thyroid cancer (Dentistry Today, 2019; Hwang, et al., 2020). The public, including the patients who dental professionals treat in their practices, becomes more alarmed with each successive report. Without question, x-radiation is harmful; it is a known carcinogen. There is considerable evidence in the literature that ionizing radiation increases the risk of certain types of cancers, including leukemia and skin, lung, and thyroid cancers, to name a few (American Cancer Society, n.d.). However, what is not known with certainty is the effect that low-dose diagnostic imaging exposures have on the human body. Although the risk of cancer from dental radiographic examinations is thought to be negligible, no radiation exposure is considered to be risk-free, and the effects of radiation are cumulative. For these reasons, radiation safety remains a top concern for the general
public, and the dental professional needs to stay up to date on the latest research and current thinking on radiation safety and protection. The purpose of this course is to review the biologic effects of radiation, the methods used in radiation measurement, and the potential sources of radiation exposure. This basic-level course will discuss radiation safety and protection measures for both patients and dental healthcare workers. Perhaps most important, this course will prepare all dental professionals – including dentists, dental hygienists, and dental assistants – to accurately respond to patient questions and concerns about radiation safety in dentistry.
HISTORICAL BACKGROUND
The discovery of x-rays, a singular event in history, occurred by accident. On November 8, 1895, while experimenting with a Crookes tube in his darkened physics laboratory in Germany, Wilhelm Conrad Roentgen noticed that a plate coated with a fluorescent material on a nearby bench was glowing. Soon he realized that he had uncovered something altogether new, an “ x ” or “ unknown ” light or ray. Roentgen thoroughly investigated this new energy form and described many of the properties of the x-ray. He presented his findings to the scientific community, and in early 1896, he produced and published the first radiograph, showing his wife’s hand with a metal ring on one of the fingers (Barton, 2019). This discovery began a revolution in medical and dental diagnostics. Several months after Roentgen’s discovery, x-ray researchers, physicians, dentists, and patients began to experience skin effects, hair loss, and anemia. In 1902, the first case of radiation- induced skin cancer was reported (Passmore, 2016). In 1904, Clarence Dally a scientist who had extensive work with x-rays died from skin cancer and was the first known x-ray fatality. It was not until the 1950’s that the risks and potential harm from x-rays was understood (Barton, 2019). The harmful effects of radiation were poorly understood at the time, and many early pioneers suffered ill effects from overexposure to radiation. The years since then have seen significant improvements in equipment, imaging techniques, dose reduction, and radiation safety and protection measures.
Many agencies exist to regulate ionizing radiation and minimize the exposure of patients and operators during radiographic examinations. For example, the National Council on Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP) have established guidelines to limit the amount of radiation received by both occupationally exposed persons and the general public. The ICRP provides recommendations and guidance to the public on all aspects of protection from ionizing radiation. In addition to the NCRP and ICRP, many organizations make recommendations and policies to govern the use of ionizing radiation. For example, the International Commission on Radiation Units and Measurements makes recommendations on radiological units of measurement. The NCRP develops concepts about radiation protection and dose limits (DLs). The Occupational Safety and Health Administration (OSHA) is responsible for occupational radiation protection policies. In addition, each state has statutes that regulate radiographic equipment, equipment inspection, and the credentialing of persons who work with radiation. The benefits of using ionizing radiation in medicine and dentistry for the diagnosis and treatment of disease and injury cannot be overstated. However, diagnostic imaging is the largest source of human-made ionizing radiation exposure. Although dental diagnostic imaging constitutes less than 1% of the exposure, dental professionals have an ongoing ethical responsibility to keep patients’ exposure to radiation as low as possible (Benn and Vig, 2021).
BIOLOGIC EFFECTS OF RADIATION
The use of x-radiation for diagnostic imaging is essential for proper patient diagnosis and treatment. Dental radiographic examinations are fundamental to the daily practice of dentistry. However, x-rays are a highly energetic form of electromagnetic radiation that, like gamma rays and ultraviolet light, are capable of damaging human tissue. It is therefore important that dental professionals bear in mind what actually takes place when they expose patients to x-radiation. Each time a radiograph is exposed, x-ray photons exit the tubehead, penetrate the patient’s tissues, and expose the image receptor. However, not all x-ray photons reach the receptor;
some pass through, and some are absorbed by the patient’s tissues, while others are deflected from their path and scattered in various directions. Ionizing radiation such as that produced from dental x-rays can cause changes to any component of a cellular membrane or the DNA of which composes the cell’s chromosomes, and which directs the cellular function (RadTechonDuty, 2018). The consequences of the absorption of x-ray energy by human tissue are referred to as the biologic effects of radiation. Radiation biology is the study of these effects on living systems.
MECHANISMS OF RADIATION INJURY
The human body at its most basic level is composed of atoms. Ionizing radiation can produce injury through interactions at the atomic level when x-ray photons remove or excite orbital electrons and deposit energy within the tissue. When an x-ray photon dislodges an orbital electron, the normal equilibrium, or ground state, of the atom is disrupted and ion pairs are formed. The ionized atom becomes positively charged ( +ion ) and the ejected electron carries a negative charge ( –ion ).
To regain equilibrium, ions either recombine or combine with other atoms or molecules to return to neutral status. With excitation, a low-energy x-ray photon interacts with an outer-shell orbital electron. The energy of the photon is transferred to the electron, causing it to become excited but not ejected. When the x-ray photon ceases to exist, the excited electron releases a secondary photon of equivalent energy, and the atom returns to the ground state. The secondary photon is ejected and may produce ionization at another site.
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