VMAT SX1

Due to the unflattened nature of the 6MV beam, traditional “2D” treatment techniques cannot be employed on most normal sized targets.  The inverse planning optimizer has to be employed to deliver a homogenous dose distribution to the target, which requires a target volume.  In this case the vertebra contours were drawn on just a few CT slices including the desired most superior and inferior slices and the rest of the CTV was created using interpolation.  Then a small uniform expansion was created to make a PTV subtracting a (3mm) margin from the skin surface.  Each plan was then optimized using only the PTV and Normal Tissue Objective (NTO).  Optimization constraints used were as follows:

VMAT: PTV 100%  30.3Gy p140; PTV 0% 35Gy p110; NTO auto p150

30Gy does not completely cover red/yellow contoured target structures (but 95%, 28.5Gy does) and cord is hotter.  Given VMAT, I would try to keep the cord/canal at 30-33Gy to meet dose coverage since it is within the target strcutre and potentially save room for SBRT if reirradiation required in the future.

_{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.
Varian does not provide medical advice and these are illustrative examples only.
Leading plans by expert planner. Your results may vary.}