Download Dental CBCT performance testing for physicists and technologists

Dental CBCT performance testing for
physicists and technologists
Thursday 16th March 2017, The Place Aparthotel, Manchester
FINAL PROGRAMME
09:00 – 09:15 Coffee and registration
Session 1 - Background and legislation
Chair: Paul Charnock
09:15 – 09:30 Introduction and questionnaire results
09:30 – 10:00 Current Status of dental CBCT
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
10:00 – 10:30 Clinical uses of dental CBCT with IRMER considerations
Prof Keith Horner, University of Manchester
10:30 – 11.00 The Radiation Protection Implications of a Dental CBCT Installation
Graham Hart, YourRPA, Morecambe
11.00 – 11.30 Coffee
Session 2 – Quality Assurance part 1
Chair: Catherine Taylor
11.30 – 12:00 QA in dental CBCT in an ideal world
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
12:00 – 12.30 Practical solutions to dental CBCT QA
Paul Charnock, Integrated Radiological Services Ltd, Liverpool
12.30 – 13:00 Update on CBCT QA protocol from EFOMP
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
13:00 – 14:00 Lunch
Session 3 – Quality Assurance part 2
Chair: Christie Theodorakou
14:00 – 14:30 Revision of HPA-CRCE-010
John Holroyd, Public Health England
14:30 – 14.45 Update from Evidence Based QA WP – Dental
Paul Charnock, Integrated Radiological Services Ltd, Liverpool
14:45 – 15:00 Contrast to Noise measurements in dental CBCT
Catherine Taylor, The Christie NHS Foundation Trust, Manchester
15:00 – 15:30 Coffee
Session 4 – Open forum & proffered papers
Chair: Paul Charnock
15:30 – 15:45 Regional comparison of dental CBCT image quality parameters
Catherine Taylor, The Christie NHS Foundation Trust, Manchester
15:45 – 16:00 How CBCT Scanners are being used in practice
Anthony Reynolds, Image Diagnostic Technology Ltd, London
16:00 – 16:30 Round table discussions
Topics suggested in questionnaire
16:30
Close
Organised by IPEM’s Diagnostic Radiology Special Interest Group
Current Status of dental CBCT
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
Dental cone beam CT (CBCT) was developed in the late 1990s and is now increasingly used in
oral and maxillofacial clinical practice. There is a wide range of CBCT machines available on the
market for oral and maxillofacial applications. This presentation will review the technical properties
of the commercially available CBCT system and the relevant radiation protection aspects of dental
CBCT such as quality control, patient dosimetry and current national and international guidance.
Clinical uses of dental CBCT with IRMER considerations
Horner K.
Division of Dentistry, School of Medical Sciences, The University of Manchester, UK. Central
Manchester University Hospitals NHS Foundation Trust, Manchester, UK.
The use of cone beam CT (CBCT) in dentistry has grown rapidly and this trend is likely to continue
as old panoramic X-ray systems are replaced. CBCT radiation doses are at least an order of
magnitude higher than those of the conventional dental radiography techniques that it is intended
to supplement or replace. Radiation dose is of concern because much dental X-ray imaging is
carried out in children and young people. Most dentistry takes place in primary care facilities and
there are challenges related to justification because of the normal situation of “self-referral”. In the
absence of on-site radiographers or medical physicists, dentists also face challenges in terms of
optimisation of exposures.
There is a lack of good quality evidence for the diagnostic efficacy of dental CBCT, apart from its
uses in implant dentistry. Intuitively, three-dimensional information seems likely to be an
advantage to dentists, particularly for planning surgery or for endodontic (“root canal”) procedures.
However, it is notable that the four randomised controlled trials that have been carried out,
comparing CBCT with conventional radiographs, have found no significant differences in patient
outcomes after surgery. With one exception, the referral criteria presented in the European and
UK Guidelines1,2 are probably still valid, despite the growth in the published scientific literature.
Clinical evaluation of images by appropriately trained individuals is not universal; neither are the
IRMER requirements for adequate training always understood by dentists.
In terms of optimisation strategies, dentists may want to keep doses to patient low, but the ways of
achieving this are not always clear. This situation is not helped by a lack of knowledge about the
levels of diagnostic image quality needed for specific clinical uses, along with the enormous
variation in image quality between CBCT systems. Only a few publications in the literature have
looked at optimisation strategies, but these suggest that there is scope for reduction of exposures
in some clinical situations (Fig. 1).
