Image guided radiotherapy (IGRT)

What is image guided radiotherapy?

Image guided radiotherapy (IGRT) uses scans and X-rays to check you’re in the correct position before, and sometimes during, your radiotherapy treatment. It’s not a treatment in its own right, but a way of making standard radiotherapy more accurate, so more radiation reaches the cancer and less reaches the healthy tissue around it.

What conditions does it treat?

IGRT isn’t used to treat one specific type of cancer. Instead, it’s a technique added to standard external radiotherapy for cancers where extra accuracy is especially valuable, including:

• cancers in parts of the body that move, such as the lungs (which move as you breathe) or the prostate gland (which shifts position depending on how full your bladder is)
• tumours located close to sensitive organs or structures, such as the spinal cord
• cancers of the head and neck.

It’s often used alongside other radiotherapy techniques, such as intensity modulated radiotherapy (IMRT), proton beam therapy, or stereotactic radiosurgery.

What are the benefits of IGRT?

By checking your exact position immediately before treatment, IGRT aims to:

• make sure the radiation reaches the cancer as precisely as possible, reducing the amount reaching surrounding healthy tissue
• reduce the risk of missing part of the tumour, which can happen if it has shifted position since your last scan
• allow smaller safety margins to be used around the treatment area than might otherwise be needed, potentially reducing side effects.

It’s worth knowing that, while this reasoning is well established, one review of the evidence found that, at the time, there weren’t yet randomised controlled trials directly proving that IGRT causes fewer side effects or better tumour control than radiotherapy without it. Research in this area continues.

Are there different types of IGRT?

Imaging method

Scans can use X-rays, CT (including 3D cone-beam CT), MRI, PET or ultrasound. Two-dimensional imaging can only match up bony structures, while three-dimensional scans, such as cone-beam CT, can also show soft tissue and detect if a tumour has moved or changed shape.

Fiducial markers

For some cancers, particularly prostate cancer, small metal markers (fiducial markers) are placed in or near the tumour beforehand, using a needle guided by ultrasound. These show up clearly on X-rays and scans, helping your team check your position accurately each time.

4D radiotherapy (4D-RT)

This involves taking images during your treatment itself, rather than just before it. The machine can adjust the treatment couch based on these images, and in some cases will automatically switch off if the cancer moves out of the treatment area, such as during breathing, switching back on once it returns to the right position.

How often imaging is used

Some healthcare providers only image at the start of treatment or occasionally during the course; others take images every single day before treatment is delivered.

What happens before the procedure?

Before starting treatment, you’ll have a planning (simulation) session, usually with a CT scan, and sometimes an MRI or PET scan too, to map the exact size, shape and position of your cancer and create reference images for your team to compare against.

If you need fiducial markers, these are usually implanted 1–2 weeks before your planning scan. Your skin may also be marked, sometimes with a small tattoo, to help line up the equipment consistently each time. Depending on the area being treated, you might be asked to fast beforehand, or to have a full bladder.

Tell your treatment team if there’s any chance you’re pregnant or breastfeeding, or if you have any loose metal or a pacemaker in your body, particularly if you’re due to have an MRI scan. There’s no other special preparation needed for IGRT itself, beyond whatever’s required for the specific radiotherapy technique you’re having.

What happens during the procedure?

1. You lie on the radiotherapy couch, and your radiographers help position you correctly, sometimes using masks or moulds to help keep you still.
2. Once you’re in place, your radiographers leave the room, though they can still see and hear you throughout; you may need to hold your breath for 30–60 seconds at points while images are taken.
3. Scans or X-rays are taken and compared against your original planning scan.
4. If needed, your radiographers adjust your position, or the couch, so you’re within millimetres of your planning position.
5. Your radiotherapy treatment is then delivered.
6. Sometimes, another scan or X-ray is taken straight after treatment, while you stay in the same position, as a further check.

You won’t feel anything during the imaging or the treatment itself, though the machine may make noise or move around you, and some people notice an unusual smell or a coloured light. The whole process, including the imaging, typically takes between 15–45 minutes. If your radiographers see that your position is very consistent over the first few sessions, they may not need to image you quite as often.

What does recovery look like?

Straight after your session

You won’t feel any different immediately after an IGRT session itself, since neither the imaging nor the radiotherapy causes pain at the time. Adding imaging to your treatment does mean each session takes a bit longer, and slightly increases the total amount of radiation you’re exposed to, though your team will always weigh this against the benefit of more accurate treatment.

Over your course of treatment

Side effects come from the radiotherapy itself, not the imaging, and IGRT is specifically intended to help reduce them by keeping the radiation focused on the cancer. Early side effects can develop during or shortly after treatment and usually clear up within a few weeks. These commonly include tiredness and skin changes in the treated area, such as redness, irritation, dryness, itching or swelling. Depending on which part of your body is being treated, you might also have hair loss in the area, problems with your mouth or swallowing, digestive changes, nausea, headaches, or urinary changes.

Less commonly, some side effects appear months or years after treatment and can be long-lasting, though they’re rare. These can include changes affecting the brain, spinal cord, lungs, kidneys, bowel, joints or mouth, lymphedema (swelling from a build-up of fluid), fertility problems, or, rarely, a second cancer. Your oncologist will check for these at your follow-up appointments.

What are the risks and complications?

IGRT is designed to reduce the risks of radiotherapy, but there are still some points worth knowing:

• taking extra images adds a small additional amount of radiation on top of your treatment dose, though this is very small compared with the treatment itself, and your team only takes images where the benefit outweighs this
• lying still for imaging and treatment for longer can be uncomfortable
• radiotherapy overall carries a small risk of causing a new cancer later in life, which is why you’ll have regular follow-up checks after treatment.