Medical uses Flashcards
medical tracers
substances that are used in biological processes in the body and contain a radioisotope
How are medical tracers used?
a patient can eat or drink the substance or it can be injected
the ionising radiation emitted by the tracer can be detected and the biological processes monitored.
Doctors can then diagnose the nature and location of any health problems
e.g. fluorodeoxglucose (FDG) is a radioactive form of glucose that is used as a tracer.
Once it is in the blood it travels to the tissues that use glucose.
When part of the brain is affected, less radioactivity is detected because glucose is not being used
PET scanners and how do they work
used to produce 3D coloured images of the internal workings of the patient
- the tracer is a radioactive material that decays quickly by emitting positrons
- when the positrons come in contact with electrons in the body the two particles annihilate each other, resulting in the formation of gamma rays
- these gamma rays are detected and then processed to create an image
- the tracers decays quickly, so need to be produced close to where they are used
treating tumours internally
cancer tumours can be treated by using a radioactive source that is inside the patient
it enters the patient by injection or consumption
e.g.
in the treatment of thyroid cancer, the radioactive element iodine-131 is used.
It is swallowed in a capsule.
The iodine is taken up by the thyroid gland but not by other parts of the body, meaning that the radiation is likely to kill the thyroid cancer without affecting other healthy cells surrounding it
treating tumours externally
- several beams of gamma rays are fired, from different positions, towards the cancer
- each beam is not energetic enough to kill the cancer, but damages it
- by moving the beam, the amount of radiation received by the surrounding tissue is reduced
Explain why internal treatments are used to treat cancer tumours [3]
when internal treatments are used, the ionising radiation can be targeted at the tumour
this means that most of the ionising radiation goes to the tumour and damage to surrounding areas is reduced
with external treatment, the ionising radiation has to pass through healthy tissue which can be damaged
Define what a medical tracer is [2]
a radioisotope that is taken into the body (by injecting/eating/drinking)
it is used to monitor biological processes in the body
Explain why several low-energy gamma ray beams are used instead of a single high energy beam when treating cancer with gamma rays from an external source [4]
a single high-energy beam would have a much higher energy in one place so that it would destroy all cells it came into contact with when fired at the body
whereas many low-energy beams will not have sufficient photon energy by themselves to harm healthy cells, but when they are focused at a point the energies of the individual beams add up to become a large energy that can kill the cancer tumour
Explain why radioisotopes that emit alpha particles are not used as medical tracers [3]
alpha particles are highly ionising so absorbtion by tissues lead to cellular mutations/cancer
alpha particles emitted from a tracer in the body would be absorbed by the tissue surrounding the tracer, and so could not be detected outside the body
brachytherapy
a type of internal radiation therapy
involves the placing of seeds, ribbon or capsules inside the patient’s body near to the tumour
or the radioisotope can be injected or ingested so it travels through the body
example of a radioisotope used in internal radiation therapy and its half life
iodine-131
half-life of 8 days - treats the cancer without causing long term harm
emits beta
used to treat thyroid cancer
a source used in external radiation therapy
cobalt-60
half life of 5 to 6 years - does not need to be constantly replaced
emits gamma
Does a patient become radioactive when treated:
a) externally
b) internally
a) no as they do not come into contact with a source
b) yes, as they do come into contact with a source, and it emits particles that can leave the body
