Radiation Therapy Field Design and Lymphedema Risk After Regional Nodal Irradiation for Breast Cancer

The occurrence of upper extremity lymphedema after regional nodal irradiation (RNI) for breast cancer treatment varies significantly based on patient and treatment factors. The relationship between the radiation therapy (RT) field design and lymphedema risk is not well-characterized. The present study sought to correlate the variations in RT field design with lymphedema outcomes.

Women with stage II-IV breast cancer receiving RNI after breast surgery that included sentinel lymph node biopsy or axillary dissection were identified. Their arm circumference was measured before RT and at each follow-up visit to assess for lymphedema. Nodal RT fields were defined using a trifurcated system. Group 1 excluded the upper level I and II axilla, defined by the lateral border of the nodal field encompassing less than one-third of the humeral head. Group 2 included the upper level I and II axilla, defined by the lateral border of the nodal field encompassing more than one-third of the humoral head treated with an anterior oblique beam. Group 3 included the upper level I and II axilla the same as for group 2 but with parallel-opposed beams delivering a significant dose to the musculature posterior to the axilla.

From 1999 to 2013, 526 women received RNI. The median post-RT follow-up was 5.5 years. For the 492 women meeting the inclusion criteria, the cumulative incidence of lymphedema was 23.5% at 2 years and 31.8% at 5 years. On univariate analysis, the patients in group 1 had a lower 5-year lymphedema rate (7.7%) than those in group 2 (37.1%) and group 3 (36.7%; P < .0001). On multivariate analysis, inclusion of the upper level I and II axilla (groups 2 and 3) remained significantly associated with increased lymphedema risk.

Variations in the RT field design significantly affect the development of lymphedema after RNI. In particular, the upper level I and II axilla appear to be important regions for lymphedema risk after axillary dissection.