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A third of the Computed Tomographies performed in the United States seems to be useless regarding the new medical information. A medical study (Reza, 2009) reveals by generalization that 4 million Americans are exposed to a cumulative effective dose of radiation that exceeds the maximum allowed dose and 28% of them are affected by Computed Tomography (CT) exposure to radiation (UNSCEAR, 2008).
In Romania, statistics show that three million people are investigated by radiographies and Computed Tomography (CTs). The investigations by radiological methods strongly increase the cumulative radiation dose of the patients. So, despite the great concern of radiation exposure, the doctors are not very careful when they prescribe such imaging investigations. The radiographies, mammographies, CT-s and other X-rays investigations can save our life but their high level radiation doses can affect our health. Despite the skyrocketing volume of imaging investigations with radiation risk, there is a major lack in monitoring and tracking of the cumulative radiation doses of the patients that are usually treated and evaluated in many health services all over the country.
Ionizing radiation is radiation composed of particles with enough kinetic energy to liberate an electron from an atom or molecule, thus ionizing it. When ionizing radiation is emitted or absorbed by an atom, it can liberate an electron, proton, or neutron, or an entire nucleus from the atom, producing ions, or ion-pairs.
There are three main kinds of ionizing radiation: alpha particles, which include two protons and two neutrons, beta particles, which are essentially electrons and gamma rays and x-rays, which are pure energy (photons).
The boundary between ionizing and non-ionizing radiation can be often a problem and it must be greater than the ionization energy of the target material.
The energy of the radiation increases as its frequency rises. Non-ionizing radiation ranges from extremely low frequency radiation through the audible, microwave, and visible portions of the spectrum into the ultraviolet range.
Cosmic rays, alpha, beta, gamma and X-rays are well known ionizing radiation. Generally, any charged particle moving at relativistic speed is considered ionizing radiation. Neutrons form a particular case because they are ionizing radiation at any speed. Radio waves, microwaves, infrared light and visible light are normally considered non-ionizing radiation, although very high intensity beams of these radiations have similar properties to ionizing radiation.
The Sievert (Sv) is the International System of Units (SI) derived unit for the radiation dose. Confusion can be caused as there are two more different radiation units: Gray and J/Kg. The Gray is used with quantities of absorbed dose in any material, while the Sievert is used with equivalent, effective and committed dose in biological tissue. Quantities that are measured in Sieverts are designed to represent the stochastic biological effects of ionizing radiation. The Sievert should not be used to express the unmodified absorbed dose of radiation energy, which is a clear physical quantity measured in Grays.
From the same category as Sievert, an older unit for the equivalent dose, still used in the United States, is the Rem. One Sievert equals 100 Rem. Rem is a unit for radiation dosage (such as from X rays) applied to humans. Derived from Roentgen equivalent man, the Rem is now defined as the dosage in rads that will cause the same amount of biological injury as one rad of X rays or gamma rays.
The Rad is a deprecated unit of absorbed radiation dose, defined as one centiGray. It was originally defined in CGS units in 1953 as the dose causing 100 Ergs of energy to be absorbed by one gram of matter. It has been replaced by the Gray in SI. A related unit, the Roentgen, is used to quantify the number of Rad deposited into a target when it is exposed to radiation. The F-factor can be used to convert between Rads and Roentgens. The Roentgen (R, also Röntgen) is a legacy unit of measurement for the kerma of X-rays and gamma rays up to 3 MeV. The unit is still used in the United States Navy nuclear propulsion program. One Roentgen of air kerma deposits 0.00877 Gray (0.877 Rad) of absorbed dose in dry air, or 0.0096 Gray (0.96 Rad) in soft tissue. One Roentgen (air kerma) of X-rays may deposit anywhere from 0.01 to more than 0.04 Gray (1 to 4 Rad) in the bone, depending on the beam energy.
All the radiation doses in this paper will be considered in Sievert as a unit for biological effects.
The International Commission on Radiological Protection (ICRP) recommends that the public limit of artificial irradiation should not exceed an average of 1 mSv efective dose per year, not including medical and occupational exposures.