Effects of Variable Placement of Superior Tangential/Supraclavicular Match Line on Dosimetric Coverage of Level III Axilla/Axillary Apex in Patients Treated With Breast and Supraclavicular Radiotherapy

Purpose: To determine the differences in dosimetric coverage of the Level III axillary node target as a function of the superior tangential/supraclavicular match line in breast cancer patients undergoing with tangential breast and supraclavicular fossa radiotherapy. Methods and Materials: The data from 20 consecutive breast cancer patients who were treated with breast conservation surgery and Level I and II axillary dissection followed by radiotherapy to the undissected Level III axilla/supraclavicular fossa were retrospectively analyzed. The nodal volumes were delineated from the computed tomography simulation data set. Three composite treatment plans were generated for each patient according to the placement of the match line. Results: Coverage of the contoured Level III/axillary apex varied significantly with respect to the ipsilateral clavicular head, depending on the placement of the superior tangential/supraclavicular match line. The mean volume of the Level III/axillary apex covered by the 90% isodose line (45 Gy) was 100% for caudal placement of the match line, significantly greater than the 92% for intermediate placement (bisecting the clavicular head; p = 0.001) and the 68% for cranial placement with respect to the clavicular head (p < 0.001). Conclusion: Placement of the superior tangential/supraclavicular match line caudal to the clavicular head results in statistically improved dosimetric coverage of the Level III axilla/axillary apex in breast cancer patients undergoing tangential/supraclavicular radiotherapy.