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So …..
The maximum gantry rotation angle is 360 degrees
plus the sum of all concavities
The concavity can be created in one 360 degree rotation
plus partial shielding of the beam.
This is the
VMAT
way. It is analogous to the
step and shoot technique in static gantry IMRT.
This is the
tomotherapy way
. Emulating it with a cone-beam MLC
means large leaf travel and is wasteful in terms of primary radiation.
(Notice, tomotherapy is also wasteful for narrow fan-beams and
long target volumes)
Courstesy of Markus Alber