IAEA International Atomic Energy Agency IAEA Regional Training Course on Radiation Protection of patients for Radiographers, Accra, Ghana, 11-15 July 2011

IAEAInternational 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

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


Dental X-ray equipment

Radiation protection in dental radiology

Quality control for dental equipment

Topics


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)


Intra-Oral Dental X-Ray Equipment


Modern Dental X-Ray Unit


Panoramic X-Ray Equipment


Cephalometric X-Ray Equipment


X-Ray Tube

• stationary Anode

• avoid overheating

• tube duty cycle:• typical: 1:30 intraoral

• 1:10 OPG

• 420 mAs/hr intraoral


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


Collimator

1. Lead Collimator

with central hole

2. Spacer Tube


Applicator Cones

Good Bad Bad


Cephalometric Holder


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


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))


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%.


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


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


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


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


Panoramic examination

• Image quality not as good as in intra-oral films

• Important global information

• Relatively low dose(one panoramic examination 35 intra-oral films)


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


What Tests ?

• Collimation

• Dose Evaluation

• Exposure Time

• Half Value Layer

• Kilovoltage (kVp)

• Leakage Radiation


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



Tests which can be performed bydental 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 ODSpeed and Contrast >0.15 OD about baseline

Every time processing solutions are changed



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 mGy70 kV: <2.5 mGy(E speed film)

1-3 yearly

Dose-width product for panoramic film

<75 mGy mm 1-3 yearly


Dental QC Methods

UnitIntra-Oral Receptors (I/O)

Cephalometric (Ceph)

Panoramic (OPG )

Test Methodas for Radiology QC

as for Radiology QC

where possible:• immobilise unit• remove slit collimator


“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


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


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


• 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


Dental Phantom


Dental Phantom


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.

IAEA

THANK YOU!

22: Optimization of Protection in Dental Radiology 35

Documents

IAEA International Atomic Energy Agency IAEA Regional Training Course on Radiation Protection of patients for Radiographers, Accra, Ghana, 11-15 July 2011