Dosimetric comparison of incidental axillary irradiation between three-dimensional conformal and volumetric modulated arc techniques for breast cancer.

Radiotherapy techniques for breast cancer have evolved with efforts to reduce treatment-related side effects. In the present study, we conducted dosimetric analysis of incidental axillary irradiation between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3D-CRT). A total of 20 patients with early stage left breast cancer who underwent breast-conserving surgery followed by postoperative radiotherapy were analyzed. For VMAT plans, dose-volume constraints were not imposed on the axilla, as with 3D-CRT. We compared the dosimetric parameters of the planning target volumes, organs at risk and axillary level I-III of the two plans. VMAT showed better target coverage and a normal organ-sparing effect compared with 3D-CRT. The incidental axillary irradiation of VMAT was lower; the mean dose and the V40 were significantly reduced at all axillary levels, with the exception of no difference in the maximum dose to axillary level I. In conclusion, VMAT decreased incidental axillary irradiation, even in the absence of a dose-volume constraint on the axilla, and can, therefore, decrease the risk of radiotherapy-related lymphedema. However, caution is also required because it is unclear whether this incidental axillary irradiation is beneficial for reducing recurrence on the axilla.