Persistence of radiation (RT)-induced cardiac perfusion defects 3–5 years post RT

625 Background: Tangential photon radiation treatment to the left breast/chest wall has been linked with cardiac dysfunction. In a prospective trial, we have demonstrated that new perfusion defects occurred 6–24 months post-RT (IJROBP 2003;57:S129) in ≈ 40% of patients. We herein assess if these perfusion defects persist with longer follow-up. Methods: Between 1998–2003, 130 patients with left-sided breast cancer were enrolled onto an IRB-approved prospective study to assess RT-induced cardiac dysfunction. All patients received tangent photons to 46–50 Gy, 1.8–2Gy/Fx. Patients had pre- and serial post-RT single photon emission computed tomography (SPECT) scans to assess changes in regional cardiac perfusion. SPECT images were acquired 30–60 min after I.V. administration of 25–30 mCi Tc-99m labeled myocardial perfusion tracer. Patients with pre-RT abnormal perfusion were excluded from this analysis. Twenty-five patients with follow-up scans beyond 2 years form the basis of this report. The incidence of new/persistent perfusion defects beyond 2-years is reported. Results: 16, 7 and 2 patients are evaluable 36-, 48-, and 60-months post-RT, respectively. These 25 patients are divided into 3 subgroups based on their 6–24 month post-RT scans. In those patients whose 6–24 month post-RT scans were consistently abnormal, 6/7 (86%) had persistent abnormalities 3–4 years post-RT. In patients whose 6–24 months post-RT scans were intermittently abnormal (i.e. some scans normal, others abnormal), 5/10 (50%) had abnormal scans 3–5 years post RT. In patients whose scans 6–24 months post-RT were all normal, 4/8 (50%) had abnormal scans 3–5 years post RT. Conclusions: RT-induced perfusion defects can persist 3–5 years post-RT. Somewhat concerning is the observation that new perfusion defects may present 3–4 years post-RT. The clinical relevance of these perfusion defects remains unclear. However, it is possible that such RT-induced perfusion defects represent subclinical microvascular injury, which may render the patients at increased risk for ischemic heart disease. Additional follow-up and study is required. Supported by Grant DAMD 17–98-1–8071 and BC010663 awarded by DOD. No significant financial relationships to disclose.