Radiation Safety

Diagnostic

Intra-Oral Radiographs

• Peri-apical
• Bitewing
• Occlusal

Extra-Oral Radiographs

• Lateral Oblique
• Panoramic
• P A Mandible
• Sub-Mento Vertex
• Sub-Mento Vertex
• Waters view
• T M J Projections; etc.

Administrative

Means that the exposed individual receives no benefits from the exposure.

Medico-Legal

Medico-legal X-rays may be taken for reasons other than diagnosis like Insurance, civil litigation, weapons or drug search, immigration and emigration, prisoners, pre employment etc

Industry

X-rays are used for non destructive testing and have a wide range of application in industries. They are used to detect crack in metal structures - the body of aeroplanes and automobiles, the quality of welding in moulds and metal castings, the presence of pearls in oysters etc

Research

X-rays are used to study the structure of crystals, which is called X-rays crystallography. Also used in pharmaceuticals, lasers etc.

The referring dental surgeon should provide a clear request describing the patient’s problem and indicating the clinical objectives, so that the radiologist can carry out the correct X-ray examination.

Before prescribing an X-ray examination the referring dental surgeon should be satisfied that the necessary information is not available, either from radiographic examinations already done, or from any other medical tests or investigations.

If two or more dental imaging procedures are available and give the desired diagnostic information, then the procedure that presents the least overall risk to the patient should be chosen.

Receiving 50 mSv of whole body radiation exposure in 1 year as a result of performing one’s occupation is considered to present minimal risk. However every effort should be made to keep the dose to all individuals as low as possible. All unnecessary radiation exposure should be avoided. This is a philosophy of radiation protection everyone should recognize. It is based on the ALARA principle (As Low As Reasonably Achievable), which recognizes the possibility that no matter how small the dose, some adverse health effect may occur.

Radiation Dose From Diagnostic Radiology

Principal sources of radiation dose for members of the public are natural background radiation and the medical / dental applications of radiation.

Absorbed Dose In The Body Tissues

Absorbed dose in body tissues are used to indicate the risk to specific tissues. The total risk from any particular X-ray examination should ideally comprise the risk from all the radiation sensitive tissues that are irradiated.

The biological effect of ionizing radiation can be extremely damaging. The effects are classified as: -

• Somatic Non – Stochastic (certainty) effects.
• Somatic Stochastic effects
• Genetic Stochastic effects

Somatic Non–Stochastic effects are predominant at high doses of radiation, while Somatic Stochastic and Genetic Stochastic effects predominate even with low doses. The ALARA principle should be followed.

Risk Of Neoplasia And Hereditary Effects

Because of radiation risk to an embryo, the possibility of a woman being pregnant has to be considered in deciding whether to conduct an examination that might cause irradiation to the lower abdomen.

During the first 10 days following the onset of menstrual period, there is minimum radiation risk since no conception will have occurred. The radiation risks to a child who had been irradiated in-utero during the remainder of the first month following the onset of menstruation (i.e. during approx. the first two weeks after conception is likely to be so small that there need be no special limitation on X-ray examinations).

Period of 18-55 days after conception is critical to organ formation. Use of lead aprons is mandatory on such patients.

X-rays cause biologic changes in living cells and adversely affects all living tissues. With the use of proper patient protection techniques, the amount of X-rays received by the patient can be minimised. Patient protection techniques can be used prior to, during, and after X-ray exposure.

• Prior To Exposure

  Patient protection measures can be employed prior to any X-ray exposure by:

  1. Appropriate prescribing of dental radiographs
  2. Proper equipment

     The dental X-ray tube head must be equipped with appropriate aluminum filters, lead collimator and position-indicating device.

  3. Size Of X-Ray Field
     • Smallest practicable X-ray field
     • Accurate positioning
     i. Total radiation energy delivered to patient is reduced
     • Reduction of scattered radiation
     i. This improves imaging quality.
     • Use of beam limiting devices (collimation)
  4. Collimation

     A collimator may have either a round or rectangular opening. When using a circular collimator, diameter of the X-ray beam of no more than 2.75 inches should be present as it exits from the position-indicating device and reaches the skin of the patient.

