Radioactive iodine MIBG (131 I-MIBG)

131 I-MIBG is a type of internal radiotherapy. MIBG stands for Meta-Iodo-Benzyl-Guanidine. 

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 that can’t be removed or that has spread to other parts of the body and is causing symptoms.

What is internal radiotherapy?

Internal radiotherapy means giving radiotherapy to the cancer from inside the body. The treatment gives a high dose of radiation to the cancer, but little to the surrounding tissues. 

There are different types of internal radiotherapy. For NETs, you might have:

  • peptide receptor radionuclide therapy (PRRT)
  • radioactive iodine MIBG (131 I-MIBG)
131 I-MIBG is also called targeted radiotherapy, radio labelled treatment or targeted radionuclide therapy.

How 131 I-MIBG works

MIBG is a substance taken up by most NET cells that make hormones (functioning NETs). Up to 80 out of every 100 functioning NETs (up to 80%) take up MIBG. Your doctor checks this before you can have treatment.

Special scans called nuclear medicine scans can check whether the NET takes up MIBG. If it does, doctors can give 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 and is taken up by the NET cells wherever they are in your body. 

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 that can’t be removed by surgery or that has spread to other parts of the body and it is causing symptoms. This 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


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. 

Staying in a single room can feel lonely. It can help to bring some old books and magazines with you. There might be a telephone in the room, so you can talk to your friends and family. Talk to your nurse if you are worried. They can reassure you.

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. 


Treatment for neuroendocrine tumours 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. 

If you have any questions about treatment, you can talk to Cancer Research UK’s information nurses on freephone 0808 800 4040, 9am to 5pm, Monday to Friday.
Last reviewed: 
19 Mar 2021
Next review due: 
19 Mar 2024
  • Gastroenteropancreatic neuroendocrine neoplasms: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    M. Pavel and others
    Annals of Oncology 2020, Vol 31, Issue 5 

  • Current Consensus on I-131 MIBG Therapy
    Daiki Kayano & Seigo Kinuya
    Nuclear Medicine and Molecular Imaging, 2018. Vol 52, Pages 254–265

  • Guidelines for the management of gastroenteropancreatic neuroendocrine (including carcinoid) tumours (NETs)
    J Ramage and others
    Gut, 2012. Vol 61, Pages 6-32

  • Treatment of Neuroendocrine Tumours in Adults with 131 I-MIBG Therapy
    JB Bomanji and others
    Clinical Oncology, 2003. Vol 15, Pages 193-198

  • EANM procedure guidelines for 131 I-meta-iodobenzylguanidine (131 I-mIBG) therapy
    F Giammarile and others
    European Journal of Nuclear Medicine and Molecular Imaging, 2008. Vol 35, Pages 1039-1047

  • Radioactive iodine MIBG treatment information for patients
    Oxford University Hospitals NHS Trust, 2015

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