| Abstract|| |
Aim: The purpose of this paper was to review various dosimeters used in dentistry and the cumulative results of various studies done with various dosimeters.
Materials and Methods: Several relevant PubMed indexed articles from 1999 to 2013 were electronically searched by typing "dosimeters", "dosimeters in dentistry", "properties of dosimeters", "thermoluminescent and optically stimulated dosimeters", "recent advancements in dosimetry in dentistry." The searches were limited to articles in English to prepare a concise review on dental dosimetry. Titles and abstracts were screened, and articles that fulfilled the criteria of use of dosimeters in dental applications were selected for a full-text reading. Article was divided into four groups: (1) Biological effects of radiation, (2) properties of dosimeters, (3) types of dosimeters and (4) results of various studies using different dosimeters.
Conclusion : The present review on dosimetry based on various studies done with dosimeters revealed that, with the advent of radiographic technique the effective dose delivered is low. Therefore, selection of radiological technique plays an important role in dental dose delivery.
Keywords: Absorbed dose, dosimetry, equivalent dose, radiation dose, types of dosimeters
|How to cite this article:|
Asha M L, Chatterjee I, Patil P, Naveen S. Dosimetry in dentistry. Indian J Dent Res 2015;26:118-25
Radiographic examination is one of the widely used investigative procedures for more than a century. Though radiograph provides valuable information, radiation dose has long-term radiation risks. Hence, the focus is to obtain high-quality radiographs with minimum radiation dose to the patient. The quality of the radiograph and its anatomical detail depends largely on the properties of the imaging system. To minimize the risk to patients from radiation exposure, more emphasis has been placed on optimization of imaging condition. The important aspects of optimization are: First recognize the level of radiographic image quality required to make a diagnosis; second to determine the technique that provides that level of image quality with the minimum dose to the patient; third to ensure that any clinical diagnostic information that could be obtained is imaged.  However, the radiation dose to the patient should not be significantly higher than necessary. Due to a minor to major radiation effects on quality of life, radiation dose measurement is becoming increasingly important. A variety of dosimeters has been used for measuring radiation dose. Several relevant PubMed indexed articles from 1999 to 2011 were electronically searched to prepare a concise review on dental dosimetry.
| Biological Effects of Ionizing Radiation|| |
With ionizing radiation passing through tissue, the component atoms get ionized resulting in damage to the cell. In particular, the genetic material of the cell, the DNA may be changed.
Two categories of radiation-induced injury are recognized: Deterministic effects and stochastic effects. Deterministic effects are usually associated with high doses and are characterized by a threshold. Above this threshold, the damage increases with dose. Stochastic effects are associated with lower doses and have no threshold. The main stochastic effect is cancer. 
Direct effect of radiation damages DNA directly, but indirect effect of radiation causes breakdown of water into hydrogen and hydroxyl ions, which in turn may react with chemicals like hydrogen peroxide to produce free radicals causing damage to nucleic acids.
| Units of Dosimetry|| |
The absorbed dose to the mass is defined as the imparted energy per unit mass of the tissue or organ.
The absorbed dose rate is the rate at which an absorbed dose is received. The units are Gy s − 1 , mGy h − 1 , etc. 
Quality or weighting factor
The biological effect of radiation depends not only to the energy deposited by radiation in an organism, but also on the way in which the energy is deposited along the path of the radiation, and this in turn depends on the type of radiation and its energy. Thus, the biological effect of the radiation increases with the linear energy transfer defined as the mean energy deposited per unit path length in the absorbing material (units keV μm − 1 ). The quality or weighting factor, wR, is introduced to account for this difference in the biological effects of different types of radiation. 
It is defined in terms of the absorbed dose weighted by a factor that depends on the type of radiation. An absorbed dose of 0.1 Gy of alpha radiation, for example, is more harmful than an absorbed dose of 0.1 Gy of beta or gamma radiation. To reflect the damage done in biological systems from different types of radiation, the equivalent dose is used. The SI unit of dose is the sievert, Sv (1 Sv = 1 J/kg 1 , the old unit is the rem, 1 Sv = 100 rem). The equivalent dose rate is expressed in Sv/s or mSv/h. 
