MR-Linac SABR: precise radiotherapy for cancer that has spread

What MR-Linac SABR is, in plain English

Two ideas sit inside the name.

SABR stands for stereotactic ablative radiotherapy. Standard radiotherapy gives a modest dose every weekday for several weeks. SABR gives a much higher dose to a small, precisely mapped target in a handful of sessions. “Stereotactic” means the target is pinned down in three dimensions, to the millimetre. “Ablative” means the dose is high enough to destroy the cells it hits. Because the dose is so high, it has to be aimed with great care.

MR-Linac is the machine. A linac, short for linear accelerator, is the machine that produces the radiotherapy beam. An MR-Linac has an MRI scanner built around it. MRI shows soft tissue, such as the bowel, the liver and lymph nodes, far more clearly than the X-ray pictures a standard machine uses. So the team can see the tumour and the organs beside it while you are on the couch, adjust the plan to how things sit that day, and pause the beam if the target moves as you breathe.

Dr Harinarayanan puts it simply: more precise radiotherapy, with more damage to the tumour and less damage to the normal structures around it.

Who it may help

MR-Linac SABR is mainly used for oligometastatic cancer. “Oligo” means few. It describes cancer that has spread from where it started to a small number of places, up to three or four, rather than widely. Those places are often the lungs, the liver, lymph nodes, bones, the spine or the adrenal glands. Bowel cancer is Dr Harinarayanan’s own specialty, and he treats it both where it started and where it has spread; he also uses the MR-Linac for oligometastatic spread from other primary cancers, such as prostate or kidney cancer. In suitable cases, treating each spot with a high, precise dose can control it, and for some people that may delay the need for more drug treatment.

It is particularly relevant when cancer has spread to the liver, from any type of primary cancer, and surgery to remove it is not possible: MR-Linac SABR can still be an option for a limited number of metastases in the liver or the lung.

It can be an option for people who have had radiotherapy to the same area before, which is called re-irradiation, because the dose can be shaped so tightly.

It suits people who want treatment over days rather than weeks, and people for whom precision matters most: a tumour next to the bowel, the stomach or the spinal cord, where a standard beam would have to be held back to protect them.

What a course involves

The first step is a consultation at Spire Southampton, where he reads your scans and history and tells you honestly whether this treatment is likely to help. Most patients are then discussed at a multidisciplinary team meeting, or MDT, where surgeons, oncologists and radiologists agree a plan together.

Next comes a planning session on the MR-Linac itself. You lie on the treatment couch while the machine takes MRI pictures, and those pictures are used to build your plan: where the dose goes, and where it must not. You may be asked to follow simple instructions about eating, drinking or breathing so that your body is in the same state at each visit.

Treatment follows as a short course, typically three to eight sessions depending on the tumour’s location and size. At each session the machine scans you again, the team adapts the plan to what it sees that day, and the dose is delivered. That checking is why a session takes longer than standard radiotherapy. You feel nothing and go home afterwards.

Follow-up scans are arranged to see how the treated areas have responded, and the results can be shared with your own oncologist.

Where it is delivered, and by whom

Dr Harinarayanan holds MR-Linac SABR accreditation from GenesisCare UK. He is one of a small number of oncologists on the South Coast who do; more clinicians are being accredited every month, so it is not a fixed number. The machines belong to GenesisCare, and he treats on them at three centres: Cromwell Hospital in London, GenesisCare Guildford, and GenesisCare Oxford.

Your consultations and follow-up happen closer to home, at Spire Southampton Hospital. You travel only for planning and treatment. Each treatment site has its own page with directions.

Being honest about what it can and cannot do

This is a precise tool with limits. It treats the spots it is aimed at; it does not treat cancer that cannot be seen on a scan. Whether it is the right choice depends on how many places the cancer has reached, their size, what sits next to them, what treatment you have had already and how well you are. Sometimes chemotherapy, immunotherapy or surgery is the better option, and he will say so.

Results vary from person to person and from cancer to cancer. He will tell you what the evidence says for your situation, without promising an outcome. Side effects depend on the area treated; tiredness is common, and most effects are short-lived.

MR-Linac SABR is not routinely funded on the NHS. The one exception is GenesisCare Oxford, which has a limited NHS contract and treats a small number of patients there on a compassionate basis; everywhere else, and for most patients at Oxford too, it remains a private treatment. He is an NHS consultant at University Hospital Southampton and will tell you what the NHS can offer you as well.

For referring clinicians

Dr Harinarayanan welcomes referrals for MR-Linac SABR from surgeons, oncologists, GPs and MDT coordinators across Hampshire, Dorset, Wiltshire, Sussex and beyond. Suitable patients are typically those with oligometastatic disease, up to three or four sites, in the lung, liver, nodes, bone, spine or adrenal; or locally recurrent pelvic disease. Re-irradiation cases are welcome.

What helps him respond quickly: a referral letter with diagnosis, stage and treatment to date; the most recent imaging (CT, MRI and PET-CT where available); the MDT outcome if there is one; and whether the patient is insured or self-funding. Send the letter and scans to his secretary at Ann.Clay@uhs.nhs.uk, or use the referral form on the clinicians page. He aims to reply to referrals promptly. He is happy to discuss a case by phone before a formal referral.