Prof. Roentgen discovered X–rays in 1895. These are used in medicine, research and industry. Medical X-rays were first used in India in 1898 within three years of discovery of X-rays. Consequently X-rays were also used in dentistry. Radiographs provide an insight on the fourth dimension that cannot be seen clinically.
Despite the inherent hazards, theri utility was more in comparisons to risks. This, coupled with the increasing use of radiology in industries, led to the formulation of the ‘Atomic Energy Act, 1962,’ to ensure radiation safety in the use of radiation generating plants Under Section 17 of the Act. Pursuant to the provisions of the Act, the Central Government had promulgated the Radiation Protection Rules, 1971, which stipulate basic safety standards for all types of radiation application in medicine, industry, research etc. Appropriate radiation surveillance procedures have been issued under Rule 15 to ensure radiation protection in various types of applications.
Practitioners who administer ionizing radiation must be familiar with the magnitude of radiation exposure encountered in medicine and dentistry, the possible risk that such exposure entails and the methods that can be used to attenuate exposure and decrease dosage. This information provides the necessary background to explain to the concerned patients the benefits and possible hazards involved in the use of X-Rays.
Numerous conditions of the teeth and jaws may not show clinical signs or symptoms but can be, detected with the help of dental radiographs. Some of the common diseases, lesions, and conditions revealed on dental radiographs are:
Means that the exposed individual receives no benefits from the exposure.
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
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
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.
Principal sources of radiation dose for members of the public are natural background radiation and the medical / dental applications of radiation.
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 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.
|Effect||Nominal risk per milligray||Nominal Ratios Total Cancers Fatal Cancers|
|Hereditary (General)||1 in 2,50,000|
|Leukemia (Active bone marrow)||1 in 5,00,000||1.05|
|Breast cancer (Females)||1 in 2,00,000||1.6|
|Lung cancer||1 in 5,00,000||1.05|
|Thyroid cancer||1 in 20,00,000||21|
|Others (Combined)||1 in 20,00,000||1.3|
|Irradiation In Utero|
|TIME AFTER CONCEPTION||NOMINAL RISK PER MILIGRAY|
|First two weeks||Minimal|
|3rd through 8th week||Potential for malformation of organs|
|8th through 15th week||Severe mental retardation (1 in 2,500)|
|15th through 25th week||Severe mental retardation (1 in 10,000)|
|Throughout pregnancy||Childhood cancer (1 in 50,000)|
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.
Patient protection measures can be employed prior to any X-ray exposure by:
The dental X-ray tube head must be equipped with appropriate aluminum filters, lead collimator and position-indicating device.
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.
There are two techniques for taking radiographs depending on the focal spot to film distance
Longer focal spot to image receptor distances have clinical advantages. Therefore long cone is preferable.
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.
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.
Patient protection measures are used not only prior to X-ray exposure but also during exposure.
Radiation dose to the thyroid is considered the largest component of the effective dose in dental radiography.
Although scatter radiation to the patient's abdomen is extremely low, lead aprons should be used to minimize patient's exposure to radiation.
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.
Receptor / Film holders that position the receptor to coincide with the collimated X-ray beam should be used.
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.
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.
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.
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.
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.
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.
Radiographic images should be viewed with an illuminated viewer to obtain maximum available information.
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.
TLD badges, electronic dosimeter.
|Design certification||The X-ray diagnostic equipment must be certified to meet the design specifications stipulated by the ‘Atomic Energy Act.’|
|Registration of equipment||the sales, transfer, lease or loan of X-ray equipment must be registered with the competent authority.|
|Report of unsafe equipment||The personnel servicing the X-ray installation must report the safety of the installation to the competent authority in case of unsafe functioning.|
|Inspection||Periodic inspection of the X-ray installation must be done and duly recorded by the dental surgeon or radiologist.|
|Guidelines||The competent authority must formulate guidelines for the standardized use of radiology and minimize the health risk involved in the procedure.|
|Operational Safety Commissioning||When diagnostic X-ray unit is installed and after structural modifications a Radiation Protection Survey is conducted. New units manufactured in the country are being type approved by AERB (Atomic Energy Regulatory Board) with technical support from BARC (Bhabha Atomic Research Centre).|
Primary beam is directed towards areas of minimum occupancy.
Installation of more than 1 X-ray unit in same room should be discouraged.
Only patient (whose examination is to be carried out) should be allowed in room.
|Control Panel||If in the X-ray unit, it must be located as far away from X-ray unit stand as possible and duly shielded by a protective barrier.|
|Furnishing & Fixtures||Room should have only essential furniture and facilities needed for the examination so as to discourage presence of uninvolved staff and patients in the room.|
|Monitoring Of Exposure To Personnel||TLD badges, dosimeters etc. should be available to monitor the radiation dose received by operating personnel.|
|X-Ray Room Layout|
|Location Of X-Ray Installation||The rooms housing diagnostic X-ray units and equipment should be located as far away as possible from areas of high occupancy and general traffic, such as maternity and pediatric wards.|
Layout should aim at providing integrated facilities so that handling of equipment
and related operations can be performed with adequate protection.
