Wide Tangent Photon Field Versus Electron Field in the Treatment of Internal Mammary Lymph Nodes in Patients With Left Breast Cancer: A Decision-Making Flowchart

Abstract

Purpose: This study of internal mammary lymph node chain (IMC) irradiation in patients with left breast cancer aimed at comparing the merits of using, on one hand, a dedicated direct IMC electron field versus a wide tangent photon field covering both breast and IMC on the other. The objective was to produce guidelines allowing clinicians to readily determine the preferred method for each patient. Methods and Materials: For 19 patients with cancer of the left breast/chest wall, we produced 2 treatment plans each using a different technique: the electron technique using 2 standard opposed photon tangents covering only the breast or chest wall along with a matching adjacent electron field targeting the IMC only or the wide tangent technique using 2 opposed wide tangents covering simultaneously IMC and breast or chest wall. All plans were then optimized for acceptable target coverage. Results: For patients where the left anterior descending coronary artery (LAD) was located outside of the wide tangent fields (13 patients), the wide tangent technique resulted in lower dose to the LAD, left lung, and heart. When the LAD was inside the wide tangents (6 patients), dose was lower with the electron technique for LAD and heart. In all cases, regardless of LAD location, the wide tangent technique returned strictly superior dose homogeneity but much higher right (contralateral) breast dose. Conclusions: A flowchart was produced based on LAD location that allows the clinician to readily determine the preferred technique for each patient without having to perform and compare 2 treatment plans, thus saving valuable planning time.