Image guided radiotherapy (IGRT) uses different scans and X-rays to treat an area of cancer.
What image guided radiotherapy (IGRT) is
Image guided radiotherapy (IGRT) is a type of conformal radiotherapy. Conformal radiotherapy can shape the radiotherapy beams around the area of the cancer.
Image guided radiotherapy uses X-rays and scans similar to CT scans before and during radiotherapy treatment. The X-rays and scans show the size, shape and position of the cancer as well as the surrounding tissues and bones.
Doctors plan the radiotherapy to give a high dose to the cancer. It is important that the radiotherapy field covers the whole cancer, plus a border around it. This helps the radiotherapy to work as well as possible in treating the cancer. Doctors try to give as low a dose as possible to the surrounding healthy tissue to reduce the risk of side effects.
Types of IGRT
In some areas of the body, tumours may move slightly during treatment or between treatments. For example the prostate gland changes position according to whether the bladder is full or not. So there is a risk that part of the tumour may be outside the radiotherapy field during some treatment sessions.
With some types of IGRT, the radiographers can take scans using the radiotherapy machine. This can be done before and/or during each treatment.
Then they can make sure the cancer is within the radiotherapy field each time.
Imaging during a patient's treatment is 4 dimensional radiotherapy (4D-RT). The 4th dimension in this case is time.
4D-RT can adjust to any changes in the position of the tumour during the radiotherapy session.
In some types of 4D-RT the machine may switch off if the tumour moves out of the radiotherapy field.
This type of treatment is helpful for cancers in areas of the body that move when we breathe, such as the lung.
The radiation beam switches on again when the tumour moves back into a certain position which can be seen on the scan.
Benefits and possible drawbacks of IGRT
With IGRT, doctors can target the radiotherapy treatment very accurately. This can mean that the treatment works better in curing or controlling a cancer. It can also reduce the risk of side effects.
The drawback is that planning the treatment may take longer. Each radiotherapy session also takes longer.
Planning IGRT treatment involves several steps.
You start with a session in the radiotherapy department and have a CT scan. 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 computer programme then designs radiation beams that follow the shape of the tumour very closely. They make sure that the whole cancer is inside the radiotherapy field and healthy tissue is avoided as far as possible. This reduces the risk of side effects.
The radiographers may make marks on your skin to make sure the same area is treated at each session.
Moulds and masks
If you are having conformal radiotherapy to your head or neck, you may need to wear a plastic mould during your treatment. You may hear this called a shell or mask.
Some types of mask are see through, others aren't. 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. This also means that you can have any markings you need made on the mask, instead of on your skin.
Your doctor or radiographer may ask you to have small metal markers (fiducial markers) put in or near your tumour.
To place the markers, your doctor inserts a needle into the area of skin over the tumour. They do this while you are having an ultrasound. Once the tip of the needle is in the right place the doctor releases a small gold pellet or rod.
The radiographers can then see the markers on X-rays and scans while you are having treatment.
This makes sure that the treatment is targeted very precisely.
After your planning session
You may have to wait a few days or up to 2 weeks before you start treatment. During this time the physicists and your radiotherapy doctor decide the final details of your plan.
Your doctor will plan the areas that need treatment and outline areas to limit the dose or avoid completely. They call this contouring.
Then the physicists and staff called dosimetrists plan the treatment very precisely using advanced computers.
To have the treatment you lie on a radiotherapy couch. The radiographers help you to get into the right position and put on any moulds that you need.
IGRT is commonly given by standard radiotherapy linear accelerator (LINAC) machines that are specially adapted and have specialist computer programmes.
Some types of image guided radiotherapy use specially designed radiotherapy machines. The CyberKnife machine gives image guided stereotactic radiotherapy.
It has a robotic arm that moves around the patient. The arm gives the radiotherapy from many different angles.
A TomoTherapy machine gives image guided intensity modulated radiotherapy. It combines a CT scanner and an external beam radiotherapy machine.
Part of the TomoTherapy machine can rotate completely around the patient to take CT scans and give radiotherapy to a very localised area.
Once you are in the right position the staff leave you alone in the room. This is so they are not exposed to the radiation.
The staff watch you carefully on a closed circuit television screen. 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 takes between 15 to 45 minutes.
Possible side effects of IGRT
With IGRT techniques there is less normal tissue in the field of the radiotherapy than with some other types of radiotherapy. So the risk of side effects is lower.
Unfortunately you can still have side effects. As with any external beam radiotherapy, the side effects only affect the part of the body that the radiotherapy treatment is aimed at.