Serial Measurement of Global Longitudinal Strain Among Women With Breast Cancer Treated With Proton Radiation Therapy: A Prospective Trial for 70 Patients

Purpose: Conventional photon radiation therapy (RT) for breast cancer is associated with a reduction in global longitudinal strain (GLS) and an increase in troponin, N-terminal pro hormone B-type natriuretic peptide (NT-proBNP), and incident heart failure. The cardiac radiation exposure with proton-RT is much reduced and thus may be associated with less cardiotoxicity. The objective was to test the effect of proton-RT on GLS, troponin, and NT-proBNP. Methods and Materials: We conducted a prospective, observational, single-center study of 70 women being treated with proton-RT for breast cancer. Serial measurements of GLS, high-sensitivity troponin I, and NT-proBNP were performed at prespecified intervals (before proton-RT, 4 weeks after completion of proton-RT, and again at 2 months after proton-RT). Results: The mean age of the patients was 46 ± 11 years, and the mean body mass index was 25.6 ± 5.2 kg/m²; 32% of patients had hypertension, and the mean radiation doses to the heart and the left ventricle (LV) were 0.44 Gy and 0.12 Gy, respectively. There was no change in left ventricular ejection fraction (65 ± 5 vs 66 ± 5 vs 64 ± 4%; P = .15), global GLS (–21.7 ± 2.7 vs –22.7 ± 2.3 vs –22.8 ± 2.1%; P = .24), or segmental GLS from before to after proton-RT. Similarly, there was no change in either high-sensitivity troponin or NT-proBNP with proton-RT. However, in a post hoc subset analysis, women with hypertension had a greater decrease in GLS after proton-RT compared with women without hypertension (–21.3 ± 3.5 vs –24.0 ± 2.4%; P = .006). Conclusions: Proton-RT did not affect LV function and was not associated with an increase in biomarkers. These data support the potential cardiac benefits of proton-RT compared with conventional RT.