Abstract P1-15-01: Association between ischemic cardiac events and targeting of the internal mammary nodal region with adjuvant radiation for breast cancer

Abstract

Abstract Background: Cardiac toxicity has been well documented following adjuvant breast cancer radiation therapy (RT) using outdated treatment methods. Limited information exists, however, regarding cardiac outcomes following contemporary RT fields and techniques. Inclusion of the internal mammary nodal (IMN) field for appropriately selected patients with breast cancer coincided with our department’s transition to computed-tomography (CT) based planning. The objectives of this study, therefore, were to assess the risk of ischemic cardiac events following IMN irradiation and to assess the risks following CT-based versus two-dimensional (2D) planning. Methods: All patients treated with adjuvant RT for breast cancer and without history of additional chest RT from January 1, 1984 – December 31, 2007 in our department were assessed. CT planning for breast cancer began for select patients in 1997 and was used for all patients as of 2001. The inclusion of the IMN region was determined by review of our clinical database. Ischemic cardiac endpoints were defined as myocardial infarction, coronary artery bypass grafting procedure, angioplasty/stent placement, and/or diagnosis of coronary artery disease. A text-based and diagnosis code-based search was used to flag possible endpoints which were then confirmed by manual chart review. Hypertension (HTN), diabetes (DM), hyperlipidemia (HLD), and anthracycline use were identified by a diagnosis code-based search. Results: We identified 2,126 patients who received adjuvant RT. Median follow-up was 9.6 years. 311 (14.6%) patients had IMNs targeted and 1,813 (85.3%) did not (data not available for 2 patients). RT to the IMNs was not associated with a higher risk of ischemic cardiac events (HR: 0.88, P = 0.731). 1,072 (50.4%) patients had CT planning, 1,003 (47.2%) had 2D planning, and no information was available for 51 (2.4%) patients. Overall, there were 56 (5.6%) ischemic events in the 2D cohort and 27 (2.5%) in the CT cohort. After truncating follow-up to 10 years to account for differential potential follow-up, there were 28 (2.8%) and 23 (2.2%) ischemic cardiac events, respectively. The table lists the association of patient and treatment characteristics and risk of ischemic cardiac events. HTN, HLD, and DM were each associated with a significantly increased risk of ischemic cardiac events. Conclusions: After reviewing all patients treated in our department for breast cancer from 1984 – 2007, we were unable to find an association between IMN irradiation and ischemic cardiac events. CT-based planning has been shown to allow accurate targeting of the IMNs. These data suggest that even with inclusion of the IMNs, CT-based planning minimizes dose to the heart and coronary arteries thereby decreasing the risk of ischemic cardiac toxicity. These results will be followed with time. Association between characteristics and ischemic cardiac eventsCharacteristicHazard Ratio95% Confidence IntervalP-valueRT to the IMNs0.880.42-1.830.7312D vs. CT planning1.140.68-1.910.613Left vs. right1.210.79-1.850.372Anthracycline use0.750.44-1.260.270HTN5.612.06-15.300.001HLD1.901.25-2.900.003DM3.111.99-4.86<0.001 Citation Format: Adam L Liss, Kent A Griffith, Reshma Jagsi, Jean M Moran, Robin B Marsh, Todd M Koelling, Lori J Pierce. Association between ischemic cardiac events and targeting of the internal mammary nodal region with adjuvant radiation for breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-01.