Stereotactic body radiotherapy (SBRT or stereotactic ablative radiotherapy (SABR) is a way of giving radiotherapy to a tumour from different directions.
What SBRT is
Stereotactic radiotherapy (SBRT) gives radiotherapy from many different positions around the body. The beams meet at the tumour. So the tumour receives a high dose of radiation and the tissues around it only receive a low dose. This lowers the risk of side effects. Usually you have between 1 to 8 treatments. It is also sometimes called stereotactic ablative radiotherapy (SABR).
SBRT may be used to treat brain tumours and is called cranial stereotactic radiotherapy.
This type of radiotherapy is mainly used to treat very small cancers, including:
- cancer in the lung
- cancer that started in the liver or cancer that has spread to the liver
- cancers in the lymph nodes
- spinal cord tumours
SBRT is also being used in clinical trials for other types of cancer.
Planning SBRT treatment involves several steps.
You start with a session in the radiotherapy department. You 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 all of the tumour 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 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 dose of radiotherapy.
Having SBRT treatment
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 may need.
Different machines can be used to give stereotactic radiotherapy.
The most commonly used one is a linear accelerator (LINAC). But there are other machines, including CyberKnife.
SBRT with a LINAC
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.
You will be alone for the treatment, which lasts between 15 minutes to 2 hours. You may have the treatment in one go or it may be broken up with short breaks.
The radiographers can speak to you by intercom. It is important that you stay very still throughout the treatment.
The radiographers watch you on a closed circuit television screen. You won't feel anything and the machine doesn't touch you.
The machine will beep from time to time. Once the treatment is over the radiographers come in and help you get down from the treatment couch.
The CyberKnife radiotherapy machine has a robotic arm that moves around the treatment couch to give doses of radiation from different angles.
The radiotherapy machine takes regular scans or regular scan results are fed into the machine's computer.
This allows your radiographers to target radiotherapy beams accurately at the tumour, even if the tumour moves as you breathe.
Treatment may take between 30 minutes to 4 hours depending on the type of cancer and the position of the tumour in the body.
You may have the treatment in one go or it may be broken up with short breaks.
Radiosurgery is a type of stereotactic radiotherapy. It gives extremely high doses of very precisely targeted radiotherapy over 1 to 5 treatment sessions.
It is used for some types of brain tumour but is not currently used for cancers elsewhere in the body.
At the moment it is being tested in clinical trials for some other cancer types.
Possible side effects of SBRT
Stereotactic radiotherapy targets the tumour very precisely and the risk of damage to normal surrounding tissues is low. Therefore the side effects may be less than with other types of radiotherapy.
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.
Getting SBRT treatment
Stereotactic radiotherapy is available at many treatment centres in the UK. This includes at NHS radiotherapy units that have specialised radiotherapy machines (LINACs).
If you think this treatment may be right for your type of cancer ask your doctor.
You can ask your doctor to refer you to another centre if your centre can't give it and it would be an appropriate treatment for you. You can't approach the hospitals to refer yourself.