Types of external radiotherapy

Conformal radiotherapy is also called three-dimensional (3D) conformal radiotherapy. It is a very commonly used type of radiotherapy. The radiation beams are precisely focused so that nearby healthy tissue is spared. This results in fewer side-effects, allowing a higher dose of radiation to be given.

Stereotactic radiotherapy (SRT) is a type of highly precise radiation therapy used to treat tumours and other abnormalities in the body. It delivers focused, high-dose radiation beams to a specific target while minimising exposure to the surrounding healthy tissues. There are 2 main types:

1. Stereotactic radiosurgery (SRS) – Despite the name, SRS is not surgery. It’s a one-time, high-dose treatment typically used for small brain tumours or metastases (disease that has spread from another area). Rarely, the treatment may require between 3-5 sessions.

2. Stereotactic body radiotherapy (SBRT) – Also called stereotactic ablative radiotherapy (SABR), this involves multiple (usually between 1–8) sessions of focused radiation. It's used for tumours in the lung, liver, spine, prostate, and other parts of the body.

Stereotactic radiotherapy is a non-invasive alternative to surgery, has a shorter treatment time compared to conventional radiotherapy and and is effective at controlling small tumours. Your medical team will advise you if stereotactic radiotherapy might be a suitable treatment for your type of cancer.

DIBH is used when radiotherapy is given to the chest area. The idea is that you take deep breaths and hold them for short periods while the radiation is delivered, to shift your heart and other structures away from the beam of radiation. For example, when giving radiotherapy to the left breast, which is near the heart. When you stop holding your breath, the radiation beam is switched off. Your radiation therapist will help you during this treatment so that you know how to breathe the right way.

Intensity-modulated radiotherapy (IMRT) can shape the radiotherapy beams so that different doses of radiotherapy can be given to different parts of the treatment area. For example, if you are having radiation to your throat for throat cancer, the lymph nodes in your neck will also need treatment but at a much lower dose. 

With IMRT you will receive a higher dose to your throat and a lower dose to your neck lymph nodes. IMRT also helps to reduce doses of radiation to normal, healthy tissues compared to standard radiotherapy.

VMAT is a form of IMRT that allows for even more efficient and accurate use of intensity-modulated radiotherapy. VMAT is not suitable for everyone – your multidisciplinary team will decide about this treatment based on your needs. It is also not as widely available as IMRT. 

Often tumours can move between and during radiotherapy. For example, when you breathe, swallow or fill your bladder. Image-guided radiotherapy (IGRT) allows for changes in your tumour’s location. 

Images are taken of your body every time you have treatment. These images help your therapists to adjust your radiotherapy so that it is targeting the tumour. By constantly checking the size and location of the tumour, your doctors can make sure that your treatment is as accurate as possible.

For some types of blood cancers like leukaemia you may need radiotherapy to your whole body. This is called total body irradiation, or TBI.

TBI is usually part of the preparation before you have a bone marrow or stem cell transplant. The radiation helps by destroying your existing bone marrow, including any cancer cells. After this, you will receive healthy bone marrow or stem cells to help your body make new, healthy blood cells. 

Read more about total body irradiation.

Contact radiotherapy can be used to treat cancers on the surface of your skin. These include basal cell carcinomas (BCCs), squamous cell carcinomas (SCCs) and other skin conditions. It uses energies much lower than those of the linear accelerators. Sometimes it is used to treat secondary cancer in the bone, for example in the ribs. Different sizes of applicators can be used, depending on the size of the treatment area. The applicator is put into the head of the machine and then placed on the skin surface. This is why it is called contact radiotherapy.

PBT is a type of radiation treatment that uses protons rather than X-rays (photons) to treat tumours. With PBT, a dose of high-energy protons is targeted directly at the tumour, reducing the radiation given to surrounding healthy tissues and vital organs. 

PBT is only suitable for a small number of people with specific types of tumours. PBT is not currently available in Ireland. 

If your doctor recommends PBT, you will need to travel abroad to receive it.

More information on proton beam therapy

Carbon ion radiotherapy is an advanced type of radiation treatment that uses heavy particles (carbon ions) instead of X-rays. 

It delivers high-energy radiation that can destroy cancer cells more effectively, especially in hard-to-treat or radioresistant tumours – these are tumours that are less sensitive to radiation therapy, which makes traditional radiotherapy treatment less effective. 

The treatment is very precise, so it spares healthy tissue near the treatment site. 

Carbon ion radiotherapy is not currently available in Ireland. If your doctor recommends this treatment, you must travel abroad to receive it.