dependent. Long term verification studies using on-line imaging systems will be important in the understanding of treatment uncertainties.

Development of a second-generation fiber-optic on-line image verification system☆

PURPOSE We have previously reported the development of a fiber-optic fluoroscopic system for on-line imaging on radiation therapy machines with beam-stops because of space limitation. While the images were adequate for clinical purposes in most cases, an undesirable grid artifact existed and distracted visualization. The resolving power of the system, limited by the 1.6 mm x 1.6 mm dimension of the input fibers, appeared insufficient in some cases. This work identifies solutions to reduce grid artifact and to improve the resolution of the system. METHODS AND MATERIALS In the clinical system, it was found that the scanning mechanism of the newvicon camera was deflected differently at various gantry positions because of the different orientation of the earths magnetic field. The small image misregistration produced grid artifact during image normalization, particularly near boundaries of the fiber bundles. One approach taken to reduce magnetic field effects was to shield the camera with mu-metal. Alternatively, a charged-coupled-device camera was used instead of the newvicon camera. As for improving spatial resolution, fibers with smaller input dimension were used. A 20 cm x 20 cm high resolution fiber-optic prototype consisting of 250 x 250 fibers, each with an input dimension of 0.8 mm x 0.8 mm was constructed. Its performance was tested using several phantoms studies. RESULTS Both shielding the newvicon camera with mu-metal or replacing it with a charge-coupled-device camera reduced grid artifact. However, optimal shielding could not be made for our clinical system because of the space limitation of its housing. High contrast resolution was improved, the 30% value of the modulation transfer function occurred at 0.3 linepairs per mm for the clinical system and at 0.7 linepairs per mm for the high-resolution prototype. However, because of the larger degree of transmission non-uniformity of the prototype, it was less effective using the current setup in detecting low contrast objects. CONCLUSIONS The results are encouraging and demonstrate successful reduction of grid artifact and improvement of high contrast spatial resolution using the proposed methods. The less effective low contrast detection was related to reduced light collection efficiency due to use of prototype fibers whose productions were not closely monitored. The findings are being considered in our construction of a second generation clinical fiber-optic on-line image verification system.

Cosmic-Ray Origins

The detection of distributed, high-energy gamma-ray emission points to cosmic-ray acceleration in a superbubble. The origin of cosmic rays has been a mystery since it was conclusively shown by Victor Hess (1) that ionizing radiation impinges on Earth from space, and subsequently shown by Arthur Compton (2) that this cosmic radiation is primarily composed of charged particles. Since that time, there has been great interest in understanding the origin of these cosmic nuclei accelerated to nearly the speed of light—identifying the source of the material that is accelerated, the nature of the accelerator, and the mechanism by which the source material is injected into the accelerator. On page 1103 of this issue, Ackermann et al. (3) report observations with NASAs Fermi Large Area Telescope that are directly related to the origin of cosmic rays. They identified distributed emission of gamma-rays over the energy range of 1 to 100 GeV in the Cygnus X region of the sky with a “cocoon” of freshly accelerated cosmic rays.

FiberGLAST: a scintillating fiber approach to the GLAST mission

FiberGLAST is a scintillating fiber gamma-ray detector designed for the GLAST mission. The system described below provides superior effective area and field of view for modest cost and risk. An overview of the FiberGLAST instrument is presented, as well as a more detailed description of the principle elements of the primary detector volume. The triggering and readout electronics are described, and Monte Carlo Simulations of the instrument performance are presented.

Elemental Abundances of Ultra-Heavy GCRs measured by SuperTIGER and ACE-CRIS and the Origin of Galactic Cosmic Rays

The Super Trans-Iron Galactic Element Recorder (SuperTIGER) long-duration balloon instrument and the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) satellite have measured the abundances of galactic cosmic-ray elements from _(10)Ne to _(40)Zr with high statistics and single-element resolution. SuperTIGER launched from Williams Field, McMurdo Station, Antarctica, on December 8, 2012, flying for a record 55 days. During that flight we detected ∼1,300 nuclei with atomic number Z ≥ 30. The resolution in charge (Z) of SuperTIGER is excellent, with σ_Z ≈ 0.16 c.u. at _(26)Fe. SuperTIGER is sensitive to nuclei with energy at the top of the atmosphere of E > 0.8 GeV/nucleon. The instrument has now been recovered and preparations are underway for its next flight. ACE/CRIS has been taking data in space for more than 17 years since launch in 1997, has collected ∼625 nuclei with atomic number Z ≥ 30, and shows excellent resolution with clear separation between the charges for 30 ≤ Z ≤ 40. ACE/CRIS is sensitive to nuclei in the energy range 150 ≤ E ≤ 600 MeV/nucleon. Preliminary results from the balloon-borne SuperTIGER show good agreement with ACE measurements in space, validating our corrections to SuperTIGER abundances for nuclear interactions in the atmosphere. The results from these experiments will be discussed in the context of the OB association model for the origin of galactic cosmic rays. Future missions to measure elemental abundances to higher Z, the SuperTIGER-II LDB instrument and the orbiting Heavy Nuclei eXplorer (HNX) mission, will also be discussed.

