To evaluate the dosimetric parameters of level II lymph nodes in chest wall three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) of mastectomy patients using dual-isocentric (DIT) and mono-isocentric techniques (MIT).

Computed tomography (CT) images of 20 mastectomy patients undergoing chest wall external radiotherapy were used as the input data for the abovementioned techniques. Selected dosimetric parameters were calculated for the axillary level I–III lymph nodes, chest wall, heart and lung. Paired t-test statistical analysis was used for comparing the results of MIT and DIT in both 3D-CRT and IMRT methods.

There were significant differences in Dmin (minimum dose), Dmax (maximum dose) and maximum–minimum dose between MIT and DIT techniques (13, −8·6, −52·2% differences for Dmin, Dmax and maximum–minimum, respectively) in IMRT. There were also significant differences for Dmean (mean dose), Dmax and maximum–minimum dose (7·8, −11·4, −44·6% differences in Dmean, Dmax and maximum–minimum, respectively) in 3D-CRT (p < 0·05). In addition, there were not any differences in the dosimetric parameters for heart, lung and level I and III lymph nodes.

In both 3D-CRT and IMRT methods, level II lymph node dose distribution in MIT was closer to the prescribed dose compared with DIT due to the position of these nodes in the field junction area. To achieve a better dose homogeneity, it could be recommended to use MIT instead of DIT in 3D-CRT and IMRT for mastectomy patients.