  5. Distance From The Focal Spot To The Skin Or Image Receptor

     There are two techniques for taking radiographs depending on the focal spot to film distance

     • Short cone technique (8” distance)
     • Long cone technique (16” distance)

     Longer focal spot to image receptor distances have clinical advantages. Therefore long cone is preferable.

  6. Position-Indicating Device: There are three basic types of PIDs
     • Conical
     • Rectangular
     • Round

     The open-ended, lead-lined rectangular or round PIDs that do not produce scatter radiation are used. The long PID is preferred because less divergence of the X-ray beam occurs.

  7. Total Filtration In The X-Ray Beam

     For dental equipment with X-ray tube voltages not exceeding 70 kVp the total permanent filtration in the X-ray beam should be equivalent to not less than 1.5 mm of aluminum. At higher X-ray tube voltages the total filtration should be equivalent to not less than 2.5 mm of aluminum of which 1.5 mm should be permanent.

• During Exposure

  Patient protection measures are used not only prior to X-ray exposure but also during exposure.

  1. Control Of Irradiation & Recording Of Time
     • Operating switches should be constructed such that irradiation can be terminated manually at any time.
     • Also, the spring loaded type “Deadman” switches should be cautiously used to avoid accidental exposure
  2. Thyroid Collar

     Radiation dose to the thyroid is considered the largest component of the effective dose in dental radiography.

  3. Lead Apron

     Although scatter radiation to the patient's abdomen is extremely low, lead aprons should be used to minimize patient's exposure to radiation.

  4. Fast Film

     The use of faster films (E- or F-speed) is preferred because they reduce the radiation dose by more than 50 percent compared with D-speed film.

  5. Film-Holding Devices

     Receptor / Film holders that position the receptor to coincide with the collimated X-ray beam should be used.

  6. Exposure Factor Selection

     The dental radiologist cannot control all the exposure factors as the kilovoltage peak (kVp), milliamperage are preset by the manufacturer, but the time settings on the control panel can be adjusted as per the requirement. A setting of 65 to 70 kVp and 7 mA to 10 mA is the range available in dental intra oral machines.

  7. Intensifying Screens & Films

     Screens containing high efficiency materials require less radiation than conventional ones to provide similar image quality. The materials used are rare earths, samarium, barium, tantalum, terbium, etc.

  8. Proper Technique

     Proper technique helps to ensure the diagnostic quality of films and reduce the amount of exposure a patient receives and avoids the need to retake radiographs.

  9. Control Of Scattered Irradiation To The Image Receptor
     • The use of grids should be moderated. Stationary and moving grids are used in practice.
     • The grid ratio should be 10:1.

• After Exposure
  1. Proper Film Handling

     From the time the films are exposed until they are processed, careful handling is of the utmost importance. Artifacts due to improper film handling result in non-diagnostic films.

  2. Proper Film Processing

     Correct processing techniques are necessary to give reproducible radiographs of optimum diagnostic value with minimum dose to the patient. Film processing should be performed under the manufacturer recommended conditions with proper processing equipment and a darkroom with safe-lights. Alternatively, an automatic processor with an appropriate safe light hood may be used.

  3. Darkroom practices

     Proper radiological darkroom practices should be followed. These include maintaining a darkroom with adequate ventilation, avoiding repeated skin contact with processing chemicals and avoiding microbial contamination in handling film packets. Darkrooms should be checked routinely for light leaks.

  4. Proper Reading And Interpretation Of The Resultant Radiograph

     Radiographic images should be viewed with an illuminated viewer to obtain maximum available information.

  5. Quality Assurance

     All radiographic images captured by using radiographic facilities should establish quality assurance programmes whose structure and scope are determined by the needs and complexity of each facility.

  6. Personal Facility Monitoring Devices

     TLD badges, electronic dosimeter.

Regulatory Controls

• Apply universal precautions.
• Wear gloves during all radiographic procedures.
• Disinfect and cover X-ray machine, working surfaces, chair and apron.
• Sterilize non–disposable instruments.
• Use barrier protected film (sensor) or disposable container.
• Prevent contamination of processing equipment.

