(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: investigate whether field-in-field (FIF), hybrid intensity-modulated radiation therapy (IMRT), IMRT, standard volumetric modulated arc therapy (STD-VMAT), non-coplanar VMAT (NC-VMAT) and multiple arc VMAT (MA-VMAT) can provide comparable coverage than the current standard of care (SOC) while reducing doses to organs at risk (OARs) for Whole Breast Radiation Therapy (WBRT) patients.
Methods: patients who received left side lumpectomy and treated with SOC were retrospectively studied. The SOC plans included two opposed tangential beams. FIF plans utilized the same beam angles and energies as the SOC plans. Hybrid IMRT plans included a pair of open tangent fields and a pair of dynamic IMRT tangent fields. IMRT plans included 7 beam equidistantly distributed in a sector of 180° that avoided direct exposure to the contralateral breast. Two tangential arcs at co-planar plane were used for STD-VMAT. Two tangential arcs that with 20° and 340°couch angle were used for NC-VMAT. Six coplanar partial arcs that each covered 50°were used for MA-VMAT, and jaw opening was minimized for each arc. All plans used a prescribed dose of 50Gy in 25 fractions. Collimator was rotated for each arc to align with the long axis of planning target volume (PTV) for STD-VMAT, MA-VMAT and NC-VMAT.
Results: techniques produced clinically acceptable WBRT plans. For the two forward planning techniques, FIF plans show better PTV coverage and provide superior OAR sparing than SOC. STD-VMAT provides good sparing of contralateral breast with larger low dose cloud for lung and heart. MA-VMAT plans show the most optimal OARs sparing and minimum risk of developing late side effects among all inverse planning techniques. NC-VMAT provides the most conformal PTV coverage and good sparing of lung and heart.
Conclusion: and NC-VMAT could be the optimal radiation technique for certain early stage breast cancer patients after breast conserving surgery.
Funding Support, Disclosures, and Conflict of Interest: The authors have no conflicts of interest. This work was partially supported by National Institutes of Health (grant no. K22CA204464).
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