Is the Berg axillary lymph node categorization useful in the 3D Era

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 ...