RADIATION SAFETY AND PROTECTION

One characteristic of x-radiation is its ability to impart some of its energy to the matter it traverses. If that matter is living tissue, then some biologic injury may occur. Much information about high levels of radiation and subsequent damage is available. The effects of low levels of x-radiation (as used in diagnostic radiology) on biologic systems are virtually unknown. Our assumptions of damage are based on extrapolation of data from high levels to lower levels of radiation.

Still, dental health professionals must be concerned about any risk that the patient may encounter during therapy. Concern is focused on three primary biologic effects of low-level radiation: (1) carcinogenesis, (2) teratogenesis (malformations), and (3) mutagenesis. Carcinogenesis and malformations are a response of somatic tissues and in most instances are believed to have a threshold response; that is, a certain amount of radiation is necessary before the response is seen. Mutation may occur as a response of genetic tissue (gonads) to x-radiation and is believed to have no threshold. In general, younger tissues and organs are more sensitive to radiation, with the sensitivity decreasing from the period before birth until maturity. It must also be recognized that far higher doses of radiation can be withstood by localized areas than by the whole body. We know that we live in a world that exposes us to natural background radiation averaging 360 mrem per year (3.60 millisievert) in the United States. Medical and dental radiographic examinations add to that exposure and so must be ordered judiciously.

With regard to patient protection, evidence has shown that there are critical organs vulnerable to possible development of late effects. These organs should be shielded when possible. These critical organs and the associated adverse biologic effects are the following: (1) the skin (cancer), (2) red bone marrow (leukemia), (3) the gonads (mutation, infertility, and fetal malformations), (4) the eyes (cataracts), (5) the thyroid (cancer), (6) the breasts (cancer), and (7) possibly the salivary glands (cancer).

The practitioner and staff can physically protect the patient and indirectly protect themselves from unnecessary exposure to radiation by using correct technique. The most obvious method of protecting the patient is to shield those areas not being evaluated. This is easily accomplished using a lead apron and thyroid collar (Fig. 5-1).

Figure 5-1 Lead apron and thyroid collar in place.

The apron and collar may be incorporated as a single unit or used separately. The apron protects the gonads and chest from the primary beam and scatter radiation whereas the collar shields the thyroid. This method does not provide complete protection, particularly of the thyroid, but it does provide a great reduction in exposure. Aprons used in panoramic radiography have a front and back because the source of radiation is from the side and the rear of the patient.

Faster film speeds have contributed most significantly to the reduction in radiation to the patient. Film speeds of the D and F groups are available for intraoral radiography. Faster film also reduces error from patient movement, a consideration with the pediatric patient. Extraoral (panoramic) radiography uses film-screen combinations that also have reduced exposure times. Recently, there has been an increased use of beam-positioning devices (Fig. 5-2), which virtually eliminate some of the technical errors, particularly film cone cuts. Using different lengths and shapes of the cone (Fig. 5-3) has also aided in the reduction of patient radiation exposure. Use of a long rectangular collimator reduces the area unnecessarily exposed to radiation by almost 4 square inches compared with a round collimator. The use of higher kilovolt peak techniques reduces patient exposure to radiation and lowers contrast, thus increasing the number of shades of gray on the film. An additional benefit of using high kilovolt peak technique is that the exposure time is shortened, which potentially reduces retakes caused by patient movement.

Figure 5-2 Use of the Rinn XCP positioning device.

Figure 5-3 Rectangular and round cones of various lengths.

Finally, quality control (and thus patient protection) begins with proper processing. With the shift toward using digital radiography, this concern becomes reduced. However, the majority of dental practices still use traditional film and wet tank chemical processing. If the processing does not function at an optimal level, retakes will be required, necessitating additional patient exposure. The dentist must insist on time-temperature developing and the use of proper-strength chemicals if wet tanks are used. The processing area should be clean and free of white light (light leaks). If automatic processing is used, chemical parameters must be continuously monitored and the unit must be cleaned weekly.

SELECTION CRITERIA AND RADIOGRAPHIC EXAMINATIONS

The decision to make radiographs is based on a thorough evaluation and examination of the patient. Radiographs should be made only when there is an expectation that disease is present or when an undetected condition left untreated could adversely affect the patient’s dental health. Therefore the decision to use ionizing radiation is based on professional judgment (Table 5-1).

Table 5-1 Guideline for Prescribing Dental Radiographs

The recommendations contained in this table were developed by an expert dental panel comprised of representatives from the Academy of General Dentistry, American Academy of Dental Radiology, American Academy of Oral Medicine, American Academy of Pediatric Dentistry, American Academy of Periodontology, and American Dental Association under the sponsorship of the Food and Drug Administration (FDA).

* Clinical situations for which radiographs may be indicated include the following:

† Patients at high risk for caries may demonstrate any of the following:

Courtesy Carestream Health, Inc.

Selection criteria are clinical signs or symptoms that allow the practitioner to identify patients who will benefit from a radiographic examination. Two important considerations when deciding whether to perform a radiographic examination for children are (1) the stage of dentition development and (2) the risk of dental caries.

The criteria for making radiographs, developed in part by the Conference on Radiation Exposure in Pediatric Dentistry, were summarized by Nowak and colleagues¹ as follows.