The Role of Radioisotopes in Medical Diagnostic Procedures

Have you ever wondered what nuclear medicine expects to accomplish? Well, nuclear imaging is a part of the medical branch involving radiopharmaceuticals, used to diagnose or monitor a patient’s disease. Specifically, radioisotopes make effective tracers, meaning the radiation they emit can be traced and utilised to make a diagnosis.  In fact, there are a total of 3,800 known radioisotopes, and their application in medicine has advanced such that 200 of them are used on a daily basis [1].

By introducing small amounts of a radioactive substance (i.e. a radioactive tracer) into the patient’s body and taking images, doctors can visualise and assess the function of organ and tissue structures. This ultimately gives a deeper insight into tissues and organs than a traditional x-ray would allow. In some cases, radioisotopes can also be used to treat disease, but this article will focus on their diagnostic applications.

What are Radioisotopes?

Isotopes are different atomic forms of the same element, with the same number of protons but a different number of neutrons. Isotopes may or may not be radioactive, but the majority of naturally occurring isotopes tend to be stable. The unstable isotopes which undergo radioactive decay (i.e. are radioactive) are known as radioisotopes. Due to the atom’s instability, the nucleus of each atom will vibrate in order to achieve stability. For example, think about hydrogen - there are three main isotopes of the element hydrogen: protium, deuterium, and tritium. Of those three, only tritium is radioactive.

Radioactivity was first discovered by French scientist Henri Becquerel, thus the SI unit of radioactivity was named after him. One becquerel is referred to as 1 disintegration per second (dps). This discovery led Ernest Rutherford and Frederick Soddy to investigate further and eventually conclude that radioactivity results from the impulsive decay of an atom to form a new element. The discovery of radioisotopes occurred in 1936, where a radioactive isotope was to cure a disease for the first time.

Radioisotope Production

Medical radioisotopes are produced from materials bombarded by neutrons in a reactor or alternatively, by protons in a cyclotron, a type of particle accelerator. There are, however, disadvantages and advantages for both methods. 

Nuclear reactors ensure that a high amount of neutron-rich radionuclides are produced, making them advantageous in larger regions or even worldwide. However, they can be expensive and produce serious levels of long-lived hazardous waste. There is also no access to an alternative route in case of an unexpected intermission - a limitation that is potentially critical given the medical applications.  Additionally, nuclear reactors may not be accessible in some countries; this emphasises the importance of SDG 9: Industry, Innovation and Infrastructure, which calls for upgraded infrastructure and technologies.

Cyclotrons generate proton-rich radioisotopes, which are used in positron emission tomography (PET) scans. Their decentralised production facilitates chain backups which are effective in strengthening the reliability of radioisotope supply. The quantity of long-lived nuclear waste is low, meaning that it’s useful even in a small quantity. The output of radionuclides is limited based on the installed beam energy, so varying quantities can be produced.

Radioisotopes are increasingly growing in demand. Therefore, we need to inspire innovation and increase the number of cyclotrons in hospitals to produce more radioisotopes that would enable effective treatment [1]. Technological support must also be established in hospitals, especially in developing countries, to enhance treatment and to ensure an individual’s well-being. This again corresponds to SDG 9 that aims to build durable infrastructure as well as an inclusive future.

Medical Applications of Radioisotopes

Radioisotopes have been utilised in nuclear medicine for more than 30 years and remain indispensable in today’s society [2]. But how are they used, and what makes them a practical asset in the medical industry?

Today, over 10,000 hospitals worldwide use radioisotopes [1]. There are two uses of radioisotopes: they can be utilised as a source of radiation energy and as a diagnostic tracer.

Radioactive tracers are composed of carrier molecules that are closely bound to a radioactive atom. However, these carrier molecules differ substantially depending on the intent of the scan. Some tracers use chemicals that bond with a certain protein or sugar in the body and may utilise a patient’s own cells.

