Modified partially wide tangents technique in post-mastectomy radiotherapy for patients with left-sided breast cancer.

Abstract

The role of internal mammary nodes (IMN) irradiation for breast cancer patients after mastectomy remains controversial. This study aimed to compare different techniques for radiation of the chest wall (CW) and IMN post-mastectomy for left-breast cancer patients in terms of dose homogeneity within planning target volume (PTV) and dose to critical structures. Thirty patients underwent CT simulation, while CW, IMN, left lung, heart and contralateral breast were contoured. Three three-dimensional conformal radiotherapy (3D-CRT) techniques, namely, standard tangents, partially wide tangents (PWT), and modified PWT techniques plus intensity modulated radiotherapy (IMRT) technique have been used to radiate CW and IMN. In addition to the target coverage and dose homogeneity, we also evaluated the dose to the critical structures including heart, left lung and contralateral breast. All three 3D-CRT techniques provided satisfactory coverage regarding total PTV. The PWT and the modified PWT gave better coverage of IMN PTV with V(47.5) of (96.83 ± 4.56)% and (95.19 ± 3.90)% compared to standard tangents ((88.16 ± 7.77)%), P < 0.05. The standard tangents also contributed the biggest IMN V(D105%), V(D110%), V(D115%) and V(D120%). The lowest mean dose of the heart was achieved by the modified PWT ((8.47 ± 2.30) Gy), compared with PWT ((11.97 ± 3.54) Gy) and standard tangents ((11.18 ± 2.53) Gy). The mean dose of lung and contralateral breast with the modified PWT was significantly lower than those with PWT. Comparing IMRT with the modified PWT, both techniques provided satisfactory coverage. The conformity indexes (CI) with IMRT (CI1: 0.71 ± 0.02; CI2: 0.64 ± 0.02) were better than those with the modified PWT (CI1: 0.50 ± 0.02; CI2: 0.45 ± 0.02). The mean dose, V(5), V(10) and V(5-10) of heart and left lung with the modified PWT were significantly lower than those with the IMRT. The mean dose and V(D2%) of contralateral breast with the modified PWT were not significantly different from the IMRT (P = 0.868 and P = 0.212). No single technique provides both the best CW and IMN coverage with minimum lung and heart dose. The modified PWT technique can be used as a clinical tool for the treatment of the left-sided post-mastectomy breast cancer patients to provide homogeneous target coverage while maintaining low doses to normal tissue.