Radionuclide therapeutic unsealed sources and application Flashcards
what sort of radiation are used for imaging purposes and why
gamma rays as they are relatively low dose and have the ability to penetrate through the body
what sort of radiation are used for therapeutic purposes and why
Alpha and Beta as they highly ionising and are easily stopped
what are the three types of Half-life
physical, biological and effective
what is physical half life
The time taken for a radionucleotide to decay to half of its original activity i.e. radium = 1620 year
what is biological half life
the time taken for half the activity to be removed from the patient.
- The patient is radioactive.
what is effective half life
this is calculated from the combined effects of both physical and biological half-life.
what is radio pharmacy
attaching radiation to drugs with a known biological pathway
what forms a radiopharmaceutical
radionuclide + compound
what can radionuclides be used for
- Diagnosis, staging and monitoring.
- Cancer treatment
radionuclide generator systems
it is logistically difficult to use radionuclides with half-life, so what should one do.
Logistically difficult to use radionuclides with a half-life of less than a day. One way to keep supply is a radionuclide parent that decays into another daughter where they can be separated.
o Most common – molybdenum/technetium generator 99Mo/99mTc
how does a gamma camera work?
the patient is administered a radiopharmaceutical and circulates with the physiological process of the body. This circulation is mapped by the gamma camera.
* A collimator, which is honeycomb-shaped shaped absorbs rays at random angles that have the potential to distort images.
The gamma camera gives flashes of light when gamma photons impart energy into it as the Compton scatter event results in kinetic energy loss followed by photoelectric interaction.
how does the Single photon emission computed tomography (CT + radionucleotide imaging) work
Works by generating cross-sectional images of the distribution of the radiopharmaceutical in the body, it rotates around the patient so reduces the effects of attenuation.
how does Positron emission tomography (PET) imaging work
- emitting positrons from a nucleus with too many protons, the protons decay into neutrons which results in the emission of a positron and neutrino.
- A positron travels short distance and interacts with an electron = the annihilation reaction
what is the problem with PET imaging
PET scanners have lots of noise and distortion as some errors can occur for example if two gamma photons are detected within the same time window the camera assumes they are from the same annihilation reaction (electron collimation) but it is not necessarily right.
what is hybrid imaging
combining other diagnostic imaging modalities with radionuclide imaging (RNI)
Name the most common materials in a storage and separator system
99Mo/99Tc
what is 18-FDG and what is it used for?
Most commonly used as a radiotracer for PET imaging PET and is produced by cyclotrons so more expensive than generator-produced RN.
o 18-FDG is useful in oncological applications as it is a glucose analogue and is required for energy in mitotic energy cells. There is an increased demand for glucose to support increased metabolism during cancer.
Can be issues with confusion such as inflammation infection and active muscle contraction requiring glucose uptake.
Tumours with poor glucose uptake have poor 18-FDG uptake.
what can PET-MRI used for?
sentinel lymph node involvement
what is molecular radiotherapy treatment (MRT)
- A compound tracer is administered to establish where uptake in the body is, and a gamma emitter is attached to the compound to image dose uptake.
- After the radiopharmaceutical (either alpha or beta radiation) can be used and has to be equal to the uptake of the tracer
- The therapy is then administered.c
considering that alpha and beta cannot be imaged how can we determine excretion rates
through urine and blood
how can ensure radiation safety during radionuclide unsealed sources
Every practitioner must hold a licence which complies with the department.
Avoid unnecessary contact with pregnant women and children for 24hrs
Express and dispose of breastmilk for at least 24 hours after injection.
o In the patient’s best interest, we can reduce the rate and increase scanning time to achieve a useful number of counts.
the time of excretion (biological half-life) depends on
The time depends on the type of radionucleotide, the physiological functioning of the body and the target organ.
radioactive iodine is used in both imaging and treatment of
thyroid
what are the positives of using iodine-131 for cancer treatment
- localised to desired tissue
- follows known biodistribution in the body
it is logistically difficult to use radionuclides with a half-life of less than a day why?
as decay must be slow enough for imaging.
what images a radionuclide in the body
gamma camera
3 main principles to make RN administration safe
- distance - inverse square law
- time - reduce handling of injections
- shieldding
what is palladium used in
hair pins