Committed effective dose, E (τ)
A person irradiated by gamma radiation outside the body will receive a dose only during the period of irradiation. However, following an intake by ingestion or inhalation, some radionuclide persists in the body and irradiates the various tissues for many years. The total radiation dose in such cases depends on the half-life of the radionuclide, its distribution in the body, and the rate at which it is expelled from the body. Detailed mathematical models allow the dose to be calculated for each year following intake. The resulting total effective dose delivered over a lifetime (70 years for infants, 50 years for adults) is called the committed effective dose. 
Collective effective dose
On the assumption that radiation effects are directly proportional to the radiation dose without a threshold, then the sum of all doses to all individuals in a population is the collective effective dose with unit - manSv. 
Radiation hormesis and the linear non-threshold model
Although it is generally believed that low doses arising from chemicals, pharmaceuticals, radiation, etc., produce effects proportional to high doses, there is evidence to suggest this is incorrect and that low doses may have a beneficial effect to biological systems. This positive effect arising from low doses is referred to as "hormesis" from the Greek word "hormaein" which means "to excite." Radiation hormesis refers to the stimulation of biological functions by low doses of radiation. ,,,
Assessment of radiation dose and image quality
Before discussing optimization in radiography in more depth, it is worth considering briefly the ways in which dose and image quality can be measured.
The dose quantities that can be measured for radiographic exposures are the entrance surface dose (ESD) and the dose-area product (DAP). The ESD is the dose to the skin at the point where an X-ray beam enters the body and includes both the incident air kerma and radiation backscattered from the tissue. It can be measured with small dosimeters placed on the skin, or calculated from radiographic exposure factors coupled with measurements of X-ray tube output. ,,
The DAP is the product of the dose in air (air kerma) within the X-ray beam and the beam area and is, therefore, a measure of all the radiation that enters a patient. It can be measured using an ionization chamber fitted to the X-ray tube. 
| Materials and Methods|| |
Several relevant PubMed indexed articles from 1999 to 2013 were electronically searched by typing "dosimeters", "dosimeters in dentistry", "properties of dosimeters", "thermoluminescent and optically stimulated dosimeters", "recent advancements in dosimetry in dentistry." The searches were limited to articles in English to prepare a concise review on dental dosimetry. Titles and abstracts were screened, and articles that fulfilled the criteria of use of dosimeters in dental applications were selected for a full-text reading.
Literature was reviewed under following groups:
- Properties of dosimeters
- Types of dosimeters
- Recent advancements in dental dosimetry
- Results of studies using different dosimeter in dentistry.
Properties of dosimeters
The ideal properties of a dosimeter are: Accuracy and precision, linearity, energy dependence, the directional dependence, spatial resolution and physical size, readout convenience, convenience of use. 
Types of dosimetry
- Ionization chamber dosimetry systems
- Film dosimetry
- Luminescence dosimetry
- Semiconductor dosimetry. 
Other dosimetry systems
- Alanine/electron paramagnetic resonance dosimetry system
- Plastic scintillator dosimetry system
- Diamond dosimeters
- Gel dosimetry systems. 
Optically stimulated luminescence dosimeter
Optically Stimulated Luminescence (OSL) is based on a principle similar to that of thermoluminescence dosimetry. Instead of heat, light (from a laser) is used to release the trapped energy in the form of luminescence. OSL is a novel technique offering a potential for in vivo dosimetry in radiotherapy. The integrated dose measured during irradiation can be evaluated using OSL directly afterward. The optical fiber of optically stimulated thermoluminescent dosimeter (TLD) consists of a small (~1 mm 3 ) chip of carbon doped aluminum oxide (Al 2 O 3 :C) coupled with a long optical fiber, a laser, a beam splitter and a collimator, a photomultiplier tube, electronics and software. To produce OSL, the chip is excited with laser light through an optical fiber, and the resulting luminescence (blue light) is carried back in the same fiber, reflected through 90° by the beam splitter and measured in a photomultiplier tube. 
A TLD is a type of radiation dosimeter. A TLD measures ionizing radiation exposure by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated. The amount of light emitted is dependent upon the radiation exposure. 
