D119. The No Flow Zone: Effects of Radiation on Lymphatic Anatomy of the Trunk

PURPOSE: Radiation can cause extensive damage to the lymphatic anatomy of the trunk. Using indocyanine green (ICG), lymphatic damage can be visualized as areas of dermal backflow or absent lymphatic flow following severe destruction. We aim to analyze the effects of radiation on lymphatic structures of the chest, exploring the incidence of no flow zones and identify changes in lymphatic drainage pathways. METHODS: We reviewed breast cancer patients receiving ICG lymphography of their chest from December 2014 to January 2024. Patients were separated into radiation and non-radiation groups. Lymphatic patterns were compared using chi-square test of independence. RESULTS: Our cohort included 173 hemi-trunks (95 patients). 73 sides had undergone prior radiation and 100 had not. Radiation was significantly associated with absent lymphatic flow (p=0.031). Most no flow zones were seen in the inferior mastectomy flaps. On multivariate analysis, controlling for chemotherapy, axillary dissection, and mastectomy, radiation was associated with 2.42 times increase in odds of no flow zones. When assessing lymph drainage, radiated hemi-trunks showed significantly increased incidence of aberrant contralateral flow (p=0.030). There was no significant change in drainage to the ipsilateral nodes. CONCLUSION: We show that prior radiation is significantly associated with zones of no lymphatic flow to the inferior mastectomy flap and increases drainage to contralateral lymph node basins. This represents severe damage to lymphatic vessels resulting in truncal lymphatic stasis.