A practical and easy method to locate the first three internal mammary lymph node-bearing areas.

Purpose: To assess the distance from a clinically recognized anatomic landmark to the different costocondral interspaces in female patients to facilitate the design of radiation fields intended to include specific internal mammary nodal areas.

Methods And Materials: The distance from the suprasternal notch (SSN) to the caudal portion of the first through fourth interspace was measured on a computer display of the chest skeleton of 65 female patients with left-sided breast cancer. The relationship between these distances and bone size (sternal length and standing height) was assessed via linear regression. In 21 of the 65 patients where myocardial perfusion imaging of the heart was available, the relationship between the location of the 3rd costochondral interspace and the left ventricle was assessed.

Results: In 90% of patients (59/65), the first, second, third, and fourth interspace were within 5, 8.5, 11, and 14 cm of the SSN, respectively. The SSN-interspace distances did not correlate well with sternal length (r = 0.28) or standing height (r = 0.31). In 20 of 21 patients (95%), the third interspace "shadowed" the cephalad aspect of the left heart ventricle. Median "shadowing" was 3 cm (range 0.5-6 cm).

Conclusion: The caudal portion of the third costochondral interspace is < or = 11 cm caudal to the SSN in 90% of patients. These measurements can be used to clinically design radiation therapy fields intended to treat the upper three interspaces. The distance from the SSN to the 1st through 4th interspaces is not related to sternal length or to standing height. In patients with left-sided breast cancer, radiation treatment fields designed to include the internal mammary lymph nodes in the upper three interspaces may incidentally include a portion of the heart.