The Study: This study took a detailed look at which parts of the axilla are associated with lymphedema risk in a cohort of over 250 women who received regional nodal radiation for breast cancer. The axilla was contoured into 8 separate anatomically-defined regions. The biggest difference in these regions and your standard axillary volumes was the inclusion of much more supero-lateral portions (in front of and lateral to the humeral head). They then associated lymphedema risk with a variety of dose levels to each region, and dose to the region of the axillary-lateral thoracic vessel junction (ALTJ) seemed most important. Anatomically, this region typically falls just lateral to level II where the lateral thoracic vessels branch from the axillary vessels. On 2D-imaging, it typically falls just under and/or lateral to the humeral head. As you can imagine, the decision to extend the lateral field border beyond the humeral head plays a big role in ALTJ dose. The best dosimetric cut-off for lymphedema risk was a minimum dose of 38.6 Gy to the ALTJ: With a minimum dose above and below this threshold, the risk of lymphedema was 37% versus 6%.
TBL: Minimizing dose specifically to the region of the axillary-lateral thoracic junction is associated with a lower risk of lymphedema in women receiving radiation for breast cancer. | Gross, Int J Radiat Oncol Biol Phys 2019