ESTRO 2021 Abstract Book

S1632

ESTRO 2021

3.7 in 0 Gy, 2.8 in 0.5 Gy, and 1.8 in 1 Gy, p = 0.003). The osteoclast activity also appeared to be significantly reduced in the LDRT group. Conclusion Taken together, LDRT could mitigate osteoarthritis progression by exerting its anti-inflammatory effects through modulating mitochondrial function. PO-1912 Feasibility study on stereotactic radiotherapy for total pulmonary vein isolation in a canine model J.H. Chang 1 1 Seoul National University Hospital, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective To test the feasibility of pulmonary vein (PV) and left atrial (LA) posterior wall isolation using non-invasive SABR and investigate pathological changes in irradiated lesions in a canine model. Materials and Methods Seven male Mongrel dogs received single-fraction 33-Gy SABR. We designed the en-bloc circular target of total PVs and LA posterior wall to avoid the esophagus. The circular box lesion included the LA roof and ridge, low posterior wall, and posterior interatrial septum. At 6 weeks or 4 months after SABR, electrical isolation of the SABR lesion was confirmed using LA posterior wall pacing, and histopathological review was performed. Results Electrical isolation of all PVs and the LA posterior wall was achieved in three of five dogs in the 4-month group. There was one target failure and one sudden death at 15-weeks. Although two dogs in the 6-week group failed to achieve electrical lesion isolation, the irradiated atrial myocardium showed diffuse haemorrhage with inflammatory cell infiltration. In successfully isolated 4-month model dogs, compared to the adjacent non-irradiated atrial wall, we observed transmural necrotic scarring with extensive fibrosis on irradiated atrial tissue. Conclusion Electrical isolation of PVs and the LA posterior wall was achieved with this novel circular box-design radiotherapy technique using SABR within 4-months in canines. The irradiated lesion showed haemorrhagic inflammation at 6-weeks and extensive fibrotic necrosis at 4-months. This technique could be applied to humans after further studies are conducted to confirm safety. PO-1913 Effects of Nigella sativa oil and thymoquinone on radiation-induced oxidative stress in rat kidney H. Alkış 1 , E. Demir 2 , M.R. Taysi 3 , S. Sagir 4 , S. Taysi 5 1 Marmara University, School of Medicine, Radiaiton Oncology, ISTANBUL, Turkey; 2 Harran University, College of Health, Biochemistry, Şanlıurfa, Turkey; 3 Bingöl University, Faculty of Agriculture, Bingöl, Turkey; 4 Gaziantep University, Urology, Gaziantep, Turkey; 5 Gaziantep University, Biochemistry, Gaziantep, Turkey Purpose or Objective Ionizing radiation leads to release of free radicals into the systemic circulation from irradiated tissues. These free radicals cause oxidative stress in distant organs. Oxidative status may be reversed by naturally occurring antioxidant agents. The aim of this study is to investigate protective and antioxidant effects of Nigella sativa oil (NSO) and thymoquinone (TQ) in kidney tissue of rats exposed to cranial irradiation. Materials and Methods Forty-eight Sprague-Dawley rats were divided into six groups: IR only group received irradiation (IR) to total cranium plus saline; IR plus NSO group received IR and NSO; IR plus TQ group received IR and TQ; sham group did not receive NSO, TQ or IR; control group of TQ received dimethyl sulfoxide and sham IR; control group of NSO received saline and sham IR. Oxidative parameters; total oxidant status (TOS), oxidative stress index (OSI) and lipid hydroperoxide (LOOH) levels, and antioxidative parameters; total antioxidant status (TAS), total sulfhydryl levels, paraoxonase (PON), ceruloplasmin (Cp) and arylesterase activities were determined in kidney tissue of rats. Results Kidney TOS, OSI and LOOH levels were significantly lower in IR plus TQ, IR plus NSO and sham groups compared to IR only group (p<0.05). TAS, PON and Cp activities in IR only group were significantly lower compared to the control group (p<0.05). PON and Cp activities were significantly higher in IR plus NSO and IR plus TQ groups compared to IR only group (p<0.05). Conclusion In conclusion, free radicals generated by cranial ionizing radiation exposure cause oxidative stress in kidney. NSO and TQ exhibit protective and antioxidant effects against oxidative damage in rats. Purpose or Objective Non-invasive cardiac radioablation is employed to treat ventricular arrhythmia. However, myocardial changes leading to early-period antiarrhythmic effects induced by high-dose irradiation are unknown. This study investigated dose-responsive histologic, ultrastructural, and functional changes within 1 month after irradiation in rat heart. Materials and Methods Whole hearts of wild-type Lewis rats (N = 95) were irradiated with single fraction 20, 25, 30, 40, or 50 Gy and explanted at 1 day or 1, 2, 3, or 4 weeks post-irradiation. Microscopic pathologic changes of cardiac structures by light microscope with immunohistopathologic staining, ultrastructure by electron microscopy, and functional evaluation by electrocardiography (ECG) and echocardiography were studied. Results Despite high dose irradiation, no myocardial necrosis and apoptosis were observed. Intercalated discs were widened and disrupted, forming uneven and twisted junctions between adjacent myocytes. Diffuse vacuolization peaked at 3 weeks, PO-1914 Early changes in rat heart after high dose irradiation J.H. Chang 1 1 Seoul National University Hospital , Radiation Oncology, Seoul, Korea Republic of