Lymphovenous Bypass and Radiotherapy: A Dosimetric Approach to a Multi-Modality Mystery

Abstract

<h3>Purpose/Objective(s)</h3> Prophylactic lymphovenous bypass (LVB), in which a severed lymphatic channel is anastomosed to a low-pressure venule, is a microsurgical technique performed after axillary lymph node dissection (ALND) and intended to prevent breast cancer related lymphedema (BCRL). However, the location of these fragile anastomoses in related to radiotherapy (RT) fields remains unstudied. We aimed to identify the typical location of LVB anastomoses and evaluate the feasibility of shielding them from RT dose. <h3>Materials/Methods</h3> Patients underwent LVB with the placement of a circular clip for identification following ALND and received RT at a single institution. Delineation of the target volumes and lymph nodes levels was performed using NRG atlases. Additionally, the axillary and lateral thoracic vessels junction (ALTJ) -previously correlated with BCRL development- was delineated. The LVB clip was contoured and a 0.5cm expansion used to define a LVB volume. RT plans were created with 3D CRT and VMAT. The mean maximum dose to the LVB volume was compared between the two groups using T Test. <h3>Results</h3> Five patients underwent the procedures described above; all underwent mastectomy, ALND and LVB. The LVB anastomoses were identified in axillary Level 1, immediately subjacent (caudal) to the ALTJ. Owing to their location in the tangent fields, the mean maximum dose to LVB volume was 47.2 Gy using 3D planning and 18.7 Gy using VMAT (p<0.0001). <h3>Conclusion</h3> Prophylactic LVB following ALND is increasing in utilization. However, almost all patients undergoing ALND will also receive RT, and effect of RT on the viability of the LVB anastomoses is unknown. In this proof-of-concept study, the location of LVB was consistently identified in level 1 of the axilla. Owing to its location in the tangent fields, exclusion of the LVB volume was typically difficult with 3D CRT. VMAT allowed superior sparing of this structure. Further study is required to clarify the viability of the anastomoses after RT, their dose tolerance, and whether active dose avoidance is necessary.