IMRT SX1 A

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 can 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:

AP PA: PTV 100%  30.3Gy p140; PTV 0% 35Gy p110; NTO man p100 DTB1.0cm SD105% ED60% FO.05

Alternatively, the irregular surface compensator tool can be used to create a homogeneous dose at depth.  This method would likely involve manual edits to the ideal fluence prior to plan approval thereby maintaining a completely forward planned workflow.

40Gy is too hot for the heterogeneity of this plan.  I would favor more weighting on PA beam to decrease dose to the anterior structures which are not the target lesion.  Coverage of the target lesion is good.  I usually keep cord <35Gy and it appears that it may be >33Gy based on the isodose lines.
 

_{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.}