Schematic diagram showing the effect of undersampling of the angular gantry locations. A quadrant of the gantry rotation is shown. For targets at machine isocenter (on-axis target), the intersecting beamlet rotates about the center of the target. For targets away from machine isocenter (off-axis target), the intersecting beamlet scans across the target since the center of rotation is not at the location of the target. Expected dose profile shapes are shown at the bottom left.
(a) The DMG in the custom made acrylic insert for the Lucy phantom (b) the DMG mounted in the Lucy phantom.
Treatment duration for (a) 10 mm diameter targets and (b) 5 mm diameter targets for the cheese phantom plans.
Difference between the planned and the measured peak target doses in the Cheese phantom, normalized to the planned peak dose for (a) 10 mm diameter targets and (b) 5 mm diameter targets. The error bars represent the standard deviation of three measurements.
Planned and measured dose maps from the Lucy phantom at 9.7 cm off-axis. Dose maps represent the dose in Gy to the central, coronal plane of the Lucy phantom. The white tick marks represent 1 cm increments.
Planned and measured dose profile through the center of the targets. (a) and (b) the EBT2 film measured profiles through the 10 mm and 5 mm targets respectively. (c) and (d) the DMG measured profiles through the 10 mm and 5 mm targets respectively. The error bars on the EBT2 film and DMG data are the standard deviations of three measurements.
Distance the centre of a beamlet traverses over a target during one projection for 51 and 153 projections. The horizontal dotted line represents the width of one leaf when projected to isocenter. The inset figure shows the beamlet FWHM for each target at each gantry angle. This FWHM is the lateral dose coverage of each beamlet.
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