Radioactive tracers are typically administered via intravenous injection, but can sometimes be administered through direct injection into an organ, inhalation, or ingestion, depending on the disease process being studied. After the tracer has been administered to a patient, there will be a progressive increase of the radiopharmaceutical in the target organ. It will undergo radioactive decay, and the emitted radiation is visualised through PET and single-photon emission computed tomography (SPECT). 

PET

PET is a nuclear medicine imaging technique that gives an accurate 3D image. In PET, positrons are emitted from the radioactive tracer, which counteracts electrons close to them and emits radiation. The unhealthy cells later absorb the tracer at high speeds, which are shown as bright areas on the image produced by the scanner. 

Moreover, the decay of the radiotracers used in PET scans produces tiny particles called positrons which react with electrons in the body. When these two particles combine, they eliminate each other. As a result, small amounts of energy are released in the form of two photons that travel in opposite directions. The detectors in the PET scanner measure these photons and use this data to generate internal organ images [3].

PET scans play an important role in the evaluation of heart disease and neurological disorders as well as the identification of cancerous tumours. Specifically, they highlight the differing levels of chemical activity, and when used following the administration of a radioactive tracer, areas of chemical activity appear as bright spots on the scan. Again, global disparities in access to PET scans and nuclear medicine exist, meaning doctors (and patients) may have limited or no access to this valuable diagnostic tool. Undoubtedly, these inequalities are concerning.

SPECT

Where SPECT imaging is used, unlike the radioactive tracers used for PET scans, the radioactive tracer does not emit a particle. Instead, they radiate gamma rays, which are detected by cameras to form an image. The vast number of body images projected at various angles, generated on a computer or software device, produce 3D images. To achieve this, the cameras are positioned on a revolving gantry, enabling the detectors to shift in a tight circle around a patient lying on a pallet [3].

An Example of Supply Challenges

One of the most common isotopes is Technetium-99 (Tc-99). Tc-99 is produced by a complex method involving irradiation of uranium in nuclear research reactors for the production of Molybdenum-99 (Mo-99). Sadly, the availability of Tc-99 depends on an unsustainably low number of development reactors. These reactors were installed in the EU during the 1950s and 1960s and are now reaching the end of their lifetime [4]. This creates a growing need for routine maintenance shutdowns and an increasing number of unplanned supply disruptions. The disrupted supply of Mo-99 and its decay product, Tc-99, resulted in the cancellation of critical diagnostic tests for many patients between 2008 and 2010 [4]. It’s clear that there needs to be an amelioration in the availability of Mo-99/Tc-99. If the supply doesn’t enhance, the main medical imaging facilities will be undependable for several patients and the treatment therefore will be ineffective.

Hazards of Radioisotopes

Although the practical uses of radioisotopes are effective, there are also some disadvantages - the main one being that radiation exposure can cause DNA damage. The response to the radiation is contingent on the dose rate, overall dose, and the quality of the radiation used. The response will determine the effect of radiation on the human body, which can be categorised into two categories: acute or somatic. An acute effect would damage biological cells if the radiation dose were large enough to allow the cells to recede. It will be noticeable if you appear to develop some of the complications such as skin burns and epilation. A somatic effect arises over several years, so it doesn’t depend on other factors. This delayed effect of radiation can alter genes, leading to an increase in germ cells, therefore causing cancers such as leukaemia, thyroid, and skin [4].

To combat this, special precautions must be taken when using radioisotopes. The triad of radiation protection - time, distance, and shield - ensures that the risk of harm is minimised and that radioisotopes are used when the risk is outweighed by the diagnostic and therapeutic benefits.

Benefits of Radioisotopes

Radioisotopes open an opportunity for doctors to treat patients using less invasive methods, minimising pain, and reducing recovery times. Another benefit of radioisotopes is that treatment can also be applied to unseen areas of the body. In the past, doctors have had to use invasive methods of treatment; however, since the evolution of radioisotopes, this issue has been rectified so that they can avoid risky surgical operations.

Specific Diagnostic Applications of Radioisotopes

In the hospital setting, radioisotopes are used to treat a range of diseases such as thyroid disease, arthritis, and liver tumours [6]. The most common radioisotopes used in the medical industry are Technetium-99m, Iodine-131, and Molybdenum-99. 85% of all nuclear medical examinations use Mo/Tc generators for diagnosing problems with the liver, bones, or lungs [6].

