Room: Karl Dean Ballroom A1
Purpose: Hypofractionationated WBRT with a SIB offers patients the opportunity to complete treatment in three weeks. A hybrid of 3D and VMAT planning could enhance the delivery of homogenous dose to the breast while delivering a conformal boost to the lumpectomy bed.
Methods: A retrospective study of eleven patients previously treated using RTOG 1005 guidelines was performed to compare 3D, VMAT, and Hybrid-VMAT planning; Hybrid-VMAT plans were optimized using base-dose optimization from calculated open (HO), FiF (HF), and IMRT (HI) tangents. Prescribed doses were 4005cGy and 4800cGy to the whole breast lumpectomy, respectively, in 15 fractions.
Results: All three methods of hybrid planning yielded similar results to 3D in terms of D95 for whole breast [0.3% difference] while reducing D30 by 4.4%. When compared to the 3D plans, Hybrid-VMAT improved whole breast and lumpectomy PTVeval conformity from 1.62 and 2.39 to 1.28 and 1.5, respectively. Hybrid plans compare favorably with VMAT in terms of PTV coverage and conformity, improving upon hot spot reduction and OAR sparing. Hybrid plans met OAR dose constraints, including heart, ipsilateral lung, and contralateral breast, three structures VMAT planning struggled to spare. For left-sided breast cases, Hybrid plans averaged a mean heart dose of 217cGy, compared to 182cGy for 3D plans. Gamma analysis of delivered Hybrid variants yielded pass rates greater than 99%. HF arcs were found to be modulated less than HO and HI [7% on average]. HF plans exhibited the smallest statistical variation in PTV coverage amongst all described techniques, suggesting greater reproducibility and consistency.
Conclusion: Hybrid-VMAT enables the user to deliver a more conformal and reproducible plan than methods solely using 3D or VMAT. The combination of the two treatment modalities enables consistent coverage of treatment volumes while minimizing dose to nearby OARs below accepted standards for both left and right sided cases.