RADIATION SAFETY AND PROTECTION

FOR DENTAL RADIOGRAPHY

PREPARED BYDR. NITIN SHARMA

Postgraduate StudentDept. Of Oral Medicine & Radiology

Introduction

Licensed dentists play an important role in maintaining radiation exposures of patients and staff as low as reasonably achievable (ALARA). Greater numbers of intra-oral radiographs are being requested and a wide range of other dental radiographic examinations (panoramic, cephalometric) are being performed on a routine basis with the addition of advanced imaging modalities (CBCT). Individuals who operate dental X-ray equipment must have a basic knowledge of the inherent health risks associated with radiation and must have demonstrated familiarity with basic rules of radiation safety.

Responsibilities of Licensed Dentist and X-ray Machine Registrant

1. Registration of Dental Radiographic Equipment

All institutes who are possessing diagnostic x-ray equipments are required to obtain Licence for operation from AERB (Atomic Energy Regulatory Board).

To facilitate issuance of licence, AERB has launched an e-governance application e-LORA(e-Licensing of Radiation Applications).

2. Radiation Protection – General Requirements

Take all precautions necessary to provide reasonably adequate protection to the health and safety of individuals.

Provide radiation safety rules to dental personnel

Individuals who requires use of X-rays should be provided individual or personnel monitoring devices.

Assure that dental personnel do not stand in the path of the useful beam.

Dental personnel must not expose any individual to the useful beam for training or demonstration purposes

In areas or rooms where X-ray equipment is used, post a sign (that may include the radiation symbol) stating: CAUTION X-RAYS

Dental X-ray equipment and imaging software should be operated only by individuals adequately instructed in safe operating procedures Maximum permissible dose equivalent (MPD)

• Whole body (total effective dose equivalent) – 5 rem or 0.05Sv• Skin and extremities (shallow-dose equivalent) – 50 rem or 0.5 Sv• Lens of the eye (eye dose equivalent) – 15 rem or 0.15 Sv

Dental Radiographic Machine Requirements

A. X-ray Tube Housing :“DIAGNOSTIC TYPE TUBE HOUSING”

Leakage radiation does not exceed 100 mrems, or 1mSv, in any one hour at a distance of 1 meter (39.37 inches)

B. Collimating Device

C. X-ray Beam Filtration

Only the X-rays with higher energies can penetrate the tissue of the patient’s face and react with the image receptor area. Low-energy X-rays that have no effect on image production and are absorbed by the tissues, can cause tissue damage.

The regulations specify the minimum total filtration as shown below:

Tube Operating Minimum Total Potential (kV) Filteration

Below 50 0.5

50 to 70 1.5

71 and above 2.5

(“Aluminum-equivalent” is defined as a substance equivalent to aluminium in its ability to absorb preferentially less penetrating radiation.)

D. Exposure Cord

The exposure switch must be permanently fixed in a safe shielded location or must be long enough to permit the operator to make exposures while positioned at least six feet from the patient.

E. Exposure Timer“Dead-man” type exposure switch

F. X-ray Tube Head and Flexible Arm Assembly

The flexible extension arm allows the X-ray tube head to be adjusted to various positions required for dental radiography. The mechanical support of the X-ray tube head and cone shall maintain the exposure position without drift or vibration.

Patient Protection

All individuals unnecessary to the dental radiographic examination leave the X-ray room prior to making an exposure. Anyone who is in the X-ray room at the time of exposure must be behind a protective barrier or they can wear protective apron. The apron should be preferably 0.5 mm of lead or lead-equivalent but not less than 0.25 mm of lead or lead-equivalent thickness.

The reduction in exposure resulting from placing 0.25 mm lead-equivalent apron material in a primary X-ray beam of 100 kVp would only be 60% as compared to 0.50 mm lead-equivalent apron that will attenuate the beam by 85%.

Lead-impregnated leather or vinyl aprons must be used to cover the reproductive organs of all patients who undergo dental X-ray examinations.

Aprons should be evaluated periodically (at least yearly) for tears and cracks.

Aprons should be properly hung because creases eventually become cracks which allow radiation to penetrate.

A specially designed lead-impregnated thyroid collar can be used to protect the thyroid gland from excessive and/or unnecessary radiation during intraoral X-ray exposures.

Responsibilities of Dental Personnel Operating X-ray Equipment

A. Protect Patient from Unnecessary Radiation Exposure

Use appropriate protective devices, such as protective aprons and a protective lead collars.

Rectangular collimation of the X-ray beam is highly recommended.

B. Use Fast Image Receptors

Patient exposure may be reduced by more than 50 percent by changing to a faster film speed or to a digital image receptor.

