How is SABR different from conventional radiotherapy?
Both SABR and conventional radiotherapy use radiation to damage cancer cells. The difference is not a different kind of radiation. It is the way the dose is planned and delivered.
SABR usually involves:
- a tightly shaped high-dose region;
- a larger dose in each treatment, called a fraction;
- fewer fractions than many conventional courses;
- detailed imaging and position checks;
- careful attention to movement and nearby organs.
A conventional course may spread the total dose across more visits using a smaller dose per fraction. Neither approach is automatically stronger or better. The schedule has to fit the cancer, the treatment aim and the normal tissues close to it.
Why can SABR be given in fewer treatments?
The high level of precision allows a larger dose to be given in each fraction in selected situations. A complete course may therefore involve only a few visits.
This works only when the team can define and reproduce the target position reliably and keep the dose to nearby organs within accepted limits. The biological effect of a few large fractions is not the same as simply removing visits from a conventional course. The dose and schedule are calculated as a complete treatment plan.
When might SABR be considered?
Examples include selected early lung cancers, some prostate cancers, certain cancers in the liver or spine, and a limited number of areas where cancer has spread. The exact uses supported by evidence and commissioned within the NHS change over time.
Suitability can depend on:
- the cancer type and treatment aim;
- the size, shape and position of the target;
- how close it is to bowel, airways, spinal cord or another sensitive structure;
- movement with breathing;
- previous radiotherapy to the area;
- general health and the ability to maintain the treatment position.
An example from one patient cannot show whether SABR is appropriate for another.
Planning and image guidance are central to SABR
SABR needs detailed radiotherapy planning. The planning scan is performed in the treatment position. Additional scans may be combined with it where they help define the target.
Imaging is used before each fraction, and sometimes during treatment, to check the target and nearby anatomy. Small position changes may be corrected before the beam is delivered. This is called image-guided radiotherapy.
What if the tumour moves with breathing?
For targets in the lung, liver or upper abdomen, the team may need to measure and manage breathing-related movement. Options can include a 4D CT scan, treatment during breath-hold, respiratory gating, tracking, or a plan that safely covers the measured range of motion.
The article on how radiotherapy targets moving tumours explains these approaches in more detail.
What are the possible advantages?
For a suitable target, SABR may offer:
- a short treatment course;
- a highly focused dose;
- limited dose outside the planned high-dose region;
- a non-surgical local treatment option in some circumstances.
These are potential advantages, not a guarantee of benefit. The outcome still depends on the cancer and the reason for treatment.
What are the limitations and risks?
SABR can cause important side effects if the high-dose region is close to a sensitive organ. The relevant risks are very different for a lung target, a liver target and a spinal target. Some risks occur during or shortly after treatment; others can appear months or years later.
SABR may not be appropriate if the target is too large, too close to a structure that cannot safely receive the dose, difficult to see or track, or within an area that has already received substantial radiotherapy. A longer course or a different treatment may be safer or better supported by evidence.
Questions to ask
- Why is SABR being considered in my case?
- What is the treatment trying to achieve?
- How many fractions are planned, and why?
- How will my position and any tumour movement be checked?
- Which side effects are most relevant to this target?
- What alternatives were considered?
SABR is one precise way of delivering radiotherapy. SABR is not suitable for every tumour. Whether it can be used depends on factors including the treatment aim, the tumour's size and location, nearby organs, previous radiotherapy and whether treatment can be delivered safely.
