“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

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

Introduction CBCT

Cone Beam CT / Digital Volume Tomography Dentomaxillofacial Radiotherapy Cardiac imaging

Cone Beam CT / Digital Volume Tomography Dentomaxillofacial

Cone Beam CT / Digital Volume Tomography Dentomaxillofacial

Cone Beam CT / Digital Volume Tomography Advantages 3D (isotropic voxels) Detail (voxel size mm) Cost, size, ease of use, … Applications ‘Low dose’ (generally D E = µSv) Viewing possibilities

Cone Beam CT / Digital Volume Tomography Dentomaxillofacial

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

Introduction CBCT SEDENTEXCT project

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

Introduction CBCT SEDENTEXCT project CBCT dosimetry

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

Introduction CBCT SEDENTEXCT project CBCT dosimetry Effective dose (phantom)

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

Thermoluminescent dosimeters (LiF:Mg,Ti) Harshaw Reader 6600

WP 2: Dosimetry Calibration: C → gU → Gy

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

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

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

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

WP 2: Dosimetry

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

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

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

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

Typically available dosimeters

WP 2: Dosimetry Central measurement? Ionization chamber

WP 2: Dosimetry Accuracy? TLD

WP 2: Dosimetry Sensitivity? Calibration? Film

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

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

Introduction CBCT SEDENTEXCT project CBCT dosimetry Effective dose (phantom) Standardised dose index CBCT 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) 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? WP 3: Optimisation

Development of QA tools PMMA cylinder Inserts

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?

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

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?

WP 3: Optimisation

XY plane

Resolution < 3 lp/mm Artefacts Saturation XY plane → line pair pattern on PMMA background 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?

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

WP 3: Optimisation

Cauchy distribution

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?

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

WP 3: Optimisation Gumbel distribution

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?

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

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?

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

WP 3: Optimisation

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

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?

WP 3: Optimisation Titanium rods

WP 3: Optimisation

Smoothing + subtracting background 2 ROIs, ignore black streaks

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

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

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?

WP 3: Optimisation Cfr. spatial resolution

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?

WP 3: Optimisation

Small FOV (truncation, …) Non-homogeneous slices

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

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