VMAT SX1

Plan or PlanSum ID: Arcsm1IDS1a

Four (4) arc VMAT technique was chosen and (4) four almost complete arcs were used. Each arc used a different start and stop angles offset by 1 degree in order to stagger the available control points throughout each arc rotation. VMAT is an excellent treatment technique for regular (spherical) shaped targets when the isocenter can be placed inside the target volume, however, for highly irregular shaped targets like the lowest dose level target in this head and neck plan, a VMAT technique proved to be unable to match the plan quality achieved in the static gantry plan (#4 Bilateral Head & Neck (IMRT). With a treatment delivery time within 60 seconds of the comparable IMRT plan and more optimization time required for VMAT planning, the IMRT plan could be considered preferable to in this case. This plan might have been improved by utilizing unique collimator rotations in each arc. This VMAT plan scored better than 80%-90% of the plans submitted to the plan challenge.

There is very little difference between this VMAT plan versus for the 9F IMRT plan for the same case. Homogeneity and conformity are respected. OARs are well within constraint goals. Both plans do an excellent job at sparing the contralateral parotid, with mean doses around 25 Gy. This is clearly an acceptable plan.

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