1. IAEA
International Atomic Energy Agency
IAEA Regional Training Course on Radiation
Protection of patients for Radiographers,
Accra, Ghana, 11-15 July 2011
Optimization of Protection in Dental Radiology

2. IAEA 22: Optimization of Protection in Dental Radiology 2
Introduction
• Dental radiology makes use of specific types
of equipment, needed for different purposes.
• Frequent exposures (though each with low
dose) involve a risk for the practitioner and
for the patient

3. IAEA 22: Optimization of Protection in Dental Radiology 3
Dental X-ray equipment
Radiation protection in dental
radiology
Quality control for dental
equipment
Topics

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Dental x-ray equipment: Types of units
• “Intra-Oral” units
• Standard dental tube
• uses an intra-oral image receptor
• has extra-oral x-ray tube
• Panoramic (orthopantomography (OPG))
• Cephalometric ( Ceph)

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Intra-Oral Dental X-Ray Equipment

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Modern
Dental X-
Ray Unit

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Panoramic X-Ray Equipment

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Cephalometric X-Ray Equipment

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X-Ray Tube
• stationary Anode
• avoid overheating
• tube duty cycle:
• typical: 1:30 intraoral
• 1:10 OPG
• 420 mAs/hr intraoral

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Generators & Pre-Heat
• Medium frequency - stable waveform
• Single phase (SP) - pulsed
• Pre-Heat: separate circuit for heating
filament
• Single Phase units without a pre-heat circuit
• initial pulses of variable kV

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Collimator
1. Lead Collimator
with central hole
2. Spacer Tube

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Applicator Cones
Good Bad Bad

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Cephalometric Holder

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Intra-Oral Dental X-Ray Equipment
(technical data)
 Exposure time from 60 ms to 2.5 s
 Tube Min. 50 kV, ~7mA
 Focal spot size 1 mm
 Inherent filtration ~2 mm Al equivalent
 Focus-skin distance 20 cm
 Irradiated field 28 cm2 with round
section, 6 cm
diameter collimator

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Panoramic X-Ray Equipment
(technical data)
 Focal spot 0.5 mm
 kV 60 - 80 kV in 2 kV steps
 mA 4 - 10 mA steps 4, 5, 6, 8, 10
 Exposure time 12 s (standard projections)
0.16 - 3.2 s
(cephalometric projections)
 Flat panoramic cassette 15x30 cm (Lanex Regular
screens))

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Image Receptors in Dental Radiology
• Small films (2 x 3 or 3 x 4 cm) in light-tight
envelopes (no screen)
• Digital intraoral sensors - compared with
category E film, the radiation dose is
reduced by 60%.
Intraoral Radiology
Panoramic Radiology and Cephalometry
• Film-screen combination
• Digital sensors - compared with film-
screen sensitivity class 200, the radiation
dose is reduced by 50-70%.

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Dental Radiology Film Types
Sensitivity class D
• Very good spatial resolution
• Typical delivered dose: about 0.5 mGy
• Typical exposure times: 0.3 - 0.7 s
Sensitivity class E
• Good spatial resolution
• Typical delivered dose: about 0.25 mGy
• Typical exposure times: 0.1 - 0.3 s

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Facts
 Very frequent examination (about 25% of all
the radiological examinations)
 Delivered doses may differ of a factor 2 or 3.
(entrance doses between 0.5 and 150 mGy)
 Image Quality often very low
 Organs at risk: parathyroid, thyroid, larynx,
parotid glands
Radiation Protection in Dental
Radiology

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 Keep under control time and temperature
of the developing process.
 Do not use oxydized chemicals
 Do not adjust development time by
viewing the film
Quality Control of Film Processing
Technical hints to reduce patient
doses

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Lead apron and collar
•Useful when the path of primary beam
intercepts the protected organs
(downward bite-twin projection).
Technical hints to reduce patient doses

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Panoramic examination
• Image quality not as good as in intra-oral
films
• Important global information
• Relatively low dose
(one panoramic examination  35 intra-oral films)

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Why Dental QC ?
• Widespread use of dental units
• Lack of QC history on most units
• Dental practitioners working in the primary
health care sector do not have the
continuous medical physics support
available in a hospital-based diagnostic
imaging department

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What Tests ?
• Collimation
• Dose Evaluation
• Exposure Time
• Half Value Layer
• Kilovoltage (kVp)
• Leakage Radiation

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The recommended tests are
consequently divided into:
 those simple tests which can be
performed by dental practice staff
 those more complex tests which can
be carried out by medical physicists.
Quality Control for Dental Equipment

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Quality Control for Dental Equipment
Tests which can be performed by
dental practice staff
Physical parameter Tolerances Frequency
Image Quality ±10% reference
values
Quarterly
Developer
temperature and
condition of
processing solutions
Specified by the film
manufacturer
Every time processing
solutions are used
Processing Base+Fog: >0.2 OD
Speed and Contrast
>0.15 OD about
baseline
Every time processing
solutions are changed

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Quality Control for Dental Equipment
Tests performed by medical physicists
Physical parameter Tolerances Frequency
Tube voltage >50 kV and error
<10%
3 yearly
Beam size/collimation <60 mm diameter
(intra-oral)
<150 x 10 mm at
cassette (panoramic)
3 yearly
Dose at cone tip 50 kV: <5.0 mGy
70 kV: <2.5 mGy
(E speed film)
1-3 yearly
Dose-width product
for panoramic film
<75 mGy mm 1-3 yearly

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Dental QC Methods
Unit
Intra-Oral Receptors
(I/O)
Cephalometric
(Ceph)
Panoramic
(OPG )
Test Method
as for Radiology QC
as for Radiology QC
where possible:
• immobilise unit
• remove slit collimator

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“Dead man” Switch
• timer at 50 cm from focus
• set low kV, mA, long time
• start exposure
• release switch during exposure
Require exposure cut-out when switch is released.
Check exposure time is less than set time

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Dose Evaluation
Skin dose from I/O units:
• place cone 10 mm from dosimeter
• set maxillary molar/ bitewing setting
• Should be (65-70 kVp):
2-3 mGy for molar view
< 5 mGy for any view

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kVp HVL (mm Al)
Intraoral Ceph/OPG
60 1.5 1.8
70 1.5 2.1
80 2.3 2.3
90 2.5 2.5
HVL- Minimum Values

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• Keep under control time and
temperature of the developing process.
• Do not use oxidized chemicals
• Regularly check processing with
phantom
Quality Control of Film Processing

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Dental Phantom

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Dental Phantom

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Summary
• Although doses are generally low, the high
frequency of examinations requires radiation
protection (for the practitioner) in dental
radiology
• Some tests are detailed for Quality control of
dental equipment.

35. IAEA
THANK YOU!
22: Optimization of Protection in Dental Radiology 35