What is radiotherapy for rectal cancer?

Radiotherapy uses high-energy rays to kill cancer cells. It’s often given with chemotherapy. This is called chemoradiation.

Radiotherapy can be given both externally and internally. External radiotherapy uses a large machine to aim high-energy x-rays at the affected area. It’s usually given as an outpatient from Monday to Friday for 4–5 weeks. Internal radiotherapy involves having radioactive material placed inside the body for a set time and then removed.

These treatments don’t make you radioactive. It’s safe to be with other people throughout your treatment.

Radiotherapy may be given before an operation to remove rectal cancer. It’s used to shrink the cancer and reduce the chance of it coming back. If radiotherapy hasn’t been given before surgery, it may be used afterwards if the cancer was difficult to remove or if there is a chance some cancer remains. Radiotherapy is also sometimes used to relieve symptoms if a cancer can’t be cured.

The type of radiotherapy you’re given will depend on the type of cancer you have and your individual situation.

What is radiotherapy for rectal cancer?

Radiotherapy treats cancer by using high-energy rays to destroy the cancer cells, while doing as little harm as possible to normal cells.

Radiotherapy only treats the area of the body that the rays are aimed at. It is often given in combination with chemotherapy. This is called chemoradiation. Chemotherapy makes cancer cells more sensitive to radiotherapy.

Radiotherapy doesn’t make you radioactive. It’s perfectly safe for you to be with other people, including children, throughout your treatment.

How radiotherapy is given

There are two ways of giving radiotherapy: externally and internally.

External radiotherapy

This is normally given in the hospital radiotherapy department as a series of short, daily sessions. It uses equipment similar to a large x-ray machine. Each treatment takes 10–15 minutes. They are usually given Monday– Friday, with a rest at the weekend. Your doctor will discuss the treatment and possible side effects with you.

Internal radiotherapy

This involves having a radioactive material (the source) placed close to or inside the tumour for a limited period of time. This is called high dose rate (HDR) brachytherapy. As with external radiotherapy, high-energy rays are used to kill the cancer cells.

Before the treatment, the rectum needs to be emptied. This involves having a mini enema (liquid is put into the back passage to empty it). Brachytherapy is usually given under a general anaesthetic and the procedure takes about an hour.

A small number of people with early-stage rectal cancers may be treated with a type of brachytherapy called Papillon treatment. This can be given as an outpatient and doesn’t need a general anaesthetic. It is only available in a few hospitals, so you may need to travel some distance to have it. There is a website dedicated to radiotherapy called Papillon where you can read more about what it is.

When radiotherapy is given

Radiotherapy before surgery

Radiotherapy is sometimes given before an operation. The aims are to:

  • shrink the cancer so that it is easier to remove
  • reduce the chance of the cancer coming back.

You may have a short course of external radiotherapy. Treatment is given once a day, Monday–Friday, the week before surgery.

If the cancer is large, you may have a longer course of radiotherapy that lasts up to six weeks. This is usually given with chemotherapy, which can help make the radiotherapy more effective (chemoradiation).

After a longer course of radiotherapy, you wait for at least six weeks before you have surgery. During this time, the radiotherapy or chemoradiation will continue to work, shrinking the cancer.

Some people with cancer in the middle or lower third of the rectum are offered internal radiotherapy (HDR brachytherapy) before surgery. The aim is to shrink the tumour and reduce the need to remove the anus during surgery.

HDR brachytherapy is a new treatment, so not all the potential risks and benefits are known. Before you decide to have this treatment, your doctor will explain what is involved and discuss the possible benefits and risks with you. They will also give you written information to help you make your decision.

Brachytherapy may be given in combination with external radiotherapy or on its own. Your doctor will discuss with you whether this treatment may be suitable for you.

Radiotherapy after surgery

If radiotherapy wasn’t given before surgery, you may have it afterwards if:

  • the cancer was difficult to remove
  • some cancer cells may be left behind
  • the cancer had spread through the bowel wall or into nearby lymph nodes.

External radiotherapy is usually given every weekday for 4–5 weeks.

Radiotherapy for advanced cancer

External radiotherapy may be used to treat rectal cancer that has spread or come back after treatment. It’s most likely to be used to treat cancer in the pelvis (the area between the hip bones). The aim is to shrink the cancer and relieve symptoms such as bleeding or pain.

Radiotherapy can usually only be given once to any particular area of the body, because of the effects it has on healthy tissues close by.

If bowel cancer has spread to the liver, specialised radiotherapy techniques such as stereotactic radiotherapy and selective internal radiotherapy (SIRT) may be used. We have more information about radiotherapy for secondary cancer in the liver.

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