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, computed tomography and magnetic resonance tomography (magnetic resonance imaging) 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 very rarely receive the full radiation dose all at once. It's typically 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.

Just like when you have an ordinary x-ray done, you don't feel anything during the actual radiotherapy itself. 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. 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.