How nuclear medicine helps treat cancer
What does nuclear medicine do?
This is a field of medicine that uses radioactive isotopes. Atomic nuclei of the same element contain the same number of protons, which determines the chemical properties of a given element. However, they can differ in the number of neutrons in the nucleus, which means they can create isotopes that have different physical properties. Some can be stable. others unstable, which makes them radioactive. The latter can emit different types of radiation from the atomic nucleus. The isotopes of a given element do not differ in chemical properties. For example, iodine-127 and iodine-131 are isotopes of the same element, iodine. They have the same chemical properties and follow the same pathway in the body. The first one is a stable isotope and is the basic building block of thyroid hormones. The second is a radioactive isotope emitting gamma radiation, which enables you to track its position in the body using a special device called a gamma camera. One test using this technique is scintigraphy, which shows where in the body a radioactive isotope has been accumulated, e.g. iodine-131 in the thyroid gland. More advanced than scintigraphy is the PET examination, also known as positron emission tomography. In this case, radioactive isotopes emitting positrons (anti-electrons) are used, which make it possible to obtain images with much better resolution. The resolution of the scintigraphic examination is about 10 mm; in the PET examination, it is 3-5 mm.
It should be remembered that the use of a simple mechanism of accumulation of radioactive isotopes in the body, for example, the transport of iodine to the thyroid gland using a sodium-iodine pump is very limited. Increasingly, to introduce radioactive isotopes into the body, we use special chemicals (proteins, antibodies, peptides, amino acids, glucose, hormones, drugs) called vectors, which are specifically bound to selected tissues.
The combination of an isotope with a specific chemical is called a radiopharmaceutical. We select the radiopharmaceutical depending on what we need to diagnose and what question the clinician needs to answer. For example, if we wish to examine the respiratory surface of the lungs, we need to inhale the radiopharmaceutical. And if we need an assessment of blood flow in the lungs at the level of microvessels, we administer the preparation intravenously.
Can radiopharmaceuticals only diagnose or also treat?
Radiopharmaceuticals are also used in therapy. Today, this applies mainly to oncological diseases. We can introduce an isotope into the tumor that emits radiation with high energy but a small range. We want to destroy abnormal cells, to get the best therapeutic effect, but still cause as little damage as possible to healthy cells so as not to produce any side effects. In our therapies, we look for very specific mechanisms for taking up radiopharmaceuticals. For example, antigens or receptors that are specific to a specific cancer can be used here. Radiopharmaceuticals can also be successfully used in the treatment of non-oncological diseases, such as mild thyroid diseases or in the treatment of inflammatory joint changes.
Are radioactive isotopes harmful to health?
If they were harmful, they could not be used. Until we knew how radiation worked and what the effects of individual doses might be, there were some risks. However, today our knowledge of radiation is highly developed, and the doses of radiopharmaceuticals used in nuclear medicine are approved and safe for the patient. I know that many patients are afraid of radiation, which is probably because of the disaster at the Chernobyl nuclear power plant. However, I stress that the explosion in the power plant was an accident; the level of radiation was uncontrolled. In nuclear medicine, we control the dose with precision. We prepare radiopharmaceuticals "tailor-made" for a specific patient. And it is always the smallest possible dose, which at the same time enables diagnostics or effective therapy.
When treating the thyroid gland with radioiodine, special precautions are observed. Why?
Radioiodine treatment is the oldest therapy in nuclear medicine, introduced in 1941. When it comes to the thyroid gland, we must distinguish two things. The first is its benign diseases, such as nodular goiter, autonomic nodules or Graves' disease, which we can treat if they proceed with an overproduction of hormones. Of course, we can stabilize the thyroid gland with drugs, but when this is not enough, we start using therapy with radioactive iodine. This involves administering an oral dose of radioactive iodine selected individually for each patient and disease. Iodine reaches the thyroid gland, depositing energy there. In this way, we destroy nodules – when we have nodular goiter or thyroid – in the case of Graves' disease. In this therapy, we use small doses of radioiodine, and it is not necessary for the patient to be put into the radioisotope therapy ward.
