Thyroid Cancer And Dental Radiography

Thyroid cancer and dental radiography

Introduction

Radiation is the emitted energy that is transferred through space with influence or not in the atomic structure of matter, this can be classified into non -ionizing and ionizing radiation according to the effects produced by corpuscular contact. X -rays constitute electromagnetic radiation that are generated after the excitation of the electrons of the internal orbit of an atom, with the ability to cross opaque bodies. With the growing use of X -rays in the diagnosis, the vast majority of people are exposed to radiation several times throughout their lives.

The thyroid gland is odd and is located in the anteromedial part of the lower third of the neck, at the level of the vertebrae C4 to T1. Due to its location, the thyroid gland is considered highly vulnerable to X -rays. Together, iodine deficiency and high dose ionizing radiation exposure are environmental causes established for thyroid cancer. For every 10 dental radiographs, there is a 13% increase in the risk of thyroid cancer. 

Theoretical framework

Professionals of the Health Area require certain complementary aids in various specialties, capable of contributing to the diagnosis, execution of procedures and control in the evolution of the state of some conditions and treatments. Radiography constitutes a useful tool, since it offers a vision of non -superficial structures and injuries that clinically cannot be differentiated from others, due to compromised structures and their extension.

X -rays are potentially harmful to both the patient and specialists . The ionizing effects of the-X rays originate proportionally to the amount of absorbed radiation and the radiosensitivity that cells can absorb. Radiation transfers energy to cell molecules. Because of this interaction, the functions of the cells can be temporarily or permanently altered and caused in some cases even their death. The severity of the lesion depends on the type of radiation, the absorption speed, the absorbed dose, and the sensitivity that the tissue has. 

The damage that the radiography represents is the reason why the laws and protection regulations demand a justification for each patient exposure. When an exposure is justified, it is done based on the “alara” principle as low as reasonably possible.  That is why it is very important to reduce the radiation dose. This may be possible when using individualized exposure parameters, collimation of the beam and safeguarding those organs that are sensitive to the radiation of the primary beam and lost radiation. 

The dose of a radiographic exposure of dental diagnosis can be expressed in Sieverts, which is the unit used for the ‘effective dose’ (e). This is a measure that was created to represent the risk of harmful effects depending on the type of radiation and radiosensitivity that each organ or tissue presents. A dose of 3 to 4 SV causes death in 50 % of cases. For the effects that are developed from high doses, they are called deterministic or non -stochastic. While, the damage caused by low doses is known as statistical or stochastic.

With the use of a risk factor (RF), the effective dose can be expressed in terms of total deterioration, which means the formation of cancers that can be fatal or not and of hereditary effects. The detriment of radiation depends on age and gender, being notoriously greater for children and slightly for women. 

The dose received by an individual who is close to a radiation source is determined by three factors: 

1.  The distance between the source and the individual: the X -rays of a radioactive source spread through the air, continuing the law of inverse proportionality to the square of the distance, so that, when moving away from the source, bending the distance of the patient , the exhibition would be a quarter. In the same way, having an approach to the source the intensity of radiation increases in the same proportion. The largest radiation source is the patient, which serves as a means of radiation dispersion. Generally, the dispersion of the radiation of a patient at 1 m is approximately 0.1% of the radiation that enters. It is transcendental to know that when we use the lateral vision with the arc the dispersion of radiation on the X-ray input side is 2-3 times greater than on the opposite side of the image intensifier. Therefore, being on the side of the image intensifier, lower exposure is offered. 
2.  Radiation time: Exposure time must. The large part of the teams have an automatic 5 -minute limit, in the form of a whistle or exposure stop. In some ancient devices this notice does not exist, therefore it is necessary to keep the radiation time account used. 
3. The matter filed between one and the other: all radiation, by transferring the matter, supports a decrease or attenuation of its intensity. Depending on the type and energy of the radiation and attenuation that you want to achieve, different types and shields will have to be used. To stop alpha radiation, a sheet of paper is enough. While, beta radiation would be completely absorbed by a few centimeters of some light material such as wood, plastic or glass. To build an adequate armor for X -rays or gamma radiation it is necessary to use heavier materials (concrete, lead, etc.) 

The thyroid gland is one of the most sensitive radio organs in the head and neck area. When making an intraoral radiography in the anterosuperior area, it is within the primary beam of radiographs. 

In the last three decades the incidence of thyroid cancer has increased in several countries. Much of this increase is probably due to the verification of subclinical cases, but other contributing factors should be considered. In most of the population, this cancer represents approximately 1 to 6% of all cancers present in the female gender and 2% in the masculine; The standardized incidence rates per 100,000 inhabitants vary from approximately 1 to 23 in women and 0.5 –6 in men. In addition, dentists and their assistants, but also those X -ray workers are more likely to contract it. 

The evidence of the interrelation between exposure to ionizing radiation in high doses and thyroid cancer has been the result of a series of studies in children who had received X -ray treatment, for a series of benign conditions such as enlarged tonsils, Hemangioma, skin disorders, and painful osteoarthritis and spondylosis of the cervical spine. Similar evidence of Japanese survivors of the US atomic bombs of 1945 and the accident of the Chernobyl nuclear power plant in 1986. 

To avoid the irradiation of the thyroid gland, the use of a thyroid shield or a lead apron has been proposed. The hand thyroid shield is a practical and easily accessible form to protect the gland on an intraoral radiography while periapical images are executed in the upper arch and during bite exhibitions.  Lead aprons absorb 90-95% of dispersed radiation. If the X -ray current is 100 kVP a lead mandil must have at least 0.25 mm thick. A greater thickness, from 0.5 to 1 mm, is clearly better, although at the expense of greater weight than the equipment, which can constitute an important impediment if it is carried out for a long time. The thyroid protector must have at least 0.5 mm thick. The use of plumb gloves is recommended, with a layer of at least 0.25 mm, when the specialist’s hands are in the direction of the lightning, although their hands should still be out of the field. You have to wear glasses with transparent crystals but that contain a plumb protection equivalent to 0.35 mm, since they can significantly attenuate disseminated radiation that affects eye lenses and reduce the accumulation of radiation.

The collimation of the primary beam must correspond to the size of the receiver, and therefore rectangular collimation must be used. This has been demonstrated to reduce patient exposure by at least 50% compared to a standard 7 cm collular collide collimator. However, the use of rectangular collimators in dental practice is very rare. 

The intraoral exposure beam is collimated and probably the thyroid gland is partially irradiated during intraoral exhibitions. When placing dose meters in the spectrum in the thyroid area, it is possible that this twoimeter is just inside the primary beam, but much of the thyroid does not. This results in overestimation of thyroid dose. Inversely, if the meter is just outside the primary beam, while the thyroid receives a considerable dose. 

The use of a solid state detector that provides the average dose during the exhibition The thyroid. 

When cancer has already been developed, a systematized treatment is performed, which begins with surgical intervention and then the patient is kept in iodine with iodine 131, which aims to eliminate any microscopic deposit of thyroid carcinoma and normal thyroid tissue. 

Conclusions

1. The thyroid gland due to its location is considered extremely susceptible to ionizing radiation, becoming, as well as one of the main causes of thyroid cancer.
2. The risk of thyroid cancer from exposure to radiation depends largely on age. This risk is higher in children and pregnant women. Dentists, their assistants and people who work with radiation are also part of this vulnerable group.
3. The ideal measures to reduce as much as possible the irradiation that the thyroid gland may suffer are the use of a thyroid shield or a lead apron.

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