Radionuclide Therapy

Question 1

What radiation safety matters must be considered in radionuclide therapy.

Answer 1

• Limit radiation dose to parts of patient not intended.
• Limit radiation hazards to staff, public and others (e.g. family, carers and comforters etc.).
• Minimise risk of contamination.

Question 2

What is the dose limiting factor with regards to justification of radionuclide therapy?

Answer 2

Normal tissue toxicity. This can be limited with lower dose radiopharmaceutical with short half life. A radiopharmaceutical with high target/background ratio can also help.

Question 3

What is the general equation for absorbed dose in radionuclide therapy?

Answer 3

D = (del phi A)/m_t where del is the mean energy emitted per decay, phi is the fraction of energy absorbed by the target organ, A is the total number of decays and m_t is the mass of the target organ.

Question 4

What are some typical radiation protection measures associated with a radionuclide therapy?

Answer 4

• Instruction card explaining patient has recently had radionuclide therapy (e.g. in case of seeing another health professional).
• Flush toilet twice for certain amount of time after treatment.
• Do not give routine bloods for certain amount of time after treatment.
• Time (reduce time handling radiative substances), distance (use of tongs etc.), shielding (e.g. syringe shielding).

Where there is increased chance of external exposure to those in close contact with patient (e.g. I-131 therapy for overactive thyroid):
- Avoid long periods of close contact with everyone.
- Avoid close contact with children and pregnant women.
- No blood samples or invasive procedures for 1 month.
- Carry instruction card for 1 month or 3 months if travelling abroad.

For I-131 therapy for thyrotoxicosis:
- Patient to stay on ward in private radio-iodine suite (includes dedicated shower, toilet, kitchen, waste etc.).
- Patient asked to shower twice a day.
- Dose rates from patient measured until they drop below certain levels.