Radiation doses atc Flashcards
What is the approximate radiation does for a extra-oral DPT?
0.02 mSv
When were xrays first developed?
1895 by Roentgen
Edmund Kells took the first dental xray in 1896
Which radiation legislation do us as dentists use?
Ionising Radiation Regulations (IRR) 1999
Ionising Radiation Medical Exposure Regulation (IRMER) 2000
What does the IRR (ionising radiation regulation 1999) relate to?
It relates to the workplace and employees
It provides a framework for ensuring that exposure to ionising radiation arising from work activities, is kept as low as reasonably practical and does not exceed specific limits
What is IRMER 2000?
A document aimed towards patient protection
Minimies risks to patients undergoing medical exposures
It is enforced by the CQC England and the Healthcare inspectorate Wales
What 4 classes of duty holder does IRMER 2000 define?
Employer (legal person)
Referrer
Practioner
Operator
Who is the referrer?
An authorised person that requests the radiograph
The referrer has to perform an adequate history and examination and provide sufficient details regarding the clinical exposure to enable the practictioner or operator to justify the procedure
SUPPLY CLINICAL DETAILS TO ALLOW JUSTIFICATION
What is the function of the practitioner?
TO JUSTIFY THE PROCEDURE
do the benefits outweigh the risks?
Who is responsible for justifying the radiological procedure?
Practitioner
is the radiogrpah going to change the way that you manage the patient?
JUSTIFICATION SHOULD BE RECORDED IN THE PATIENT NOTES
What is meant by the term authorisation?
Recording that justification has been carried out prior to the exposure
(medico-legal exposures must be authorised by the dentist)
What is the function of the operator?
OPTIMISATION OF ALARA
identify the patient, position the tube head, set the exposure, develop the film, evaluate the film
How do you keep doses of radiation as low as possible to patients?
Justify the radigraph
use collomators
What is the dose limit for patients?
There is no written dose limit
What is the role of the IRMER Employer?
They have legal responsibilities to apply IRR and IRMER
they need to be suitably trained and know the dose limits and be able to carry out risk assessments
What does HSE stand for?
Health and saftey executive
When (in terms of radiography) will a dental practitioner need to contact the HSE?
When they want to take radiographs and would like to install equiptment
when there is new ownership of a practice or change of address
THE HSE DO NOT NEED TO BE CONTACTED WHEN EQUIPTMENT IS CHANGED OR RENEWED
Who is responsible for contacting the HSE?
The IRMER Employer
What is the HSE 5 step approach to risk assessment?
- Identify the hazards
- decide who might be harmed and how they might be protected
- evaluate the risks- protective measures
- record the findings
- review and revise the risk assessment.
Give 5 duties of the Employer
Undertake risk assessments
notify the HSE when required
ensure all neccessary systems are in place
establish a Quality Assurance programme (QA)
Ensure that written protocols are in place for every type of radiological exposure
What is the role of the medical physics expert?
To provide adive on:
- Patient dosage
- development and use of new and/or complex techniques
- other matters realting to radioation exposures for dental procedures
True of false
Each dental practice must have a Radiation Protection Advisor (RPA)
TRUE
The appointment must be in writing (IRR 1999)
What is the role of the Radiation Protection Advisor (RPA)?
Safety management
training
What does RPS stand for and what is their responsibility?
Radiation protection supervisor ( IRR 1999)
Each practice needs one. It is usually a dentist but can be a dental nurse
They ensure that the necessary rules are followed
What is a DRL?
A diagnostic reference level
ie the doses for typical examinations of the average sized patient
this information is usally displayed next to the xray machine
EMPLOYERS MUST TAKE ACTION IF THESE ARE EXCEEDED
When do you have to report an over exposure?
When a patient is perceived to have 20x the intended dose
The RPA must be contacted and the patient should be informed of the incident
What is the atomic mass of an atom?
