Internal mammary lymph node (IMN) coverage by standard radiation tangent fields in patients showing IMN drainage on lymphoscintigraphy: therapeutic implications

The purpose of this report is to evaluate the variability in coverage of the internal mammary nodal chain (IMN) by standard radiation tangential fields in those patients with medial drainage on lymphoscintigraphy. Twenty-two patients who showed lymphoscintigraphic IMN drainage underwent radiation simulation planned with computed tomography (CT). Standard tangent fields were placed and CT scans were reviewed to assess IMN inclusion and correlation with presternal fat thickness. Of the 22 patients who showed IMN drainage on lymphoscintigraphy, 10 (45%) had lateral primary lesions, 9 (41%) had medial lesions and 3 (14%) had subareolar lesions. Of these 22 women, 4 (19%) had the IMN completely within the standard tangent fields. Twelve women (55%) had only partial coverage of the IMN and the remaining 6 women (27%) had the IMN region completely outside. Presternal fat thickness greater than 10 mm was less likely associated with complete IMN coverage than fat thickness 10 mm or less, P = 0.001. Lymphoscintigram drainage to the IMN in breast cancer patients may suggest an increased risk of IMN involvement. Our data show that a majority (73%) of these patients had complete or partial incidental inclusion of the IMNs with standard tangents, which may in part explain the historically low IMN failure rate.