Fig. 1: Slices from CBCT
images of an unerupted
canine tooth. Left 70kV, 3mA;
right 90kV, 5mA. The lower
exposure image is probably
adequate for diagnosis.
The simplest optimization strategy is to limit the field of view of the scan to the minimum, where
this is possible; this also reduces the volume of data requiring clinical evaluation. The use of
reference doses and involvement of medical physicists will assist in improving this situation,
although without good image quality criteria the process is not easy.
1
European Commission. Radiation Protection 172. Cone beam CT for dental and maxillofacial
radiology. Evidence-based guidelines. Luxembourg, European Commission, Directorate for
Energy, 2012. https://ec.europa.eu/energy/sites/ener/files/documents/172.pdf
2
Faculty of General Dental Practice (UK) Royal College of Surgeons of Surgeons of England.
'Selection Criteria for Dental Radiography’, 3rd edition, FGDP(UK), 2013.
The Radiation Protection Implications of a Dental CBCT Installation
Graham Hart
YourRPA, Morecambe, UK
Background
YourRPA provides the services of a Radiation Protection Adviser (RPA) and Medical Physics
Expert (MPE) to approaching 25 general dental practitioners (GDPs) with dental Cone Beam
Computed Tomography (CBCT) systems. A number of key issues have arisen both pre- and postinstallation that have significant implications for the protection of both staff and patients.
Observations
The key issues observed have been:
- purchasing a CBCT system (or upgrade of an existing panoramic machine to a CBCT) by GDPs
without a sufficient understanding of the shielding requirements; choice of field of view; patient
radiation dose; the need for ongoing quality assurance (QA) by the practice and on an annual
basis by an external provider; and the training requirements for both operators and interpreters of
the resultant clinical images. Many of these issues have been caused by lack of adequate
RPA/MPE involvement;
- variable information supplied by the installers of the equipment about the need for adequate
RPA/MPE involvement pre-purchase and installation; and variable levels of training on the use of
the CBCT set, the reconstruction and handling of the images and the ongoing quality assurance
of the CBCT set;
- lack of a machine-specific QA test object supplied with the CBCT set to enable comparison
between the critical examination, initial performance assessment / acceptance testing and
ongoing QA. This contrasts sharply with medical CT units, where machine-specific QA test
objects have been provided with the set on purchase for many years, facilitating the local QA
process;
- differences in the radiation footprint between different CBCT sets in terms of both the radiation
dose to the patient and the scattered radiation field to ensure staff doses are as low as
reasonably practicable (ALARP). This emphasises the need for the RPA/MPE to be closely
involved to ensure that adequate advice about both shielding and operation of the set can be
given;
- the lag between the writing and production of guidance on the use of CBCT sets and
technological developments of those sets. Whilst this is understandable, given the pace of
technological change and the writing and approval of guidance, it leads to a degree of
obsolescence which may cause some confusion amongst those for whom the guidance is
intended.
Discussion
The presentation will expand on and discuss each of these issues.
Conclusion
Given the increased radiation protection requirements of CBCT for both staff and patients, more
emphasis needs to be given to radiation protection at both undergraduate and postgraduate levels,
especially as CBCT sets are becoming increasingly more common in general dental practice.
Suppliers and installers of CBCT equipment should also be made aware of the need for adequate
involvement of the Practice’s RPA/MPE during the procurement process.
Quality Assurance in dental CBCT in an ideal world
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
The purpose of Quality Assurance (QA) in oral and maxillofacial cone beam CT (CBCT) is to
ensure consistently adequate diagnostic information, while radiation doses are kept as low as
reasonably practicable. This talk will discuss the quality assurance aspects of oral and maxillofacial
CBCT with a particular emphasis on the quality control requirements and practical challenges.
Practical Solutions to dental CBCT QA
1
Charnock P,
1
IRS Ltd, Liverpool, UK
Dental cone beam CT is a relatively new technology being used predominantly in the private dental
sector. Under UK regulations, the Employer is responsible for ensuring that a QA programme is in
place.
Although the majority of other imaging devices would have a QA programme set up based on
recommendations from IPEM report 91, this technology has only come into common use following
the publication this report and therefore the best source of guidance for QA testing is HPA report
CRCE-010.
