Radiaiton Dose Measurements Flashcards
What are the 6 radiation dose measurement methods and see they ionisation or excitation.
- Free air ionisation chamber - ionisation
- Thimble ionisation chamber - ionisation
- Chemical conversion - ionisation
- Photographic density - ionisation
- Calorimetry - excitation
- Thermoluminescent dose meter - modified form of excitation only one used to measure staff doses.
Properties of X-rays
Travels in straight lines at the speed of light
Obeys the inverse square law
Small Changes in distance cause large changes in dose
Penetrates excites and ionises matter
Photographic and fluoroscopic effect
Unaffected by magnetic or electric fields
Can’t see taste smell or feel X-rays
When they hit a pt they spray
Can only respond to energy higher than green
Why use filtration and what level above and below 70kv
Removes low energy photons - they would affect pt without providing any diagnostic benefit
Below 70kv 1.5mm thick al
Above 70kv 2.5mm thick al
Differences or maim features of IRR1999 and IR(ME)R 2000
IRR1999 is not about pts
IR(ME)R 2000 is all about patients
Both are enforced under the HASAW 1974
Any breaches in both regulations could result in criminal negligence charges.
IRR1999 is about
Providing a safe working environment
Protecting workers
Protecting members of the public
Demonstrating adequate management of radiation protection
Quality assurance of hardware
Hse notifiable
New practices have to write to hseat least 28 days before opening to let them know they will be using ionising radiation.
Any change in ownership or address of practice is notifiable
IR(ME)R 2000 is about It is the law Justification and optimisation Defines the 4 key roles Employer Referrer Practioner Operator and the entitlement to act in these roles Procedural quality assurance
What is a Controlled area ; how big for below and above 70kv and where the operator is advised to stand
Controlled area is anywhere that a pt can potentially receive 3/10 of their annual dose limit
Only person allowed on controlled area is the pt - unless unable to comply with instructions due to age or physical/mental disability then a carer is allowed in the controlled area
Should not be a member of staff, should be a sensible adult preferably not pregnant and have full explanation and small risk
60-65kv 1 meter around the tube and pt
70kv 1.5 meters around tube and pt
Controlled area continues in direction of primary beam until beam is attenuated by physical Barrier or enough distance
Operator advised to stand 2 meters away and behind the tube.
What are the responsibilities of the practitioner
Fully accept all legal responsibility for the decision to give the pt a dose of radiation
Must make sure that delivering a dose is clinically justified and benefit to pt is greater than the risk
If someone else taking xray must make sure they are competent
Who can be rpa and rps and differences in their roles.
RPA can not be anyone who works on the premises
Must be an external person
Doesn’t have to visit practice in person
Doesn’t have to help to put things right
Provide advice by telephone email or letter
Has to be reaccredited every 5 years, practice has to check this on hse website.
RPS
Must work in the practice
Must be in practice for majority of the week
Provides supervision to ensure everyone works within local rules, regs and standard operating procedures.
What would you say to a patient worried about radiation dose
X-rays are dangerous Only take them if essential Only use trained staff Dose is low Talk about equivalent doses If stiff unsure refer back to dentist
Dose limit for staff working with radiation, not working with radiation and pregnant staff.
1 mSv for staff working with radiation
0.3 mSV for under 18’s or staff not working with radiation
1 mSv for pregnant staff during the notified period.
What is the preferred measurement unit for radiation protection and why
Effective way dose because it’s the only measurement that gives a realistic assessment of the potential for harm
How is effective dose calculated
Absorbed dose x radiation weighting factor x 22 tissue weighting factors
Gy x WR x
Why do we use QA and what are its main principles
To identify problems in imaging systems before they affect the pt
Helps us ensure best possible image at lowest dose
4 key elements
Equipment
Accessory equipment
Staff training
Audits
