Radiation around us everywhere, we can receive natural or artificial radiation caused by man. Radiation produced when the atom changes its internal structure by emitting electromagnetic radiation or particles (beta and alpha) trying to be stable or radiation can be produced when some particles interact with the atom. We receive radiation from cosmic rays, building materials, and terrestrial sources such as rocks and soils that contain small amounts of the radioactive elements uranium with derivative products. The dose rate from natural radiation is 1 mSv/year. The other source of radiation is the artificial radiation produced in diagnostic and therapeutic departments or the radiation produced by radioactive waste, and the rate of man-made doses is about 0.4 mSv/year. When radiation passes through matter it produces ionizing radiation which causes biological effects. The effects produced by radiation are grouped into two types, stochastic effects which occur randomly and its probability increases as the absorbed dose increases also there is no threshold for the stochastic effects so they occur randomly like cancer and the effects genetic, these effects often take years to manifest, the other type is non-stochastic effects which cause most biological effects and their severity varies with dose also there is a threshold for non-stochastic effects if the specific dose of the organ exceeded must increase the occurrence of the non-stochastic effect for example erythema, infertility, death and skin burns. According to these effects scientists learned that the radiation was not only beneficial, but could be dangerous to the human body, so they try to minimize harmful radiation... middle of paper... there is no threshold for this, so radiation must be low to prevent any possibility of cancer and other diseases. The ALARA principle must be applied in any procedure. It is important to weigh the benefit of radiation and it must outweigh the harm even if there is no benefit, so there is no reason to expose the person to radiation. In all applications it is necessary to justify whether there is any benefit. The responsibility for any procedure lies with the technologist who will perform the examination and provide a good procedure in a short time and take care of the patient without overexposure. The radiologist assumes responsibility to the technologist to reduce exposure as much as possible. The doctor who orders the test is also responsible for exposing the patient to the necessary tests and should avoid exposing the patient to unwanted radiation.