Intensity-Modulated Radiation Therapy (IMRT)

What is intensity-modulated radiation therapy (IMRT)?

Intensity modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and tomotherapy further improve the shaping of a radiation dose to match the tumour shape, compared to 3D conformal radiation therapy (3D-CRT).

In 3D-CRT, the shape of the radiation dose are essentially limited to simple squares or rectangles because of the uniform intensity across each radiation field.

In IMRT, VMAT or tomotherapy, use of a greater number of radiation fields combined with variation of beam intensity within each radiation field allows the oncologist to create any shape to match the tumour and spare normal organs.

For example, where a tumour wraps round a normal organ, IMRT, VMAT and tomotherapy can create a C-shaped radiation dose to treat the tumour and spare the normal organ in the centre. Whereas in 3D-CRT, the central normal organ would get the same full dose as the surrounding tumour.

IMRT, VMAT and tomotherapy use different methods to achieve the same dose-shaping outcome and are largely interchangeable.

IMRT and image-guided radiation therapy

Image-guided radiation therapy (IGRT) can be used to complement IMRT to improve the positional accuracy of the radiation therapy treatment. IGRT uses imaging technology such as X-rays to visualise the position of the tumour so that radiotherapy can be delivered accurately.

Why do you need IMRT?

IMRT has several advantages such as:

• Improved cure rates. Higher doses of radiation can be given to treat the tumour.
• Fewer side effects. Concentrating the radiation beams at the target allows us to limit side effects by avoiding or reducing exposure to the surrounding healthy tissue.
• Option of re-treatment. If re-treatment is needed, IMRT is preferred to reduce injury to normal organs.
• More people can be treated. Radiation therapy allows your tumour to be treated even if it is difficult to reach or is located close to an important organ.
• Better quality of life. Your body recovers better with IMRT than with conventional radiation therapy.

What are the risks and complications of IMRT?

Radiation therapy can cause side effects. They may be the result from the treatment itself or from radiation damage to the healthy cells around the treatment area. Side effects may vary depending on the kind of tissue structures near the tumour being irradiated.

In rare instances, a new cancer different from the first one being treated may develop years later. After treatment, your doctor will regularly check for complications and recurrent or new cancers.

Find out more about the risks of radiation therapy.

How do you prepare for IMRT?

There are several steps to planning IMRT treatment:

1. Your doctor will conduct a physical examination and review your medical history.
2. There will be a treatment simulation session, which includes computerised tomography (CT) scanning. Your doctor will use this scan to make an individual plan for you.
3. During the session, a small mark or tattoo may be placed on your skin to help align and target the equipment.

In some cases you may need to:

• Wear a special mask or mould to keep you still during treatment.
• Follow certain bowel and bladder preparation regimen or fast prior to the simulation and treatment.
• Receive an intravenous contrast material injection during the CT scan to help define the tumour better.
• Undergo additional scanning procedures, such as positron emission tomography (PET) and magnetic resonance imaging (MRI). These diagnostic images can be merged with the planning CT and help your doctor determine the precise location of the tumour target.
• Have radio dense markers inserted into the target (tumour) for more accurate positioning.

IMRT sessions usually begin about 1 – 2 weeks after simulation.

What can you expect in IMRT?

IMRT often requires multiple (fractionated) treatment sessions spread over different days. To decide the number of treatments, your doctor will consider:

• Doses to normal tissue structures
• The location, type and size of the tumour
• Your health

Typically, patients are scheduled for IMRT sessions 5 days a week for 5 – 8 weeks.

Estimated duration

Treatment sessions usually take between 15 – 60 minutes.

Before the procedure

At the beginning of the treatment session, you will be positioned on the treatment table, guided by the marks on the skin (tattoos) defining the treatment area.

If moulded masks or devices were made, they will be used to help you maintain the proper position.

You may be repositioned during the procedure.

Your doctor or radiologist will use imaging systems on the treatment machine such as X-ray or CT to check positioning and marker location.

During the procedure

Once you are in the right position, the medical staff will leave you alone in the room. This is so they are not exposed to the radiation.

You will be able to communicate with your doctor or the staff through an intercom. They may ask you to take shallow breaths or to hold your breath during the treatment.

You should not experience any pain or discomfort during the actual treatments with IMRT. However, if you experience discomfort, do inform the staff so that they can stop the machine.

After the procedure

As treatment progresses and you have undergone a few sessions, you may experience treatment-related side effects.

The number and severity of side effects will depend on the type of radiation, dosage and body part under treatment.

Early side effects happen during or right after treatment and are usually gone within a few weeks. They include:

• Diarrhoea
• Eating and digestion problems
• Fatigue
• Hair loss in the treatment area
• Headaches
• Mouth problems and difficulty swallowing
• Nausea and vomiting
• Skin problems - skin in the treatment area may become sensitive, red, irritated, or swollen. Other changes include dryness, itching, peeling, and blistering
• Soreness and swelling in the treatment area
• Urinary and bladder changes

Talk to your doctor or nurse so they can help to manage them.

Late side effects may occur months or years following treatment. While they are often permanent, they are rare. They include:

• Brain changes
• Colon and rectal changes
• Infertility
• Joint changes
• Kidney changes
• Lung changes
• Lymphedema
• Mouth changes
• Secondary cancer
• Spinal cord changes

Your doctor will discuss with you the potential side effects and how they will be managed.

Care and recovery after IMRT

You may have to go for regular follow-up appointments with your doctor to check on your recovery and look out for any side effects, which may occur well after the procedure.

Contact your doctor if notice any new symptoms so that they can help you manage them.