“Dosimetry and optimisation of Cone Beam CT for dentomaxillofacial applications”

1. “Dosimetry and optimisation of Cone Beam CT for dentomaxillofacial applications” Safety and Efficacy of a New and Emerging Dental X-ray Modality Cone Beam CT Ruben Pauwels Oral Imaging Center Faculty of Medicine

2. Introduction CBCT • SEDENTEXCT project • CBCT dosimetry Effective dose (phantom) Standardised dose index • CBCT Optimisation QC phantom development & analysis • Work in progress

3. Introduction CBCT

4. Cone Beam CT / Digital Volume Tomography • Dentomaxillofacial • Radiotherapy • Cardiac imaging

5. Cone Beam CT / Digital Volume Tomography • Dentomaxillofacial

6. Cone Beam CT / Digital Volume Tomography • Dentomaxillofacial

7. Cone Beam CT / Digital Volume Tomography • Advantages • 3D (isotropic voxels) • Detail (voxel size 0.08-0.4mm) • Cost, size, ease of use, … • Applications • ‘Low dose’ (generally DE=20-100 µSv) • Viewing possibilities

8. Cone Beam CT / Digital Volume Tomography • Dentomaxillofacial

9. Can CBCT replace traditional radiographic methods?

10. Can CBCT replace traditional radiographic methods? • Excessive use: collective dose ↑ • Used in primary care (by dentists) • Optimisation? ALARA? • Justification • Optimisation (dose & image quality) • Referral criteria • Training

11. Introduction CBCT • SEDENTEXCT project

15. Introduction CBCT • SEDENTEXCT project • CBCT dosimetry

16. WP 2: Dosimetry Patient dosimetry Protection of personnel Standardised dose index Phantom effective dose In vivo dose Mathematical models

17. Introduction CBCT • SEDENTEXCT project • CBCT dosimetry Effective dose (phantom)

18. WP 2: Dosimetry • Which organs are the major contributors to the effective dose for dental CBCT imaging? • Which acquisition parameters influence the effective dose, and in what way? kV, mAs, filtration, … FOV, ROI • How can we use this info to reduce patient dose?

19. WP 2: Dosimetry • Thermoluminescent dosimeters (LiF:Mg,Ti) • Harshaw Reader 6600

20. WP 2: Dosimetry • Calibration: C → gU → Gy

21. WP 2: Dosimetry • Alderson Radiation Therapy phantom • 147 organ TLDs, 10 background TLDs, 20 calibration TLDs • ICRP 103 tissue weighting factors

22. WP 2: Dosimetry

23. WP 2: Dosimetry Scanora 3D Picasso Trio ProMax 3D Galileos Kodak 9000 3D

24. WP 2: Dosimetry Scanora 3D Upper jaw 100x75mm Upper and lower jaw Lower jaw Galileos Upper and lower jaw 150x150mm Kodak 9000 3D Lower jaw (part) 50x37mm Picasso Trio Lower jaw 120x70mm ProMax 3D Lower jaw 80x80mm

25. WP 2: Dosimetry

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33. WP 2: Dosimetry • Large dose range • Thyroid & salivary glands are crucial • FOV reduction should always be considered • mAs should be selected in function of diagnostic needs • Thyroid shielding & avoidance Ideal CBCT practice? → FOV selection (single tooth, …, full head) → Resolution (=mAs) selection → Training!!!

34. Introduction CBCT • SEDENTEXCT project • CBCT dosimetry Effective dose (phantom) Standardised dose index

35. WP 2: Dosimetry • Routine measurements → predict effective dose • Conversion factors (input: dose index + positioning) • Existing methods (CTDI) • Also include: - patient (skin) entrance dose - simulations

36. WP 2: Dosimetry

37. WP 2: Dosimetry Typically available dosimeters

38. WP 2: Dosimetry Ionization chamber Central measurement?

39. WP 2: Dosimetry TLD Accuracy?

40. WP 2: Dosimetry Film Sensitivity? Calibration?

41. WP 2: Dosimetry DAP FOV size and shape Uniform Distribution? (Practical) application for CBCT?

42. WP 2: Dosimetry → Combine measurements → Assesment of distribution (anthropomorph / homogeneous)

43. Introduction CBCT • SEDENTEXCT project • CBCT dosimetry Effective dose (phantom) Standardised dose index • CBCT Optimisation

44. WP 3: Optimisation • Technical image quality assessment • Image quality vs. Radiation dose! • Diagnostical performance < technical parameters • Optimising beyond available options • Optimising on others levels: also in progress Monte Carlo simulations (G.Zhang, Leuven) Reconstruction (e.g. artefact reduction)

45. WP 3: Optimisation • What are the most relevant image quality parameters in dentomaxillofacial imaging, and how are they best measured using a test object? • How do CBCT devices relate to each other for these parameters? • How do CBCT pixel values correlate to actual densities and CT numbers (Hounsfield Units)? Are pixel values uniform throughout the reconstructed volume? Which are the most relevant acquisition parameters affecting the stability and linearity of pixel values? • Are CBCT datasets truly isotropic? • How can metal artefacts be evaluated and which parameters influence their appearance?

46. WP 3: Optimisation Development of QA tools PMMA cylinder Inserts

47. WP 3: Optimisation • Spatial resolution (XY and Z) • Point spread function • Line spread function • Contrast resolution • CT number • Artefact analysis • Geometric accuracy (XY and Z) • Homogeneity • Uniformity • Dose?

48. WP 3: Optimisation Scanora 3D Picasso Trio 3D Accuitomo ProMax 3D Galileos Kodak 9000 3D SkyView i-CAT

49. WP 3: Optimisation • Spatial resolution (XY and Z) • Point spread function • Line spread function • Contrast resolution • CT number • Artefact analysis • Geometric accuracy (XY and Z) • Homogeneity • Uniformity • Dose?

50. WP 3: Optimisation