The clinical beam line is compared to the external target beam line. In the mode, the therapy target is present above the primary collimator, the flattening filter is in place, and there is no polystyrene electron filter. For the low- imaging case, the linac is operated in electron mode with the therapy target retracted and the external target is mounted in the carousel in place of the flattening filter. A polystyrene filter is placed in the upper accessory tray to stop any primary electrons.
The digitized film regions after exposure to the (a) and (b) incident electron beams at the level of the external targets. (c) shows the profile and Gaussian fit through the digitized electron spot.
Monte Carlo simulated values for all target combinations as a function of the target thickness as a percentage of . Simulated values for the 4.5 and , 60% thickness aluminum targets at the location of the target arm are included for comparison. Also included for comparison is the value for a simulated clinical beam.
Experimental values for all target combinations as a function of target thickness as a percentage of . The value from the clinical beam is also included for comparison.
Actual thicknesses of the external targets in mm.
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