Ghidurile Europene pentru CBCT - partea I

RADIATION PROTECTION: CONE BEAM CT FOR DENTAL AND MAXILLOFACIAL RADIOLOGY
Evidence based guidelines , a report prepared by the SEDENTEXCT project 2011

www.sedentexct.eu

 

The SEDENTEXCT project (2008-2011) is supported by The Seventh Framework Programme of the European Atomic Energy Community (Euratom) for nuclear research and training activities (2007 to 2011) http://cordis.europa.eu/fp7/euratom/.

Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use that might be made of the following information. The views expressed in this publication/document/guidelines are the sole responsibility of the author and do not necessarily reflect the views of the European Commission.

PREFACE 

SEDENTEXCT was a collaborative project that aimed to acquire key information necessary for sound and scientifically based clinical use of Cone Beam Computed Tomography (CBCT) in dental and maxillofacial imaging. In order that safety and efficacy are assured and enhanced in the “real world”, a parallel aim was to use this information to develop evidence-based guidelines dealing with justification, optimisation and referral criteria for users of dental CBCT. The aim of this document is to provide such evidence-based guidelines to professional groups involved with CBCT in dental and maxillofacial imaging, including:

• Dental and Maxillofacial Radiologists
• Dentists working in primary care and their assistants
• Radiographers/ Imaging technicians
• Medical Physicists
• Equipment manufacturers and suppliers

The core guidance in preparing the document has been from the two relevant Council Directives of the European Union:

• Directive 96/29/Euratom, of 13 May 1996, laying down the basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionising radiation (Basic Safety Standards Directive)

• Directive 97/43/Euratom, of 3 June 1997, on health protection of individuals against the dangers of ionising radiation in relation to medical exposure (Medical Exposures Directive).

Beyond these sources, the detailed guidelines have been prepared by systematic review of the currently available literature. No exposure to X-rays can be regarded as completely free of risk, so the use of dental CBCT by practitioners implies a responsibility to ensure appropriate protection. 

This document supersedes the Provisional Guideline document published in May 2009, incorporating new research, including work carried out within the SEDENTEXT project itself. 

Guidelines are not a rigid constraint on clinical practice. Local variations will be required according to national legislation, healthcare provision and practice and the unique clinical circumstances of patients.

I hope that the document will be of help to professional groups and contribute to optimizing the use of ionizing radiation in dental imaging. 

K. HORNER

SEDENTEXCT project Co-ordinator

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2: RADIATION DOSE AND RISK

2.1: X-rays

X-rays are a type of electromagnetic (EM) radiation. EM radiation also includes visible light, radio waves, microwaves, cosmic radiation, and several other varieties of “rays”. All can be considered as “packets” of energy, called photons, which have wave properties, most importantly a wavelength and frequency. EM radiation can vary in wavelength from 10-13 to 103 m with X-rays having a small wavelength of 10-9 to 10-13m. The importance of this is that small wavelengths mean high energy, deeper penetration though matter and high energy transfer to the matter. When X-rays hit atoms this energy can be transferred, producing ionisation of atoms. Other examples of ionising radiation are alpha, beta and gamma radiation, which are mostly associated with the decay of radioactive materials. All ionising radiations have the capability cause harm to the organs and tissues of the body of exposed persons.

2.2: Radiation damage

When patients undergo X-ray examinations, millions of photons pass through their bodies. These can damage any molecule by ionisation, but damage to the DNA in the chromosomes is of particular importance. Most DNA damage is repaired immediately, but rarely a portion of a chromosome may be permanently altered (a mutation). This may lead ultimately to the formation of a tumour. The latent period between exposure to X-rays and the clinical diagnosis of a tumour may be many years. The risk of a tumour being produced by a particular X-ray dose can be estimated; therefore, knowledge of the doses received by radiological techniques is important. While doses and risks for dental radiology are small, a number of epidemiological studies have provided some limited evidence of an increased risk of brain (Longstreth et al, 1993; Preston-Martin & White, 1990), salivary gland (Preston-Martin & White, 1990; Horn-Ross et al, 1997) and thyroid (Hallquist et al, 1994; Wingren et al, 1997; Memon et al, 2010) tumours for dental radiography.

