A dosimetric comparison of 3D-CRT, IMRT, and static tomotherapy with an SIB for large and small breast volumes.

Radiation therapy to the breast is a complex task, with many different techniques that can be employed to ensure adequate dose target coverage while minimizing doses to the organs at risk. This study compares the dose planning outcomes of 3 radiation treatment modalities, 3 dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and static tomotherapy, for left-sided whole-breast radiation treatment with a simultaneous integrated boost (SIB). Overall, 20 patients with left-sided breast cancer were separated into 2 cohorts, small and large, based on breast volume. Dose plans were produced for each patient using 3D-CRT, IMRT, and static tomotherapy. All patients were prescribed a dose of 45Gy in 20 fractions to the breast with an SIB of 56Gy in 20 fractions to the tumor bed and normalized so that D98% > 95% of the prescription dose. Dosimetric comparisons were made between the 3 modalities and the interaction of patient size. All 3 modalities offered adequate planning target volume (PTV) coverage with D98% > 95% and D2% < 107%. Static tomotherapy offered significantly improved (p = 0.006) dose homogeneity to the PTVboost eval (0.079 ± 0.011) and breast minus the SIB volume (BreastSIB) (p < 0.001, 0.15 ± 0.03) compared with the PTVboost eval (0.085 ± 0.008, 0.088 ± 0.12) and BreastSIB (0.22 ± 0.05, 0.23 ± 0.03) for IMRT and 3D-CRT, respectively. Static tomotherapy also offered statistically significant reductions (p < 0.001) in doses to the ipsilateral lung mean dose of 6.79 ± 2.11Gy compared with 7.75 ± 2.54Gy and 8.29 ± 2.76Gy for IMRT and 3D-CRT, respectively, and significantly (p < 0.001) reduced heart doses (mean = 2.83 ± 1.26Gy) compared to both IMRT and 3D-CRT (mean = 3.70 ± 1.44Gy and 3.91 ± 1.58Gy). Static tomotherapy is the dosimetrically superior modality for the whole breast with an SIB compared with IMRT and 3D-CRT. IMRT is superior to 3D-CRT in both PTV dose conformity and reduction of mean doses to the ipsilateral lung.