Speed Ratings of Commonly Used Dental Films

Film Brand Speed Group

Kodak Ultra Speed D AGFA-Dentus, Flow DKodak Intraoral EAGFA-Dentus E/FKodak Insight, Flow F

C. Digital Receptors

Digital receptors include rigid wired or wireless sensors such as the charged-coupled device (CCD) and the complementary metal oxide semiconductor (CMOS) and photostimulable phosphor plate (PSP) or storage phosphor plate (SPP) receptors. It is estimated that digital radiography reduces patient radiation dose by 75% compared with D speed film, 50% compared with E speed film and approximately 40% compared with F speed film. Digital receptors cannot be sterilized so the clinician must use careful disinfection and barrier coverage techniques to avoid cross-contamination of the receptor.

D. Intensifying Screens

With regard to film-based extraoral radiography, rare earth intensifying screen phosphors are recommended to reduce radiation exposure. Rare earth elements like lanthanum and gadolinium have replaced calcium tungstate crystals in intensifying screens. When rare earth screens are combined with green light sensitive film, exposure can be reduced approximately 55% for panoramic and cephalometric radiographs.

E. Plan Dental Radiographic Procedures Carefully and Avoid unnecessary retakes.1. Five of the most important factors relating to the production

of quality radiographs are:

• Patient positioning and instruction • Alignment of the X-ray beam and the film. • Use of rectangular collimating device • Selection of proper exposure factors (kV, mA, time, distance) • Proper film or digital image processing2. Long axis of the body part being radiographed should be perpendicular to the main X-ray beam and parallel to the image receptor

3. Receptor holding instruments with beam alignment devices should be used.

4. Use an exposure time that is as short as possible to minimize the radiation dose and motion artifact during exposure.

5. Ensure that the focal spot-to-film distance (FFD) is correct.

6. All patient exposures procedures must be documented in the patient’s record and the images should be properly labeled. 7. The diagnostic information obtained from the radiographic images also should be recorded in a notation or formal report in the patient’s record.

F. Using Proper Kilovoltage (kV)

Kilovoltage determines the penetrating ability (quality) of the X-ray beam. When a high kV is used in a film system, there will be more shades of gray (i.e., low contrast) than when low kV is used.

G. Milliamperage (mA) and Time Setting

Milliampere-seconds (mAs) determines the amount (quantity) of x-radiation being produced which is calculated by multiplying the milliamperage (mA) x time (in seconds) = mAs (milliampere-seconds). Set the mA at the highest setting and then establish the proper timer settings. This technique results in the use of shorter time settings, which are helpful in avoiding patient motion artifacts on the radiograph.

Dental Radiographic Quality Assurance (QA) and Quality Control (QC)

Quality assurance (QA) program should include the X-ray and ancillary imaging equipment, education of dental personnel to perform quality control (QC), and preventive maintenance procedures.

DENTAL X-RAY MACHINE

The following parameters should be measured:

• X-rays output : Use radiation dosimeter to measure the intensity radiation output.

• Collimator alignment should be checked.

• Beam energy : HVL (half-value layer) of the beam should be measured to ensure that there is sufficient energy for film exposure.

Timer : Electric pulse counter counts the number of pulses generated by an X-ray machine during present time interval.

• Tube head stability : It should be stable when placed around the patient’s head.

• Focal spot size : Measure the focal spot size as it may become enlarged with excessive heat build in the X-ray machine.

SPINNING TOP TEST FOR TIMER ACCURACY

It consists of rotating radiopaque disc with a hole or notch at the periphery of disc. Top is spun by the operator and the exposure is made when the top slows down at the speed of one revolution per second. Each radiation impulse produced by the X-ray machine makes an image of the hole or notch.

COLLIMATION

Four dental films are placed on a sheet of paper, crossed with edge of cone crossing the middle of film. The outline of cone end and films are marked on the paper.

Radiopaque objects such as paper clips, coins, pins or nails are placed on the film inside the X-ray beam and films are exposed with one half of the exposure time used for an anterior radiograph. Radiographs are processed and relocated in their original position on the paper using the image of the different radiopaque objects.

PINHOLE CAMERA TECHNIQUE FOR FOCAL SPOT ASSESSMENTA piece of lead of 1 mm in thickness is placed over the collimator opening in the base of the cone. A small hole not larger than 0.5 mm in diameter is made in the centre of lead.A dental film is placed on a small box in the middle of cone at the same distance from the lead hole as the focal spot of the X-ray machine. Exposure time of five impulses is needed to produce a clear image of focal spot on the radiograph.

