Are Myocardial Perfusion Defects Noted Soon after RT for Breast Cancer Associated with “Late” Cardiac Events?

Article Outline

• Purpose/Objective(s)
• Materials/Methods
• Results
• Conclusions
• Copyright

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Purpose/Objective(s) 

Tangential radiotherapy (RT) for left-sided breast cancer has been associated with cardiac perfusion changes 6-60 mos post-RT. We herein assess the association between perfusion defects and the late cardiac morbidity.

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Materials/Methods 

Between 1998-2004, 160 patients were enrolled onto an IRB-approved prospective clinical study to better understand RT-induced cardiac injury for left-sided breast cancer. Patients had pre-and serial post-RT myocardial single photon emission computed tomography (SPECT) scans, to assess for changes in regional myocardial perfusion, wall motion, ejection fraction. Rates of clinically-significant late myocardial events were compared (chi-square, and t tests) among patients with/without perfusion defects 6-24 mos post-RT, and % in subgroups based on % left ventricle (LV) volume irradiated. Patients with equivocal symptoms, without objective findings of heart disease, were included in the no-event group. Median follow-up 6 years (range 2-9). The impact of pre-RT cardiac risk factors was also assessed.

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Results 

Of 99 evaluable patients with normal pre-RT SPECT scans, 5 patients (5%) developed significant “symptomatic” cardiac events: 3 with congestive heart failure at 24, 39, and 51 mos, and 2 with coronary artery disease at 38 and 49 mos. The rates of late clinical events in the patients with/without an abnormal post-RT perfusion scan 6-24 mos post-RT were 2/51 and 3/48, respectively (p = 0.6). The rate of clinically meaningful cardiac events in patients with <1%, 1-5%, >5% of the LV in the fields was 1/30, 2/23, 2/46, respectively (p = 0.6). The 5 patients with clinical events appeared to have greater cardiac risk factors than the other patients; National Heart, Lung, and Blood Institute cardiac risk assessment mean score of 1.72 vs. 1.28 (p = 0.05) (i.e., their relative risk for cardiac disease, compared to an age-matched healthy population without cardiac risk factors, is greater in the 5 pts with events).

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Conclusions 

The development of cardiac perfusion defects 6-24 mos post-RT appears not to be related to subsequent development of objective clinically significant cardiac events at 2-9 (median 6) years post-RT. Similarly, the %LV within the radiation field appears not to be associated with the subsequent clinically meaningful cardiac events. The small number of events (5) in our population limits the detection power. Events in our patients appear to be perhaps related more to pre-RT cardiac risk factors. Further follow-up is needed to better understand the long-term implications of these perfusion defects.

Acknowledgement: UNC for PLUNC software.

Supported by U.S. DOD (grants 17-98-1-8071, BC010663), Duke School of Medicine, and IAEA.