Program Information
Improving Normal Tissue Sparing Using MRI-Identified Regional Nodal Volumes in Breast Cancer Radiotherapy
K Kainz*, E Paulson , A Currey , C Bergom , X Li , Medical College of Wisconsin, Milwaukee, WI
Presentations
TU-FG-FS2-8 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: Four Seasons 2
Purpose: Using an innovative MRI technique to identify individual axillary and supraclavicular nodes, we investigate the reduction of dose to regional organs-at-risk (OAR) when using MRI-identified nodes in place of conventional CT-based nodal PTVs.
Methods: The axillary and supraclavicular nodes were delineated based on neurography MR images, generated from T2 STIR including elements of diffusion weighting and water excitation, and were populated to the planning CT. The conventional CT-based axillary and supraclavicular PTVs were comprised of regions encompassing the likely locations of the nodes based on clinical judgment. Both the right and left side breast and nodal groups were contoured; all MRI-based nodal contours were expanded 5 mm isotropically to create nodal PTVs. VMAT plans were created consisting of 8 overlapping 240-degree arcs, to cover ≥95% of the ipsilateral breast, IMC, axillary, and supraclavicular PTVs with ≥95% of the 50-Gy prescribed dose.
Results: For the cases studied, the MRI-based nodal PTV was reduced by up to 70% of the CT-based volume for the axillary nodes and by 93% for the supraclavicular nodes. The corresponding reduction in total plan MU was 14%. When planning upon MR-based nodal PTVs in place of CT-based volumes, decreases in the maximum dose to the esophagus and cord were approximately 45% to 65%, which was expected given these structures’ proximity to the supraclavicular region. Decreases in the mean doses to the ipsilateral lung and brachial plexus of approximately 4% to 8% were observed.
Conclusion: T2-based neurography MRI allows for visualizing regional lymph nodes and reducing nodal PTVs. The use of MRI-defined nodal PTVs results in reductions in beam-on time and proximal-OAR doses, including modest sparing of the brachial plexus and ipsilateral lung.
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