Content

Introduction

Introduction

With the term radiation we mean the physical phenomenon of the transport of energy through space that can occur in very different ways, for example through electromagnetic waves (which can also be described as photons, particles that travel at the speed of light and that do not have mass and electric charge); via subatomic particles, such as alpha particles (helium nuclei, composed of two protons and two neutrons) or beta (electrons) emitted by radioactive isotopes; through i protons used in proton therapy; through mechanical vibration waves in a material medium, as in the case of ultrasound.

All types of radiation interact with matter, including the human body, transferring all or part of their energy to it.

Radiation is generally divided into two broad categories according to its ability to change the number of electrons in an atom or molecule (ionize) the biological matter on which the nature of the possible damage to exposed organisms depends:

  • ionizing radiations (X and gamma rays, whose photons are high energy, and high energy subatomic particles)
  • non-ionizing radiation (electromagnetic waves whose photons are low-energy, ultrasound)

Ionizing radiation can irradiate the human body from the outside (for example, during an X-ray examination) or from the inside with the inhalation or ingestion of so-called radioactive isotopes (for example the radon present in the air or some isotopes present in food as a result of contamination produced by nuclear accidents).
Globally, according to data published in 2010 by UNSCEAR, the main source of exposure of the population to ionizing radiation is radon (42% of the total), followed by exposures for medical reasons (20% of the total).

Ionizing radiations

Ionizing radiation has sufficient energy to release electrons from an atom (ionization). The energy transferred by ionizing radiation to living matter can damage cells and therefore have an influence on normal biological processes.

The amount of energy absorbed (expressed in joule, J) by the organ or tissue irradiated divided by its mass (expressed in kilograms, kg) is called absorbed dose, whose unit of measurement is the gray (Gy = J / kg). For example, the dose of 1 Gy to an organ weighing 2 kilos indicates that this organ has absorbed an amount of energy equal to 2 joules from the radiation.

This unit of measurement, however, does not take into account that ionizing radiations of different types (alpha, beta, gamma, protons, etc.) interact in a different way with matter and can therefore produce more or less significant damage to organs and human body tissues. To compare the absorbed doses by a determined organ or tissue irradiated with different types of radiation, the absorbed doses must therefore be “weighed” with the different potential to produce damage by the different types of radiation. Weight", for example, 1 for gamma radiation and 20 for alpha radiation. The weighted dose is called equivalent dose, whose unit of measurement is the sievert (Sv). Like the absorbed dose, this too must refer to a specific organ or tissue. For example, an absorbed dose of 1 Gy to the lungs corresponds to an equivalent dose of 1 Sv or 20 Sv depending on whether the lungs have been irradiated by gamma or alpha radiation, respectively.

Furthermore, it must be considered that some parts of the human body are more vulnerable (radiosensitivity) than others to the action of ionizing radiation. In particular, some organs or tissues are more likely to develop cancer than others for the same equivalent dose. For example, this probability is 12 times higher for the lungs than for the skin. Therefore, a further quantity called is used to compare the equivalent doses of different irradiated organs and tissues effective dose, obtained by weighing the equivalent dose of a given organ or tissue by a weight proportional to the probability of that organ or tissue of developing a tumor.

The effective dose is, therefore, the most appropriate reference for assessing the risk of the appearance of a tumor following exposure to ionizing radiation. The unit of measurement of the effective dose is called sievert (Sv), as for the equivalent dose. The effective dose, however, is not specific to an organ or tissue and can, therefore, be compared with others. An equivalent dose of 1 sievert to the lungs, for example, corresponds to an effective dose of 0.12 Sv, while an equivalent dose of 1 Sv to the skin corresponds to an effective dose of 0.01 Sv.

This system of different quantities and relative units of measurement, which at first sight may appear complex, is necessary to adequately assess the consequences of exposure to ionizing radiation and allow for an adequate assessment for the purposes of protecting the population and workers from radiation. and those who are exposed to medical examinations or therapies that involve their use.

The use of ionizing radiation for medical reasons, for example for the purposes of treatment or detection (diagnosis) of diseases, is controlled and regulated in such a way that any risks resulting from exposure to radiation are very small and justified by the diagnostic benefit and / or curative.

Some examples of using ionizing radiation to treat or detect (diagnose) disease include:

  • radiographs and computed tomography (CT), which make it possible to produce internal images of the body to ascertain diseases
  • nuclear medicine, which involves the injection, in the patient, of a radioactive substance to have detailed images of the organs or bones useful for ascertaining (diagnosing) a disease or for specific oncological therapies
  • radiotherapy, used in oncology to destroy cancer cells in a targeted way, i.e. by minimizing the dose to surrounding healthy organs and tissues

Non-ionizing radiation

Non-ionizing radiation includes electromagnetic radiation where i photons they do not have sufficient energy to ionize the atoms and molecules that make up biological matter.

Some examples of non-ionizing radiation are:

  • ultraviolet radiation (UV)
  • light (visible to the human eye)
  • infrared radiation (IR)
  • radio frequency and microwave electromagnetic fields (radio and television broadcasts, mobile phones, Wi-Fi)
  • electric and magnetic fields at the grid frequency (50 Hz)

Non-ionizing radiations, even if they do not have the ability to ionize the biological matter with which they interact, however, have energy capable of producing biological effects (thermal, mechanical and bioelectrical changes) which, if not compensated by the human body, can produce a damage to health.
For radiofrequency and microwave electromagnetic fields, the deposition of energy in biological tissues is defined by SAR (from the English Specific Absorption Rate), expressed in W / kg, which is an indicator of any heating effects in the tissues. For practical purposes, since the SAR is not an easily measurable quantity, human exposure to radio frequency and microwave electromagnetic fields is often characterized in terms of electric field and of magnetic field.

For lower frequency fields, including zero frequency (static) fields, the concept of SAR is no longer useful as for these fields any biological effects are not thermal in nature.

The medical applications of non-ionizing radiation range from procedures for ascertaining (diagnostic) diseases such as, for example, ultrasound and magnetic resonance imaging, to those for treating them such as high-intensity focused ultrasound for applications in oncology and neurology, HIFU. There are also cosmetic applications such as, for example, laser or pulsed light hair removal treatments.

Bibliography

Bibliography

United Nations Environment Program (UNEP). Radiation: Effects and Sources

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Sources and Effects of Ionizing Radiation (UNSCEAR 2008 Report)

Further links

Further links

World Health Organization (WHO). Radiation, Ionizing (English)

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (English)

World Health Organization (WHO). Radiation, Non-ionizing (English)

International Commission on Non-ionizing radiation protection (ICNIRP) (English)

International Radiation Protection Association (IRPA) (English)

Radiation Effects Research Foundation (RERF). Library (Papers / Data) (English)

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