A schematic representation of the Hitachi proton beam nozzle showing the components in the beam paths that influence the beam output and characteristic.
Representations of depths used to measured output at the center of the SOBP, proximal 95% depth dose, distal 90% depth dose, and measurement of SOBP width. Daily QA consists of measuring these parameters at the corresponding depths in solid water plastic. The parameters are determined from depth-dose curves measured in water.
A homemade device used for verification of the treatment couch positional accuracy. The predetermined coordinates on the device (shown in circle) positions the central BB in the cube at the gantry isocenter. This device is also used to check the treatment couch movement and the alignment of the orthogonal x-ray unit. The markings at ±10 cm from the gantry isocenter, shown by arrows, are used to check the table movement accuracy.
A plastic slab with an inserted ion chamber at its center attached to the snout of the nozzle to measure the beam output as a function of gantry angles.
Setup for checking gantry isocentricity using the projection of a pencil tip and the cross-wire device that is attached to the gantry. The cross wires are in the brass aperture. The intersection of the pencil tip and the intersection of the cross wires in the device is examined at different gantry angles.
Setup for verification of gantry mechanical isocentricity using systems. A metallic ball is positioned precisely at the isocenter by iterated position checking. The micrometer touching the sliding ball measures the deviation of gantry isocentricity as a function of angles in three dimensions when the gantry is rotated 360°.
Setup for measurement of proton range uniformity at the distal edge using picket fence film. Picket fence film is shown in the lower right corner of the picture. The upper left corner and upper right pictures show where the film is positioned. The lower left corner shows the measured profile using Picket fence film. A uniform saw tooth profile indicates a consistent proton range at the distal edge.
Variation of daily beam parameters for 250–100 MeV proton beams over a 1 year period. The data represent (a) output at the center of SOBP, (b) proximal 95% depth dose, (c) distal 90% depth dose, and (d) distal 10% depth dose.
List of QA procedures performed at the M. D. Anderson PTC-H.
A typical set of measured flatness and symmetry values obtained using MatriXX for seven proton beams at four gantry angles. The flatness is measured in terms of maximum percentage variation of the dose across the central 80% of the full width. The field width is defined as the full width at half maximum of the lateral beam profile. The symmetry is the maximum percentage variation of dose for a pair of points located symmetrically with respect to the central ray. Abbreviations: in plane (IP); cross plane (CP).
Values of the differences in the SOBPF from annual QA measurements and from the clinical data for the medium snout. The average differences and their corresponding uncertainties to within one standard deviation are indicated.
Values of percentage differences in the range-shifter factors (i.e., for range shift of 0–4 cm) from annual QA measurements and from clinical data for the medium snout. The differences and their corresponding uncertainties to within one standard deviation are indicated.
Results of annual verification of ROF for the medium snout.
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