Decorative image

What is internal radiotherapy?

Internal radiotherapy gives radiation from inside the body. There are different types of internal radiotherapy treatments, such as nuclear medicine (radioactive liquids) or brachytherapy (radioactive implants). The type you have depends on your cancer type and where it is in your body.

Nuclear medicine involves putting radioactive liquids inside the body. These liquids can come in the form of capsules, drinks or injections. And can treat or diagnose cancer. 

Whereas, brachytherapy uses radioactive metal. This metal is put into the body either inside or close to the cancer.

How radiotherapy works

Radiotherapy treatment works by damaging the DNA within the cancer cells. DNA is the genetic code that controls how the body's cells behave. 

Why you might have internal radiotherapy

Internal radiotherapy delivers a higher 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 fewer healthy cells receive a dose of radiation. 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 treatment 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 seeds, wires or pellets. 

Nuclear medicine 

You have a scan to help plan your nuclear medicine treatment. For the scan you might have a radioactive liquid or tablet. This can highlight the area that needs treatment. Using the scan your doctor can 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.

Nuclear medicine

Examples of radioactive liquids include:

  • phosphorus – used for blood disorders
  • radium – for cancer that has spread to the bones (secondary bone cancer)
  • strontium – for secondary bone cancers
  • iodine – used for benign (non cancerous) thyroid conditions and thyroid cancer

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.


Internal radiotherapy implants are radioactive metal. They might be wires, balls or seeds. They are put into your body, close to the cancer or in the area where the cancer was removed.

The radioactive metal is called a source and is left inside the body for a period of time.

The source might be left in for: 

  • a few minutes
  • a few days
  • permanently

For most types of implants the radioactivity only travels a few millimetres through body tissue and so it can't be detected outside the body.

In some types of cancer, small metal implants, or seeds, are left in the body permanently. After a few days, the radiation has usually dropped to a safe level. And after 8 to 10 months almost all of the radiation has been released.

Information and help

Dangoor sponsorship

About Cancer generously supported by Dangoor Education since 2010.