(S031) Dosimetric Analysis of Left-Sided Breast Cancer Treatment With Tomotherapy IMRT, IMRT, VMAT, and 3D-CRT

Twisha Chakravarty, MD, Eugene C. Endres, Brent Parker, PhD, DABR, Sandra Hatch, MD; University of Texas Medical Branch

OBJECTIVES: Previous studies have demonstrated that the risk of ischemic heart disease is increased as a result of exposure to ionizing radiation in women treated for breast cancer. Alternative radiation techniques, such as intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), and TomoTherapy IMRT, have been shown to improve dosimetric parameters of the heart and substructures. However, these techniques have not been compared with each other to potentially guide treatment decisions.

METHODS: Treatment plans from 10 patients treated to the whole breast for left-sided breast cancer in 2014 were collected. Treatment plans using TomoTherapy IMRT, IMRT, VMAT, and three-dimensional (3D) conformal radiation therapy with TomoDirect and opposed tangents were generated for each patient. Dosimetric parameters for the heart, left ventricle, and left anterior descending artery (LAD), including V2, V5, V10, D_max, and mean doses, were collected and analyzed using paired t-test and analysis of variance (ANOVA).

RESULTS: For V2 of the LAD, no statistically significant difference was found between TomoTherapy IMRT and 3D conformal plans (67.2% vs 70.5% vs 75.0%; P = .49); however, TomoTherapy IMRT plans had significantly reduced V5 of the LAD when compared with 3D conformal plans, as well as IMRT and VMAT (2.0% vs range: 12.0–49.0%; P < .01). With regard to the heart and left ventricle, the V2 was significantly lower for 3D conformal plans vs TomoTherapy IMRT, VMAT, and IMRT (P < .01). This difference was maintained for V5 for the heart but not for the left ventricle. Across all three cardiac parameters, the average D_max was significantly lower with TomoTherapy IMRT plans when compared with all other planning techniques (P < .01). 

CONCLUSIONS: Our analysis of this single-institution population of women with left-sided breast cancer treated to the whole breast demonstrates that differing radiation treatment techniques have statistically significant impacts on dosimetric parameters of the heart, left ventricle, and LAD. TomoTherapy IMRT was shown to be superior for reducing low-dose radiation to the LAD and maximum dose to all cardiac structures, particularly when compared with VMAT and IMRT. No significant difference was demonstrated in low-dose radiation exposure from treatment with TomoDirect vs opposed tangents. These results provide insight into treatment differences that may help guide clinical practice in the future, with an emphasis on reducing long-term patient toxicity. 

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org