There are over 10,000,000,000,000 cells in your body. Each one has a nucleus with the same set of 46 chromosomes. By copying the original 46 chromosomes, your body has created more than a hundred billion kilometers of DNA.
Cancer is a disease that originates in our own cells. A change in the DNA causes a special gene called an oncogene to be switched on irreversibly leading to uncontrollable cell reproduction. The uncontrolled growth of cells forms a lump called a tumor. Malignant tumors are called cancers.
Cancer can start anywhere in the body and there is a danger that, if not treated early enough, they can spread to form secondary tumors. High-energy gamma radiation is aimed at the growing tumor. This damages the DNA in rapidly dividing cells and so helps to destroy the tumor. There are many different types of radiation. Exposure to ultraviolet, alpha, beta and gamma radiation can cause cancer.
Ionizing radiation can damage chromosomes and cause mutations that may trigger a tumor to develop. Different types of radiations that are used in radiotherapy are gamma, beta and X-rays. Beta radiations are weakly ionizing. Gamma radiation is only really hazardous if it is very intense and this happens after a nuclear explosion.