Iodine-131 is beneficial for diagnostic purposes involving the thyroid gland, as it could help destroy any tumour cells that were located. About half of the iodine in your body is absorbed by the thyroid gland. As a result, radioactive iodine (RAI, also known as I-131) can be used to cure thyroid cancer. The RAI mostly accumulates in thyroid cells, where the radiation will kill the thyroid gland as well as all other thyroid cells (including cancer cells) that take up iodine, with no impact on the rest of your body. This procedure will be used to kill all thyroid tissue that was not removed after surgery. It will also treat some forms of thyroid cancer that have spread to lymph nodes and other areas of the body.

By injecting Tc-99 and scanning the head with suitable scanners, the tracer can play a role when identifying a tumour in the brain. Here, detecting tumours without surgery is essential, as the brain is an extremely fragile organ responsible for all the reactions that take place within your body. Therefore, radioisotopes minimise the chances of harm being caused to the brain.

The Importance of Radioisotopes

Radioisotopes work to our advantage, since they can be used in very small amounts and be directed to specific organs in the body. The length of the half-lives of the radioisotopes determines which applications they are suitable for. Radioisotopes that have short half-lives decay rapidly, so they are suited for diagnostic purposes. Radioisotopes with longer half-lives take much longer to decay, so they would be appropriate for therapeutic purposes [4].

With the aid of radioisotopes, doctors can obtain an analysis of the function of specific organs and diagnose certain diseases. This ensures that illnesses can be deduced or identified at an earlier stage, leading to a faster approach with the appropriate treatment. More simply, doctors can recognise if there is an aberration and re-route to a treatment that is most suitable for their patient [1].

Radioisotopes and the SDGs in the Global Health Sector

It cannot be denied that there is a decline in prevention and treatment due to the current lack of services within the health sector [5]. The World Health Organization reports that the world is facing a lack of almost 4.3 million doctors as well as other healthcare professionals [5]. Global under-supply challenges the efficiency and survival of health services worldwide. This is a real concern and we can’t ignore that global healthcare services are in demand. The high demand means that illnesses would develop further, contradicting SDG 3, which aims to reduce illnesses and deaths. 

Think about cancer, for example. Will the undesirable cells in the human body duplicate and worsen the condition of an individual? The longer the treatment is delayed, the more time the cancerous cells will have to replicate and spread to other parts of the body. This causes more damage to healthy cells and thereby results in a poorer prognosis - quality medical care and treatment must be available for everyone when they need it.

Linking directly back to radioisotopes, if people can’t receive suitable treatment, their condition would continue to deteriorate. Key schemes need to be put in place to ensure that care is given to those in critical condition.

More radioisotopes would lead to faster and effective treatment, so in connection to SDG 9, we can obtain a more direct approach to health services. By introducing and promoting current technologies, we can ensure the effective utilisation of resources. Of course, it won’t be an immediate improvement, especially for developing countries, where this needs to be accompanied by enhanced manufacturing and investment in scientific research. To obtain sustainable healthcare solutions and overcome economic challenges, it is vital to progress with innovation and technology.                      

Wider Health Inequalities

The UN set targets to achieve better and inclusive futures for people, with SDG 3 focussing on Good Health and Wellbeing. Some people don’t have access to doctors or treatment within their region, so expanding the provision of healthcare, diagnosis, and treatment would be more effective. Within Sub-Saharan Africa and Southeast Asia, only one doctor is available per 2000 people [7]. Countries with the fewest doctors include Liberia, Ethiopia, Malawi, and Rwanda. Liberia has access to 14 physicians per million, which is seen to be the lowest when compared to the remaining countries [8]. The scarcity of doctors within these countries makes it difficult to provide the treatment necessary for an individual. 

However, there is also a serious predicament regarding cost. In many countries, every person that requires medical attention must pay for their treatment. Failure to pay puts them in a situation where they are left untreated, causing further health complications. They could be living in this condition for an indefinite period of time, unaware of their illness and the cure that they need to relieve the pain. 

