10643 Background: The Berg muscle-based categorization of axillary lymph node location has been used extensively by pathologists and surgeons to describe the extent of axillary node dissection in breast cancer patients, but its reproducibility with different arm positions and its utility in 3-D radiation treatment planning have not been tested. Methods: CT scans were obtained in 16 patients in 2 positions: historic position (HP), arms 90 degrees to the body axis; standard position (SP), arms above head. The volume, contents, and location of each Berg lymph node level (LNL) and the location of lymph nodes, surgical clips, pectoral muscles, and vascular structures relative to reference points were compared between the two scans. Results: Relative to T3, the LNL positions in SP were shifted from HP as follows: Level I, 23.1 mm anteriorly, p < 0.01; Level II, 7.5 mm medially, p = 0.04; Level III, 18.8 mm medially, p = 0.05. The pectoralis major and minor muscles were displaced medially (23.9 mm, p < 0.01 and 7.5 mm, p = 0.09) and anteriorly (18.2 mm, p < 0.01 and 11.2 mm, p < 0.01). At Level I, the axillary vessels (18.0 mm, p < 0.01), subscapular artery (25.4mm, p < 0.01) and lateral thoracic artery (8.4 mm, p < 0.01) were displaced anteriorly. With arm position change, lymph node position moved with vessel position rather than muscle position. Discrepancies were also observed in the number and location of lymph nodes (60%) and clips (66%) in given LNL’s between arm positions. Conclusions: Surgeons, radiologists, and radiation oncologists alike should be aware that lymph node position relative to muscle boundaries will vary significantly with arm position changes, making objective comparisons of information collected in different arm positions unreliable. This has significant implications for radiation treatment planning. No significant financial relationships to disclose.
Computed tomography imaging parameters for inhomogeneity correction in radiation treatment planning