DARKROOM

Safelight requires checking of the following:

• Types of filter : Type of filter which should be compatible with the colour sensitivity of film used, i.e. blue, green, ultraviolet.

• Condition of filter : Scratched filter should be replaced.

• Watt of bulb : It should be not more than 25 W.

• Distance from work area : The distance from the work surface should not be more than 4 ft.

Coin test/penny test

Place the coin on the film, turn on the safelight and leave for approximately 1–5 min. Process the film in the normal way. Fogging of the film due to safelight will then be obvious when compared to the clear area protected by the coin.

X-RAY FILM

Take an unexposed film from newly opened box and process it in freshly prepared solution. The film is then viewed.

• Fresh film : It appears clearer with blue tint which means film is properly stored and protected.

• Fogged film : It appears fogged, meaning that film has expired, improperly stored or exposed to radiation.

PROCESSING

Developer Strength

The solution must reached optimum temperature of 20°C for manual processing and 28°C for automatic processing.

Step-wedge film :

Step-wedge film is a device with small, graduated increase in the thickness of its material.Step wedge can be made in dental office by following method :

• Tape six pieces of lead foil from the film packets on the end of tongue blade.

• The first two pieces should be 1 in. long, second two pieces ¾ in. long and third two pieces should be ½ in. long.

• Tape these foil pieces in three steps, with one step having six layers, second having four layers, and third having two layers.

• Cut the excess foil from the side and tape the foil layer to the tongue blade.

Step-wedge radiograph

Take a radiograph of step wedge using known exposure factors.

Process the film in fresh solution and produce a standard reference film with level of increasing density.

Repeat using the same exposure factor every day as the solution becomes depleted.

Compare it every day with standard reference step wedge film to determine objectively any decrease in blackening of the processed film which would indicate deterioration of the developer.

Fixer Strength

To monitor fixing following tests are carried out:

• Preparation of film : Unwrap one film and immediately place it in the fixer solution. Check the time taken for clearing.

• Fast clearing : If the film clears in 2 min, the fixer is of adequate strength.

• Slow clearing : If the film is not completely cleared after 2 min, then fixer strength is not adequate.

Guidelines for Prescribing Dental Radiographs

Use of these guidelines should promote the appropriate use of X-rays, by reducing overutilization and excessive radiation, and minimizing underutilization of imaging with potential inadequate diagnosis

The guidelines categorize patients first by type of visit (new or recall), then by dental status (child with primary or transitional dentition, adolescent, or adult dentulous or edentulous). Lastly the patient’s risk category for caries, periodontal disease or growth and development assessment is considered.

A. Positive Historical Findings

1. Previous periodontal or endodontic treatment

2. History of pain or trauma

3. Familial history of dental anomalies

4. Postoperative evaluation of healing

5. Remineralization monitoring

6. Presence of implants, previous implant-related pathosis or evaluation for implant placement

1. Clinical evidence of periodontal disease

2. Large or deep restorations

3. Deep carious lesions

4. Malposed or clinically impacted teeth

5. Swelling

6. Evidence of dental/facial trauma

7. Mobility of teeth

8. Sinus tract (“fistula”)

9. Clinically suspected sinus pathosis

10. Growth abnormalities

B. Positive Clinical Signs/Symptoms

11. Oral involvement in known or suspected systemic disease

12. Positive neurologic findings in the head and neck

13. Evidence of foreign objects

14. Pain and/or dysfunction of the temporomandibular joint

15. Facial asymmetry

16. Unexplained bleeding

17. Unexplained sensitivity of teeth

18. Unusual eruption, spacing or migration of teeth

19. Unusual tooth morphology, calcification or color

20. Unexplained absence of teeth

21. Clinical tooth erosion

Maximum permissible dose and maximum accumulated dose Dose limits have been established for occupationally exposed persons, non-occupationally exposed persons (general public) and occupationally exposed pregnant women.

The maximum permissible dose (MPD) is the dose of whole body radiation that is not expected to produce any significant somatic or genetic effects in a lifetime.

GUIDELINES FOR SHIELDING OF X-RAY INSTALLATIONS The adequacy of shielding depends on the material and

thickness used for this purpose. Different materials can be used for shielding. However, brick or concrete are considered the best materials, as they are easily available, economical, and have good structural strength. DENTAL CBCT/OPG

DENTAL – INTRAORAL RADIOGRAPHY

Dental radiographic examinations are not without risk. X-radiation has the potential to damage tissue through either the indirect effect or direct effect of radiation. The biologic effects of radiation are cumulative and every effort must be taken to keep radiation exposures as low as reasonably achievable. A variety of radiation safety and protection measures can be employed to reduce exposure to dental patients and minimize occupational exposure.