الفهرس 
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Abstract
The incidence of abscopal effects draw attention to possibility of unexpected effects of ionizing radiation (IR) in distant bystander organs during radiotherapy (RT). The present study investigated radiation induced abscopal effect in terms of oxidative stress, apoptosis and Deoxyribonucleic acid (DNA) damage in spleen following cranial X-rays irradiation of rats. Rats were cranially irradiated using 2 Gy X-rays. For comparison, another group was exposed to 2 Gy whole-body X-rays irradiation and a third group was exposed to scattered radiation (measured to be ~3 mGy). Compared to the sham-irradiated animals, the cranially irradiated animals showed a significant increase in the levels of glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) with no significant change in the lipid peroxidation product (MDA) in the spleen cells with a significant increase in the C-reactive protein level (C-RP) in the plasma 24h following irradiation. Accompanying these events, apoptotic cell death in the spleen cells was demonstrated as indicated by the decrease of Bcl-2; the increase of p53, Bax, caspase-3 and caspase-8. Additionally, an induction of DNA damage in the spleen in both of the cranially irradiated rats and whole-body exposed rats 24h following irradiation was demonstrated. The exposure to 3 mGy scattered radiation produced an increase in the MDA level; decrease the levels of GSH, SOD and CAT in the spleen cells; and increase the plasma level of C-RP. Scattered radiation also induced apoptosis in the spleen cells 24h following irradiation. In conclusion, cranial irradiation enhanced the antioxidant capacity but induced an abscopal effect in the form of apoptosis and DNA damage in distant spleen cells. Very low doses of radiation can induce apoptosis in the spleen cells. Therefore, it is essential to perform more studies to explain the mechanism of the bystander effect to more precisely evaluate radiation risks and for better management of radiotherapy protocols.