Healthcare must therefore be accessible worldwide to ensure that those in a critical condition obtain the care they need. I personally believe it is paramount that universal health coverage is maintained across countries. We cannot deny that providing healthcare universally will be a battle, as the current inequalities are substantial. Everyone should have access to quality healthcare and the fullest range of diagnostic tools and treatments available, including radioisotopes. 

Health and Wealth

A major concern for the health welfare of individuals is that radioisotope therapy is not affordable for everyone, for both the individual patient and at the country level. Health financing and recruitment should be established in the future to ensure everyone has access to treatment as well as greater investment in health personnel in less economically developed countries. The current statistics state that over 40 percent of all countries have fewer than 10 medical doctors per 10,0000 [9]. Not everyone has the opportunity to receive the treatment. But by reinforcing the advancement in technology needed to produce radioisotopes, we can fully realise their role in medicine.

With the advancement of healthcare globally, there will be greater opportunities for all countries to have better health. By supporting the research and development of medicines, especially in less developed countries, new treatments and diagnostic tools can be developed. They may one day even provide an alternative to radiation therapy that has minimal damage to the human body, while still being effective.

Conclusion

Radioisotopes have advanced healthcare immensely. We must appreciate the effectiveness of radioisotopes and realise their potential within both diagnosis and treatment. They allow doctors to make better diagnostic conclusions, and therefore the availability of nuclear medicine should be global. The UN Sustainable Development Goals plan to improve society, and with advances in medicine coupled with increased infrastructure, we can secure a prosperous future with radioisotopes. 

Who knows what the future will hold for nuclear medicine? What applications do you expect to see for radioisotopes? Has their potential been discovered or will new techniques be applied so radioisotopes can further improve the quality of human health?

References

[1] World Nuclear Association, ‘‘Radioisotopes in Medicine,’’ May 2020. [Online]. Available: https://www.world-nuclear.org/information-library/non-power-nuclear-applications/radioisotopes-research/radioisotopes-in-medicine.aspx. [Accessed 20 December 2020].

[2] Australian Nuclear Science and Technology Organisation, ‘‘What are radioisotopes,’’ n.d. [Online]. Available: https://www.ansto.gov.au/education/nuclear-facts/what-are-radioisotopes. [Accessed 22 December 2020].

[3] National Institute of Biomedical Imaging and Bioengineering, ‘‘ Nuclear Medicine,’’ July 2016. [Online]. Available: https://www.nibib.nih.gov/science-education/science-topics/nuclear-medicine. [Accessed 3 March 2021].

[4] European Commision, ‘‘European Observatory on the supply of medical radioisotopes,’’ n.d. [Online]. Available: https://ec.europa.eu/euratom/observatory_radioisotopes.html. [Accessed 27 February 2021].

[5] C. Aluttis, T. Bishaw and M. W. Frank, ‘‘The workforce for health in a globalized context-global shortages and international migration,’’ Global Health Action, vol. 7, 2014.  Available: https://dx.doi.org/10.3402%2Fgha.v7.23611.

[6] United States Atomic Energy Commission, “Radioisotopes in Medicine.” Osti.gov, 1967. [Online]. Available: https://www.osti.gov/includes/opennet/includes/Understanding%20the%20Atom/Radioisotopes%20in%20Medicine.pdf . [Accessed 21 May 2020].

[7]  Humanium, “Right to health around the globe,” n.d. [Online]. Available: https://www.humanium.org/en/right-to-health/. [Accessed 2 December 2020].

[8] J. Burton, “25 countries with fewest doctors,” WorldAtlas, April 25, 2017. [Online]. Available: https://www.worldatlas.com/articles/the-countries-with-the-fewest-doctors-in-the-world.html. [Accessed 21 December 2020].

[9] World Health Organization, “Medical doctors (per 10 000 population),” n.d. [Online]. Available: https://www.who.int/data/gho/data/indicators/indicator-details/GHO/medical-doctors-(per-10-000-population). [Accessed 28 December 2020].