Coordinate Conventions in Prism
Unless otherwise specified:
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Scales are in cm
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All angular coordinates are in degrees
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Patient space and couch space
Geometric data describing the patient’s anatomy are defined in the patient coordinate system. The z axis increases toward the patient’s feet, the X axis increases toward the patient’s left side and the Y axis increases toward the front of the patient (see Figure 1)
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The couch can be rotated around the y-axis.
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The transversal view is normal to the z-axis.
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The sagittal view is normal to the x-axis.
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The coronal view is normal to the y-axis.
Figure 1: Patient coordinate system
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Gantry coordinate space
The origin is at the treatment machine isocentre. When facing the treatment machine, the x-axis points to the right, the y-axis points directly toward the machine and the z-axis points from the isocentre toward the beam source (see Figure 2).
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The gantry can be rotated around the y-axis.
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The collimator can be rotated around the z-axis.
Figure 2: Gantry coordinate space
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