The two most common types of TLDs are calcium fluoride and lithium fluoride, with one or more impurities to produce trap states for energetic electrons. The former is used to record gamma exposure, the latter for gamma and neutron exposure (indirectly, using the Li-6 n, alpha) nuclear reaction; for this reason, LiF dosimeters may be enriched in lithium-6 to enhance this effect or enriched in lithium-7 to reduce it). As the radiation interacts with the crystal it causes electrons in the crystal's atoms to jump to higher energy states, where they stay trapped due to intentionally introduced impurities (usually manganese or magnesium) in the crystal, until heated. Heating the crystal causes the electrons to drop back to their ground state, releasing a photon of energy equal to the energy difference between the trap state and the ground state. The electrons can also drop back to ground the state after a long period; this effect is called fading and is dependent on the incident radiation energy and intrinsic properties of the TLD material. As a result, each material possesses a limited shelf life after which dosimetric information can no longer be obtained. This varies from several weeks in calcium fluoride to up to 2 years. It can be used both for environmental monitoring and for staff personnel in facilities involving radiation exposure, among other applications.
Types of dosimeters
- Body Dosimeter: Depending on the situation, a body dosimeter is worn at collar level (fluoroscopy, X-ray), chest level (nuclear medicine) and waist level (during pregnancy)
- Ring Dosimeter: Ring dosimeters (used for measuring beta and gamma dose to the hand) should be worn on the hand which is closest to the radiation source so that the label is on the palmar (inside) surface of the finger, toward the radiation source
- Luxel + OSL whole body dosimeter: Assigned to all individuals using/operating radioactive materials/radiation producing machines. These dosimeters are sensitive to beta, gamma, X-ray, and neutron radiations. These are also used as quarterly area monitors to help determine compliance with the public dose limit
- Thermoluminescent dosimeter ring dosimeter: Assigned to individuals conducting X-ray diffraction beam alignments and placing samples for analysis. These dosimeters are sensitive to X-rays, beta, and gamma rays
- Bubble Technologies Neutron Bubble Dosimeter: Given to visitors who are in need of temporary neutron exposure monitoring
- Dosimeter Corporation Pocket Dosimeter: Given to visitors who are in need of temporary monitoring of X-ray, beta and gamma ray exposure. 
Recent advancement in dosimetry
Instadose Tm device
Based upon direction storage technology and smaller than a flash drive, this rugged, fully accredited dosimeter provides an instant readout when connected to any computer with internet access via a universal serial bus connector. The instadose™ device does not require batteries to capture radiation exposure, it is always on. The device does not need to be sent in for processing to view dose levels. The instadose™ device is perfect to accurately measure photon dose.  Advantages and disadvantages of different dosimeters are summarized in [Table 1].
Classification of individuals addressed by the dosimetry program
The individuals are classified into three groups as follows: 
Required to wear dosimeters
Adults who are likely to receive an annual effective dose equivalent of 100 mrem (1 mSv), included is the committed effective dose equivalent of internally deposited radionuclides and minors or pregnant women who are likely to receive an annual dose equivalent of 50 mrem (0.5 mSv).
May request a dosimeter
Adults who are likely to receive a radiation exposure, but their annual exposure is likely to be less than an effective dose equivalent of 100 mrem (1 mSv). Minors and pregnant women who work in the vicinity of a radiation source, but are unlikely to receive an annual dose equivalent of 50 mrem (0.5 mSv).
It is recognized that a great deal of judgment is required to place an individual in a group and to apply a specific method of monitoring. These decisions are made by the Radiation Safety Officer as recommended by the Radiation Safety Committee based on the following criteria:
- Exposure history of the individual and similar workers
- Work habits
- Nature of the work
- Quantity of radioactive materials and/or strength of the radiation source
- Other relevant parameters.
Exposure Reports: The Radiation Safety Officer reviews exposures on a regular basis. Subsequently, high or unusual exposures are reported to the Radiation Safety Committee. All monitored individuals included receiving an annual exposure report.
Enforcement of External Dosimetry Program: External dosimeters will be provided to required individuals on an appropriate basis that is, monthly or quarterly. All individuals in this group are required to return the dosimeters promptly. A delay by more than 1 month in returning the dosimeter without a written explanation may be considered a violation of University policy and may lead to the revocation of authorization to use radioactive materials or a monetary penalty.
