Q&A: Prof Val Lewington
Q&A - 14TH FEBRUARY 2017
Prof Val Lewington on working with doctors from almost every other specialty
What is nuclear medicine?
Nuclear medicine is a field that uniquely links imaging to treatment. The technique uses drugs designed to target specific types of cells, such as those of the bone, brain, lungs or some type of cancer. We tag the targeting drug with a tiny amount of radioactivity that can be detected using special scanners.
Once we have identified the correct carrier medicine, we can choose the type of radioisotope we attach. We choose some radioisotopes for detection by the scanners and others to actually treat cells. Therefore, depending on the radioisotope we use, this technique can be used for both imaging and therapy.
Can you give an example of a nuclear medicine treatment?
We have been treating benign and malignant thyroid disease and some types of cancer successfully for over 60 years. So, for example, one of the main treatments for thyroid cancer is surgery to remove the thyroid gland. But because of the location of the thyroid, it can be difficult for the surgeon to make sure that they remove all of the thyroid safely. If you follow up the surgery with radioactive iodine treatment, any remaining cells can be targeted and killed. Cure rates for thyroid cancer are very high using this combined approach.
The pace of research in the field is now increasing rapidly. One of the latest advances is radium-223 therapy, which is used to treat men with prostate cancer that has spread to the bones. Radium-223 has very few side effects, so can be given safely on an outpatient basis and combined with other therapies.
How is the drug combined with the radioisotope?
The work is done by highly skilled scientists and pharmacists working in a facility called a radiopharmacy. The carrier drug is produced in a ‘kit’ form, which is specific to the type of cell or part of the body we want to study. The isotope we use most often is technetium-99m, but a newer tracer, _uorine-18, is becoming a mainstay of cancer diagnosis and dementia imaging.
What can lead to the decision that somebody needs nuclear medicine?
Diagnostic scans will be used when a specialist wants to establish the cause of a patient’s symptoms and plan their treatment. Nuclear medicine tests can also be used later on to check whether that treatment was successful. Alternatively, we can provide nuclear medicine treatments that deliver highly selective internal radiotherapy. By targeting a tissue or tumour specifically, we can reduce damage to other parts of the body. As a result, nuclear medicine therapies tend to cause far fewer side effects than other types of treatment.
Can any drug be used in this way?
In theory, any chemical that selectively targets a particular tissue could be labelled with a radioisotope and used for nuclear medicine. We are getting better and better at finding drugs to target specific types of cancer, for example and to investigate suspected dementia. The important point is that the carrier drug and radio isotope we use for imaging are only used in minute doses, far too small to have any clinical impact, so patients are very unlikely to have any side effects.
How does the targeting work?
It all depends on understanding how particular tissues or different parts of the body function. For example, the thyroid gland is the only part of the body that uses iodine, so we can use radioactive iodine to cure thyroid disease. One of the most common nuclear medicine tests for cancer detection uses a form of radioactive sugar (glucose). Growing cancer cells need lots of energy, so they use more glucose than healthy tissues. If we give the patient an injection of radioactive glucose and then take a picture of where the sugar goes to in the body, we can find the cancer, wherever it is
Is that all it does?
No. Measuring how much sugar a tumour uses can tell us a lot about how the cancer is behaving and responding to treatment. A tumour that is growing aggressively has a high rate of glucose turnover. If we do a PET scan before treatment commences and another quite soon into treatment, we can see whether the glucose turnover has changed, which will tell us whether treatment is working or not. This is having a major impact on cancer care and helps oncologists to tailor treatment better to individual patients’ needs.
What are the advantages of nuclear medicine scans?
The big advantage is that nuclear medicine scans show us how parts of the body react in response to illness or damage. Those changes tend to occur before differences in shape or structure are detected with conventional x-rays or other types of scan, so nuclear medicine imaging often allows earlier diagnosis. The thing that I want to emphasise is that different types of scanning techniques are complementary and not in competition with each other.
Can you give an example of different scans working together?
The concept is called ‘fusion imaging’ which we can use to precisely locate an abnormality. The nuclear medicine scan tells us about the function or behaviour of a part of the body whereas the CT scan provides an accurate roadmap to locate the problem accurately. In orthopaedics, for example, nuclear medicine scans are often used to pinpoint the source of back pain or discomfort relating to joint replacements. By combining nuclear medicine and CT scans, we can see exactly where the problem lies in a single examination. This is a more efficient way of working than undertaking a whole succession of different tests separately.
Is this tricky to achieve?
We now have machines with both kinds of scanner built in—most commonly a nuclear and a CT scanner. So critically the patient can have both scans while in the same body position. This means we can combine the images much more accurately, which has hugely increased the sensitivity of the scans compared to the days when we fused images from different machines.
What are the downsides of nuclear medicine?
We go to great lengths to keep radiation exposure as low as possible. We always make sure that the low dose of radiation a patient receives from a nuclear medicine scan is justified by the information the test is likely to provide to their specialist. Many of the medicines we use are cleared from the body through the kidneys when the patient passes urine, so we make sure the patient understands that they need to drink more than usual to keep the kidneys flushed through afterwards. But these are known issues which can be addressed quite simply. The word ‘nuclear’ has negative connotations for some people and can add an unnecessary layer of worry. We are working on changing the names to ‘molecular imaging’ and ‘molecular therapy’. This places the focus more on the carrier drugs we use and reflects the fact that we are looking at things on a molecular level.
What do you like about what you do?
As a specialty, nuclear medicine allows me to work with a whole team of physicists, biologists, pharmacists, nurses, technologists, radiographers, doctors from almost every other specialty and, of course, to maintain contact with patients. When faced with a difficult clinical or research decision, it really helps to draw on the expertise of others who approach problems from different perspectives. The teamwork is stimulating, productive and puts nuclear medicine at the cutting edge of both imaging and treatment. You can’t ask for much more than that.