Incidence, Radiologic and Dosimetric Parameters Associated with Radiation Induced Breast Lymphedema

Abstract

Radiation induced breast lymphedema (BL) is an underreported but common finding. This study aimed to report the incidence of clinical BL and investigate the radiologic and dosimetric parameters associated with higher risk of BL. This IRB approved study included women with breast cancer who underwent breast conservative surgery followed by adjuvant radiation therapy between 2019 and 2021 at our institution. We reviewed the eligible patients' charts for incidence of clinical BL resulting in symptoms and requiring physical therapy referral. Thickness of the skin at defined center and bottom points of the breast was measured for patient' baseline and follow up mammograms. Dosimetric parameters were imported from patients' radiation plans including mean, maximum doses, and volumes receiving 20, 30, 40, & 50 Gy (V20, V30, V40, & V50), of the whole breast (WB), breast_eval (BE), and breast skin (BS) (defined as the superficial 5 mm of the skin). A chi-square test was used to test the association between clinical BL and radiation treatment regimens and beam energies and the association of skin thicknesses between those who had clinical BL and those who did not. A Wilcoxon rank sum test was used to test the association of the dosimetric parameters with clinical BL. We identified 268 patients who were eligible for the study. After chart and radiologic review, 119 patients had complete records available and were included in this study. Twenty-nine patients (24.4%) of the patients presented with symptomatic BL. Most patients (68%) received hypofractionated (42.56 Gy with or without 10 Gy boost), while 25% received conventional and 7% received ultra-hypofractionated radiotherapy. There was no association between the fractionation and incidence of BL (p = 0.4). There was no association between breast size and BL (mean 1065 cc vs 1232 cc, p = 0.35). There was significant association between BL and BS V30 (142cc vs 162 cc, p = 0.02), and BS V40 (82 cc vs 102 cc, p = 0.02), and a trend towards significant association with BS V20 (172cc vs. 193cc, p = 0.08), BS V50 (8 cc vs. 16 cc, p = 0.06). There was no significant association between BL and BS mean dose (36.9 Gy vs 39 Gy p = 0.11), or BS max dose (53.9 Gy vs 54.1 Gy, p = 0.21). None of the dosimetric parameters of WB and BE had significant association with clinical BL. Utilizing ROC analysis, there was significant association between clinical BL and the change of baseline mammogram breast skin thickness and skin thickness at 6 months follow up mammograms (+13 mm center point p = 0.04, +9 mm bottom point p<0.5), and at 12 months mammograms (+15 mm center point p<0.5, +11 mm bottom point p<0.5). Almost 1 in 4 women experienced radiation induced BL in our cohort. BS V30 & V40 are significantly associated with higher risk of BL. There was significant association between increased skin thickening in 6- and 12-months follow up mammograms and BL. Further analysis will follow to assess the association between surgical and clinical characteristics and BL.