SP08. Quantifying Radiation at the Site of Immediate Lymphatic Reconstruction

PURPOSE: Axillary lymph node dissection (ALND) and regional nodal irradiation (RNI) both contribute to lymphedema risk in breast cancer patients. Immediate lymphatic reconstruction (ILR) reduces the incidence of lymphedema in patients undergoing ALND in prior studies; however, patients treated with RNI in addition to ALND and ILR have higher rates of lymphedema than those that do not get RNI. The purpose of this study was to understand the radiation dose distribution in relation to the location of the ILR anastomosis. METHODS: A retrospective review was conducted to identify breast cancer patients who underwent ILR and breast or chest wall radiation plus RNI from October 2020 through June 2022. A twirl clip deployed at the site of the ILR anastomosis was identified during radiation treatment planning. All cases were planned with a 3D technique with opposed tangents and an obliqued supraclavicular (SCV) field. Demographics, baseline patient characteristics, and treatment data were collected. RESULTS: Eleven patients who underwent ILR with clip deployment and RNI were identified. The ILR clip was in the axillary Level 1 nodal basin in 10 patients and in Level 2 in 1 patient. RNI targeted axillary Levels 1-3 and the SCV nodal region in 3 patients and Level 3 and SCV nodes in 8 patients. In the 8 patients where Levels 1 and 2 of the axilla were not specifically targeted, the ILR clip still fell within the radiation fields in 4 patients; the ILR clip was located in the breast/chest wall tangential field in 3 of these patients and spanned the tangent and the SCV field in 1 patient. The clip was outside of all the radiation fields in the remaining 4 patients where only Level 3 and the SCV regions were targeted. Overall, the mean dose to the ILR clip was 2670 cGy (range, 139-4961 cGy). In patients where the ILR clip was within any radiation field, the mean dose was 4070 cGy (range, 2192-4961 cGy); in those patients with the ILR clip outside all radiation fields, the mean dose was 221 cGy (range 139-280 cGy). CONCLUSION: The dose to the ILR anastomotic site was highly variable. Even when the planned radiation fields did not directly target the anastomotic site, the site often received radiation from the tangential or SCV fields. Studies examining the potential for limiting radiation dose at the anastomotic site are currently being conducted.