244 MRIdian® system L-0009 Release 4.5 ViewRay, Inc.
Chapter 6: Treatment Planning
6.24 Couch and Isocenter Placement
The patient’s treatment planning position defines the relationship between the patient and
the radiation beams. The ability to accurately reproduce the patient’s planning position on a
daily basis is crucial for the precise delivery of each treatment fraction. The relationship
between the patient and couch must remain the same for simulation, planning, and
treatment. Dosimetric variations can occur when there are couch attenuation variations.
Couch placement is an important aspect of this patient-beam relationship. Use the Co
uch
Placement feature to automatically find a couch position in which the center of the image
volume is placed between two table notches and where the skin contour’s lowest point does
not intersect with the couch, or key in the simulation couch coordinates that are available
on the RealViewer screen. See "RealViewer” on page 319.
Use the Couch Placement feature to show the valid isocenter region.
A valid isocenter region is an area of safe point placement that will not cause a collision of the
pa
tient or couch with the bore of the gantry.
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