Radiation doses to axillary lymph nodes in patients with early breast cancer receiving field-in-field forward-planned intensity-modulated radiotherapy for whole breast irradiation after breast-conserving surgery

Abstract

Objective To evaluate the radiation doses to the axillary lymph nodes in patients with early breast cancer receiving field-in-field forward-planned intensity-modulated radiotherapy (FIF-FP-IMRT) for whole breast irradiation after breast-conserving surgery,and to analyze the factors influencing the doses to the axillary lymph nodes.Methods Thirty-seven patients with breast cancer treated by breast-conserving surgery were evaluated.All patients received FIF-FP-IMRT for whole breast irradiation (not involving regional lymph nodes).Delineation of axillary levels Ⅰ-Ⅲ,interpectoral lymph nodes,and axillary vein was made on CT images,and a dosimetric analysis was made using 3D treatment planning software.The influential factors for the dose distribution in axillary lymph nodes were analyzed by paired t-test.Results The mean percent volumes receiving at least 95％ of the prescribed dose (50 Gy/25 fractions for whole breast PTV)(V95) for axillary levels Ⅰ,Ⅱ,and Ⅲ and interpectoral lymph nodes were 34.7％,6.1％,0.4％,and 39.6％,respectively,and the mean doses to axillary levels Ⅰ,Ⅱ,Ⅲ and interpectoral lymph nodes were 30.8 Gy,15.7 Gy,5.0 Gy,and 28.8 Gy,respectively.The mean V95 values for the lymph node areas below and above the axillary vein were 45.6％ and 0.7％,respectively,and the mean doses were 38.2 Gy and 6.7 Gy,respectively.The distance between the upper border of the radiation field and the humeral head was the only significant factor influencing the mean dose to the lymph node area below the axillary vein (P =0.037).Conclusions In FIF-FP-IMRT for whole breast irradiation,the actual dose delivered to the axillary lymph nodes below the axillary vein cannot be neglected and should be taken into consideration when analyzing the local control of the axillary lymph nodes after breast-conserving surgery. Key words: Breast neoplasms/three-dimensional conformal radiotherapy; Axillary lymph nodes; Dosimetry