VMAT SX1

Name (ID): GBM Patient 4SKT, (GBM80876)
Plan or PlanSum ID: Plan Sum

Brain GBM treated sequentially following RTOG 0825.  Initial seven (7) field IMRT plan created with custom gantry positions to mimic the flat edges on the PTV1 target shape on the transverse planes.  Also, consideration was given to place beam edges so that a sharp gradient could be achieved against the highest value OARs (brainstem, optic nerve).  Further plan quality improvements would have been achieved, if from a beam's eye view, unique collimator rotations were selected per field to match the general angle of the target volume.

For the sequential boost, due to the round nature of the boost volume, VMAT technique was chosen and 3 almost complete arcs were used.  All target constraints were assessed separately in the boost plan. 

A plan sum was created to evaluate organs at risk and all the constraints were eventually met.  The challenge was achieving target coverage goals and max target dose limit while not exceeding maximum dose allowed to the optic nerve, chiasm and brainstem.  To achieve all goals in the initial plan and boost plan, both plans had to be re-optimized after an evaluation of the plan sum.  Finally, plan normalization of each separate plan was adjusted until the plan sum was satisfactory.

This large field GBM treatment with a low dose area and a sequential boost has all OARs within tight limits. Homogeneity is excellent. The optic nerve limits are on the higher side, but the achieved gradients are fine. This is a clinically acceptable plan.

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