The relationship between radiation fields and regional lymph nodes in carcinoma of the breast.

PURPOSE: To examine the relationships between tangential, anterior, and posterior radiation fields and regional lymph nodes, including Levels I-III axillary and supraclavicular lymph nodes.

METHODS AND MATERIALS: Fifty-five patients underwent computed tomography (CT) scanning in the supine treatment position, and radiation fields were developed to treat appropriate breast and lymphatic regions. After conventional fields had been selected, Levels I-III axillary and supraclavicular lymph nodes were identified on multiple CT slices performed at 3-5-mm intervals and their depths to the anterior skin surface and the anterior-posterior separations at multiple levels were measured.

RESULTS: The mean depths of the Levels I-III axillary nodes were 4.6, 5.1, and 3.6 cm, respectively. The mean depth of the supraclavicular nodes was 3.9 cm. The mean anterior-posterior separations at these levels were 15.4, 15.2, 15.2, and 14.6 cm. The mean depths of the nodes, therefore, were well anterior to the midline. In the two-field treatment group, Level I axillary nodes appeared in the tangential portals in 9/9 patients, either alone or with other lymph node groups. In the three-field group, Level I axillary nodes were in 16/16 tangential fields either alone or with level II nodes (8 patients). In 8 patients, Level III and the supraclavicular nodes were included in the anterior field and in the other 8, Levels II, III, and the supraclavicular nodes were in the anterior field. There was considerable variation in the nodal groups present in the posterior axillary boost field. No nodal groups were observed in 6 patients.

CONCLUSION: There is considerable variation both in the depth of supraclavicular and axillary lymph nodes and the fields in which these nodal groups appear. To be certain that nodal groups which one plans to treat are actually treated, as well as to minimize nodal treatment when such treatment is not planned, it is recommended that before the placement of radiation fields, the nodal groups be outlined on a CT scan much as one would outline a tumor volume in other disease sites.