Film Speed

Film speed is controlled largely by the size of the silver halide grains and their silver content. The silver halide grains are composed mainly of crystals of silver bromide. Iodide is added to Ultra speed films because of its large diameter (compared to bromide). It disrupts the regularity of the silver bromide crystal structure, thereby increasing its sensitivity to X–rays.

The photosensitivity of the silver halide crystals also depends on the presence of trace amounts of a sulphur containing compound. In addition trace amounts of gold are sometimes added to silver halide crystals to improve their sensitivity.

Radiographic Speed

It refers to the amount of radiation required to produce an image of standard density. Film speed frequently is expressed as the reciprocal of the exposure (in roentgens) required to produce an optical density of 1 above gross fog. A fast film requires a relatively low exposure to produce a density of 1, whereas a slower film requires a longer exposure for the processed film to have the same density.

The speed of the dental intra-oral X–ray film is indicated by a letter designating a particular group. The fastest film available has a rating of ‘F’.

Intensifying Screens

The presence of intensifying screens creates an image receptor system that is 10 to 60 times more sensitive to X–ray than the film alone. The use of intensifying screens means a substantial reduction in the dose of radiation to which the patient is exposed. They are used with films in virtually all extra-oral radiography.

Processing Of X-ray Films

Dark room equipment

The darkroom should be lightproof and well ventilated. There should be optimal conditions for developing fixing and washing of radiographs.

Safe-lighting

A low intensity illumination of relatively long wavelength (red) that does not rapidly affect open film but allows adequate workability. To minimize the fogging effect of prolonged exposure, the safe light should have a 15 watt bulb and should be mounted at least 4 feet above the surface. The red GBX-2 filter is recommended as a safe light in dark rooms.

Manual processing tanks

The tank must have hot and cold running water and a means of maintaining the temperature between 60 and 75 F. The developer is placed on the left side and the fixer is placed on the right. The master tank should have a cover to reduce oxidation of the processing solutions, to protect the developing film from accidental exposure to light and minimize evaporation of the processing solutions. The following time and temperature combinations have been suggested for optimal developing of X-ray films:

The radiographer must be able to educate patients about the importance of dental radiographs. The dental radiographer must also be prepared to answer common questions asked by patients about the need for dental radiographs, X-ray exposure, the safety of dental X-rays and other miscellaneous concerns.

The dentist must be aware of the legal implications involved in taking dental radiographs. Furthermore, because exposing dental radiographs has implications for patient care, including the diagnosis of dental disease and treatment planning, the possibility of negligent care exists when dental radiographs are not properly exposed or used.

Licensure Requirements

The licensed dentist is not required to obtain additional certification to expose dental radiographs legally.

Informed Consent

Persons seeking health care services, including dental care, have the right to self-determination; they have the legal right to make choices about the care they receive, including the opportunity to consent to or to refuse treatment. Therefore, prior to receiving treatment, the dental patient should be informed of the various aspects of the proposed treatment, including such diagnostic procedures as the exposure of dental radiographs.

Patient Records

A dental record must be established for every patient and dental radiographs are an integral part of such a record.

Documentation

It is very important that the dental record include documentation of the exposure of dental radiographs. The dental record must include documentation of the following:

• Informed consent.
• The number and type of radiographs exposed.
• The rationale for exposing such radiographs.
• The diagnostic information obtained from the interpretation of the radiographs.

Confidentiality

All the information contained in the dental record, including dental radiographs, is confidential or private.

Ownership And Retention Of Dental Radiographs

Legally, dental radiographs are the property of the dentist. The dentist owns the dental radiographs even though the radiographs were paid for by the patient. Patients do, however, have a right to reasonable access to their records. When a patient transfers to another dentist, he or she can request in writing that his or her dental records be forwarded to that dentist. The original radiographs should not be forwarded; duplicates should be made and forwarded instead. The patient's written request should be placed in the dental record as evidence of the patient's directive. Dental records and dental radiographs should be retained indefinitely.

Patients Who Refuse Dental Radiographs

Patients may refuse dental radiographs. When this occurs, the dentist must carefully consider the situation. The dentist must then decide whether an accurate diagnosis can be made and treatment can be provided. In most cases, patient refusal of dental radiographs compromises the patient's diagnosis and treatment. In such cases, the dentist cannot treat the patient.

