Radiation Safety & Protection

Supervised by Dr. Alaa Mahmoud

Done by

Dr. Mohammed Sa’ad & Dr. Marwan N. Natah

Acknowledgments

The chief of Al Sha’ab specialized center Dr. Hassan A. Hassan

The head of X-Ray’s department Dr. Alaa Mahmoud

All my fellows dentists

Subjects Index

Introduction

Digital Radiography in Dentistry

Sources of Radiation Exposure

Dose Limit

Safety Part

References

Goal of this seminar

Introduction

Dentists must be prepared to intelligently discuss with patients the benefits and possible hazards involved with the use of x rays and to describe the steps taken to reduce the hazard. This seminar considers sources of exposure, estimates of risks from dental radiography, and means to minimize exposure from dental examinations.

Digital Radiography in Dentistry

Digital radiography was introduced in Dentistry in 1987. The technology has been gaining in acceptance, and in 2005 more than 22% of dentists were using digital radiography.

Sources of Radiation Exposure

Dose Limit Dose limits from man-made sources for members of the

general public, not occupationally exposed, have been established at 10% of that of occupationally exposed individuals. The negligible individual dose, established by the NCRP, is considered to be the dose below which any effort to reduce the radiation exposure may not be cost-effective. In spite of the NCRP ’ s endorsement of the no threshold hypothesis for purposes of radiation safety, it is thought that the impact on society of radiation exposure of this magnitude is negligible. Dentists and their staff are occupationally exposed workers and are allowed to receive up to 50 mSv of whole-body radiation exposure per year. Although this is considered to present only a minimal risk, every effort should be made to keep the dose to all individuals as low as practical.

RISK ESTIMATES

Reducing Dental Exposure

the first is the principle of justification. In making dental radiographs this principle obligates the dentist to do more good than harm.

The second guiding rule is the principle of optimization. This principle holds that dentists should use every means to reduce unnecessary exposure to their patient and themselves.

The third principle is that of dose limitation. Dose limits are used for occupational and public exposures to ensure that no individuals are exposed to unacceptably high doses.

Safety Part

Operator Location

The operator of the dental unit must stand at least six feet from the useful beam or behind a protective barrier. [Stand at an angle of from 90 to 135 degrees from the central ray. Do NOT stand in the path of the primary x-ray beam.]

If a protective barrier is used, it must have a viewing window to allow the operator to see the patient.

Personnel Radiation Badges

The individuals who operate only dental radiographic systems are exempt from the radiation badge requirements

X-ray Tube Housing

The tube housing must not drift from its set position during an exposure. The tube housing must not be hand-held during an exposure by the operator or the patient due to leakage radiation through the tube housing. If you note problems with the tube housing, immediately report this to your supervisor so that any instability of the suspension arm can be corrected.

Film and Digital Imaging

Currently, intraoral dental x-ray film is available in three speed groups: D, E, and F . Clinically, fi lm of speed group E is almost twice as fast (sensitive) as film of group D and about 50 times as fast as regular dental x-ray film ( Fig. 3-3 ). The current F-speed films require about 75% the exposure of E-speed film and only about 40% that of D-speed. Faster films are desirable from the standpoint of exposure reduction. Multiple studies have found that F-speed film has the same useful density range, latitude, contrast, and image quality as D- and E-speed films and can be used in routine intraoral radiographic examinations without sacrifice of diagnostic information.

Current digital sensors offer equal or greater dose savings than F speed film and comparable diagnostic utility.

Required Distances

Source-to-Skin Distance

Use of long source-to-skin distances of 40 cm, rather than short distances of 20 cm, decreases exposure by 10 to 25 percent. Distances between 20 cm and 40 cm are appropriate, but the longer distances are optimal. (ADA, 2006)

Intensifying Screens and Film or Digital Imaging

Contemporary intensifying screens used in extraoral radiography use the rare earth elements gadolinium and lanthanum . These rare earth phosphors emit green light on interaction with x rays. Compared with the older calcium tungstate screens, rare earth screens decrease patient exposure by as much as 55% in panoramic and cephalometric radiography. Unlike digital intraoral imaging, there is no significant dose reduction to be gained by replacing extraoral screen-fi lm systems with digital imaging. Image resolution with digital systems is comparable to that obtained with rare earth screens matched with appropriate film.

