What is selective Internal Radiation Therapy (SIRT)? And what are SIR- Microsphere?

SIRT is a targeted treatment for liver tumours that delivers millions of tiny radioactive beads called SIR-Spheres microspheres directly to the liver tumours. The development of SIR-Spheres microspheres started in Australia in the 1980s, with regulatory approval being granted in Europe and the United States in 2002. Thousands of patients have now been treated at centers of excellence around the world. SIR-Spheres microspheres are approved for the treatment of liver tumours that cannot be surgically removed. These may be tumours that start in the liver (also known as primary liver cancer), or they may be tumours that have spread to the liver from another part of the body (also known as secondary liver tumours being or metastases).

Who is SIRT suitable for?

SIRT is only suitable for patients who have liver tumours where either the liver is the only site of disease or the liver is the major site of disease. SIRT has no effect on tumours outside the liver. Before SIRT can be offered as a treatment option for patients, there are a number of other factors that have to be considered. Most importantly, you need to have a relatively healthy liver that is working satisfactorily. This is usually determined by a simple blood test.

Who performs the SIRT procedure?

The SIRT procedure is conducted by a medical team that includes a specialist known as an interventional radiologist, together with other specialists trained to work with radiation.

What will my treatment team do before administering SIRT?

Your treatment team will want to know about your previous cancer history and any other medical conditions. They will then conduct a number of initial tests to ensure that it is possible for you to receive SIRT safely. Normally patients will undergo two procedures under conscious sedation. Both procedures will include a radiology procedure known as an angiogram. The purpose of the first angiogram or mapping is to prepare your liver for the SIRT treatment. During the mapping procedure your interventional radiologists will block (embolize) the vessels to minimize the potential for the microspheres to travel to areas outside your liver (e.g. the stomach or intestine). You will also receive a small amount of radioactive “test beads” to check the amount of blood that flows from the liver to the lungs. Assuming that the results of these initial tests are acceptable, the dose of SIR-Spheres microspheres will be determined. The SIR-Spheres microspheres will then be administered during a second procedure which is typically conducted one to two weeks after the initial tests are completed.

How are SIR-Spheres microspheres administered?

The interventional radiologist makes a small puncture in either the femoral or radial artery. A small flexible tube, known as a catheter, is then guided through the artery into the liver. The SIR-Spheres microspheres are administered through this catheter. The whole procedure may take about 90 minutes. You will be sleepy during the procedure but you will be able to communicate with your treating doctor and the team.

How do SIR-Spheres microspheres work?

The SIRT procedure enables radiation – which is often used to treat cancer – to be sent directly into the liver tumours by using the tumor’s blood supply. SIR-Spheres microspheres are targeted directly at the liver tumours via the hepatic artery, so exposure to the remaining healthy liver tissue is minimized. The majority of microspheres are approximately 32 microns (ranging between 20-60 micron) in diameter, about a third of the width of a human hair. The microspheres are small enough to flow through the hepatic arteries, but are too large to pass through the small blood vessels within the tumor, where they become permanently lodged in the tumor bed. SIR-Spheres microspheres contain the radioactive element yttrium-90, which delivers beta radiation over a relatively short distance: an average of 2.5 mm in human tissue. Yttrium-90 has a half-life of approximately two and- a-half days, therefore most of the radiation (over 97%) is delivered to the tumor in the first two weeks following treatment. Since SIR-Spheres microspheres are delivered directly to the tumours, this allows a larger dose of radiation to be implanted locally than is possible with conventional external beam radiotherapy.

What side effects are associated with SIR-Spheres microspheres?

Almost all treatments and drugs can produce unwanted side effects. Some side effects can be minor, making you feel uncomfortable, but a small number can be serious. Everyone is different in how he or she reacts to a treatment. Many patients experience abdominal pain and/or nausea which normally subside after a short time and/or with routine medication. Many patients also develop a mild fever that may last for up to a week and fatigue which may last for several weeks. As a precaution, you may receive additional medications such as pain-killers, anti-inflammatory, anti-nausea and anti-ulcer drugs with your treatment with the aim of preventing or minimizing these side effects.

What are the potential complications from SIR-Spheres microspheres?

In rare instances and even in experienced hands, there is the possibility that a small number of microspheres may inadvertently reach other organs in the body, such as the gall bladder, stomach, intestine or pancreas. If SIR-Spheres microspheres reach these organs, they may cause inflammation of the gall bladder (cholecystitis), stomach (gastritis) or intestine (duodenitis). These complications are rare, but if one of these occurs, they normally require additional treatment. Your treatment team will have received special training to minimize these risks and to prevent them from happening

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