(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Hypofractionationated WBRT with a SIB presents an opportunity to reduce treatment time to three weeks. Jaw Tracking-enabled VMAT could deliver a highly conformal and homogeneous dose to the breast while simultaneously boosting the lumpectomy bed.
Methods: A retrospective study of eleven patients previously treated per RTOG 1005 guidelines was performed, comparing 3D and VMAT planning techniques. Jaw tracking VMAT plans utilized pairs of 60o tangential arcs to cover the breast; an additional 90o arc, rotating between tangential arcs, was collimated to the lumpectomy. All VMAT plans were optimized with virtual bolus, yielding arcs with skin flash to account for setup uncertainty over the course of treatment. 4005cGy and 4800cGy were prescribed to the whole breast and lumpectomy bed, respectively, over 15 fractions.
Results: VMAT planning achieved similar results in terms of breast PTVeval D95 [0.7% difference] while reducing D30 by 2.8%. Compared to 3D, VMAT improved whole breast and lumpectomy PTVeval conformity from 1.62 and 2.39 to 1.22 and 1.69, respectively. VMAT improved ipsilateral lung V20Gy by 3% while comparing favorably in terms of V5Gy [27.7% versus 25.4%]. For left-sided breast cases, VMAT plans averaged a mean heart dose of 158cGy, compared to 182cGy for 3D plans. VMAT plans exhibited smaller statistical variation in terms of PTV coverage and OAR dose-volume criteria, suggesting greater reproducibility and consistency. Gamma analysis of delivered VMAT plans yielded pass rates greater than 99.2%.
Conclusion: Jaw tracking VMAT can deliver a more conformal WBRT+SIB plan while sparing the ipsilateral lung and heart at levels achieved by 3D planning. By optimizing for skin flash and enabling jaw tracking, planners can consistently generate reproducible plans that not only achieve desired target volume coverage, but also minimize dose to nearby OARs below accepted standards for both left and right sided cases.
Keywords
Inverse Planning, Breast, Treatment Techniques
Taxonomy
TH- External Beam- Photons: treatment planning/virtual clinical studies
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