Intensity modulated radiotherapy (IMRT) is a type of conformal radiotherapy. Conformal radiotherapy shapes the radiation beams to closely fit the area of the cancer.
You can have IMRT on a standard radiotherapy machine, called a linear accelerator (LINAC).
How does IMRT work?
The LINAC has a device called a multileaf collimator. The multileaf collimator is made up of thin leaves of lead which can move independently.
They can form shapes that fit precisely around the treatment area. The lead leaves can move while the machine moves around the patient. This shapes the beam of radiation to the tumour as the machine rotates.
This means that the tumour receives a very high dose and normal healthy cells nearby receive a much lower dose.
Each radiotherapy beam is divided into many small beamlets that can vary the intensity of radiation. This allows different doses of radiation to be given across the tumour.
IMRT can be very helpful in areas such as the head and neck, for example to avoid the spinal cord or salivary glands.
Planning IMRT
There are several steps involved in planning IMRT.
You begin with a CT scan at the radiotherapy department.
You may also have MRI scans or PET scans of the area of the body to be treated.
The information from these scans feeds directly into the radiotherapy planning computer.
The treatment team carefully plans the treatment using the scan images. They use advanced computerised dose calculations to find the dose strength pattern that best matches the tumour shape.
The planning may take longer than for some other types of radiotherapy.
Skin markings
The radiographers might make marks on your skin that act as reference points to make sure every treatment session is accurate.
Radiotherapy masks and moulds
If you are having radiotherapy to your head or neck, you may need to wear a radiotherapy mask during your treatment. You may hear this called a shell or mould.
Most types of masks are made of a mesh material with lots of small holes. You can have a mould for other parts of the body, such as the breast or limbs.
The mould or mask keeps the treatment area completely still, so your treatment will be as accurate as possible.
After the planning session
After the planning session you usually have to wait a few days or up to 2 weeks for the physicist and your radiotherapy doctor to create your treatment plan.
You then get an appointment for your first session of radiotherapy.
Having IMRT
To have the treatment you lie on a radiotherapy couch. Your radiographers help you to get into the right position and put on any moulds that you may need.
You might have the treatment from a machine called a LINAC. Or another type of radiotherapy machine, for example a TomoTherapy machine. TomoTherapy is a CT scanner combined with IMRT.
Once you are in the right position your radiographers leave you alone in the room. This is so they are not exposed to the radiation.
They will often take x-rays before you have treatment. This is to ensure that you’re in the correct position and is called image guided radiotherapy (IGRT).
Your radiographers watch you carefully either through a window or on a closed circuit television screen (CCTV). They can talk to you through an intercom. They may ask you to hold your breath or take shallow breaths during the treatment.
You can’t feel radiotherapy when you actually have the treatment. It doesn’t hurt. It may take between 15 and 30 minutes or more.
https://www.cancerresearchuk.org/about-cancer/cancer-in-general/treatment/radiotherapy/external/types/intensity-modulated-radiotherapy-imrt