Pregnant Workers: University policy relies upon the as low as reasonably achievable (ALARA) principle, thus reducing the necessity for a special policy for pregnant women. However, there is recognition that a pregnant worker may require specific information to make an informed decision. To be considered under the Pregnant Worker policy, a woman must declare her pregnancy in writing and provide other relevant information, for example, approximate date of conception or delivery.
The worker will be assigned a monthly fetal monitoring dosimeter. In the event of elevated exposures, the RSO may seek reassignment of duties.
Individuals that are assigned dosimeters due to the voluntary request are required to comply with all policies governing monitored individuals. This group is also expected to return the dosimeter promptly. Failure to return a dosimeter by more than 1 month may be considered a violation of University policy.
Internal dosimetry program
This program applies to anyone utilizing 1 mCi or more of unsealed radioiodine or 100 mCi or more of unsealed tritium. It applies to anyone involved in an accident or spill or become personally contaminated.
Enforcement of Internal Dosimetry Program: The method and the frequency of bioassay depend upon the nature including the half-life of the radionuclide of concern. Once the frequency of bioassay is established, the enforcement follows the external dosimetry enforcement by replacing the month with the appropriate interval (e.g. 14 days).
Instructions to employees
Employees have certain responsibilities to ensure radiation exposure is properly monitored.
- Wear dosimeters when required
- Wear dosimeters properly
- Whole body dosimeters should be worn on the chest area. This area is on or between the neck and the waist
- Store the dosimeter in the proper storage location along with the Control dosimeter
- The dosimeter should not be worn for nonoccupational purposes
- Another person's dosimeter should not be tampered with or intentionally exposed. 
Radiation dosimeters ("film badge") should be worn whenever working with X-ray equipment, radioactive patients, and radioactive materials. Radiation dosimeters should not be worn while having X-rays that are part of your medical or dental care, radiation exposure from these sources is not included in your occupational exposure. 
Previous studies done to calculate radiation doses in dental radiology
Mortazavi et al. conducted a study for the ESD Measurement on the Thyroid Gland in Orthopantomography using LiF TLDs-100 on the thyroid and he found-the mean ESD for radiographies performed with 66 kVp (20 patients) and 68 kVp (20 patients) were 0.072 ± 0.019, and 0.070 ± 0.016 respectively. No statistically significant difference was found between these means. 
Mortazavi et al. conducted a study on ESD measurement in intraoral radiography using LiF TLDs-100 on the skin (either mandibular or maxillary arch) of 40 patients. The ESD at the center of the beam on the patients' skin in intraoral radiography was 1.173 ± 0.606 mGy (ranged from 0.01 to 0.40 mGy). The mean ESD for male and female patients were 1.380 ± 0.823, and 1.004 ± 0.258 respectively. No statistically significant difference was found between these means. 
Baechler et al. did a study to compare between Intra-oral, Panoramic and Tomographic Examinations. For intraoral-the ESD and DAP indicators were measured using a Radcal dosimeter (Radcal3036) connected to a 11 cm 3 ionizing chamber. For orthopantomography dose width product were measured using a pencil ionization chamber connected to a Radcal dosimeter (Radcal 1515). Effective dose measured was Kodak Film Ultra-speed (D) - 1.7, Film Kodak Insight (E/F) - 0.72, radiovisiography (RVG) Trophy mode high-resolution - 0.13, RVG Trophy mode high sensitivity - 0.03. Effective dose measured in OPG machine 1, 2 and 3 were 11.4, 4.2 and 5.7 respectively with highest measured effective dose from machine 1 which was 20 years old. 
Gijbels et al. did a study to compare the effective dose from scanography with periapical radiography. TLDs-700 were inserted in the parotid glands (bilateral), submandibular glands (bilateral) and bone marrow (left ascending ramus) of three human cadavers. Dosimeters were also attached to the skin, thyroid gland and lens of both eyes. The effective doses for the scanograms were 0.001 mSv (central), 0.011 mSv (lateral) and 0.015 mSv (posterior). The effective doses for periapical radiographs were 0.001 mSv (anterior), 0.001 mSv (lateral) and 0.003 mSv (posterior) for rectangular collimation and 0.001 mSv (anterior), 0.002 mSv (lateral) and 0.005 mSv (posterior) for round collimation. 
