Precision radiotherapy: IMRT, VMAT and re-irradiation

What radiotherapy does

Radiotherapy uses high-energy X-rays to damage the DNA inside cancer cells so they cannot keep dividing. Healthy cells in the path of the beam are affected too, but they are better at repairing themselves. Giving the treatment in daily doses, and shaping it tightly, gives healthy tissue the best chance to recover while the cancer does not.

Dr Harinarayanan is a clinical oncologist, which in the UK means a cancer doctor trained in radiotherapy, chemotherapy, immunotherapy and other targeted anti-cancer treatment agents. He plans each course himself, with a team of physicists and radiographers, and he sees you during it.

IMRT and VMAT, explained

Older radiotherapy used simple square beams. The dose covered the tumour but also a good deal of what sat around it. Two techniques changed that.

IMRT stands for intensity-modulated radiotherapy. The machine delivers beams from several fixed angles, and within each beam it varies the strength across the field, a bit like a dimmer switch applied to hundreds of tiny segments. Added together, the beams wrap the full dose around the tumour and drop away quickly at its edge.

VMAT stands for volumetric modulated arc therapy. It does the same shaping while the machine rotates around you in a continuous arc, adjusting the beam as it goes. It is usually quicker, which means less time lying still.

Which is used depends on the area and on the plan that protects healthy tissue best. Both are standard tools in his work on rectal cancer, where the bowel and bladder sit close to the target.

Re-irradiation: treating an area a second time

Sometimes cancer comes back in a place that has already had radiotherapy. Healthy tissue keeps a memory of the earlier dose, so a second course needs particular care. This is called re-irradiation, and it is one of Dr Harinarayanan’s special interests, especially for rectal cancer that has returned in the pelvis.

Whether it is possible depends on what was given before, where, how long ago and what sits nearby. Precise techniques, IMRT, VMAT and SABR, make it an option in more cases than it once was. It is not an option in every case, and he will say so honestly.

What a course involves

The first step is a consultation at Spire Southampton. He reads your scans and history and explains whether radiotherapy is the right next step, on its own or with chemotherapy, and what course he recommends.

Then comes planning. You have a CT scan in the treatment position, with small marks on the skin used to line you up the same way each day. From that scan, the plan is built: the tumour and the organs to protect are outlined, and the beams are shaped to fit.

Treatment is usually given on weekdays over a number of weeks, depending on the cancer. Each visit is short. The machine takes pictures to line you up, then delivers the dose while you lie still. You feel nothing and go home afterwards. You are seen regularly during the course so side effects are caught early.

After the course ends, side effects often peak for a week or two and then settle. Follow-up scans are arranged at the right interval, and the results go to your surgeon or oncologist as well.

Side effects, honestly

Side effects depend on where the beam goes, and they build up over the course. Tiredness is common to all of it. Skin in the treated area can redden like sunburn. Pelvic treatment can bring looser or more frequent bowel motions and bladder irritation.

Most of these settle in the weeks after treatment. A few can last longer, and he will tell you which ones apply to you before you start. Radiotherapy does not make you radioactive; you are safe to be around anyone throughout.

For referring clinicians

Dr Harinarayanan accepts referrals for radical and palliative radiotherapy, chemoradiotherapy and re-irradiation, with particular expertise in rectal cancer, including organ-preserving approaches and recurrent pelvic disease. He is a core member of the regional lower GI MDT at University Hospital Southampton.

Please send a referral letter with diagnosis, stage, histology and treatment to date, the most recent imaging, any previous radiotherapy plan and dose, the MDT outcome, and the patient’s funding route. Letters and scans go 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.