The number of doors for entry to room should be minimum.
Doors and passages leading to installation should permit safe and easy transport of equipment and patients.
Dark room should be located such that primary X-ray beam is not directed on it.
|Position And Distance Rule||Operator should be at least 6 ft. away from source at an angle of and 90 - 135 degrees.|
Must be spacious
There should be a minimum area of 150 sq. feet for dental radiography.
Appropriate structural shielding should be provided for wall, ceiling and
floor so that maximum permissible dose i.e. 50 mSv for occupational workers and
1 mSv for public should not be exceeded.
9-inch brick wall.
|Opening & Ventilation||Unshielded openings if provided in an X-ray room for ventilation or natural light etc. must be located at a height of 6 ft. above finish floor level outside the x-ray room.|
|Illumination Control||Safelights (red light) 1.2 m away from work surface with 15 watts bulb and filters suitable for the types of films being used.|
Installed in a way that in normal use the beam is not directed towards
control panel, doors, windows or areas of high occupancy.
1 mm of lead sheet protection for entrance door.
1.5 mm lead barrier should be used.
Lead glass for the windows should be used
Control panel should be contiguous
Stretchable cable length 2 mts. (at least) should be provided
For higher than 125 kV control panel should be in separate room
|Waiting Areas||Should be outside the X-ray room.|
Warning Light &
|Warning signal (red light) and a radiation warning sign at a conspicuous place outside room must be kept on when unit is in use and placard should be displayed prominently.|
Compare radiographs with reference films.
Enter findings in retake log.
Replenish processing solutions.
Check temperature of solutions.
Make step-wedge test of processing system.
Replace processing solution.
Clean processing equipment.
Clean view boxes.
Review retake log (Auditing).
Check darkroom safe lighting.
Clean intensifying screens.
Rotate film stock.
Check exposure charts.
|Yearly||Calibrate X-ray machine.|
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.
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’.
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.
|Green||Terbium activated Gadolinium-oxy-sulphide|
|Blue and UV||Niobium activated Yttrium tantalate|
The darkroom should be lightproof and well ventilated. There should be optimal conditions for developing fixing and washing of radiographs.
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.
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:
|68 F||5 minutes|
|70 F||4 ½ minutes|
|72 F||4 minutes|
|76 F||3 minutes|
|80 F||2 ½ minutes|
|Apical ends of teeth cut off||Film is placed too close to teeth in maxillary arch in paralleling technique. Flat vertical angulation which causes elongation||Move film away from the teeth. Increase vertical angulation (in shallow palatal vault)|
|Overlapping of teeth||Plane of film not parallel with lingual surface of teeth. Incorrect horizontal angulation of cone||Place film parallel to the teeth and direct central ray of X – ray beam perpendicular to facial surface of the teeth|
|Lesion not showing completely||Faulty film placement||Center the film over the teeth to be radiographed|
|Crowns of the teeth not showing||Not enough film showing below or above the crowns of the teeth. Vertical angulation too steep||Increase amount of film showing below and above the crown of the teeth. Decrease vertical angulation|
|Partial image (cone cut)||Cone of radiation not covering area of interest||Correct horizontal and vertical position of cone|
|Shape distortion or fore-shortening||Bisecting technique: Vertical angulation of cone too acute. Paralleling technique: Film not parallel with long axis of teeth. Long cone not positioned correctly||Reduce vertical angulation. Place film parallel to long axis of teeth. Position long cone such that central ray strikes film at right angle|
|Elongation||Bisecting technique: Vertical angulation of cone too flat. Paralleling technique: Film not parallel with long axis of teeth. Long cone not positioned correctly||Increase vertical angulation. Place film parallel to long axis of teeth. Position long cone such that central ray strikes film at right angle|
|Image distorted||Film is bent as patient bites on film holder, bite-block or while patient holds film in mouth||Use a film backing|
|Herring bone effect||Back side of film placed towards the cone of radiation||Place film correctly|
|Black dots in apical area||Manufacturers identifying mark on film placed towards apical area of teeth||Place black dot of film towards occlusal or incisal surface of the teeth|
|Artifacts: Writing lines on radiographs, Black marks on radiographs, Black lines on radiographs||Write on film packet with pressure. Moisture contamination. Routine bending of film to reduce patient discomfort||Use less pressure while writing. Blot film packet after removing from patients mouth. Avoid bending of films|
|High contrast||Insufficient penetration. Over development. Use of film and / or intensifying screen of too high contrast. Too long exposure||Increase kilovoltage. Use proper technique. Use low contrast or slow speed screens. Decrease exposure time|
|Low contrast||Excessive penetration. Under development. Use of film and / or intensifying screen of low contrast. Scattered radiation||Decrease kilovoltage. Use proper technique. Use high contrast or high speed screens. Check diaphragm size and use appropriate cone|
