246 MRIdian® system L-0009 Release 4.5 ViewRay, Inc.
Chapter 6: Treatment Planning
6.25 Beams
There are three radiation beam types:
• IMRT
• Optimized Conformal
• Fixed Conformal
6.25.1 Beams Types
IMRT: Intensity Modulated Radiation Therapy separates the radiation into segments of
intensity (fluence) modulated beamlets. Each segment consists of beamlets that are shaped
and their fluence modified by passing through a multileaf collimator. To use IMRT beams, you
start with the desired outcome parameters (inverse planning) by entering the patient’s
prescription and setting the beam angles and number of fluence levels—then choose
Optimize Dose and the treatment planning system calculates the MLC shapes and fluences for
the beam-on segments.
Optimized Conformal: Op
timized Conformal beams consist of one segment shaped to fit the
target. The beams maintain the one shape during the entire fractionated treatment. The
treatment planning system uses operator-chosen constraints to calculate the fluence of
optimized conformal beams based on the prescription weighting points. Because these beams
are shaped to conform to the tumor volume, the radiation to the surrounding normal tissues
is restricted.
Fixed Conformal: Both
the shape and angle of fixed conformal beams are operator selected.
The treatment planning system calculates and sets the beam fluence based on the
prescription weighting points.
The Beam
Placement box is on the right of the Beams screen. From this box you can load
beam templates, place new beam groups, delete beam groups, add pseudo-arc beams and
save beam templates.
To Next Page