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 D E =20-100 µSv) Viewing possibilities

8. Cone Beam CT / Digital Volume Tomography Dentomaxillofacial

9. Can CBCT replace traditional radiographic methods?

10. 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

14. WP 0Financial and administrative management WP 1Justification and Guideline development WP 2Dosimetry WP 3Optimisation WP 4Diagnostic accuracy WP 5Cost effectiveness WP 6Training and Valorisation

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. 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? WP 2: Dosimetry

19. 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 OrganICRP 60ICRP 103 Gonads0,20,08 Red bone marrow0,12 Colon0,12 Lung0,12 Stomach0,12 Bladder0,050,04 Breast0,050,12 Liver0,050,04 Oesophagus0,050,04 Thyroid0,050,04 Skin0,01 Bone surface0,01 Brain00,01 Salivary glands00,01 Remainder0,050,12

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

24. WP 2: Dosimetry Scanora 3D Upper jaw100x75mm Upper and lower jaw Lower jaw GalileosUpper and lower jaw150x150mm Kodak 9000 3DLower jaw (part)50x37mm Picasso TrioLower jaw120x70mm ProMax 3DLower jaw80x80mm

25. WP 2: Dosimetry

32. Organ Contribution (%) to effective dose Red bone marrow15 Thyroid44 Skin1,4 Bone surface1,5 Brain1,1 Salivary glands36,9

33. 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!!! WP 2: Dosimetry

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

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

37. Typically available dosimeters

38. WP 2: Dosimetry Central measurement? Ionization chamber

39. WP 2: Dosimetry Accuracy? TLD

40. WP 2: Dosimetry Sensitivity? Calibration? Film

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

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. 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) WP 3: Optimisation

45. 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? WP 3: Optimisation

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

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

52. XY plane

53. Resolution < 3 lp/mm Artefacts Saturation XY plane → line pair pattern on PMMA background WP 3: Optimisation

54. 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?

55. WP 3: Optimisation 0.1 mm0.25 mm Steel wire in air

57. WP 3: Optimisation

58. Cauchy distribution

59. WP 3: Optimisation

63. 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?

64. WP 3: Optimisation PTFE cube PMMA surrounding ESF ↓ LSF ↓ MTF Gumbel distribution

66. WP 3: Optimisation Gumbel distribution

67. WP 3: Optimisation

70. 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?

71. WP 3: Optimisation Air Aluminium Hydroxyapatite (50, 100, 200)

72. 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?

73. WP 3: Optimisation CNR = MPV1-MPV2 (SD1+SD2)/2

74. WP 3: Optimisation

76. Pixel value: relation HA 50,100,200? Work in progress

77. WP 3: Optimisation

79. 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?

80. WP 3: Optimisation Titanium rods

81. WP 3: Optimisation

83. Smoothing + subtracting background 2 ROIs, ignore black streaks

84. WP 3: Optimisation Measure along intervals, keep extreme values Distribute (e.g. Gumbel) and evaluate parameters

85. ProMax 3D 84 kV 9 mA ProMax 3D 84 kV 14 mA WP 3: Optimisation → Inter-device variability → Intra-device variability?

86. 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?

87. WP 3: Optimisation Cfr. spatial resolution

88. 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?

89. WP 3: Optimisation

90. Small FOV (truncation, …) Non-homogeneous slices

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

92. Dose index Effective dose / organ dose analysis (+paediatric) QC phantom: second prototype Image analysis: artefacts, LSF, MTF Pixel homogeneity / uniformity Compare devices & evaluate differences