Dosimetry & radiation protection

SIR-Spheres microspheres are transported directly to liver tumours, this allows a larger dose of radiation to be delivered locally than is possible with conventional radiotherapy.

SIRT microspheres contain the radioactive element, yttrium-90, which delivers a form of radioactivity called beta radiation over a relatively short distance: an average of 2.4 mm in human tissue. This is how the radiation can be more localised than other treatments. Beta radiation consists of electrons, rather than traditional X-rays. All radioactive sources decay in a predictable time (half life) as they deliver the radiation. Yttrium-90 has a half-life of approximately two and-a-half days (64 hours), therefore most of the radiation (over 97%) is delivered to the tumour in the first two weeks following treatment, although the microspheres remain in place permanently.

Radiation protection

There are simple precautions required by law when radioactivity is handled. These aim to reduce exposure of people who are not undergoing treatment, including staff, friends and family.

Since advice may vary slightly between hospitals, your local team will advise you on specific timeframes. The following is general guidance, which may differ slightly from the exact advice offered by your treating centre:

• For the first 24 hours, thorough washing of hands after going to the toilet helps to clean away any radioactive contamination. Cleaning up any spills of body fluids such as blood, urine, or stools and disposing of them in the toilet is also necessary to reduce accidental exposure.
• Avoid sharing a bed with your partner for 5 days.
• Avoid all non-essential close contact with children, infants and pregnant women for 10 days.
• You must not receive SIRT treatment if you are pregnant and you must not become pregnant within two months of being treated as this may cause irreversible harm to the unborn baby. Effective contraception must therefore be used at all times during this period.
• You must not breastfeed during the first two weeks after treatment and must not use any milk expressed during this period for bottle feeding of your baby.

How much radioactivity will be given?

Your doctors, typically the nuclear medicine team, will prescribe how much radioactivity is required to treat your tumour safely. This is often calculated by measuring how large the tumours and how large the liver is, taking into account the height and weight of the patient. This is usually done by studying any CT or MRI scans taken and also studying the MAA scan taken after the first intervention. All this is done to ensure the optimal treatment is delivered as effectively and safely as possible.