A completely different situation is with thyroid cancer. Here, the basic treatment is surgery. In the case of lesions that exceed 1 cm, or when there are metastases to the lymph nodes, adjuvant radioiodine treatment should be initiated after surgery. The idea is to destroy the cancer cells remaining after surgery. Then you need to use up to 20 times the dose of the isotope than in mild thyroid diseases. Therefore, the patient must stay for several days in a special ward, where certain restrictions are introduced.
We’ve mentioned the oldest therapy in nuclear medicine. But what are the latest therapies?
Our latest "baby" is radioisotope therapy for prostate cancer registered by the European Medicines Agency on December 13 last year. It is based on the prostate-specific membrane antigen "prostate specific membrane antigen (PSMA)". It has been known for over 20 years, but it was only in 2012 that a derivative was synthesized, which enabled stable marking and obtaining very high quality diagnostic images. The same preparation was then used in therapy. Studies were published in 2021, proving its effectiveness. We are talking about two multicenter studies (VISION and TheraP). They showed that treatment with a PSMA molecule (capable of binding to prostate cancer cells) labelled with a beta-emitter (an isotope emitting high-energy, short-range particles) based on a ligand (a compound capable of binding to the receptor) of PSMA in prostate cancer resulted in reduced risk of death in almost 40% of patients who had other forms of treatment. It also managed to increase the time to relapse of the disease. The results obtained cannot be overestimated, which is why this therapy has been introduced in the United States and Europe and is recommended for patients with metastatic prostate cancer resistant to other types of therapy.
Is it known when this therapy will be available with us on the NHS?
This is a question for the National Health Service. We must fight together with patients for a drug program. It is unlikely that the therapy will be widely available within the NHS, because it is very expensive and requires appropriate qualification and protection within a nuclear medicine facility.
Is it still possible to treat any oncological diseases radioactive isotopes?
Yes, a drug program for the treatment of neuroendocrine tumors will be launched this year. Research on the diagnosis and treatment of these cancers using nuclear medicine methods has been conducted for a long time. Since the 1980s, we have known that the receptor for somatostatin present on the cell membrane is characteristic of these cancers. This opened the way for research. The breakthrough came in 2015, when the results of the NETTER-1 study were published. Porównano w nim wyniki terapii z wykorzystaniem radioaktywnego analogu somatostatyny z leczeniem preparatem nieradioaktywnym. It turned out that the former brings significant benefits. Therefore, the preparation for treatment was registered already in 2017, which theoretically made the therapy available. However, in Poland we will not be able to treat patients using this method until March this year (we fought for a drug program for so long).
Nuclear medicine is one of the fastest growing fields. Can we count on the fact that more isotope therapies will soon appear in oncology, or that this treatment can be used at an earlier stage of an oncological disease?
Studies conducted so far have shown that therapy using radioactive PSMA is highly effective in patients in whom other types of therapy have proven ineffective. No one can introduce this new therapy at an earlier stage of treatment. Appropriate tests must first be carried out. Currently, studies are underway in which isotope therapy is introduced at earlier stages of prostate cancer development. For example, a very interesting study is underway in Australia, in which isotope therapy is used before surgery. It is about so-called high-risk patients who have a poor prognosis. They are given two doses of isotope therapy to prevent metastases and then performed surgery.
While we're at the research, we need to mention the fibroblast activation factor factor inhibitor (FAPI) in oncology. This is a great source of hope for the diagnosis of cancer. We "descend" to the level of studying the microenvironment of cancer cells and watch as fibroblasts begin to develop around the tumor. So far, 28 types of cancer have been studied this way. FAPI enables us to "catch cancer" at a very early stage of its development. What's more, research on the use of this factor in cancer therapy is also underway. We are constantly looking for new antigens, new solutions, because tailor-made isotope therapies for a specific patient and disease will be our future.
Interviewed by Iwona Kołakowska
Photo by Michał Teperek
University Communication and Promotion Office