The total number of protons and neutrons in an atom
What is the mass of an electron?
1/1840
What is the atomic number
The number of protons in an atom
If an atom is exctied, what happens to the electron?
It moves from an inner shell to an outer shell. Ie the electron moves to a higher energy level
What is the binding energy?
The energy required to overcome the attraction and remove an electron from an atom. The binding eneergy is greatest for the electron in the K shell, ie the one closest to the nucleus.
What is ionisation?
The removal of one or more electrons from an atom, giving it a positive charge
What is an xray?
Xrays are descibed as wave packets of energy. Each packet is called a photon.
Xrays are a form of electromagnetic radiation
Dental xrays are made up of millions of photons
TRUE OR FALSE
XRAYS are a type of ionising radiation?
TRUE
What is the greatest source of ionising radiation?
RADON
Give 5 properties of Xrays
- They travel in straight lines
- They are invidible and weightless
- They travel at the speed of light in a vacuum
- They obey the inverse square law
- They have a range of wavelengths from 0.01-0.05 nm
How do you produce Xrays
This needs to be done in a vacuum to prevent collision with other atoms
1. produce lots of electons
- accelerate them to a very high energy
- smash them into a target without destroying it
What are the main components of the tubehead?
- Glass xray tube (filament, copper block and target)
- stepdown transformer
- step up transformer
- lead casing
- Oil
- Aluminium filtration
- Collimator
- Beam indicating device
What charge is the anode and cathode?
Anode is positive
Cathode is negative
How are xrays produced in the tubehead?
- Electrons are produced as the filament heats, thermionic emission - Cathode)
- The elctrons are accelerated towards the anode ny a high potential difference (kV)
- Rapid deceleration of the electrons as they hit the tungesten target
- As the electrons collide, the energy is converted as heat (99%) or xrays (1%)
- The heat is removed and dissipated by the oil and they copper block
What is the relevance of kV, mA and Secs on a dental xray machine?
**kV - **Determines the quality of the xray beam, ie the energy of the photons. it affects their penetration and so the contrast of the film
**mA and time - **determines the quantity of the xray photons. Affects the degree of blackening of the film
What are the two methods by which xrays can be produced?
- Bremsstrahlung Radiation
- Characteristic radiation
What are the 3 components of a dental x ray set up?
Tubehead
positioning arms
control panel and circuitary
What is the importance of the aluminium filtration in the tubehead?
It removed low energy photons and reduces the radiation dose to the patient
What is the purpose of the rectangular collimator?
Tries to match the beam size to the image receptor size in order to reduce the dose to the patient
a rectangular collimator reduces the dose to the patient by 50%
What are the advantages of a constant potential?
- Xray production per unit time is more efficient
- More high energy photons per exposure
- fewer low energy harmful photons are produced
- shorter exposure times
What is the benefit of a beam indicating device?
it is a 20cm long cone
It produces a near parallel beam and so reduces any magnification and there is a less irradiated area
What are the 2 types of conventional image receptors?
- Direct action film - the xray photons interact with the film
- Indirect action films - the photons interact with an intensifying screen which produces light that ineracts with the film
What are the components of a film packets?
- Black paper
- Lead foil
- Moisture resistant outer cover
- Film
TRUE OR FALSE
The intra oral xray film has one side coated with emulsion
FALSE
both sides are coated with an emulsion
What is the composition and purpose of the emulsion on the film?
90% silver halide crystals in a gelatin matrix
10% silver iodo-bromide (increases sensitivity)
x-ray or light photons, sensitize the silver-halide crystals that they strike, forming a latent image
What is meant by the film speed?
The amour of exposure a film needs to produce an optical density of 0.1 above the background fog
The faster the film speed, the less exposure required and the smaller the dose to the patient
What film speed for we use at the BDH and how does that compare to digital radiographs?
F speed
Digital dose is 50% less that than of F speed
What determines the film speed?
