Diagonal profiles measured with different injector currents with the target and flattening filter in place. Upper traces, ; lower traces, . Data points with errors are measured with low beam current, and binned into bins. Solid lines are measured with clinical beam current. The low injector currents were used for the measurements with no target or flattening filter, and the high injector currents were those used for the clinical beam. Data were averaged over two sides of isocenter.
(a) Percent-depth ionization measured with different injector currents with the target and flattening filter in place and a field. Data points with errors were measured with low beam current and binned into bins. Solid lines were measured with clinical beam current. Left traces, ; right traces, . (b) Difference between percent-depth ionization traces measured with high and low injector currents, for . [(c) as (b)], for .
Comparison of measured (lines) and simulated (circles) percent-depth ionization curves with only the exit window in the beam for bending magnet currents of 12.6, 15, 18, 21, 24, and (left to right). Simulations shown used the thicker exit window. Normalization is arbitary.
Measured depth at which ionization falls to half its maximum value (left scale), and electron source energy as determined by Monte Carlo simulation (right scale) vs bending magnet current. Line is a fit of electron source energy derived from Monte Carlo vs bending magnet current. Simulated results used the thicker exit window geometry to match the measured results. Filled diamonds are the measured with the electron secondary scattering foil and monitor chamber in the beam path.
Comparison of measured (lines) and simulated (circles) profiles at with only the exit window in the beam, for bending magnet currents of 12.6, 15, 18, 21, 24, and , from the outside in. Simulations shown used the thicker exit window geometry. Normalization is arbitary.
Comparison of measured (solid) and simulated (hollow) profiles in the bremsstrahlung region, beyond the maximum electron range, with only the exit window in the beam. For clarity, only results with bending magnet currents of 12.6 (outer trace) and (inner), as used for the 6 and clinical beams, respectively, are shown. Data are binned into bins. Simulations shown used the thicker exit window geometry. Normalization is arbitary.
Width of profile at . Measurement (solid circles), simulation with the manufacturer-specified exit window and nondivergent beam (diamonds), manufacturer-specified exit window and divergent beam (squares), and thicker exit window (triangles) are shown.
Profiles with target in, but not the flattening filters. Top, at depth. Bottom, at depth. Solid lines are measured, filled diamonds are simulated with divergent beams, and circles simulated with the thicker exit window. Relative normalization of simulations for each energy is by dose per pulse.
Depths used to measure profiles. is the depth of maximum ionization and is sufficiently deep that dose only involves bremsstrahlung generated in the phantom and exit window.
Measured and Monte Carlo parameters of the incident electron beam used to match measured data. Energy and spectral width are the values for the simulation with the thicker exit window. Divergence values are those used with the manufacturer-specified exit window thickness. Spectral width is full width of half maximum: absolute uncertainty is 4%.
Amount of dose in the bremsstrahlung tail relative to dose at . , expressed in percent. Uncertainties in the simulations represent the statistical errors of 1%. Ratios: Thick∕Div is the ratio of simulations with the thicker exit window and beam divergence; meas∕thick is the ratio of the measured value to the value from the simulation with thicker exit window. The uncertainty in the ratio of simulated doses only includes the statistical uncertainty.
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