• Digital Radiography

  Digital imaging has revolutionized the field of radio diagnosis. This aims at greater image enhancement, feature extraction and lesser dose of radiation to patients and operators and larger gray scale contrast. The chemical processing is eliminated so there are lesser chances of errors and repeat radiographs.

• Orthopantomography (OPG)

  An Orthopantomogram (OPG), also known as an "orthopantogram" or "panorex", is a panoramic scanning dental X-ray of the upper and lower jaw. It shows a two-dimensional view of a half-circle from ear to ear. It is commonly used to determine the status of wisdom teeth.

• Computed Tomography

  Computed tomography (CT) is a medical imaging method employing tomography. Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. Although it is still quite expensive, it is the gold standard in the diagnosis of a large number of different disease entities. It is also used for preventive medicine or screening for disease.

• Magnetic Resonance Imaging

  Magnetic resonance imaging (MRI), noninvasive diagnostic technique that uses nuclear magnetic resonance to produce cross-sectional images of organs and other internal body structures. MRI is used in the diagnosis of brain tumors and disorders, spinal disorders, multiple sclerosis and cardiovascular disease as it is unhampered by bone and capable of producing images in a variety of planes. The procedure is considered to be without risk, but the scanner may interfere with pacemakers, hearing aids or other mechanical devices.

• Ultrasonography

  Use of ultrasonic waves to produce images of body structures. The waves travel through tissues and are reflected back where density differs (e.g. the border between a hollow organ's wall and its inside). The reflected echoes are received by an electronic apparatus that measures their intensity level and the position of the tissue reflecting them. The results can be displayed as still images or as a moving picture of the inside of the body. Unlike X-rays or other ionizing radiation, ultrasound carries minimal risk.

• Nuclear Medicine Scans

  Nuclear scanning uses radioactive substances to see structures and functions inside your body. Nuclear scans involve a special camera that detects energy coming from the radioactive substance, called a tracer. Before the test, the patient receives the tracer, often by an injection. Although tracers are radioactive, the dosage is small. During most nuclear scanning tests, the patient lies still on a scanning table while the camera takes images. Most scans take 20 to 45 minutes.

Practitioners should stay informed of new information on radiation safety issues, as well as developments in equipment, materials and techniques. Dentists and dental auxiliaries should participate in continuing education in the many aspects of diagnostic radiology and technology.

Prior to the introduction of International System of Units (abbreviated as SI units) quantities for radiation measurements were expressed in special units such as roentgen for radiation exposure and RAD for absorbed dose. Further, the unit REM was exclusively used for radiation protection dosimetry. The following table provides the conversion factors for SI / Special Units including their multiples and submultiples used for routine radiation measurements in X-ray installations.

Certain measurements, which were performed in exposure quantity and expressed in its special unit the roentgen, have now been replaced by air kerma measurements in free air. An exposure of 1 roentgen is equivalent to an air kerma of 8.7 milligray (mGy). An air kerma of 10 microgray per hour (Gyh-1) corresponds to an exposure rate of 1.15 milliroentgen per hour (mR/hr).

S.I. Prefixes

Mirco () = 10-6 Mega (M) = 106

Milli (m) = 10-3 Giga (G) = 109

Centi (c) = 10-2 Tera (T) = 1012

Adequate Protection means protection against radiation to keep levels of radiation, As Low As Reasonably Achievable (ALARA Principle) and in no case exceed the prescribed operational limits.

Dose means energy absorbed in matter from ionizing radiation per unit mass of the matter. The SI unit of dose is Gray (Gy). Special unit of dose is rad. 1 rad = 1 cGy

Dose Equivalent means the quantity obtained on multiplying the absorbed dose in tissue by appropriate weighting factors to correct and normalize for variation in the degree of biological effect produced by the same dose of different ionizing radiations or under different irradiation conditions. The unit is Sievert (Sv) : 1 Sv = 100 rem

Operational Limits means limits on levels of radiation as the competent authority may specify by notification from time to time.

Quality Assurance Tests means tests performed to ensure the performance and reliability of X-rays equipment as per the design specifications.

Protective Barrier or Shielding means a barrier of radiation attenuating material used to reduce radiation levels.