What is radiation? One night in December 1895, a world-renowned German physicist Röntgen discovered in a physics laboratory: the glass tube of the discharge not only emits visible light, but also emits some kind of invisible rays, which are very penetrating and can penetrate glass, wood and muscle, etc. They can also penetrate black paper to make the negatives wrapped inside light sensitive, and can make the cardboard coated with barium cyanate flash light green fluorescence, but It is difficult to penetrate bone. He thought that the newly discovered rays were mysterious in nature and called them “x-rays”. It is essentially a stream of photons, an electromagnetic wave, with the characteristics of light, and because x-rays are very high energy, they can penetrate a certain thickness of material. The higher the energy, the thicker the object that can be penetrated, so it is used in medicine for fluoroscopy, radiography and radiation therapy. What is radiation oncology? Radiation oncology is abbreviated as radiation therapy for tumors. It is the science of treating malignant tumors by using alpha, beta and gamma rays produced by radioisotopes; x-rays of different energies produced by x-ray therapy machines and various gas pedals; electron beams, proton beams, neutron beams, negative π meson beams and other heavy particle beams produced by various gas pedals. Simply put, it is the science of using radiation to treat tumors. What is the principle of radiation therapy? When a large amount of radiation enters an organism, it has direct and indirect killing effects on cells. The direct killing effect can cause damage to dna (deoxyribonucleic acid), an important genetic material in the cell, while the indirect killing effect is to produce free radicals – hydrogen peroxide – which are harmful to the cell, causing the cell to die of poisoning. The magnitude of the cell killing effect of radiation is directly proportional to the cell growth rate and inversely proportional to the degree of cell differentiation. Tumor cells grow faster than normal cells and have a lower degree of differentiation, so the killing effect of radiation on them is much greater than that on normal tissue cells. Radiotherapy is based on this mechanism to achieve the purpose of treating tumors without damaging normal cells.