Adaptive Radiotherapy in Rectal Cancer

Ask a radiation oncologist what adaptive radiotherapy actually changes and you'll usually get an answer about precision. Two of them, speaking at Elekta Connect in Bengaluru in August, gave a more specific one. Both talked about rectal cancer, and both talked about it in terms of what their own patients had and hadn't gone through.

Dr. Vikram Maiya leads radiation oncology at a hospital that had been treating patients with online adaptive for about six weeks. Dr. Lokesh Vishwanath spent 25 years in a public regional cancer center handling around 400 radiation therapy patients a day. Different settings, different pressures, and the same understanding on where adaptive earns its place in the pelvis.

Why the pelvis is a hard place to hold a plan

A radiotherapy plan is drawn from a scan taken on one particular day. It's an accurate map of that patient at that moment. Then the patient goes home, comes back, goes home, and comes back again, twenty or thirty times over.

By which point the map's out of date. The bladder fills and empties. The bowel shifts. The tumor starts to shrink, which is the entire point of the exercise, but it does mean the shape you planned around isn't the shape that's there anymore.

Dr. Maiya puts it plainly. “We cannot give the same dose, what we had decided on day one. So based on that anatomy, we have to give the radiation for that particular moment.”

The anatomy on the day of treatment may differ from the planning scan. Adaptive radiotherapy allows the plan to respond to those changes.

In the pelvis this matters more than almost anywhere, because the organs you're trying to protect are the ones least inclined to stay put. Online adaptive radiotherapy answers it by scanning the patient on the couch and redrawing the plan before the session runs. Same patient, same day, current map.

What one patient didn't get

One of the first cases Dr. Maiya's team treated this way was a cancer of the rectum. Nothing unusual about the patient. What was unusual was the ending: by the time the course finished, he says, there were no complications at all.

To see why that surprised him, you need his department's usual definition of ‘normal.’ Pelvic radiotherapy irritates the bowel, and an irritated bowel means, almost always, diarrhea.

“On an average, we would have got at least around 90% or 95% of our patients having diarrhea, at least midway through the treatment or by the end of treatment. But this patient never complained of diarrhea.”

What stood out to the team was what the patient didn’t report: diarrhea during treatment. One patient’s experience, but a notable observation for the team.

So, this wasn't a patient having a slightly easier time of it. This was the expected complication not turning up at all.

His explanation is about where the dose landed. The small bowel sits somewhere slightly different every day, and every day the plan was recalculated around where it actually was. By the end of the course the tumor had responded too, so the team pulled the treatment volumes in to match the smaller target.

He doesn't offer this as proof, and it isn't. It's one case, six weeks into a new service, with no control group and nothing to compare against. But it's the sort of thing a department does notice, and that's usually where the clinical questions start.

The colostomy question

Dr. Vishwanath reaches the same tumor site from the other end of the system. He'd been talking about how adaptive holds up in a public hospital treating hundreds of patients a day and was working through the operational side of it when he stopped to talk about who benefits.

“Many of the rectal cancer patients, they end up with a colostomy for life. So, there is a huge scope for these rectal cancer patients to save their anal sphincter, and they're able to pass and defecate in a normal way, so that the colostomy bag can be kind of stopped over a period of time, and they can go back to a normal life.”

Beyond tumour control, preserving function and quality of life is a central goal — and a key question for further research.

For someone who's been told they'll be wearing a bag for the rest of their life, the difference between temporary and permanent isn't just a clinical detail. It’s a much better outcome and quality of life for the patient.

Thirty years in oncology, and that's his measure for success. Not tumor control. Not dose conformity. Whether a person gets their life back.

Two very different departments, one conclusion

One is working through the first patients on a new service. The other is running a department where the pressure is volume and always has been.

They land in the same place regardless, and they get there from their own patients rather than from the literature. The gain that shows up first isn't the one on the dose map. It's what the treatment really means to the person having it.

What this doesn't prove

Neither of these is a trial. Dr. Maiya is describing early experience in a service still finding its feet. Dr. Vishwanath is describing an indication he sees emerging rather than one he has years of adaptive data on. Both said as much themselves.

There are practical limits too. In Dr. Maiya's department, online adaptive is currently used for pelvic cases only, a session runs to around 40 minutes on the couch, and choosing the right patient matters as much as the technology does.

What these conversations add to the published rectal cancer literature isn't evidence. It's context. They tell you which benefit clinicians see first when adaptive reaches the pelvis, and how fast it comes up when you ask the people actually running the service.

What would settle it

The first is whether that early signal on side effects holds up across a proper series, rather than a handful of patients treated in the opening weeks of a new service. The second is time: 40 minutes on the couch is manageable for a department running a few adaptive patients a day and impossible for one treating hundreds, so adaptive reaches everyone who'd benefit only when that number comes down. The third is Dr Vishwanath's, whether preserving the sphincter becomes something rectal cancer treatment sets out to achieve rather than something it manages when the anatomy allows.

Both of them expect all three, and neither is in a hurry to call any of it settled, which is the right position to hold this early. What's already clear is smaller and harder to argue with. Asked what adaptive had changed, both of them answered by describing a patient.