What Selective Internal Radiation Therapy (SIRT) is
How SIRT works
Which cancers SIRT can treat
Research into SIRT
How you have SIRT
What Selective Internal Radiation Therapy (SIRT) is
SIRT stands for Selective Internal Radiation Therapy. It is a new way of using radiotherapy to treat liver cancers that can’t be removed with surgery. SIRT is internal radiotherapy, which is also called ‘brachytherapy’. It sends tiny beads called microspheres containing a radioactive substance directly to the tumours through a small tube called a catheter. The microspheres are also called ‘SIR-spheres’, and the radioactive substance is called ‘yttrium 90’.
The catheter goes into the hepatic artery. This is the main artery that supplies blood to the liver. The liver gets most of its blood supply from a blood vessel called the portal vein. But tumours in the liver get theirs from the hepatic artery. So by using the hepatic artery, SIRT is able to target the tumours without affecting the normal liver.
How SIRT works
The microspheres travel through the hepatic artery into the blood supply of the tumours. They then get trapped in the tumours’ small blood vessels where they release the radiation.
The radiation damages the tumours’ blood supply so the tumours can’t get the nutrients they need. This is why this is process is sometimes called ‘radioembolisation’. The radiation also damages the DNA of the cancer cells, which stops the cancer cells growing.
The liver can only cope with small doses of external radiotherapy. But because SIRT targets the tumours, not the liver, doctors can use it to give the tumours a larger dose of radiation.
The microspheres give off radiation to an area only 2 to 3mm around where they are trapped. This means they cause very little damage to the surrounding healthy tissue. The microspheres only stay radioactive for 10 to 14 days but stay in the liver permanently. They are harmless.
Which cancers SIRT can treat
Doctors only use SIRT if they cannot remove the tumours with an operation. They have looked at how well this treatment works for both primary and secondary tumours of the liver, including
Advanced bowel cancers that have spread to the liver
Cholangiocarcinomas
Hepatocellular cancers
Secondary neuroendocrine tumours that have spread to the liver
Research into SIRT
In 2004 NICE issued guidance stating that
SIRT was safe to use
Research showed SIRT could reduce the size of liver tumours
The NICE guidance says that doctors can use SIRT to treat people
Who can’t have surgery
Who have been told that SIRT is a new treatment
The guidance also said we needed more research to see if SIRT could help people live longer and reduce symptoms.
A phase 1 trial in 2007 used SIRT to treat people whose bowel cancer had spread to their liver. The researchers treated the people in the trial with SIRT along with FOLFOX chemotherapy.
As this was a phase 1 trial, the researchers were mainly trying to find out
How safe it was to combine these two treatments
What the doses should be
The results from this trial showed that the combination treatment was safe. They also suggest that the people who had the combination treatment were free of cancer for longer than people who had chemotherapy alone. However as this was a small, early trial, we need further research to confirm these results. The researchers are now planning a phase 3 trial to test SIRT in combination with chemotherapy.
How you have SIRT
You may have SIRT on its own or with chemotherapy.
Before you can have the SIRT, you have an angiogram. This is to look at the blood supply to the liver and to check your hepatic artery. This can vary between people. Occasionally people can't have treatment because their hepatic artery also supplies blood to their lungs or other sensitive tissue. This means that the SIRT microspheres could reach these areas and damage them.
Immediately before you have the treatment you will have
A sedative to relax you
Anti sickness medicine
Antibiotics
Then the doctor gives you an injection into your groin to numb the area. Once the area is numb they make a tiny cut in the groin and put a fine tube called a catheter into the artery in the groin (the femoral artery). Using scans the doctor passes the catheter up the femoral artery and into the hepatic artery. Once this is in place the doctor gives the treatment. The whole process takes about an hour.
After the treatment you will have a dressing put over the small wound. Most people need to stay in hospital overnight. Your doctor will give you painkillers and anti sickness medicine to take if you need it.
Generally the side effects are mild. They include raised temperature, chills, nausea, and stomach ache or a feeling of pressure in the abdomen. These side effects are usually gone in a few days. Tiredness may last for a couple of weeks.
Some research shows that people who had SIRT had a fall in the number of white cells in the blood. White cells help the body fight infection. As SIRT is often given with other treatments we need more research to find out exactly how and why this happens. More rarely, people have had inflammation of the liver.
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