VMAT SX1

Name (ID): UniLateral_HN, (UniLateral_HN)
Plan or PlanSum ID: 3arcSX1fulID

Unilateral head and neck treated SIB following RTOG 0920.  Three (3) arc VMAT plan created with each arc using a different start and stop angle (offset by 1 degree) to stagger the available control points throughout each arc rotation.  Unique collimator rotations were selected per arc and ordered for fastest treatment delivery (315,0,45).  Zero degree collimator arc rotations make sense on this machine due to the significantly reduced interleaf leakage of the two stage stacked and staggered MLC design.

The challenge was achieving the minimum PTV coverage constraint for targets that were overlapping or abutting OARs which could not be adequately spared due to the target size, location and overlap.  When a protocol enforces a minimum dose to the target, the temptation is to simply perform a uniform expansion on the target and optimize on the expanded target.  However, in this case, an optimization PTV was created and stretched outward only along the edges of the real PTV where the minimum dose was not met.  Careful attention was paid to minimize stretching where the target interfaced/overlapped with an OAR.

Not much difference between this VMAT plan and the 7F IMRT plan for the same case (the 7F IMRT plan being marginally better). Same expected overlap areas and ensuing hotspots are seen, and clinically justifiable. The delivery time is remarkably fast. This is a clinically acceptable plan.

_{Any reference to a "plan study" are simply what the organizers call each case and may not be a "study" in the FDA sense as they may not have been published in a peer reviewed journal.
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