Lead aprons and shields

Collimators

Collimators limit the size and shape of the useful beam which reaches the patient. Rectangular collimators are recommended for periapical radiographs as their use significantly reduces the area of the patient’s body that is exposed to radiation.

Cones

The ADA discourages the use of short, closed, pointed cones because of the increased scatter radiation close to the face and adjacent areas of the patient’s body.

Rectangular Collimation

Since a rectangular collimator decreases the radiation dose by up to fivefold as compared with a circular one, radiographic equipment should provide rectangular collimation for exposure of periapical and bitewing radiographs. (ADA, 2006).

System Speed

Faster image receptor systems result in decreased radiation exposure to the patient.

Film and Sensor Holders

Film holders that align the fi lm precisely with the collimated beam are recommended for periapical and bitewing radiographs. (ADA, 2006) Film or digital sensor holders should be used when intraoral radiographs are made because they improve the alignment of the fi lm, or digital sensor, with teeth and x-ray machine. Their use results in a significant reduction in unacceptable images.

Kilovoltage

The operating potential of dental X-ray machines must range between 50 and 100 kilovolt peak but should range between 60 and 80 kVp. (ADA, 2006)

Film Processing

Radiographs should not be overexposed and then underdeveloped, because this practice results in greater exposure to the patient and dental health care worker and can produce images of poor diagnostic quality. Dental radiographs should not be processed by sight, and manufacturers ’ instructions regarding time, temperature and chemistry should be followed. (ADA, 2006) A major cause of unnecessary patient exposure is the deliberate overexposure of films compensated by underdevelopment of the fi lm. This procedure results in both needless exposure of the patient and in films that are of inferior diagnostic quality (because of incomplete development). The use of machines to process dental x-ray fi lm has become widespread. More than 90% of dentists surveyed have reported using dental fi lm processors. Automatic fi lm processors should be used in a darkroom.

References

American Dental Association Council on Scientifi c Affairs : The use of dental radiographs: update and recommendations , J Am Dent Assoc 137 : 1304 - 1312 , 2006 .

2 Code of Federal Regulations 21, Subchapter J: Radiological health, part 1000, Offi ce of the Federal Register, General Services Administration, Washington, DC, 1994.

Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiations : Health risks from exposure to low levels of ionizing radiation: BEIR VII , Washington, DC , 2006 , National Academy Press . 4 Hall EJ , Giaccia AJ : Radiobiology for the radiologist , ed 6 , Baltimore , 2006 , Lippincott Williams & Wilkins .

5 Horner K , Rushton VE , Walker A et al : European guidelines on radiation protection in dental radiology: the safe use of radiographs in dental practice , Radiat Protect 136 : 1 - 115 , 2004 .

6 National Council on Radiation Protection and Measurements : Control of radon in houses , NCRP Report 103, Bethesda, Md , 1989 , National Council on Radiation Protection and Measurements . N 7 ational Council on Radiation Protection and Measurements : Q uality assurance for diagnostic imaging , NCRP Report 99, Bethesda, Md , 1990 , National Council on Radiation Protection and Measurements . N 8 ational Council on Radiation Protection and Measurements : L imitation of exposure to ionizing radiation , NCRP Report 116, Bethesda, Md , 1993 , National Council on Radiation Protection and Measurements

N 9 ational Council on Radiation Protection and Measurements : D ental x-ray protection , NCRP Report 145, Bethesda, Md , 2003 , National Council on Radiation Protection and Measurements . N 0 1 ationwide Evaluation of X-Ray Trends (NEXT), tabulation and graphical summary of the 1999 dental radiography survey , CRCPD Publication E-03-6, Bethesda, Md , 2003 , Center for Devices and Radiological Health, U.S. Food and Drug Administration . P1reston RJ : Radiation biology: concepts for radiation protection , H ealth Phys 88 : 545 - 556 , 2005 . 12 Sources and effects of ionizing radiation , volume 1 : sources, New York , 2000 , UNSCEAR, UN Publication . 13 Wall BF , Kendall GM , Edwards AA et al : What are the risks from medical X-rays and other low dose radiation? Br J Radiol 79 : 285 - 294 , 2006 .

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