This guidance has been written in the style of IPEM report 91, perhaps with a view to being
incorporated at some point in the future.
As a RPA/MPE provider to a number of private dentists, IRS have had access to a relatively large
number of these units and have therefore been able to assess the testing recommendations from
HPA-CRCE-010.
This presentation will show the experiences of trying to perform the recommended tests,
highlighting in particular where the test has been performed using materials and objects that a
medical physics department may have available rather than a specific test phantom
Update on CBCT QA protocol from EFOMP
Dr Christie Theodorakou, The Christie NHS Foundation Trust, Manchester
The European Federation of Organisations for Medical Physics (EFOMP) set up a working party in
2014 to develop a practical and unifying protocol for image quality assessment and dose for cone
beam CT (CBCT). This includes CBCT for oral and maxillofacial, radiotherapy, interventional
radiology and image guided surgery applications. This talk will summarise and discuss the key
points of the EFOMP CBCT QA protocol.
Revision of HPA-CRCE-010: Guidance on the Safe Use of Dental Cone Beam CT Equipment
1
Gulson, A.D, 1Holroyd, J.R
1
Public Health England
The guidance for dental users of CBCT was published by a working party led by HPA (the
predecessor to PHE) in 2010. At the time CBCT was used by only a small number of specialist
dental practitioners. Today there are approximately 500-600 units in use in the UK, including
general dental practices. The upcoming changes in UK radiation protection regulations and the
publication of several key international guidance documents, together with an improved knowledge
of dental CBCT equipment, mean it is timely to revise the current guidance.
PHE convened a working party in 2016 to review the existing UK guidance alongside recent
international guidance covering areas such as quality assurance and training; and then publish
updated UK guidance. The working party is comprised of dentists, medical physicists, radiologists
and radiation protection regulators. It is hoped that this guidance will be published in 2017. This
presentation will show the key areas under review and current thinking as to how international
guidance will be translated to the UK.
The 2010 report proposed an achievable dose as a guide to optimisation of CBCT imaging, but
due to a lack of available data was not able to propose a National Diagnostic Reference Level
(NDRL). The next PHE medical and dental patient dose survey will be launched shortly and this
will request data for dental CBCT imaging for the first time. It is hoped that the results will be
available later this year and a NDRL will be set. Data collected by PHE during surveys of dental
CBCT units over the last few years will be presented during this talk to show typical patient doses
from dental CBCT equipment.
Update from the Evidence Based QA Working Party
1
Charnock P, Fazakerley J
1
IRS Ltd, Liverpool, UK
Under current UK regulations, an Employer of a premises where ionising radiation is used is
required to ensure that a suitable QA programme is in place.
Within the medical sector, there is guidance as to how a QA programme should be structured and
what testing should be performed as part of a QA programme. This will be in the form or level A
and Level B QA where level B is normally more detailed tests done with more complex equipment
but on a less frequent basis.
The evidence based QA working party was set up in to investigate results from level B QA across a
number of different modalities including dental. The aim of the investigations is to determine if the
current tests that are recommended are still fit for purpose and if any specified tolerances are still
appropriate.
The remit of the dental stream is to investigate results from intra oral, pan oral, cephalometric and
dental cone beam CT examinations and so results from tests described in IPEM report 91 and
HAP-CRCE-010 have been collated
This presentation will describe the method of collection, show and describe the results obtained so
far from the dental stream, and highlight any potential outcomes and recommendations.
Contrast to Noise measurements in dental CBCT
Catherine Taylor, The Christie NHS Foundation Trust, Manchester
Objectives: This study evaluated the effect of phantom positioning and the configuration
of phantom inserts on the measurement of contrast-to-noise ratio (CNR) in dental CBCT.
The work aimed to make pragmatic suggestions for the remedial tolerances for CNR
measurements in the routine quality control (QC) of a three-dimensional Accuitomo 170
dental CBCT system (J Morita, Kyoto, Japan).
Methods: Images of the SEDENTEXCT (safety and efficacy of a new and emerging dental
X-ray modality) IQ (image quality) dental CBCT phantom (Leeds Test Objects Ltd,
Boroughbridge, UK) were acquired and measurements of CNR were obtained in three
configurations of inserts and in six phantom orientations for one of the configurations. Five
consecutive images were acquired in each case, to assess the reproducibility of measurements.
