The evolving role of radiotherapy in the treatment of gastrointestinal cancers

What are gastrointestinal cancers and which organs do they affect? 

Gastrointestinal cancer is a family name rather than a single disease. It covers tumours anywhere in the digestive system: the oesophagus (food pipe), stomach, liver, pancreas, bile ducts, small bowel, colon, rectum and anus. These organs are close neighbours, but each keeps different company, so each cancer sets its own challenges. 

What role does radiotherapy play in treating gastrointestinal (GI) cancers, and how has it evolved? 

Radiotherapy uses carefully measured doses of high-energy x-rays to stop cancer cells from growing, to shrink a tumour, or to destroy it completely. The principle has never changed: give the tumour as much as it needs, and the healthy tissue around it as little as possible. 

This can be challenging with some GI cancers as it’s a dynamic environment - these tumours often sit within and close to vital organs and naturally shift position with breathing and digestion. A tumour in the liver or the pancreas, for example, doesn't sit still - whereas one in the rectum is much more static. 

To overcome this previously, our solution was the safety margin - a generous border drawn around the tumour - so that wherever it wandered, it stayed inside the beam. It worked well, but the border took in healthy tissue too, which limited the dose we could give. There was a ceiling. 

That ceiling has now lifted. A technique called SABR allows us to deliver a higher, more concentrated dose of radiotherapy with far greater precision; and now with the MR-Linac we’re able to take this a step further, adjusting treatment to account for how the body behaves during a treatment session - how organs shift with digestion or breathing, for example. 

What strikes me most is that we can now safely treat tumours I would not have attempted to treat with radiotherapy even ten years ago. 

What is SABR and what role does it play in treatment for gastrointestinal cancers? 

SABR stands for stereotactic ablative body radiotherapy. It is a mouthful, but each word earns its place. ‘Stereotactic’ means the target is pinpointed in three dimensions and ‘ablative’ means the dose is high enough to destroy the tumour, rather than merely hold it back or control it. 

Compared to other radiotherapy techniques, SABR delivers very high doses of radiation with extreme accuracy over fewer treatment sessions, and is best suited to small, well-defined tumours. Detailed imaging and careful planning allow these higher doses of radiotherapy to be delivered safely, targeting the tumour accurately while reducing exposure to surrounding healthy tissue. This is particularly valuable in the digestive system, where a tumour and a sensitive organ can be just millimetres apart. 

Different radiotherapy machines can be used to deliver SABR. Your consultant will recommend which machine is best for your treatment. SABR can also be delivered using MR-Linac technology - where real-time imaging allows the treatment to be adapted on the day, improving precision further still. 

What is the MR-Linac and how is it different to conventional radiotherapy? 

The MR-Linac is one of the most significant developments in radiotherapy in recent years. It is two machines in one: an MRI scanner, which sees, and a linear accelerator, or ‘linac’, which treats – both machines work together to deliver radiotherapy with exceptional accuracy. Organs in the abdomen shift position with breathing, digestion, and the natural variations we see each day. With conventional radiotherapy, we account for that by building in margins. With MR-Linac, we can see those changes happening and respond to them directly in real time. That's a fundamentally different way of working. 

Conventional radiotherapy relies on scans taken before the course begins, rather like navigating with a map you printed before you set off. The MR-Linac is closer to live navigation: it shows us the road as it is today, and we adjust the route to match. This guidance allows us to adapt the treatment plan in the moment, based on how the patient's exact anatomy is behaving on that specific day. This means we can treat with greater confidence - tighter margins, higher doses, higher precision and – critically - with less exposure to the surrounding healthy tissue. 

What role will MR-Linac play in the treatment of gastrointestinal cancers? 

This ability to see the tumour in real-time and adapt treatment on the day means we can now consider radiotherapy for some of these cases where we couldn't before. More precise targeting also means more of the radiation goes to the tumour and less reaches the healthy tissue around it. This means that certain side effects such as nausea, diarrhoea and fatigue, which can occur when surrounding organs receive radiation, can be significantly reduced. 

Final thoughts from Dr Amen Sibtain 

What makes this so exciting is that the technology has caught up with what we have always wanted to achieve in complex radiotherapy. Advances in imaging, treatment planning and adaptive technology are changing what is possible. We can now treat tumours that were once out of reach, with far fewer side effects, and dynamically adapt the treatment through the course. For some, this means complex radiotherapy is an option where once it was not. For others, it means treatment is more precise, more effective, and safer than ever before. 

At The Harley Street Clinic, part of HCA Healthcare UK, the introduction of the Elekta Unity MR-Linac represents one of the most significant steps forward in this area.