Speaker
Description
Synchronous bilateral breast cancer (SBBC) requiring regional nodal irradiation (RNI) presents profound dosimetric challenges, particularly in sparing the heart and lungs. This study comprehensively evaluates the dosimetric impact of varying nodal irradiation targets using volumetric modulated arc therapy (VMAT) with two full arcs in hypofractionated regimens. Thirty SBBC patients were retrospectively analyzed and categorized into three groups (n=10 each) based on the RNI extent: bilateral breasts with bilateral nodes (Group 1), right nodes (Group 2), and left nodes (Group 3). Target volumes included the medial supraclavicular fossa (SCF), axillary lymph nodes (AXLN), and internal mammary nodes (IMN). A hypofractionated prescription of 40.05 Gy in 15 fractions was delivered via dual-arc VMAT. Plan quality (conformity and homogeneity indices) and critical organ doses (whole lungs, heart, trachea, esophagus, thyroid, liver, stomach, and spinal cord) were evaluated. In terms of whole lungs, the average V5Gy , V10Gy , and V20Gy in the group 1 for ten patients was 69.5 ± 6.5%, 48.4 ± 5.8%, and 20.5 ± 3.5%. In group 2 and group 3, the average V5Gy , V10Gy , and V20Gy was 55.4 ± 5.5%, 40.2 ± 5.1%, and 12.5 ± 1.8% as well as 60.8 ± 6.2%, 44.5 ± 4.5%, and 15.8 ± 2.2%. As for heart, the average heart dose was 8.5 ± 1.5 Gy, 4.5 ± 0.8 Gy and 6.8 ± 1.8 Gy in group 1,2 and 3, respectively. This is the first research to collect complete dosimetric data for the bilateral breast cancer with lymph node irradiations. The pronounced low dose bath (e.g., lung V5Gy) and elevated heart doses, is particularly when bilateral or left-sided nodes are targeted. This underscores the necessity of weighing dosimetric constraints when delineating irradiation ranges in clinical decision-making.