Zammit-Maempel et al. calculated radiation dose to the lens of eye and thyroid gland in paranasal sinus multislice computed tomography (CT) using TLDs. TLDs were placed on the eyelid and thyroid gland of 29 patients scanned axially in the supine position and a further 28 patients scanned coronally in the prone position with gantry tilt. The results show mean doses of 35.1 mGy (lens) and 2.9 mGy (thyroid gland) in the coronal plane compared with 24.5 mGy (lens) and 1.4 mGy (thyroid gland) in the axial plane. 
Ludlow in Dose and risk in dental diagnostic imaging: With emphasis on dosimetry of cone beam CT (CBCT) used a phantom simulation approach, utilizing a radiation analogue dosimeter (RANDO) phantom and commercially processed TLD 100 TLD chips. Chips are placed at 24 sites representing the location of weighted tissues of the head and neck area that are potentially directly exposed during maxillofacial imaging. Effective dose in panoramic - charge-coupled devices was 16.1 μSv, posteroanterior cephalometrinc - photo-stimulable phosphor (PSP) was 5.6 μSv, Lateral Cephalometric - PSP was 5.1 μSv, New Tom 3G-Large field of view (FOV) was 68 μSv and CB Mercuray-"Facial" FOV was 569 μSv. 
Ludlow et al. in Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and maxillofacial radiology calculated average tissue-absorbed dose, equivalent dose, and effective dose were calculated using TLD chips in a radiation analog dosimetry phantom. Large- FOV CBCT E ranged from 68 to 1,073 μSv. Medium-FOV CBCT E ranged from 69 to 560 μSv, whereas a similar-FOV multiple-row detector CT (MDCT) produced 860 μSv. 
Gibbs calculated effective dose equivalent and effective dose for common projections in oral and maxillofacial radiology. Doses to all organs and tissues in the head, neck, trunk, and proximal extremities were determined for each projection (intraoral full-mouth radiographic survey, panoramic, cephalometric, temporomandibular tomograms, and submentovertex view) by computer simulation with Monte Carlo methods. HE and E were calculated from these complete distributions and by methods prescribed by the International Commission on Radiological Protection (ICRP). HE and E computed from complete dose distributions were found comparable within a few percentage points. 
Avendanio et al. calculated effective dose and risk assessment from detailed narrow beam radiography with the use of a tissue equivalent human phantom and thermoluminescent dosimetry, the effective dose from detailed narrow beam radiography was found to vary from 5 to 35 μSv depending on the anatomic location of the image layer and intraoral radiography from 9 to 150 μSv depending on the type of survey. Effective doses of these magnitudes represent 0.6-18.8 days of equivalent natural radiation exposure and the probability for stochastic effects on the order of 0.37-10.95 × 10 − 6 μSv. 
Bianchi et al. in his study of in vivo, thyroid and lens surface exposure with spiral and conventional CT in dental implant radiography used lithium fluoride TLDs. Dosimeters were placed over the thyroid gland, lateral orbit and infraorbital foramen of each patient. He found, in maxillary and mandibular region there was 57.4% reduction at the lateral orbit in the regions, 47% and 60% at the infraorbital region and 60.8% and 70.9% and at the thyroid gland respectively with spiral CT instead of conventional CT. 
Qu et al. calculated the average tissue-absorbed dose for a NewTom 9000 CBCT scanner using TLD chips in a phantom. The scans were carried out with and without thyroid collars. Effective organ dose and total effective dose were derived using ICRP 2007 recommendations. He concluded that the effective organ doses for the thyroid gland and esophagus were 31.0 μSv and 2.4 μSv, respectively, during CBCT scanning without a collar around the neck. When the thyroid collars were used loosely around the neck, no effective organ dose reduction was observed. When one thyroid collar was used tightly on the front of the neck, the effective organ dose for the thyroid gland and esophagus were reduced to 15.9 μSv (48.7% reduction) and 1.4 μSv (41.7% reduction), respectively. Similar organ dose reduction (46.5% and 41.7%) was achieved when CBCT scanning was performed with two collars tightly on the front and back of the neck. However, the differences to the total effective dose were not significant among the scans with and without collars around the neck. 
