VMAT SX1

Name (ID): Z002442-ABD, AAPM (AAPM Z002442-ABD)
Plan or PlanSum ID: 4arcAID

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 (330, 0, 30, 90).  Zero degree collimator arc rotations make sense on this machine due to the reduced interleaf leakage of the two-stage, stacked and staggered MLC design.  At first, VMAT would seem like the ideal technique to meet the challenging metric of no 50% of Rx dose (more than 3cm from the target anteriorly and 3cm from the skin surface elsewhere -- enforced by a “peripheral ring” metric in the scoring criteria).  However, all efforts to improve upon the static field IMRT plan (utilizing VMAT technique) failed and this VMAT plan scored lower than the IMRT attempt, took slightly longer to deliver and took longer to optimize.  From the CMD perspective the IMRT plan is the clear choice for this case.

Both pancreas RT plans were acceptable. The IMRT plan is slightly better. In both cases, the OARs, specifically the bowel. The homogeneity requirements are pretty tight and a priority in this case. These are achieved with good sparing of bowel and kidneys.

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