A novel method for CT-scan-based localization of the internal mammary chain by internal mammary catheterization: an aid in breast cancer radiation therapy planning.

The purpose of the study was to evaluate the localization of the internal mammary lymph node chain (IMC) using CT scan data acquired after intraoperative placement of a catheter into the internal mammary vessel (IMV). CT data sets comprising 58 suitable patients with breast carcinoma undergoing placement of a catheter into the IMV during breast conservative surgery were evaluated for the study. CT was performed with a radio-opaque dummy wire placed into the IMC catheter. The following measurements were recorded in the second, third and the fourth intercostal spaces: anteroposterior distance from skin to the IMC catheter; transverse distance from mid-sternum to the IMC catheter; and anteroposterior distance from the skin to the heart. Finally, the IMC angle was determined. At the second intercostal space, the mean anteroposterior distance (range) was 29.0 mm (14.6-48.6 mm) and mean transverse distance was 26.1 mm (18.2-36.3 mm). The corresponding mean values for the third space were 32.5 mm (20.0-45.6 mm) and 24.1 mm (17.8-39.7 mm) and for the fourth intercostal space were 31.6 mm (21.1-45.6 mm) and 24.3 mm (15.6-34.3 mm), respectively. The mean skin to heart distance was 36.2 mm on the left side and 47.8 mm on the right side (p < 0.001). The mean IMC angle was 40.3 degrees (95% confidence interval: 25-55.6). There appears to be a wide variation in the depth and location of the IMC, as recorded by CT measurements of the catheter in the IMV, demonstrating the need for individual planning. The IMC nodal area is likely to be out of the tangential portals employed in conventional practice.