A dosimetric comparative analysis of TomoDirect and three-dimensional conformal radiotherapy in early breast cancer

Purpose: The purpose of this study is to compare dosimetric parameters of intensity-modulated mode of TomoDirect and three-dimensional conformal radiotherapy (3D-CRT) in patients with early breast cancer. Methods: TomoDirect and 3D-CRT planning were carried out for 26 patients with early breast cancer who had received breast-conserving surgery. A total of 50.4 Gy in 28 fractions were prescribed to the planning target volume. The organs at risk (OAR) such as lung and heart were contoured. Planning target volume (PTV) dose coverage, radiation conformity index (RCI), radical dose homogeneity index (rDHI), and irradiation dose of organs at risk were compared between TomoDirect and 3D-CRT planning. Results: The mean PTV dose (51.65± 0.37 Gy) and V_47.8 (100%) in TomoDirect were significantly higher than the mean PTV dose (50.88±0.65 Gy) and V47.8 (89.23%±0.06%) in 3D-CRT (all, p< 0.001). The RCI value in TomoDirect was significantly better than that in 3D-CRT (1.00 vs. 1.13, p< 0.001). However, the rDHI value in TomoDirect was not significantly better than that in 3D-CRT (0.72 vs. 0.67, p= 0.056). The mean lung dose and V10, V20, V30, and V40 values of ipsilateral lung in TomoDirect were significantly lower than those in 3D-CRT (all, p< 0.05). There is no significant difference in the V10, V20, V30, and V40 values of heart between TomoDirect and 3D-CRT. And the mean dose for heart in TomoDirect was marginally lower than that in 3D-CRT (1.05 Gy vs. 1.62 Gy, p= 0.085). The mean dose for left anterior descending coronary artery in left breast cancer was significantly lower in TomoDirect than in 3D-CRT (7.2 Gy vs. 12.1 Gy, p< 0.001). Conclusion: Compared to 3D-CRT, TomoDirect could result in favorable target coverage while reducing the irradiation dose of the ipsilateral lung for patients with early breast cancer.