Lofthag-Hansen et al. in his study performed CT dose index (CTDI) measurements in a CT head dose phantom with a pencil ionization chamber connected to an electrometer. The rotation center was placed in the center of the phantom and also, to simulate a patient examination, in the upper left cuspid region. The DAP value was determined with a plane-parallel transmission ionization chamber connected to an electrometer. A conversion factor of 0.08 μSv/Gy cm 2 was used to determine the effective dose from DAP values. CTDI measurements showed an asymmetric dose distribution in the phantom when simulating a patient examination. Hence, a correct value of CTDI could not be calculated. The DAP value increased with higher tube current and tube voltage values. The DAP value was also proportional to the field size. The effective dose was found to be 11-77 μSv for the specific examinations. 
Hirsch et al. measured the absorbed organ doses using an anthropomorphic phantom loaded with TLDs in 16 sensitive organ sites. Both CBCT units were deployed with different FOVs: Three-dimensional Accuitomo using two protocols (anterior 464 cm scan and anterior 666 cm scan) and Veraviewepocs three-dimensional using three protocols (anterior 464 cm scan, anterior 864 cm scan and panoramic + anterior 464 cm). Equivalent and effective doses were then calculated, the latter based on the ICRP 2005 recommendations. He concluded that the lowest effective dose was observed for the three-dimensional Accuitomo 464 cm (20.02 μSv), the highest for the three-dimensional Accuitomo 666 cm (43.27 μSv). The effective dose recorded for Veraviewepocs three-dimensional was 39.92 μSv for the 864 cm scan, 30.92 μSv for the 464 cm scan and 29.78 μSv for the panoramic + 464 cm scan protocol. 
Jadu et al. in his comparative study to calculate the effective doses from CBCT and plain radiography for sialography, dose measurements made at 25 selected locations in the head and neck of a RANDO phantom, using ICRP 2007 tissue weighting factors. His results revealed the effective dose (E) changed in a relationship to changes in CBCT FOV, peak kilovoltage (kVp) and milliamperage (mA). Specifically, E decreased from a maximum of 932 mSv (30 cm FOV, 120 kVp, 15 mA) to 60 μSv (15 cm FOV, 80 kVp, 10 mA) for a parotid gland study and to 148 mSv (15 cm FOV, 80 kVp, 10 mA) for a submandibular study. The collective series of plain radiographs made during sialography of the parotid and submandibular glands yielded effective doses of 65 μSv and 156 μSv, respectively. 
Davies et al. in his study to calculate Effective doses from CBCT investigation of the jaws used an RANDO phantom containing thermoluminence dosimeters. Effective doses for each protocol were calculated using the 1990 and approved 2007 ICRP recommended tissue weighting factors (E1990, E2007).
| Results|| |
The effective dose for E1990 and E2007, respectively, were: Full FOV of the head, 47 μSv and 78 μSv; 13 cm scan of the jaws, 44 μSv and 77 μSv; 6 cm standard mandible, 35 μSv and 58 μSv; 6 cm high resolution mandible, 69 μSv and 113 μSv; 6 cm standard maxilla, 18 μSv and 32 μSv; and 6 cm high resolution maxilla, 35 μSv and 60 μSv. Conclusions: Using the new generation of CBCT scanner, the effective dose is lower than the original generation machine for a similar FOV using the ICRP 2007 tissue weighting factors.  The results of the above mentioned studies are summarized in [Table 2].
|Table 2: Various studies using different dosimeters with the effective and absorbed doses for different techniques |
Click here to view
| Conclusion|| |
The benefits of the radiographic imaging should be weighed against their harmful effects. Recently CBCT has gained a lot of importance in various fields of dentistry not only because of its ability to visualize structures in three dimensions but also for its low radiation dose to patients in comparison to medical CT. From the above mentioned studies, it became clear that radiation doses delivered to patients depends not only on exposure parameters, but also on FOV in CT and CBCT. All the aforementioned studies using various dosimeters concluded that with the use of sophisticated technique, the "ALARA" principle is being followed. Therefore, it is important to educate both dental professionals and patients about the use of this evolutionary technique and its minimal effect on the quality of life.
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Dr. Ingita Chatterjee
Department of Oral Medicine and Radiology, Sri Hasanamba Dental College and Hospital, Vidyanagar Hassan, Karnataka
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]