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4: JUSTIFICATION AND REFERRAL CRITERIA

As with any X-ray exposure, CBCT entails a risk to the patient. It is essential that any X-ray examination should show a net potential benefit to the patient, weighing the total potential diagnostic benefits it produces against the individual detriment that the exposure might cause. The efficacy, benefits and risk of available alternative techniques having the same objective but involving less (or no) exposure to X-rays should be taken into account. A record of the justification process must be made in the patient‟s clinical records.

All CBCT examinations must be justified on an individual basis by demonstrating that the potential benefits to the patients outweigh the potential risks. CBCT examinations should potentially add new information to aid the patient‟s management. A record of the Justification process must be maintained for each patient ED BP

In order that the justification process can be carried out, it is essential that selection of dental CBCT is based on the individual patient‟s history and a clinical examination. The “routine” use of dental CBCT on patients based on a generalised approach rather than individual prescription is unacceptable. A “routine” (or “screening”) examination is defined as one in which a radiograph is taken regardless of the presence or absence of clinical signs and symptoms.

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4.4 Surgical applications

Surgery of the dental and maxillofacial region encompasses minor procedures (oral surgery) that may be performed in dental practices and major surgery (maxillofacial surgery) that would always be carried out by specialists, often in a hospital environment.

4.4.1 Exodontia 

There is no literature related to the use of CBCT as part of the pre-extraction assessment of erupted teeth and there seems no good reason to suggest its use for this purpose. The literature concentrates on unerupted teeth, principally lower third molars, as demonstrated in the systematic review performed by Guerrero et al (2011).

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5:     CBCT EQUIPMENT FACTORS IN THE REDUCTION OF RADIATION RISK

        TO PATIENTS

The literature review in section 2.5 showed that the effective dose may vary significantly between different CBCT equipment. In this section, the significance of selection of appropriate exposure settings in limiting doses while maintaining the image quality at acceptable clinical levels (optimisation) is reviewed. Due account was given to any available national recommendations on CBCT optimisation (Haute Autorité de Santé, 2009; Health Protection Agency, 2010; Statens strålevern, 2010).

5.1: X-ray tube voltage and mAs

The kilovoltage (kVp) of an X-ray tube is the potential difference between anode and cathode during operation. The tube voltage determines the energy of the X-rays. Lower tube voltages give lower energy X-rays and thus increase the dose to the skin of the patient (Horner 1994). Increasing the kVp may result in a decrease in skin and effective dose (Geijer et al 2009) but an increase in scatter. Higher kVp, however, reduces the beam hardening effect (Ludlow 2011). More research is needed to explore the optimisation of kVp in CBCT. The product of the tube current measured in milliamperes (mA) and the exposure time measured in seconds (s) only affects the number of photons emitted by the X-ray tube and not their energy. Increased mAs increases dose, but the beam penetration and image contrast remain the same. The kVp and mA in dental CBCT equipment is either fixed or can be varied depending on the CBCT unit (Ludlow et al 2006; Lofthag-Hansen et al 2008; Silva et al 2008; Okano et al 2009; Roberts et al 2009). Fixed kVp and mA preclude optimisation.

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6.4.2 Reject analysis 

A simple and valuable tool in clinical image QC is reject analysis. Over a specified time period, a record is kept of radiological examinations that are rejected and that require repeats to be performed, with the date and the reason for the rejection (e.g. area of interest not imaged, image blurred etc.) and the cause if known (e.g. incorrect positioning, patient movement etc.). This allows the calculation of the proportion of examinations which are rejected over a specified period and the identification of the most frequent causes of rejection. Reject analysis can be carried out prospectively (as images are performed) and/or retrospectively. When performed retrospectively, this procedure is a form of Clinical Audit, which requires assessment against a clearly defined set of Quality Standards. Table 6.1 provides a means of comparing CBCT examinations against a standard.

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APPENDIX 1 SUMMARY OF RECOMMENDATIONS

The core recommendations and statements in this document are the “Basic Principles”, described in section 3.3. Below are listed the other specific guidelines, taken from the relevant sections, with their evidence grading:

Introduction and Guideline development

1.1: These Guidelines should be reviewed and renewed using an evidence-based methodology after a period no greater than five years after publication.