External radiotherapy

People who have cancer (a malignant tumor) generally have three treatment options: surgery, chemotherapy and radiotherapy. Radiotherapy, also called radiation therapy, aims to destroy the cancer tissue by exposing it to certain high-energy rays. The source of radiation can be located outside the body (external radiotherapy) or it can be placed inside the body and very close to the tumor (internal radiotherapy or brachytherapy).

What is external radiotherapy?

External radiotherapy is the most common form of radiation therapy. It is called “external” because the radiation is beamed from a source outside of the body through the skin into the body and right through to the tumor tissue.

The kind of radiation used in external radiotherapy is high-energy (ionizing) radiation. It has the ability to change the structure of cells. The aim is to damage the cancer cells and destroy them. Non-ionizing forms of radiation, such as normal light rays or microwaves, don't have this effect.

When is external radiotherapy used?

Whether or not it's possible to use external radiotherapy to treat a cancerous tumor depends on a number of factors:

  • Where (in which organ) is the tumor?
  • How big is it?
  • Has it spread to other parts of the body? If so, to what extent?
  • What kind of tumor is it?

When treating a malignant tumor, external radiotherapy can generally be used alone or together with surgery and/or chemotherapy. If radiotherapy is given in addition to another therapy, it is called “concomitant” radiotherapy (additional therapy for known remaining cancer cells).

If radiotherapy is used after the complete surgical removal of a tumor, to prevent it from returning, it is called “adjuvant” radiotherapy. And if it is given before surgery or chemotherapy, it is known as “neo-adjuvant” radiotherapy.

Radiotherapy can either be used to try to cure the cancer (“curative”) or to slow it down and relieve pain and other symptoms (“palliative”).

What different kinds of external radiotherapy are there?

There are basically two kinds of radiation that can be used in radiotherapy: electromagnetic radiation (for example, x-rays) and particle radiation (for example, electrons). Nowadays, most radiation treatment is carried out using machines called particle accelerators (for instance, linear accelerators). These machines produce and deliver radiation using electric fields rather than radioactive material.

One special kind of radiotherapy is called “proton therapy.” In Germany, only a limited number of radiotherapy centers currently offer proton therapy because it is very complex and expensive. For most potential areas of use, it's still unclear whether proton therapy has benefits compared to radiotherapy with a linear accelerator.

Why are tests done before beginning with radiotherapy?

No matter what kind of radiation is used, the aim is to target the tumor as precisely as possible and to minimize damage to surrounding healthy tissue. The dose of radiation that reaches the tumor also needs to be high enough. This requires thorough planning.

First of all, the tumor’s exact location is determined with the help of ultrasound pictures, x-rays, and magnetic resonance tomography () scans. Based on what they find, doctors will then decide which exact area they are going to irradiate.

A treatment plan is made, laying out details such as what kind of radiation and what doses will be used. Patients almost always receive the full radiation dose spread out across a number of sessions – an approach known as “fractionated radiotherapy” (dose fractionation). This is done because healthy tissue and tumor tissue react differently to radiation. Healthy tissue regenerates more quickly than tumor tissue does after exposure to radiation. So fractionated radiotherapy gives the healthy tissue a chance to recover a little between sessions.

Fractionated radiotherapy is typically spread out over a time period of several weeks (usually between five and eight weeks). During this time, the patient usually has one session a day on five days a week (Monday to Friday).

Sometimes the tumor is irradiated from a number of different angles at different radiation intensities. To make it easier to precisely target the same area in each session, “tattoo” marks are made on the skin using a special kind of semi-permanent ink. Making molds or casts of body parts can also help to ensure that the patient’s body is always in the same position during radiotherapy sessions.

What happens during treatment?

Radiotherapy is usually done as an outpatient procedure. In other words, you can go home after each session. One session usually lasts about 15 to 45 minutes. Most of this time is spent setting up the equipment and positioning it precisely. The actual exposure to radiation only takes a few minutes. During this time you are left alone in the treatment room but can see the medical staff and can attract their attention by pressing a button. You can normally leave your underwear on during the procedure, but it is advisable to wear outer layers of clothing that are easy to take off.

The equipment might make buzzing, humming or loud clicking noises. Sometimes the source of radiation might move to a different position during the treatment, making an audible motor-like sound.

You aren't allowed to move during treatment, and restraints may be used to help you stay in the same position. This may become uncomfortable after a while. Just like when you have an ordinary x-ray done, you don't feel anything during the actual radiotherapy itself. But the actual radiation itself doesn't hurt.

What are the possible side effects?

Whether or not you experience side effects during or after radiotherapy depends on many factors. These include the strength of the radiation dose, the part of the body being treated, and what organs are within the irradiated area. What’s more, radiation affects different people in different ways.

In most cases the side effects are only temporary. They may appear a few days after treatment and some can last for a few weeks.

Tiredness is the most common general side effect of radiotherapy. It can arise after only a few treatment sessions. Its exact cause is not known. It is suspected that it may come from the body breaking down the cancer cells that die during the therapy.

The side effects that occur directly within the scope of the applied radiation include skin irritations. Not unlike sunburn, the skin can become sensitive and slightly reddened. After three or four weeks the skin may become dry and start to peel, which is sometimes associated with itching. After that it often gets darker because of increased pigment formation.

Radiotherapy used near the digestive tract can cause nausea, vomiting or diarrhea.

Many of these side effects can be effectively treated, for example by using medication.

Whenever possible, the medical staff will attempt to protect your genitals (testicles or ovaries) from the radiation so it doesn’t affect your . If radiotherapy needs to be used in your pelvic region, the doctor will inform you of possible harmful effects and give you advice on how they can be kept to a minimum.

Ahmad SS, Duke S, Jena R et al. Advances in radiotherapy. BMJ 2012; 345: e7765.

Kauffmann G, Sauer R, Weber W. Radiologie: Bildgebende Verfahren, Strahlentherapie, Nuklearmedizin und Strahlenschutz. München: Urban und Fischer; 2011.

Pschyrembel Online. 2022.

Ringborg U, Bergqvist D, Brorsson B et al. The Swedish Council on Technology Assessment in Health Care (SBU) systematic overview of radiotherapy for cancer including a prospective survey of radiotherapy practice in Sweden 2001 – summary and conclusions. Acta Oncol 2003; 42(5-6): 357-365.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on December 15, 2022

Next planned update: 2025


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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