Radiology year 4 lecture 6 Flashcards
Name the types of ionising radiation that can cause damage
x-ray, gamma rays, alpha particles, beta particles, neutrons.
How does ionising radiation cause tissue damage?
Eergy absorbed by the tissue causes ionisation, which causes localised energy deposition in the body which can adversely affect the biochemical balance of the cell and can lead to death, abnormal growth or function.
What does the degree of damage caused by ionising radiation depend on?
the amount and type of radiation and the tissue affected.
What two general categories can the biological effects of ionising radiation be divided into?
Deterministic and stochastic effects.
What is deterministic effects of ionising radiation, give examples and draw graph. When does it occur after radiation?
When severity of abnormality increases as dose of radiation increases, but oly above a defined threshold. eg skin, erythema, cataract formation. relatively quickly normally.
What are stochastic effects of ionising radiation, give examples and draw graph.
the probability of occurence increases as dose increases. eg carcinogenesis and induced genetic defects.
What types of tissue is radiation more likley to effect and give examples.
Tissues with a high turnover rate and relatively undifferentiated cellular components. e.g. bone marrow, skin, intestine, gonads.
What two effects does the stochastic effect have and describe both.
carcinogenic: increases incidence of malignant neoplasia, though latent period may be several years eg leukaemia 3-5 years and solid tumours 20-30 years.
mutagenic effect: irradiation of the germinative cells of the gonads will increase mutation rate and increase possibility of inherited abnormalities in offspring.
Are the effects of radiation cumulative and reversible?
yes, no.
What is the absorbed dose and what is the units?
energy imparted to the tissue. Measured in Grays (Gy).
What are Grays?
joules per kg body tissue
What are the drawbacks of using grays for risk indication?
Does not take into account the type of radiation.
What is the dose equivalent and why is it used?
absorbed dose x quality factor. It is used as it takes into account the type of radiation and is used to assess risk. It is measured in Sieverts. (Sv)
What is the quality factor for xrays?
1
What are dose limits?
Levels of radiation that are unlikely to significantly increase the risk to a person’s health.
What are the annal dose limits?
Whole body: employees 20mSv trainees 6mSv other 1mSv women of reproductive capacity 13mSv rolling Extremities: employees 500mSv Trainees 150mSv Other 50mSv
what three documents is the legislation encompassed in?
Ionising radiations regulations 1999, approved code of practice and veterinary guidance notes for the ionising radiation regulations 1999.
What does the Health and Safety at Work act 1974 require of an employer?
provide and maintain safe equipment
ensure the absence of risk to health in connection with the use and handling of equipment
provide information, training and supervision of his/ her employees.
How should amount of radiation exposure be minimised?
Use of lead lined tube
Filter primary beam
collinate primaty beam
service xray machine at least annually
exposure button on long (2m) cable and release of button must terminate exposure
illuminated sign on the control panel to indicate when xrays are being produced.
How should the premises be regulated so as to minimise exposure?
Room should be large enough to keep away from primary beam
adjacent/ downstairs rooms should be made sure not to be at risk
Warning signs and lights outside xray room
exclude all unnecessary personnel
keep distance
How muhc is a single and double brick wall equivalent in lead?
single= 0.5mm lead equivalent, double= 2mm lead equivalent.
What does protecitve clothing protect against?
scattered radiation (not the primary beam!)
how much lead equivalent should gloves and aprons be?
aprons= 0.25 lead equivalent, gloves= 0.35 lead equivalent.
What should protective clothing be checked for and how often?
annually for cracks, cuts or damage.
What is the ALARA (ALARP) principle?
As low as reasonably achievable (practical).
lowest exposure factors
fastes film-screen combinations
avoid repetition through adequate technical quality
no holding patients except in exceptional circumstances
use positioning aids instead
use cassette holders with long handles for equine work
1mm lead sheet on table to prevent back scatter
anaesthesia/ sedation where possible,
lead screens ofr protection of staff or leave the room.
what should monitoring measure?
exposure dose to personnel and work practise.
What should be used to measure exposure doses?
monitoring film badge/ thermoluminescent dosimeter worn at chest or waist level under any protective clothing. The dosimeters contain lithium fluoride. Radiation causes electrons to be raised to a higher energy leated and when heated this energy is released as light. The light emitted is measured and represents the exposure to radiation.
What age do you have to be to be allowed in the xray room and who else is not allowed?
over 16. pregnant women are not allowed. 1-18 year olds can only go in intermittently.
what is the role of the principle of the practice?
obtains x ray machine, obtains regulations, notifies the health and safety executive and appoints a radiation protection adviser and radiation protection supervisor.
who is the radiation protection adviser and what is their role?
a radiation physicist or have a diploma in veterinary radiology. They check room construciton/ size. monitor machine, table, protective clothing, advises on problems. changes to room, equipment, procedures, reports to principle
what is the radiation protection supervisor and what is their role?
member of the practice. supervises procedures and training, monitoring, records, protective clothing.
What is a controlled area?
an area should be designated a controlled area if the dose rate averaged over a working day exceeds 7.5uSv per hour. This is 2m radius of the beam but in practise is the whole radiography room.
Who can be in the controlled area during radiography?
a classified worker or abey written arrangements. In vet practises, no empolyees should be classified workers since no employee should ever approach 3/10 of any dose limit.
