Principle
SIRT is a form of arterial infusion chemotherapy involving the injection of radioactive material in the form of millions of radioactive microspheres directly into tumors via the hepatic artery for the treatment of liver cancer. The microspheres follow the arterial blood flow into the small blood vessels that supply the liver tumor. The microspheres become stuck in the tumor due to size limitations, whereupon they release high doses of radiation, such as b-rays, into the tumor. The radiation directly targets the tumor in vivo, thereby allowing for higher doses than would be possible using in vitro radiation therapy, which is less likely to affect the surrounding organs.

This therapy (known as particle therapy in China) is a type of brachytherapy using radioactive isotopes, such as iodine-131. In Taiwan, yttrium-90 microspheres have also been approved for SIRT. Yttrium-90 microsphere therapy was developed in Australia in 1998, and was approved by the US FDA for hepatic metastatic disease from colorectal cancer in 2002. It was approved in the EU for patients with unresectable hepatocellular carcinoma in 2003. In Taiwan, SIRT is used mainly for patients with liver metastasis of colorectal cancer after failure to respond to third-line treatment. It is occasionally used for the treatment of malignant liver tumors, for which other conventional therapies are unsuitable. Currently, health insurance in Taiwan does not cover this therapy.

Yttrium-90 microspheres are radioactive microspheres that can be carried in glass microspheres or liposomes. The radiation range is only 1.1 cm and the half-life is short (approximately 64 hours). Over a period of approximately two weeks, local radiation is used to kill liver tumors via high-doses of b-rays over a short distance. Unlike external beam radiation therapy, which is limited to 30 Gy to prevent damage to the surrounding normal tissue, SIRT allows the delivery of 150 Gy to the tumor. Enhanced positioning accuracy through the use of angiography can enhance local tumor destruction and reduce further side effects. Overall, the toxicity of SIRT is far below that of chemotherapy.
 

Benefits of SIRT
Unlike most forms of radiation therapy, SIRT is generally required only once. This can improve the quality of life for patients and their family.
 

Limits of SIRT
SIRT is more expensive than many other forms of treatment. For patients with limited liver function, SIRT must be applied twice from different sides, thereby doubling the price. SIRT can only be applied once in any position, due to the fact that multiple applications would result in excessive exposure to radiation.

SIRT can cause liver and/or kidney failure in cases of poor kidney function, large liver tumors (more than 60% of hepatocytes) or liver dysfunction, such as severe jaundice. SIRT may cause severe hepatotoxicity in patients taking light-sensitive agents, such as capecitabine for colorectal cancer. Thus, it is generally recommended that patients withdraw from these drugs for at least two months prior to SIRT.

Individuals with numerous blood vessels branching between the liver and lungs are ill-suited to SIRT, due to the risk of radioactive agents being shunted into the lungs, which can lead to radiation pneumonitis. SIRT is also not advised for pregnant women.
 

When to use

1. Patients with liver metastases from colorectal cancer, primary liver cancer, neuroendocrine adenoma, and other liver metastasis.
2. Patients who do not qualify for surgical resection and are not amenable to conventional ablation.
3. Patients who meet the WHO-prescribed physical condition of 0 to 1.
4. Tumor(s) located in a single organ with no obvious signs of infection.
5. Normal liver function and no other symptoms such as ascites or liver failure.
6. The volume of polymeric protein is similar to that of yttrium-90, such that rate of hepatopolmunary lung shunting through the distribution of polymeric proteins can be calculated to determine the distribution of yttrium-90.
7. Medical imaging radiologists conduct angiography to pre-embilize collateral blood vessels leading to the stomach and intestines in order to reduce the possible side effects of yttrium-90 microspheres.
    

Preoperative considerations of SIRT

1. Regular testing of blood, liver and kidney function, and coagulation.
2. Consent forms.
3. Patients receiving local anesthesia do not have to fast, but they must not eat excessively.
4. Local shaving.
    

Intraoperative considerations of SIRT

1. Patients should lie down and avoid moving.
2. Local anesthesia is required.
3. Intraoperative conscious patients in any discomfort should contact healthcare providers.
    

Postoperative considerations of SIRT

1. Patients should rest in bed and drink water to promote the excretion of contrast medium via urine.
2. Pressure is applied to stop bleeding. Patients may get out of bed as long as there is no bleeding after twelve hours. Some hemostatic dressings can reduce the time patients must remain prone.
3. Patients may take antipyretic analgesics to relieve abdominal pain and fever.
4. On the third day following treatment, patients should undergo tests of liver and kidney function.
5. One month after treatment, imaging is performed to evaluate the therapeutic effects. If successful, testing is continued every three to four months. Patients may undergo treatment again, in cases of abnormally elevated fetoprotein (AFP) levels or new or recurrent tumors, as determined by ultrasound, CT, or other imaging methods.
6. For a period of 24 hours after surgery, patients should flush the toilet twice after using it.
7. For a period of one week after surgery, patients should not ride in a vehicle with other people for more than two hours.
8. For a period of one week, patients should not share a bed with anyone.
9. For a period of one week, patients should avoid close contact with children and pregnant women.
10. For a period of one week, patients should try to remain at least two meters from others.
     

Risks and Complications
Mild discomfort, such as abdominal pain, nausea, fever, and gastrointestinal discomfort. More severe side effects such as stomach ulcers are rare, and these side effects can be prevented by administering drugs or collateral vessels embolization. A small number of patients contract radioactive pneumonitis or hepatitis; no effective treatment has been identified for these symptoms.​