2946 - Evaluation of Radiation Dose to the Lympho-Venous Anastomosis (LYMPHA Procedure) in Breast Cancer Patients Undergoing Axillary Lymph Node Dissection: Implications for Lymphedema Risk and Radiation Avoidance

Purpose/Objective(s): Axillary lymph node dissection (ALND) remains standard for advanced nodal involvement in breast cancer but carries a high risk of lymphedema. The Lymphatic Microsurgical Preventative Healing Approach (LYMPHA) aims to reduce this risk by re-anastomosing lymphatics to the venous system. While LYMPHA has shown promise in lowering lymphedema rates, radiation-induced sclerosis of the lympho-venous anastomosis (LVA) may compromise its effectiveness. This study evaluates radiation dose to the LVA using modern techniques and explores the feasibility of dose reduction.

Materials/Methods: We retrospectively analyzed all patients who underwent ALND, LYMPHA, and post-operative radiation from 2022–2024. The LVA was not contoured or spared in initial treatment plans but was retrospectively identified and delineated. A 5 mm expansion defined the LYMPHA Sparing Zone (LSZ). Radiation doses to the LVA and LSZ were analyzed. The most recent three patients underwent IMRT replanning (40 Gy/15 fractions) with incremental dose constraints (LVA max/LSZ mean: 35Gy/25Gy, 25Gy/15Gy, 15Gy/7Gy).

Results: Seventeen patients (mean age 52 years, range 35–72) were analyzed. All had node-positive disease (mean: 4 positive, 12 removed nodes); 71% underwent mastectomy. Radiation fields included the chest wall/breast, supraclavicular, internal mammary, and axillary level 2–3 regions. Level 1 axilla was included in seven patients. IMRT was used in 14 patients; 3D-CRT in three. The LVA was consistently located in level 1 axilla and received high radiation doses, even in patients where the lower axilla was not targeted. Mean doses to the LVA and LSZ were 47.0 Gy and 46.9 Gy, respectively (45.1 Gy and 44.3 Gy for 3D-CRT; 47.5 Gy and 47.4 Gy for IMRT). Replanning with IMRT successfully met the most stringent dose constraints while maintaining target coverage (PTV V95% = 97.7%) and organ-at-risk limits. LVA max dose decreased from 39.0 Gy to 8.6 Gy (p=0.01), and LSZ mean dose from 36.0 Gy to 6.5 Gy (p=0.03).

Conclusion: The LVA consistently resides in the level 1 axilla and receives high radiation doses unless explicitly spared. IMRT-based planning can significantly reduce LVA and LSZ dose without compromising target coverage or organ-at-risk constraints. Integrating LVA and LSZ avoidance into radiation planning may reduce lymphedema risk in LYMPHA-treated patients. A prospective trial to validate this approach is warranted.