What is internal radiotherapy?

Internal radiotherapy gives radiation from inside the body. There are two main types of internal radiotherapy:

  • radioactive liquid treatment (radioisotope or radionuclide therapy)
  • brachytherapy (radioactive implant treatment)

The type you have depends on your cancer type and where it is in your body.

How radiotherapy works

Radiotherapy works by damaging the DNA within cancer cells so they can no longer divide and grow. DNA is the genetic code that controls how the body's cells behave. 

Why you might have internal radiotherapy

Internal radiotherapy delivers a high dose of radiation with fewer side effects than external radiotherapy. This is because internal radiotherapy delivers radiation from inside the body, close to the cancer, so affects fewer healthy cells. However, internal radiotherapy is only suitable for smaller cancers.

Sometimes you might have internal radiotherapy as a boost to a small area after having external radiotherapy.

Planning internal radiotherapy


To plan your brachytherapy, you have a scan, such as a CT or an ultrasound scan. Your doctor uses the scans to work out how much radiation you need and where to put the radioactive source (implants).  

Radioactive liquid treatment

You have a scan to help plan your treatment. For the scan you might have a radioactive liquid or tablet. This can highlight the area that needs treatment. Your doctor can then work out how much radiation you need for the treatment. 

You might have the planning and treatment on the same day. Or have 2 appointments on different days.

Radioactive liquid treatment (radioisotopes or radionuclides)

You have radioactive liquid treatment as a drink, capsule or injection.

Examples of radioactive liquids include:

  • iodine-131 – for thyroid cancer and non cancerous (benign) thyroid conditions
  • phosphorus (P-32) – for some blood disorders
  • radium-223 – for cancer that has spread to the bones (secondary bone cancer)
  • strontium-89 – for secondary bone cancers

The radioactive part of the liquid is called an isotope. It may be attached to another substance, which is designed to take the isotope into the tumour.

Although the radioactive liquid travels through your body, it mainly collects in the areas where the cancer is and so has little effect on the healthy cells of the body.

Brachytherapy (radioactive implants)

With brachytherapy, a small radioactive material is put into your body, into or very close to the cancer. Or in the area where the cancer was removed.

Doctors use brachytherapy to treat several different types of cancer, most commonly:

  • prostate cancer
  • cervical cancer
  • womb cancer

The radioactive material is called a source and is sealed inside a holder called an implant. The implants may be seeds, wires or discs. The implant is left inside the body for a certain time. This might be for:

  • several minutes
  • a few days
  • permanently (the radioactivity gradually fades until it is no longer radioactive)

Radiation safety

You may need to follow some safety procedures when you have internal radiotherapy. This is to help protect others from being exposed to the radiation. You may stay in a single room in the hospital while you have treatment. And you may need to limit visitors during this time.

When you go home you may need to follow certain precautions to protect your family and friends. This is often only for the first few days you are at home.

The safety precautions you need to take will depend on the type of treatment you are having. Your treatment team will explain what these precautions are and how long you need to follow them for.

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