Stereotactic Radiotherapy (SRT)

Stereotactic radiotherapy (SRT) aims high-energy radiation beams at a tumour from many different directions at once, so they overlap precisely on the cancer itself. Because the beams only combine to full strength at the tumour, the healthy tissue around it gets a much lower dose, which is what makes this treatment more gentle than standard radiotherapy.

What conditions does it treat?

SRT is used for small, precisely defined tumours in several parts of the body. It may be used to treat:

• small cancers that started in the lung, or cancer that has spread there
• cancer that started in the liver, including hepatocellular carcinoma (a type of liver cancer), or cancer that has spread to the liver
• cancers in the lymph nodes
• spinal cord tumours
• cancer that has spread to the brain
• some prostate cancers
• some pancreatic cancers, sometimes as part of a clinical trial
• small, low-grade brain tumours, such as acoustic neuromas, pituitary adenomas and meningiomas at the base of the skull
• an area that's already had radiotherapy before, when further treatment to the same site wouldn't normally be possible.

What are the benefits of having SRT?

Because the beams overlap only at the tumour, nearby healthy tissue receives a much lower dose than with conventional radiotherapy. This generally leads to fewer side effects than standard treatment, and for many of the cancers treated this way, doctors can achieve local tumour control in around 90% of cases.

SRT often needs far fewer hospital visits than conventional radiotherapy, which can mean daily sessions over several weeks. Many people complete SRT within a single visit, or between a few days to 2 weeks, with short outpatient appointments. Because it's so precise, it can sometimes treat an area that's already had radiotherapy before, when this wouldn't normally be possible.

Are there different types or approaches?

SRT is a family of related techniques with several overlapping names. Given to the body over a small number of visits, it's usually called stereotactic body radiotherapy (SBRT) or stereotactic ablative radiotherapy (SABR). Given to the brain, a single session is called stereotactic radiosurgery (SRS), while several brain sessions are called fractionated stereotactic radiotherapy (FSRT).

The number of sessions you will need can vary. Most people have between 1 and 8 treatments in total, but fractionated brain treatment can run to 5–25 sessions, depending on your plan.

The equipment varies between hospitals. Some use a linear accelerator (LINAC), similar to standard radiotherapy machines; others use a robotic system called CyberKnife, which tracks your breathing and adjusts as it treats; and brain tumours are sometimes treated with GammaKnife, which uses gamma rays rather than X-rays. There's no strong evidence that one type of machine works better than another.

Some centres also offer MR-Linac systems, which use live MRI scanning to track the tumour as it's treated. Whichever machine is used, SRT is non-invasive: no cuts are made, and the machine never touches you.

What happens before the operation?

Getting ready for SRT usually involves more planning than standard radiotherapy, so your team can pinpoint the tumour as accurately as possible.

• You'll have a CT scan, and often an MRI or PET scan too, so your team can see exactly where the tumour is
• You may need a lightweight mask or a mould made for the area being treated, to help you stay in exactly the same position each time
• For some brain treatments, your team fits a head frame using four small pins under local anaesthetic, which can leave the area feeling tender afterwards
• Your team may add small, permanent skin markings, a bit like a tiny tattoo, to help line you up accurately each time, though they'll only do this with your permission
• Your doctor may place tiny metal markers in or near the tumour under local anaesthetic, about the size of a grain of rice, to help pinpoint its exact position on scans
• Tell your team about any medications or allergies, as this may affect how you're prepared for treatment.

How long you wait for your plan to be ready can vary between a few days to 2 weeks. Your own team will be able to give you a more exact timeframe.

What happens during the procedure?

Once your plan is ready, the procedure itself follows a similar pattern regardless of which machine is used:

1. You lie on the treatment couch, and your radiographers help you into the right position, fitting your mask or mould if you have one
2. Your team leaves the room, but they can see and hear you throughout on a screen and intercom, and you can talk to them if you need to
3. The machine, whether a LINAC, CyberKnife or GammaKnife, delivers narrow beams of radiation from many different angles, all meeting at the tumour
4. Scans or X-rays taken during treatment let your radiographers check your position and adjust for small movements, such as breathing
5. Your team may give the whole treatment in one go, or break it up with short breaks, and some treatment rooms let you listen to music to help you relax
6. Once treatment ends, your team returns to help you off the couch, and you can usually go home the same day.

How long each session takes depends on the machine and the area being treated. A LINAC session usually takes between 15 minutes and 2 hours, while CyberKnife sessions can run from 30 minutes up to 4 hours. It's worth arranging transport home in advance, since you may feel too tired to drive safely.

What does recovery look like?

Most people go home on the same day as each SRT session. The treatment doesn't make you radioactive, so it's completely safe to be around other people, including children, straight away. After a single-session brain treatment (SRS), your doctor may occasionally want to keep you in overnight for monitoring, but this isn't routine.

Once home, tiredness is the most common effect, and it can last for a few days to a few weeks after treatment finishes. Some people notice skin changes in the treated area, such as redness, dryness or darkening, often around 10–12 days after treatment. Other effects depend on which part of the body was treated, so your team will talk you through what's relevant to you.

You'll usually be offered a follow-up appointment 4–8 weeks after treatment ends, to check on your recovery and talk through any side effects. If you've had treatment to the brain, DVLA rules mean you'll need to stop driving for a period afterwards; your consultant will tell you how long this applies to you. Contact your team sooner if anything is worrying you rather than waiting for your next scheduled appointment.

What are the risks and complications?

SRT tends to cause fewer side effects than conventional radiotherapy, though you may still notice:

• tiredness, sometimes lasting a few weeks after treatment ends
• skin changes in the treated area, such as redness, dryness, itching or darkening, often 10–12 days after treatment
• soreness or swelling where you were treated
• effects linked to the area treated, such as a cough or breathlessness after lung treatment, or more frequent, uncomfortable urination after prostate treatment
• feeling sick, dizzy or faint shortly after brain treatment, which is uncommon and usually prevented with steroid medicine beforehand
• a small chance of side effects appearing months or years later, sometimes called late effects.