The Basic Study On Radiotherapy Of Oral Squamous Cell Carcinoma With Heavy Ion Beam

Cancer is a kind of enormous dangerous disease to human health. Radiotherapy is one of the most important modalities.Conventional radiotherapy includes the treatments of X-,γ-ray and electron beam,characterized by an exponentially decreasing depth-dose distribution while penetrating the patient body.Therefore,serious damage to normal tissue would be caused after the conventional radiotherapy.Heavy ion beams is characterized by an energy deposition maximum(Bragg peak)at the end of its range and an increased relative biological effectiveness(RBE)within the peak,so it could protect the healthy tissues from damage induced by radiation.Because of these merits,heavy ion beam is an ideal method of radiotherapy.So it is considered the most scientific, the most advanced and the most efficacious method in 21th century.In 1995, China became the fourth country used heavy ion on treating tumour following America,Gremany and Japan.The medical research work,one of the top projects of national fundamental research,on the area of heavy ion radiation was started, and in this project many radiobiological effects important for radiotherapy were done by Institute of Modem Physics,Chinese Academy of Sciences and Medical Academy of Gansu Province in China.In this thesis,the radiobiological effects and mechanism of heavy ion irradiation on oral squamous cell carcinoma(OSCC) related to the cancer therapy with heavy ion radiation were studied in following experiments at cell level.¹²C⁶⁺was accelerated with Heavy Ion Research Facility in Lanzhou(HIRFL). Exponentially growing human tongue carcinoma cells(Tb)cultured in vitro were irradiated by 0,0.5,1,2,4Gy ¹²C⁶⁺ions.Survival rate of irradiated cells at various doses were measured by MTT assay;The nucleus changes of apoptosis and necrosis of cells stained by Hochest/PI were observed through fluorescence microscope;The expressions of Bax and Bcl-2 protein were detected by Western blot analysis;The cell cycle were detected by flow cytometry(FCM)and compared with that of Tb cells irradiated with X-ray at dose 0,2,4,6,8Gy.The results showed that the viability of Tb cells decreased gradually with the doses of carbon ions;The proportions of apoptosis of cells in the irradiated groups were significantly higher than those in the control group;And the expressions of Bax and Bcl-2 were significantly up-regulated and down-regulated respectively by ¹²C⁶⁺ ion irradiation.After Carbon ion irradiation,there was a positive correlation between irradiation dosage and retardation strength in G₂/M phase(P＜0.05).The peak value appeared at 12h after 0.5,1Gy exposure and then decreased significantly at 24h.After X-ray irradiation,the Tb cell cycle was arrested in G1 stage for 2 Gy group,while 4,6 and 8Gy groups were arrested in G2 stage.The rates of stagnation in 6Gy group were 70%,which was equal to 2Gy group by 12C6+ ions irradiation,namely RBE was 3.It is concluded from above that Cell apoptosis induced by heavy ion with high-LET may be mediated through the Bax/Bcl-2 way.The different changes of cell cycle show better RBE of ¹²C⁶⁺ion than of X-ray.