Radioactive iodine MIBG (131 I-MIBG) for neuroendocrine tumours (NETs)

131 I-MIBG is a type of radioisotope therapy. These treatments use radioactive medicines to treat some types of cancer. MIBG stands for Meta-Iodo-Benzyl-Guanidine. It is also called:

• targeted radiotherapy
• radio labelled treatment
• targeted radionuclide therapy

The treatment uses a radioactive form of iodine called iodine 131. The radioactive iodine circulates through your body in the bloodstream. The neuroendocrine tumour (NET) cells pick up the radioactive iodine wherever they are in the body. The radiation in the iodine then kills the NET cells.

You might have 131 I-MIBG as a treatment for a NET if you can't have surgery. Or if the NET has spread to other parts of the body and is causing symptoms. It is not a treatment for NEC.

What is radioisotope therapy?

Radioisotope therapy uses radioactive medicines to treat some cancer types. 

The radioisotope travels around your body in the bloodstream to the area where the cancer is. The radioactive part is called an isotope. It may be attached to another substance, which is designed to take the isotope to the cancer.

The cancer cells take up the radioisotope and get a high dose of radiation, which destroys them. The healthy cells receive a low dose or no radiation. 

There are different types of radioisotope therapy including 131 I-MIBG. 

How 131 I-MIBG works

Some types of NET make abnormal levels of hormones . These are called functioning NETs. Most functioning NETs take up a substance called MIBG. Your doctor checks if your NET takes up MIBG before you can have treatment.

To check, you have a special scan called a nuclear medicine scan. If your NET does take up MIBG, your doctors might give you 131 I-MIBG treatment. 

In the laboratory, doctors attach the radioactive iodine to the MIBG. When you have the 131 I-MIBG treatment, it circulates through your body. The NET cells take up the 131 I-MIBG treatment. 

The 131 I-MIBG enters the cell through a special channel in the cell wall. The radiation in the iodine then kills the cell from the inside.

When do I have 131 I-MIBG?

You might have 131 I-MIBG if you have a NET and you can't have surgery. Or if your NET has spread to other parts of the body and is causing symptoms. This treatment won’t get rid of the NET but can control your symptoms and help you feel better.   

Before the start of treatment, your doctor checks that your NET takes up MIBG. You have a radioactive scan called an mIBG scan to check for this.

You usually have 131 I-MIBG every 3 to 6 months.

How you have 131 I-MIBG

Before

You start taking potassium iodate tablets 1 or 2 days before having the 131 I-MIBG treatment. And you continue taking them for up to 2 weeks afterwards.  This helps to protect your thyroid from the effect of treatment.

Some drugs can affect the way 131 I-MIBG is taken up by the cancer cells. Your doctor or specialist nurse will tell you which drugs you need to stop before treatment.

Having 131 I-MIBG

You go into hospital to have treatment. The treatment makes you slightly radioactive, so you stay in a room on your own until the radioactivity drops to a safe level. It usually takes 5 to 7 days. 

You have treatment through a small tube (cannula) in your arm or back of your hand. There is usually a nurse, physicist and doctor in the room when you are having treatment. They attach the 131 I-MIBG drip to the cannula. It takes up to 4 hours to have the treatment.

After 131 I-MIBG

You stay in a single room until the radiation levels fall and it’s safe for you to go home. Your sweat, urine and saliva are radioactive during this time. To help reduce the amount of radiation in your body you need to:

• drink plenty of water to help flush the radioactivity out of your system
• shower twice a day
• go to the toilet regularly
• suck boiled sweets or mints to increase the amount of saliva you make

There are safety precautions you need to take to limit the amount of radioactivity to other people:

• pregnant women and children are not allowed into your room
• visitors, nurses and doctors can only spend a short time with you
• your nurse might ask you to flush the toilet more than once after you have used it

A physicist might check your levels of radiation every day with a monitor. They may also test anything that is taken out of your room. Do not take anything valuable or precious into the hospital with you. Some of your possessions may need to be disposed of or kept in hospital for quite some time after you go home if they show any radioactivity. 

Side effects

131 I-MIBG can cause side effects. These include:

High blood pressure

You might have high blood pressure during this treatment. Your nurse and doctor will check your blood pressure regularly. They may slow down or stop the 131 I-MIBG drip for some time if your blood pressure gets too high.

Feeling or being sick

You may feel sick for about 2 days after treatment. Your doctor or nurse can give you anti sickness medicine to help with this.

A drop in the number of platelets in your body

About 4 to 6 weeks after treatment, the level of platelets in your body may drop. This happens because the radioactive treatment can affect the bone marrow. 

The bone marrow is a spongy substance in the centre of the bones that make blood cells, such as platelets. Having low levels of platelets increases your risk of bleeding.

You usually have blood tests after treatment to check for this. 

Coping

Treatment for neuroendocrine cancer can be difficult to cope with for some people. Your nurse will give you phone numbers to call if you have any problems at home.