Schematic diagram of the components of the beam-line and the dual scattering system.
Geometry of proton scattering from a point source element of S2. In the plane of interest, the distance of the projected proton beam profile center from a point with radial distance ρ from the center is given by the cosine law.
Geometry of research room beam-line. From left to right, SEM and Ti exit window (green), S1 two Pb wedges (gray), first pTIC (pink), S2 (white and red), second pTIC (pink), range modulator wheel (red), and the water target (cyan).
Schematic representation of the Gantry 1 beam-line used in GEANT4 simulations. Components are described in the text.
Lexan and Cerrobend S2 profiles for the large field radiobiology (left) and the SRS/SRT (right) as a function of radial displacement from the central axis.
Cross sectional beam profile as a function of displacement from the central axis for the large field research room scattering foil.
Depth dose profiles in water created with the large field research room scattering foil. Profiles requested are uniform dose (with specified tolerance) to a given range (left). For experimental use the dose is normalized to the center of modulation (right) which acts as the prescription point. In both figures experimental measurement points are denoted by discrete markers.
GEANT4-simulated depth dose profiles of the current clinical scattering system (gray) and the new intermediate SRS/SRT scattering system (black) for 1.5 cm modulation (top) and 6.0 cm modulation (bottom). The left panel shows relative dose with the center of modulation of the SOBP of both curves scaled to 1; the right panel shows absolute dose for an identical number of particles, demonstrating the efficiency gain of the new scattering system.
Simulated cross profiles for uncollimated 150 MeV proton beams with the current scattering system (left) and the intermediate SRS/SRT scattering system (right) at two different depths in water (10 and 110 mm). Simulations calculated for 5 × 107 incident primary protons. Note that the new system was designed to create a narrower beam, and therefore a higher absolute dose for the same number of primary protons (note different scales).
Normalized cross profiles at a depth of 10 mm (left panel) and at the center of the 150 MeV SOBP (right panel) for 1.5 cm modulation (top) and 6.0 cm modulation (bottom). The newly developed intermediate SRS/SRT scattering system gives a nearly identical beam profile as the current clinical scattering system.
Two-dimensional isodose profiles on the central beam axis for the new intermediate SRS/SRT scattering system for 1.5 cm (left) and 6 cm (right) modulation of protons with 150 MeV initial energy.
Neutron energy spectra in air at isocenter as simulated using GEANT4 for the clinical and intermediate SRS second scattering foils and an 8 cm diameter 150 MeV proton field and 6.0 cm modulation. The profiles are displayed for the same number of incident primary protons (left) and for the same absorbed dose at isocenter (right).
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