Results: Reproducibility of measurements ranged from 1.8% to 4.6%. For the CNR
measurements in the three phantom configurations, the ratio of the measured CNR to the
minimum value was 2.1 ± 0.2 times the minimum value for Delrin® (DuPont UK Ltd,
Stevenage, UK). For aluminium, there was no significant variation between configurations
and for the other three materials, the ratio ranged from 20% to 50%. Significant variations in CNR
with phantom position were observed, with differences between the maximum and minimum values
ranging from 10% to 60%. Absolute differences in CNR from the minimum value ranged from 0.1 to
2.1 with phantom configuration and from 1.2 to 4.5 with phantom position.
Conclusions: The effects of phantom configuration and positioning on CNR measurements
for dental CBCT QC were investigated and possible remedial tolerances suggested.
How CBCT Scanners are being used in practice
1
Reynolds RA
1
Image Diagnostic Technology Ltd, London, UK
Background. Cone beam computed tomography (CBCT) has become the accepted standard for
three-dimensional imaging in dentistry1. Most private dental practitioners will not have received
training in interpreting CBCT images as part of their undergraduate education, and many will not
have been adequately trained to justify or optimise CBCT scans2. Trade-offs between dose and
image quality can be complex, and some practitioners will compensate for perceived poor image
quality by increasing the mAs or other parameters linked to patient dose. It is important therefore to
have in place a regular program of quality controls and measurements, to ensure that the
equipment is functioning optimally. Used in conjunction with operator training, consistently applied
scanner protocols, and evaluation of patient doses, regular performance testing can help ensure
that scans can be taken at the lowest practical dose, consistent with the diagnostic task at hand.
The purpose of this work is to take a snapshot of current CBCT imaging practices, as an indication
of whether the ALARA goal of “as low as reasonably achievable” is in practice being met.
Methods. As part of its image processing services, Image Diagnostic Technology Ltd receives a
large number of CBCT datasets from dental practices across the UK and Ireland. For every scan
received, we retrieve parameters such as scan time, field size, kVp, mAs, and (when available)
CTDIvol, DLP and DAP from the DICOM headers, and make an estimate of the effective dose 3.
For the present study, the data from approximately 1000 scans (drawn from approximately 100
dental practices and imaging centres across the UK and Ireland) was retrospectively analysed.
Results. We categorised the data in terms of (1) field size (2) patient positioning and (3) Dose
Area Product (DAP), with reference to clinical indications (where these were known). Poor
positioning can indicate a lack of understanding of the dose parameters. Table 1 illustrates a wide
variation of DAP values (expressed in mGy.cm2) for the CBCT scanners shown.
Sirona
XG3D
i-CAT
17-19
Gendex
CB-500
Carestream
9000 3D
Vatech
PaX-Flex3D
NewTom
VG
J.Morita
Accuitomo
Planmeca
Promax 3D
Min DAP
157
212
111
117
149
209
125
270
Avg DAP
304
346
358
361
410
536
663
752
Max DAP
563
947
589
708
1032
830
2170
1430
n=
34
217
20
63
105
31
497
26
Discussion. It is instructive to look at the average DAP that is currently being achieved in practice
(in comparison with the lowest DAP that can theoretically be achieved). On one level, it is
beneficial that a range of exposure settings are available to match each diagnostic task (for
example, a large adult will require higher exposures than a small child), but a high average DAP
can also indicate that the machine requires calibration and is being used sub-optimally.
Conclusion. A retrospective review of the DAP values achieved in practice shows these is a wide
variation in the scanning protocols in use from one dental practice to another. This suggest a need
for quality control and protocol optimisation, in conjunction with practitioner and operator training.
Key references.
[1] Brown J et al. Basic training requirements for the use of dental CBCT by dentists: a position
paper prepared by the European Academy of DentoMaxilloFacial Radiology. Dentomaxillofac
Radiol 2014, 43, 201 30291.
[2] Harris D et al. E.A.O. guidelines for the use of diagnostic imaging in implant dentistry 2011. A
consensus workshop organized by the European Association of Osseointegration and the Medical
University of Warsaw. Clin Oral Impl Res. 23, 2012, 1243-1253.
[3] Reynolds RA. How to estimate the dose from a dental CT or CBCT scan (abstract). Physica
Medica: European Journal of Medical Physics. 32,2, 414 (February 2016).