Radionuclide therapeutic unsealed sources and application

Question 1

what sort of radiation are used for imaging purposes and why

Answer 1

gamma rays as they are relatively low dose and have the ability to penetrate through the body

Question 2

what sort of radiation are used for therapeutic purposes and why

Answer 2

Alpha and Beta as they highly ionising and are easily stopped

Question 3

what are the three types of Half-life

Answer 3

physical, biological and effective

Question 4

what is physical half life

Answer 4

The time taken for a radionucleotide to decay to half of its original activity i.e. radium = 1620 year

Question 5

what is biological half life

Answer 5

the time taken for half the activity to be removed from the patient.

• The patient is radioactive.

Question 6

what is effective half life

Answer 6

this is calculated from the combined effects of both physical and biological half-life.

Question 7

what is radio pharmacy

Answer 7

attaching radiation to drugs with a known biological pathway

Question 8

what forms a radiopharmaceutical

Answer 8

radionuclide + compound

Question 9

what can radionuclides be used for

Answer 9

• Diagnosis, staging and monitoring.
• Cancer treatment

Question 10

radionuclide generator systems

it is logistically difficult to use radionuclides with half-life, so what should one do.

Answer 10

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

Question 11

how does a gamma camera work?

Answer 11

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.

Question 12

how does the Single photon emission computed tomography (CT + radionucleotide imaging) work

Answer 12

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.

Question 13

how does Positron emission tomography (PET) imaging work

Answer 13

1. emitting positrons from a nucleus with too many protons, the protons decay into neutrons which results in the emission of a positron and neutrino.
2. A positron travels short distance and interacts with an electron = the annihilation reaction

Question 14

what is the problem with PET imaging

Answer 14

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.

Question 15

what is hybrid imaging

Answer 15

combining other diagnostic imaging modalities with radionuclide imaging (RNI)

Question 16

Name the most common materials in a storage and separator system

Answer 16

99Mo/99Tc

Question 17

what is 18-FDG and what is it used for?

Answer 17

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.

Question 18

what can PET-MRI used for?

Answer 18

sentinel lymph node involvement

Question 19

what is molecular radiotherapy treatment (MRT)

Answer 19

1. 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.
2. After the radiopharmaceutical (either alpha or beta radiation) can be used and has to be equal to the uptake of the tracer
3. The therapy is then administered.c

Question 20

considering that alpha and beta cannot be imaged how can we determine excretion rates

Answer 20

through urine and blood

Question 21

how can ensure radiation safety during radionuclide unsealed sources

Answer 21

 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.

Question 22

the time of excretion (biological half-life) depends on

Answer 22

The time depends on the type of radionucleotide, the physiological functioning of the body and the target organ.

Question 23

radioactive iodine is used in both imaging and treatment of

Answer 23

thyroid

Question 24

what are the positives of using iodine-131 for cancer treatment

Answer 24

• localised to desired tissue
• follows known biodistribution in the body

Question 25

it is logistically difficult to use radionuclides with a half-life of less than a day why?

Answer 25

as decay must be slow enough for imaging.

Question 26

what images a radionuclide in the body

Answer 26

gamma camera

Question 27

3 main principles to make RN administration safe

Answer 27

1. distance - inverse square law
2. time - reduce handling of injections
3. shieldding

Question 28

what is palladium used in

Answer 28

hair pins