|Fog||Light leaks in darkroom. Improper safelight. Radiation: Insufficient protection. Chemical: High developing temperature. Strong developing solution. Prolonged developing. Contaminated developer.Deterioration of film||Check doors and walls for leaks. Use appropriate safe light. Store unexposed films in lead protection. Use appropriate developing technique. Store films in good ventilation and rotate film stock|
|Streaks on films||Failure to agitate films during development. Chemical deposits on hanger clips. Excessive drying temperature. Insufficient fixing. Dirty or contaminated water||Agitate films when placed in developer solution. Keep clips clean. Reduce air flow over films. Fix the films properly. Wash films in running water|
|Blisters on films||Unbalanced processing temperatures. Excessive acidity of fixer. Films not agitated when immersed in fixer||Control processing temperature. Replenish / replace fixer. Agitate films when placed in fixer|
|Reticulation (orange-peel appearance)||Extreme temperature changes while processing. Weak fixer solution||Maintain uniform processing temperature. Replenish / replace fixer|
|Frilling||Hot processing solution||Maintain uniform processing temperature|
|Air bells||Air bubbles formed on surface of film||Agitate films when placed in fixer|
|White spots or lines on films||Dirt or dust on film or on screen. Emulsion tears due to rough handling of films||Clean intensifying screens periodically and keep darkroom clean. Handle films gently|
|Black spots on films||Dirt or dust on undeveloped film. Film splashed with water before developing. Films touching tank during developing||Prevent dry chemical powder of developer to contact the film. Careful handling of films. Films should not touch tank while processing|
|Artifacts: Black crescents, Black smudge marks, Black lines||Rough handling of films. Finger prints or abrasions. Static electricity||Handle film by edges only. Dry fingers before handling films. Remove film from packet slowly|
|Stains on films: Yellow brown stains, Dichroic (two colour)||Exhausted developer. Oxidized developer. Prolonged developing. Insufficient rinsing. Old / exhausted developer. Exhausted fixer. Contamination of developer by fixing solution. Inadequate fixing. Inadequate rinsing with water||Replace developer. Keep developer covered. Use correct time. Rinse film properly. Replace developer. Replace fixer. Avoid contamination. Fix the film properly. Rinse film properly|
|Deposits on films||Contaminated solution. Chemical deposits on hanger. Dirt from dirty water. Metallic deposits. Fixer contains excessive amount of silver. Milky appearance of fixer due to aluminum sulfite deposits||Change solution.Keep hangers clean. Use running water. Keep tanks covered|
|White deposits||Fixer contains excessive amount of silver. Milky appearance of fixer due to aluminum sulfite deposits||Change fixer solution. Replenish / replace fixer|
|Faded image on radiograph||Exhausted fixer. Inadequate fixing. Inadequate final wash||Replace fixer. Use adequate time. Wash films adequately|
|Brittleness of films||Excessive drying temperature. Excessive drying time. Excessive fixer acidity.||Reduce dryer temperature. Reduce drying time. Replace fixer solution.|
|Overall light films||Developer temperature is low. Exhausted developer. Contaminated developer.||Use proper developing technique with appropriate time and temperature.|
|Overall dark films||Developer temperature high||Decrease temperature|
|Fogged film||Developer contaminated by fixer solution. Light leaks. Improper safe light.||Change solution. Check for light leaks in darkroom. Use proper safe lights.|
|Peeling of film or emulsion||Developer temperature high.Depleted fixer. Deposits in developer tanks. Improper film.||Decrease temperature. Change fixer. Clean tanks regularly. Check film type and speed|
|Pressure marks||Improper handling of films||Handle films from corners|
|Cloudy or smudge appearance on film (greenish / yellow colour)||Depleted fixer. Improper type of film||Change fixer solution. Check film type|
|White cloudy appearance||No water in wash tank||Change water in tank|
|Scratches on film surface||Improper handling of films||Handle films from corners|
|Drying pattern on film surface||Dryer too hot. Characteristic of film||Reduce dryer temperature. Check type of 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.
The licensed dentist is not required to obtain additional certification to expose dental radiographs legally.
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.
A dental record must be established for every patient and dental radiographs are an integral part of such a record.
All the information contained in the dental record, including dental radiographs, is confidential or private.
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 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 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.
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 (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 (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.
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 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.
|Radiologist||B.D.S. or an M.D.S. degree from a recognized university|
|X-ray Technologist||X-ray technologists course of minimum one year duration from a recognized institute|
|Radiological Safety Officer||Certified by the competent authority|
|Service Engineer||Degree/Diploma in electrical/electronic engineering from a recognized institute|
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.
|Radiation Quantity||S.I. Unit (and Symbol)||Special Unit|
1 gray (Gy)
1 centigray (cGy)
1 Sievert (Sv)
10 millisievert (mSv)
10 microsievert (Sv)
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).
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.