Abundances of Ultra-Heavy Galactic Cosmic Rays from the SuperTIGER Instrument

R. P. Murphy∗1, W. R. Binns1, R. G. Bose1, T. J. Brandt2, P. F. Dowkontt1, T. Hams 2,6, M. H. Israel1, A. W. Labrador3, J. T. Link2,6, R. A. Mewaldt3, J. W. Mitchell2, B. F. Rauch1, K. Sakai2,6, M. Sasaki2,6, E. C. Stone3, C. J. Waddington4, J. E. Ward1,‡, and M. E. Wiedenbeck5† 1 Washington University in St. Louis, St. Louis MO 63130 USA 2 NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA 3 California Institute of Technology, Pasadena, CA 91125 USA 4 University of Minnesota, Minneapolis, MN 55455 USA 5 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 USA 6 Center for Research and Exploration in Space Science and Technology (CRESST) ‡ Now at Institut de Fisica d’Altes Energies (IFAE), Bellaterra, Spain

Development and testing of a fiber/multianode photomultiplier system for use on FiberGLAST

A scintillating fiber detector is currently being studied for the NASA Gamma-Ray Large Area Space Telescope (GLAST) mission. This detector utilizes modules composed of a thin converter sheet followed by an x, y plane of scintillating fibers to examine the shower of particles created by high energy gamma-rays interacting in the converter material. The detector is composed of a tracker with 90 such modular planes and a calorimeter with 36 planes. The two major component of this detector are the scintillating fibers and their associated photodetectors. Here we present current status of development and test result of both of these. The Hamamatsu R5900-00-M64 multianode photomultiplier tube (MAPMT) is the baseline readout device. A characterization of this device has been performed including noise, cross- talk, gain variation, vibration, and thermal/vacuum test. A prototype fiber/MAPMT system has been tested at the Center for Advanced Microstructures and Devices at Louisiana State University with a photon beam and preliminary results are presented.

High-energy x-ray imaging spectrometer (HEXIS)

HEXIS is a MIDEX-class mission concept for x-ray astronomy. Its objectives are to improve our knowledge of the high energy x-ray sky by increasing the number of sources above 20 keV to > 2,000, discovering transient sources such as x-ray novae and gamma-ray bursts, and making spectral and temporal studies of the sources. With mission life > 3 years, a 1-year all-sky survey sensitivity of approximately 0.3 mCrab, and continuous monitoring of the entire visible sky, HEXIS will provide unprecedented capabilities. Source positions will be determined to accuracies of a few arcmin or better. Spectra will be determined with an energy resolution of a few keV and source variability will be studied on time scales from < 1 sec to years. In addition, 10 times more sensitive studies of limited fields will be performed at the same time. Gamma-ray bursts will be detected about 4 times/week at about the same sensitivity as BATSE and the sensitivity to nova-like x-ray transients will be approximately 6 mCrab in one day. HEXIS contains a set of coded mask imagers that use position-sensitive CZT detectors operating from approximately 5 keV to 200 keV. Detector planes are built with 41 cm2 CZT detector modules which employ crossed-strip readout to obtain a pixel size of 0.5 mm. Nine modules are grouped in a 369 cm2 array for each imager. In the past 2 years significant progress has been made on techniques requires for HEXIS: position-sensitive CZT detectors and ASIC readout, coded mask imaging, and background properties at balloon altitudes. Scientific and technical details of HEXIS are presented together with result form tests of detectors and a coded mask imager.

Introduction to the SalSA, a saltdome shower array as a GZK neutrino observatory

The observed spectrum of ultra-high energy cosmic rays virtually guarantees the presence of ultra-high energy neutrinos due to their interaction with the cosmic microwave background. Every one of these neutrinos will point back to its source and, unlike cosmic rays, will arrive at the Earth unattenuated, from sources perhaps as distant as z=20. The neutrino telescopes currently under construction, should discover a handful of these events, probably too few for detailed study. In this talk I will describe how an array of VHF and UHF antennas embedded in a large salt dome, SalSA (Saltdome Shower Array) promises to yield a teraton detector (> 500 km3-sr) for contained neutrino events with energies above 1017 eV. Our simulations show that such a detector may observe several hundreds of these neutrinos over its lifetime. Our simulations also show how such interactions will provide high energy physicists with an energy frontier for weak interactions an order-of-magnitude larger than that of the LHC. The flavor ID capalities of SALSA, combined with the extreme L/E of these neutrinos, will provide a window on neutrino oscillations and decay times eight orders of magnitude higher than laboratory experiments. In addition to the latest simulation results, we describe progress on detectors and site selection.

Analysis of GCR Spectra and Composition Using Penetrating Particle Data from the CRIS Instrument on ACE

The Cosmic Ray Isotope Spectrometer (CRIS) on NASA’s Advanced Composition Explorer (ACE) spacecraft has been making precise measurements of cosmic-ray elemental and isotopic composition and energy spectra for nearly 18 years. This instrument uses the dE/dx versus total energy technique to identify nuclei that stop in thick stacks of silicon solid-state detectors and to measure their energy. The energy range covered for these stopping particles extends up to ∼280 MeV/nuc for O and ∼570 MeV/nuc for Fe. We have developed a new technique for identifying particles that penetrate the entire detector stack that relies on a combination of the total energy deposited in the stack and the change of dE/dx from the front to the back of the stack. This technique allows us to extend energy spectra for cosmic-ray elements to higher energies and can be used for bridging the energy gap between the CRIS stopping-particle spectra and measurements made in low-Earth orbit by instruments such as HEAO-C2, PAMELA, and AMS-02. We describe the technique for assigning atomic number and energy to penetrating particle events and discuss the corrections needed for deriving energy spectra from these data.