VMAT SX1

Name (ID): AAPM2014 SBRT LUNG, (ROQS-24)
Plan or PlanSum ID: 4arcIDt4a

The VMAT technique was chosen and 4 almost complete arcs were used.  Each arc used 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, 90).  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.  This VMAT SBRT lung plan was limited to a coplanar arc arrangement, which therefore limited comformality of the 50% Rx dose.  This plan challenge was designed with the assumption of a noncoplaner arrangement.  However, with a large portion the optimization cost focused on this metric, the 50% RX dose volume was still able to be controlled to a relativly reasonable volume and the plan scored above the mean score of plans submitted to this challenge.

Simple early stage lung Ca treated with SBRT. An aggressive dose of 60 Gy in 3 fractions is used. All OARs are within reasonable limits. The conformality index is somewhat borderline, but the plan is clinically acceptable.

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