Abstract 38: Radiation Exposure And Coronary Atherosclerosis: Differential Effect Of The Radiation Site

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Background: Thoracic radiation is commonly used in breast cancer, Hodgkin’s lymphoma, head and neck and lung cancer patients. Accelerated coronary artery atherosclerosis is a common complication of thoracic radiation as a result of unintended cardiac radiation. It is unclear however whether specific areas of the heart are more susceptible to the effects of radiation (RT). In this study we hypothesize that accelerated development of lesions post RT is dependent upon differential sensitivity of specific areas of the heart to the effects of RT. Methods: Male Apolipoprotein E knockout mice on a high fat diet received 16Gy cardiac RT targeted to the whole or partial (apical or basal) region of the heart at 9 or 16 weeks of age (n=5 per group). Atherosclerotic lesions in H&E stained slides and inflammatory infiltrates in the hearts by IHC were assessed 8 weeks following RT and compared to control unirradiated mice. Results: Our studies show that: (1) Subendocardial atherosclerotic lesions at the base of heart in mice irradiated at 9 weeks of age after basal irradiation (7.8±2.49) were comparable to whole heart irradiation (12.2±3.29). (2) A greater number of atherosclerotic lesions were present in the basal coronary arteries (29.33±5.48 vs 9±2.70) and basal subendocardial vasculature (6.66±2.07 vs 0.2±0.2) after irradiation of the cardiac base as compared to unirradiated controls in mice irradiated at 16 weeks of age. (3) Apical or whole heart irradiation had no impact on the development of lesions in the basal region of the hearts of older mice. (4) IL-6 was significantly increased in the serum of mice 6 hours post basal cardiac irradiation (105.10±17.56 pg/ml) when compared to unirradiated controls (29.85±11.63 pg/ml), demonstrating an acute inflammatory response. (5) Infiltration of inflammatory cells (CD45 and CD3) and enhanced expression of endothelial adhesion molecules (CD31) were differentially and locally regulated based upon the site of irradiation. Conclusion: Our results indicate that the base of the heart is more prone to development of RT induced atherosclerotic lesions likely due to acute and delayed inflammatory responses. Avoiding this area from direct radiation exposure may improve the quality of life for cancer patients receiving thoracic RT.

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