262 MRIdian® system L-0009 Release 4.5 ViewRay, Inc.
Chapter 6: Treatment Planning
6.30.2 Levels
The optimized fluence map is converted into discretized parts. The default levels setting is 10-
-meaning there are 10 energy levels that segments will be assigned to. Each fluence map is
discretized into deliverable beam-on segments by using the levels setting. If the setting is 10
then the maximum value fluence will be 10 and then proceed in descending value order for
the remaining 9 levels. Type in the number of levels you want or use the mouse wheel. The
maximum number of segments for a plan is 900.
6.30.3 Using IMRT Efficiency
IMRT Efficiency smooths the fluence map intensity pattern by keeping neighboring bixels
from differing more than scaled preset amounts based on the user-set IMRT Efficiency. This
fluence map smoothing will reduce the number of segments. Fluence map smoothing creates
a less sharp beam.
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