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New PET-CT tracers could be game changer for cancer imaging

New tracers in PET-CT imaging could make a real difference to cancer patients, says Dr Kathryn Wallitt, consultant radiologist at Paul Strickland Scanner Centre.
Radiographer and patient

New tracers in PET-CT imaging could make a real difference to cancer patients, says Dr Kathryn Wallitt, consultant radiologist at Paul Strickland Scanner Centre.

Dr Wallitt is part of our dedicated team of PET-CT experts at the centre, which is headed up by our lead consultant for PET-CT, Dr Wai-Lup Wong, who is a widely recognised leader in his field.

For Dr Kathryn Wallitt, PET-CT imaging is personal: The latest addition to our team of consultant radiologists at Paul Strickland Scanner Centre is herself the daughter of a radiologist for whom PET-CT scans were a lifeline when he was treated for cancer.

She said: “My father was diagnosed with high-grade non-Hodgkin lymphoma in 2018 and had a PET-CT scan to see how advanced his disease was so the right treatment could be chosen. A mid-treatment PET-CT scan was performed to see how he had responded.” Her dad’s PET-CT scan showed that he no longer had active disease and he therefore didn’t need a change to his treatment.

Dr Kathryn Wallitt Consultant Radiologist
Dr Kathryn Wallitt, Consultant Radiologist

Dr Wallitt completed her training in radiology at Imperial College London in 2014 and received the Rohan Williams Gold Medal, which is awarded for outstanding results in the final exams. She decided to sub-specialise in nuclear medicine, which at the time included PET imaging. Her role is currently split between Paul Strickland Scanner Centre and Imperial Healthcare NHS Trust.

She joins a dedicated team of PET-CT experts at the centre which is headed up by our lead consultant for PET-CT, Dr Wai-Lup Wong, who is a widely recognised leader in his field.

Dr Wallitt became interested in radiology as a junior doctor while doing a stint in nuclear medicine, which allowed her to see how radiologists work and solve imaging problems. “It clicked with me,” she said. She found nuclear medicine, especially PET-CT imaging particularly fascinating: “I saw the potential for the future,” she said. Things have moved on since those early days and PET scans have been replaced with PET-CT, which combines a PET scan with a CT scan and adds much more information about where the abnormality is.”

How PET-CT works

“Ten to fifteen years ago, my dad would have had a CT scan instead of a PET-CT scan. The problem with a CT scan is that although the tumour might have shrunk, you wouldn’t know whether it represented residual scar tissue or active disease – the latter is the information a PET-CT scan would give us and which is particularly useful in many tumours, including high-grade non-Hodgkin lymphoma for that reason. If a scan shows someone still has active disease, they might have more chemotherapy, or their oncologist might switch to a different treatment.

“A PET-CT scan can completely change how a cancer is managed and that’s why it is routinely used in many different types of cancer nowadays.”

Having a PET-CT can therefore mean people like Dr Wallitt’s dad get the right treatment and could be spared unnecessary treatment.


Before having a PET-CT scan, you will be injected with a radioactive tracer. “The main tracer that we use, fluorodeoxyglucose (FDG), is very similar to sugar. In general, cancer cells need more sugar to grow, so at cancer sites we’ll see increased uptake of the tracer. “Although FDG is the most common tracer at the moment, there is lots of research into other tracers that can be more useful in different types of cancer. For example, a very useful tracer in prostate cancer is prostate-specific membrane antigen (PSMA), which is available at a select few centres in the UK, including Paul Strickland Scanner Centre.

“The new tracers are a major advance on the diagnostic side, but also have the potential to provide therapy in patients who have exhausted all other treatment options. We can label new tracers such as PSMA to radioisotopes such as lutetium or yttrium which release radioactivity strong enough to kill cancer cells.”

“The way this works in practice is to have a scan with the tracer, for example PSMA that stages your disease to tell you where the cancer hot spots are and how extensive the disease is; your medical team would then give you therapy by labelling PSMA to a radioisotope such as lutetium or yttrium. The therapy would target all those hotspots you saw on your diagnostic scan.
You can then follow it up later to see how things have changed. It’s still at research stage but is potentially a game-changer for prostate cancer.”

Faster and better imaging

Dr Wallitt is excited about the future of PET-CT. She is predicting that we will get faster and better scanners over the next 5-10 years and there is talk of scanners that can do a scan in less than 1 minute – as opposed to 20 minutes with many current scanners.

Faster scan times would mean we can scan more patients every day and keep up with the ever increasing demand for PET-CT scans. The quality of scan images has also radically improved. “It’s as if we’ve gone from a black and white TV to a 4K or even 8K TV; the change in quality of the imaging also means we may pick up smaller things earlier – hopefully we will be able to help diagnose patients sooner and more accurately. New scanners may also be able to provide the same quality at a lower dose of radiation exposure.”

Artificial intelligence

Another hot topic in PET-CT is machine learning. “It’s still early days, but if we had a machine that could identify sites of disease automatically it could improve radiology reporting times and accuracy.

“A field called “radiomics” looks at the texture of cancer lesions which cannot be seen with the naked eye. This could provide information on how well a patient will respond to treatment and what the outcome or survival chances might be.”

The exciting developments in PET-CT imaging are great news for people affected by cancer, many of whom have had their lives saved by PET-CT scans or have been able to spend precious extra time with family and friends.

This couldn’t be truer for Dr Wallitt and her family, who recently passed a milestone when her dad announced he has been in remission for a full year.

Thanks to the generosity of our supporters, Paul Strickland Scanner Centre will soon be able to replace its current PET-CT scanners with a new machine that is much faster, meaning patients won’t have to spend as much time in the scanner. Scan images will also be better, which could mean an earlier and more accurate cancer diagnosis and monitoring.

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