1079 - Effect of Radiation Dose on Lymphedema Development following Immediate Lymphatic Reconstruction and Axillary Lymph Node Dissection

Materials/Methods: This prospective study included 23 patients with invasive breast cancer who underwent ALND/ILR followed by breast/chest wall RT and RNI from 10/2020-6/2023. A twirl clip placed at the anastomosis allowed for contouring of the ILR site during RT planning. The median breast/chest wall RT dose was 4500 cGy/18 fractions; the median RNI dose was 4000 cGy/16 fractions. All patients received RT to axillary Level 3 and the supraclavicular fossa; Levels 1-2 were targeted in 14 patients. LE was defined by a 10-point increase in LDEX in the dominant affected extremity, 7-point in the non-dominant extremity, or 10% increase in arm volume compared to pre-ILR baseline plus patient-reported symptoms occurring > 6 months after RT. Dosimetric parameters included mean and maximum doses, V35, V40, and Dmin<36.8 Gy at the ILR site, ILR + 5 mm, and ILR + 2 cm expansion volumes. Data are presented as median and interquartile range (IQR) or n (%). Categorical data was compared using Chi-square or Fisher’s exact tests. Continuous data was compared using Mann-Whitney-U test. Poisson regression with robust error variance was used to calculate the risk ratio and 95% confidence interval (CI). ROC curves and thresholds for the dosimetric parameters were calculated based on the Youden index and the area under the curve (AUC).