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Background: Radiotherapy (RT) forms a vital component of treatment for breast cancer, contributing to the increasing number of survivors worldwide. It is known from historical cohorts that breast RT increased the risk of developing heart disease 10 years or more following treatment. It is less certain whether the lower cardiac radiation doses received during modern RT still increase cardiac risk. Cardiovascular Magnetic Resonance (CMR) imaging has the potential to provide early surrogate markers of radiation-induced heart disease that may help predict which women will be at increased risk in the future. Methods: This is a prospective longitudinal imaging study to evaluate CMR findings in a cohort of women receiving adjuvant RT for early breast cancer at the Oxford Cancer Centre. The patients undergo CMR imaging (with gadolinium enhancement and adenosine stress), Doppler echocardiography, blood testing (including BNP and troponin), ECG and clinical examination prior to RT, within 72 hours of completing RT, and at 3 months, 6 months and 5 years following RT. The results of these investigations will be related to cardiac radiation exposure estimated using 3D-dosimetric data obtained by analysis of CT-based RT planning. Recruitment and Provisional Results: As of May 2011, 30 women have been recruited. The women had a mean age of 57.1 years (range = 42.0 to 63.9). All women had left-sided cancer and none received adjuvant cytotoxic chemotherapy. The mean whole heart dose was 1.47 Gray (range = 0.65 to 4.20), the mean left ventricle dose was 2.03 (range = 0.88 to 6.99) and the mean left coronary artery dose was 7.55 Gray (range = 1.50 to 24.59). Preliminary analysis of the first 10 participants showed that all had a normal left ventricular ejection fraction at baseline (mean 76%, range 60–82%) and immediately following RT (mean reduction 3%, p=0.18). None had myocardial oedema as detected by T2-STIR imaging or fibrosis and scarring as demonstrated by late gadolinium enhancement (LGE). Conclusion and Future Plans: Preliminary results suggest that the relatively low heart doses received by the women undergoing modern CT-planned left breast RT at the Oxford Cancer Centre do not result in any cardiovascular abnormality detectable by CMR imaging. Further and updated results will be available for the San Antonio Breast Cancer Symposium. Recruitment will continue until at least 20 women have completed baseline scans and follow-up scans up to 6 months. At this stage a full analysis will be performed including a wider range of CMR endpoints including: - Overall LV systolic function (EF and volumes) - Regional wall motion analysis - T2-weighted imaging (oedema) - T1 and T2 mapping (quantitative T1 and T2 relaxation times) - Tagged myocardial strain analysis - Stress perfusion defects (endothelial/microcapillary damage) - Late gadolinium (LGE) imaging (fibrosis/scarring) Depending on the results of this analysis, recruitment may be expanded to include women with either lower cardiac risk (e.g. with right-sided breast cancer) or higher cardiac risk (e.g. receiving anthracycline chemotherapy). Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-13-06.