The number and the size of the silver halide ions
the larger the crystals, the faster the film speed, although there will be some loss in quality
WE SHOULD USE THE FASTEST FILM ALONG WITH ONE THAT WILL PROVIDE ADEQUATE DIAGNOSTIC RESULTS
What do extra-oral cassettes consist of?
contain a film sandwiches between two light intensifying screens
the cassette itself is made from light-tight aluminium or carbon fibre
How do intensifying screens reduce patient does to ionising radiation?
One x-ray photon produces many light photons
fewer xray photons are therfore needed to produce an image
patient dose is reduced at the expense of resolution
What is meant by image resolution?
The ability to differentiate between different stuctures that are close together on the radiograph
DRIECT ACTION FILM RESOLUTION - approximately 10 line paris per mm
INDIRECT ACTION FILM RESOLUTION - approximately 5 line pairs per mm
How can a film become overexposed in a developer?
if it in there for too long
it the temperature of the solution is too hot
If the developing solution is too strong
(a) What pH is the developing solution?
(b) how often should it be changed?
(c) what happens if it is too old?
10.5
every 14 days
film is too pale and underdeveloped
What are the 4 stages when developing a film?
- Development ( the developing solution hads a pH of 10.5)
- Fixation (the fix is acidic pH 4.0-4.5)
- Washing - to remove any residula fixer. If fixer is retained the film becomes stained brown
- Drying
What fo fixer and developer splashes look like on a film fault?
Fixer - White dots
Developer - dark black dots
What is meant by justification?
Is taking the radiograph going to change the diagnosis and management of the patient
When might we take a dental radiograph?
- pathology affecting a tooth +/- supporting tissues
- detecting caries
- teeth present
- assessing root morphology
- localisation of foregin bodies
Which type of intr-oral radiographs might we take?
Bitewings (hoizontal and vertical)
PAs
Occlusal
What extra-oral radiographs might we take?
DPT
Lateral ceph
lateral oblique
Why might we take bitewings?
caries detection
monitor caries/ previous restorations
assessment of periodontal status (vertical bitewings for pockets ~6mm)
Why would you take bitewings for caries diagnosis?
bitewings have a diagnositc yield 4x greater than clinical diagnosis for interproximal caries
However, 50% demineralisation is required before you can visualise caries on a radiograph
Does a low kV give you a better or worse contrast?
Better (good for caries diagnosis)
A high kV is better for looking at bone levels eg for perio
How often should you take posterior bitewings for caries diagnosis?
High risk - 6 months
Moderate risk - annually
Low risk - 24 months in the permanent dentition
12-18 months in the decidous dentition
What 2 tecniques are there for taking a pericapiacal radiograph?
long cone Parralleling technique
bisecting angle
What might you take a periapical?
Assess root morphology
assess periaplic infection
Extent of crown pathology in anterior teeth
Assessment of local anatomy, including tooth development
Why would you take periapical radiographs for periodontal disease?
Determine the severity through bone loss and furcation involvement
to identify any causative factors e.g calculus
to evaluate treatment and assist in other treatment planning
When might you take horizontal bitewings for periodontal diagnosis?
When there is uniform pocketing <6mm with little or no recession
When might you retake a radiographs during endodontic treatment?
if the apex has been missed
if the master file/GP point is >2mm from the apex
How many years after completion, may you want to retake an radiograph following endodontic treatment?
1 year
4 years
FOR ASYMPTOMATIC TEETH
When would you take a radiograph for trauma?
A baseline radiograoh is manditory following all but minor tooth trauma
When would you take a DPT
- Prior to surgery under GA e,g odontome
- Where a boney lesion or unerupted tooth is of a size or positions which precludes complete demonstration on an intra-oral film
- ortho/implant assessment
What is the taken for severe TMJDS?
MRI
Why would you take a lateral ceph?
Look at the skeletal pattern
to look at the incisal angulation
orthognathic surgical planning
