Optimization of Protection in Dental Radiology

1. IAEA Regional Training Course on Radiation Protection of patients for Radiographers, Accra, Ghana, 11-15 July 2011 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 22: Optimization of Protection in Dental Radiology

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

4. 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) 22: Optimization of Protection in Dental Radiology

5. Intra-Oral Dental X-Ray Equipment 22: Optimization of Protection in Dental Radiology

6. Modern Dental X-Ray Unit 22: Optimization of Protection in Dental Radiology

7. Panoramic X-Ray Equipment 22: Optimization of Protection in Dental Radiology

8. Cephalometric X-Ray Equipment 22: Optimization of Protection in Dental Radiology

9. X-Ray Tube • stationary Anode • avoid overheating • tube duty cycle: • typical: 1:30 intraoral • 1:10 OPG • 420 mAs/hr intraoral 22: Optimization of Protection in Dental Radiology

10. 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 22: Optimization of Protection in Dental Radiology

11. 1. Lead Collimator with central hole 2. Spacer Tube Collimator 22: Optimization of Protection in Dental Radiology

12. Applicator Cones GoodBadBad 22: Optimization of Protection in Dental Radiology

13. Cephalometric Holder 22: Optimization of Protection in Dental Radiology

14. Intra-Oral Dental X-Ray Equipment (technical data) • Exposure timefrom 60 ms to 2.5 s • TubeMin. 50 kV, ~7mA • Focal spot size1 mm • Inherent filtration~2 mm Al equivalent • Focus-skin distance20 cm • Irradiated field28 cm2 with round section, 6 cm diameter collimator 22: Optimization of Protection in Dental Radiology

15. Panoramic X-Ray Equipment (technical data) • Focal spot0.5 mm • kV60 - 80 kV in 2 kV steps • mA4 - 10 mA steps 4, 5, 6, 8, 10 • Exposure time12 s (standard projections) 0.16 - 3.2 s (cephalometric projections) • Flat panoramic cassette15x30 cm (Lanex Regularscreens)) 22: Optimization of Protection in Dental Radiology

16. Image Receptors in Dental Radiology Intraoral 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%. Panoramic Radiology and Cephalometry • Film-screen combination • Digital sensors - compared with film-screen sensitivity class 200, the radiation dose is reduced by 50-70%. 22: Optimization of Protection in Dental Radiology

17. 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 22: Optimization of Protection in Dental Radiology

18. Radiation Protection in Dental Radiology • 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 22: Optimization of Protection in Dental Radiology

19. Technical hints to reduce patient doses Quality Control of Film Processing • Keep under control time and temperature of the developing process. • Do not use oxydized chemicals • Do not adjust development time by viewing the film 22: Optimization of Protection in Dental Radiology

20. 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). 22: Optimization of Protection in Dental Radiology

21. 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) 22: Optimization of Protection in Dental Radiology

22. 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 22: Optimization of Protection in Dental Radiology

23. Collimation Dose Evaluation Exposure Time Half Value Layer Kilovoltage (kVp) Leakage Radiation What Tests ? 22: Optimization of Protection in Dental Radiology

24. Quality Control for Dental Equipment • 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. 22: Optimization of Protection in Dental Radiology

25. Quality Control for Dental Equipment Tests which can be performed bydental practice staff 22: Optimization of Protection in Dental Radiology

26. Quality Control for Dental Equipment Tests performed by medical physicists 22: Optimization of Protection in Dental Radiology

27. 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 Dental QC Methods 22: Optimization of Protection in Dental Radiology

28. “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 22: Optimization of Protection in Dental Radiology

29. 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 22: Optimization of Protection in Dental Radiology

30. HVL- Minimum Values kVpHVL (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 22: Optimization of Protection in Dental Radiology

31. Quality Control of Film Processing • Keep under control time and temperature of the developing process. • Do not use oxidized chemicals • Regularly check processing with phantom 22: Optimization of Protection in Dental Radiology

32. Dental Phantom 22: Optimization of Protection in Dental Radiology

33. Dental Phantom 22: Optimization of Protection in Dental Radiology

34. 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. 22: Optimization of Protection in Dental Radiology

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