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  1. SU-F-T-296: Modulated Therapy Down Under: A Survey of IMRT & VMAT Physics Practice in Australia and New Zealand

    Purpose: A comprehensive survey of Australasian radiation oncology physics departments was undertaken to capture a snapshot of current usage, commissioning and QA practices for intensity-modulated therapies. Methods: An online survey was developed and advertised to Australian and New Zealand radiation oncology physicists through the local college (ACPSEM) in April 2015. The survey consisted of 147 questions in total, covering IMRT, VMAT and Tomotherapy, and details specific to different treatment planning systems. Questions captured detailed information on equipment, policies and procedures for the commissioning and QA of each treatment technique. Results: 41 partial or complete responses were collected, representing 59 departmentsmore » out of the 78 departments operational. 137 and 84 linacs from these departments were using IMRT and VMAT respectively, from a total 150 linacs. 100% and 78% of respondents were treating with IMRT and VMAT respectively. There are at least 8 different treatment planning systems being used for IMRT or VMAT, and large variations in all aspects of QA policies and procedures. 29 responses indicated 72 methods routinely used for pre-treatment QA, when breaking down by device and analysis type. Similar numbers of departments use field-by-field analysis compared to composite analysis (56% to 44%) while a majority use true gantry angle delivery compared to fixed gantry at 0° (72% to 28%). 19 different implementations of gamma index analysis parameters were reported from 33 responses. A follow-up one-day workshop to highlight the results, discuss the role of QA and share equipment-specific knowledge across users was conducted in November 2015. Conclusion: While IMRT and VMAT are almost universally available in Australasia, large variations in practice indicate a need for national or consensus guidelines.« less
  2. The roles of cohesive strength and toughness for crack growth in visco-elastic and creeping materials

  3. SU-E-J-29: Automatic Image Registration Performance of Three IGRT Systems for Prostate Radiotherapy

    Purpose: To compare the performance of an automatic image registration algorithm on image sets collected on three commercial image guidance systems, and explore its relationship with imaging parameters such as dose and sharpness. Methods: Images of a CIRS Virtually Human Male Pelvis phantom (VHMP) were collected on the CBCT systems of Varian TrueBeam/OBI and Elekta Synergy/XVI linear accelerators, across a range of mAs settings; and MVCT on a Tomotherapy Hi-ART accelerator with a range of pitch. Using the 6D correlation ratio algorithm of XVI, each image was registered to a mask of the prostate volume with a 5 mm expansion.more » Registrations were repeated 100 times, with random initial offsets introduced to simulate daily matching. Residual registration errors were calculated by correcting for the initial phantom set-up error. Automatic registration was also repeated after reconstructing images with different sharpness filters. Results: All three systems showed good registration performance, with residual translations <0.5mm (1σ) for typical clinical dose and reconstruction settings. Residual rotational error had larger range, with 0.8°, 1.2° and 1.9° for 1σ in XVI, OBI and Tomotherapy respectively. The registration accuracy of XVI images showed a strong dependence on imaging dose, particularly below 4mGy. No evidence of reduced performance was observed at the lowest dose settings for OBI and Tomotherapy, but these were above 4mGy. Registration failures (maximum target registration error > 3.6 mm on the surface of a 30mm sphere) occurred in 5% to 10% of registrations. Changing the sharpness of image reconstruction had no significant effect on registration performance. Conclusions: Using the present automatic image registration algorithm, all IGRT systems tested provided satisfactory registrations for clinical use, within a normal range of acquisition settings.« less
  4. Effect of plastic deformation on the evolution of wear and local stress fields in fretting

  5. Simulation of wear evolution using fictitious eigenstrains

  6. New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei

    Here we have measured the beam-normal single-spin asymmetry A{sub n} in the elastic scattering of 1-3 GeV transversely polarized electrons from 1H and for the first time from 4He, 12C, and 208Pb. For 1H, 4He and 12C, the measurements are in agreement with calculations that relate A n to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the 208Pb result is significantly smaller than the corresponding prediction using the same formalism. Our results suggest that a systematic set of new A n measurements might emerge as a new and sensitive probe of the structure ofmore » heavy nuclei.« less
  7. Polarization orientation dependence of the far infrared spectra of oriented single crystals of 1,3,5,-trinitro-s-triazine (RDX) using terahertz-time-domain spectroscopy

    The far infrared spectra of (100), (010), and (001)-oriented RDX single crystals were measured as the crystal was rotated about the axis perpendicular to the polarization plane of the incident radiation. Absorption measurements were taken at temperatures of both 20 K and 295 K for all rotations using terahertz time-domain spectroscopy. A number of discrete absorptions were found ranging from 10-100 cm(-1) (0.3-3 THz). The absorptions are highly dependent on the orientation of the terahertz polarization with respect to crystallographic axes.
  8. DOE tries new approaches

    The US Department of Energy has finally unveiled details of its plan to have a private sector vendor treat and process liquid nuclear wastes at the Hanford weapons site in Washington state. While the document is not the official request for proposals that potential bidders had hoped for, DOE says it is planning a two-phase program under which one or more companies would build and operate a privately financed pretreatment and vitrification facility. In the first phase, a proof-of-concept to begin this year and end in 2002, one or two vendors would be selected to vitrify about 2 million galmore » of the wastes. DOE says the first-phase waste would be representative of 80% of the total wastes in Hanford`s 177 underground tanks. In the second phase, to run through 2028, DOE would choose a vendor to scale up its operations to treat the rest of the 57 million gal at Hanford. a DOE official says facilities that have been built for the initial phase could be used in the subsequent stage, although it is not clear yet technically whether pretreatment and vitrification plants could be built in a modular fashion.« less
  9. Senate tax plan seen favorable to cogenerators

    Senate tax reform proposals to encourage cogeneration feature a 10-year depreciation period, a slight reduction in corporate tax rates, a 5% cut in minimum corporate taxes, and a 12-month extension of the effective date of reform. Both the Senate and House versions eliminate the 10% Investment Tax Credit which many consider economically crucial for a number of projects. The Senate proposal does provide a cash refund at 70% for companies which meet the requirements. Cogeneration industry lobbyists will continue their efforts to retain incentives. Although more favorable to cogenerators than the House version, the Senate proposal discriminates between generating equipmentmore » and other capital investments. The bill should move to conference and be ready for approval by both houses in September.« less
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