Stereotactic ablative radiotherapy (SABR)
Stereotactic ablative radiotherapy (SABR) is a type of external radiotherapy. It is sometimes called stereotactic body radiotherapy (SBRT).
SABR may also have other names. What it is called is based on:
- the area of the body being treated
- the type of machinery being used
- the length of treatment.
In this information we use the term stereotactic ablative radiotherapy, or SABR for short.
Stereotactic radiotherapy can also be used to treat brain tumours. We have separate information about radiotherapy for brain tumours.
SABR is not available in all hospitals in the UK. Your doctor may refer you to a specialist hospital if they think it is a suitable treatment for you.
Radiotherapy uses high-energy rays, such as x-rays, to treat cancer. It destroys cancer cells in the area where the radiotherapy is given. It aims to stop the cancer cells growing and either shrink the tumour or completely destroy it.
Standard external beam radiotherapy delivers several beams of radiation to the treatment area. It is usually given as a number of daily doses over a period of weeks.
SABR uses many smaller, thin beams of radiation. The beams are directed from different angles that meet at the tumour. This means that the tumour gets a high dose of radiation, while surrounding healthy tissues get a much lower dose from the individual beams. This lowers the risk of damage to the normal cells.
SABR can be given with fewer treatments than standard radiotherapy. Treatment is normally divided into 1 to 8 sessions. The sessions are spread over a few days, and may take up to 2 weeks. Your doctor or radiographer will explain how many sessions you need and over how many days.
Different machines can be used to give SABR. Your radiographer will tell you which machine they will use for your treatment. The linear accelerator (LINAC) that delivers standard radiotherapy can be used to give SABR. There are also specially designed LINACs for SABR that are known by their brand names, such as CyberKnife™. The most commonly used brand names for SABR are CyberKnife™, Varian® and Elekta®.
SABR may be used to treat:
- a cancer that started in the lung (primary lung cancer) that is small in size
- a cancer that has spread to another part of the body, such as the lung, liver, lymph nodes or spine
- a type of cancer that started in the liver called hepatocellular carcinoma
- prostate cancer, as part of a research trial
- certain types of cancer if you cannot have surgery
- a tumour that is in a difficult area to operate on.
SABR is not suitable for everyone. Your doctor can talk to you about whether it is a treatment option for you.
Planning your treatment is an important part of SABR. You may need to visit different departments in the hospital before starting your treatment.
It is important to tell the hospital staff about any medications and allergies you have. If you take painkillers, they may advise you to take them before your planning and treatment so that you are comfortable.
Moulds and masks
You may need to have a mould or mask made before radiotherapy planning starts. This is to help you stay still and in the correct position during your radiotherapy. The radiographer may use moulds to keep a leg, an arm or other body part still during planning and treatment. Masks may be used for people having radiotherapy to the brain, head or neck.
Your doctor or radiographer will tell you more about this if you need one.
Imaging and planning
You usually start planning by having a CT scan. This takes a series of pictures of the area to be treated. The CT is taken when you are in the position you need to be in for treatment. You may also have an MRI scan or a PET scan.
The scans take pictures from different angles to build up a 3D or 4D (three or four-dimensional) picture of the tumour. The type of picture depends on the scanner. Using the information from the scans, a computer is used to make an individual plan for your treatment. This ensures that the radiotherapy:
- is precisely targeted at the tumour
- has a lower risk of causing side effects.
You may have to wait up to 3 weeks before the plan is ready and you can start treatment.
It is important that the area being treated does not move too much during your treatment. Reducing movement allows your radiographer to direct the radiotherapy more accurately. They may show you some breathing techniques, or use gentle compression on your tummy area, depending on where you are having treatment. This would be done during both planning and treatment.
You may have small metal markers placed in or near your tumour. They are sometimes called fiducial markers. The markers help find the exact location of the tumour to make sure the treatment is given accurately.
The markers are about the size of a grain of rice. They are put in using a needle during a CT or ultrasound scan. The doctor gives you a local anaesthetic injection to numb the skin. They may also give you a mild sedative to make you feel sleepy. The doctor then makes a small cut and puts a needle through the skin over the tumour. When the tip of the needle is in the right place, they release the marker. Usually 2 or 3 markers are needed.
You may have markings made on your skin to help the radiographers position you accurately for treatment.
Usually, tiny permanent markings are made in the same way as a tattoo. The marks are the size of a pinpoint and are only made with your permission. It can be a little uncomfortable while they are being made. But it makes sure that the treatment is directed accurately. If you have a mould or mask, some of the marks will be made on this.
If you are concerned about having permanent marks, let your radiographers know. They can discuss other options with you.
Before the treatment
The treatment room will be similar to the one where you had your planning scans. The radiographers position you carefully on the treatment couch and adjust its height and position. They use the marks on your skin (or on your mask, if you have one) to help get you in the same position you were in for your planning scan.
It is important that you are comfortable, as you have to lie as still as possible during the treatment. Let the radiographers know if you are not comfortable.
Having the treatment
When you are in the correct position, the radiographers leave the room and you are given your treatment. There is a camera so they can see you from outside the room. There is also usually an intercom, so you can talk to them during your treatment if you need to.
The treatment itself is painless. You may hear a buzzing noise from the radiotherapy machine during treatment. Some treatment rooms have music players so you can listen to music to help you relax. If you would like to listen to your own music, ask your radiographer if this is possible.
You may have all the treatment at once, or it might be broken up with short breaks. Treatment takes between 15 minutes and 2 hours, depending on the type of machine. Your radiographer will tell you how long your treatment will take.
The way SABR is given is different depending on which machine they use. Usually, part of the machine moves around you and gives the radiation dose from different angles. Sometimes the couch also moves.
The radiotherapy machine may take x-rays and scans during SABR treatment. The pictures show if adjustments need to be made during each treatment. For example, if the tumour moves slightly as you breathe in and out, the computer can adjust how the treatment is given.
You can usually go home when the treatment is finished. SABR does not make you radioactive. It is safe for you to be with other people, including children, during and after your treatment.
You may have some side effects during or after SABR. But this treatment usually causes fewer side effects than standard external beam radiotherapy. This is because the healthy tissue gets a lower dose of radiation.
Side effects do not usually happen straight away. They may develop during your course of treatment or in the days or weeks after treatment finishes. Sometimes side effects get worse for a time after you have finished radiotherapy before they get better. There may also be a small risk of side effects that are long-term, or that start months or years after radiotherapy (late effects).
It is difficult to know exactly how you will react to treatment. Your team will explain what to expect. Always tell them if you have side effects during or after radiotherapy. They can give advice and support to help you cope.
General side effects
The general side effects of SABR include:
- feeling tired for a few weeks after you finish treatment
- skin reactions such as red, dry or itchy skin about 10 to 12 days after treatment
- soreness and swelling in the treatment area.
Specific side effects
Some side effects depend on the area being treated. For example, you may have:
- chest pain
- a cough
- shortness of breath
- a raised temperature
- eating or digestion problems.
If you are having SABR for a liver tumour, you may:
- feel sick (nausea)
- be sick (vomit)
- have pain.
If you are having SABR for prostate cancer, you may have urinary problems such as:
- needing to pass urine (pee) more often
- discomfort when you pee.