“What is nuclear medicine? Is it part of radiotherapy?” That was what I overheard a patient asking her relative outside my clinic door on one of my clinic days.
Not surprisingly, despite these services being available in the country for more than two decades, many Malaysians still do not know what nuclear medicine is all about.
In the mind of most people, the word “nuclear” is frequently associated with the atomic bombs that devastated Nagasaki and Hiroshima in Japan during World War II, as well as the nuclear plant disasters involving Chernobyl in the then-Soviet Union in 1986 and Fukushima, Japan, in 2011.
Who would have thought that nuclear medicine has been in existence even before the introduction of penicillin in 1940?
The term “nuclear medicine” is derived from the use of radioactivity harnessed from the unstable nucleus within an atom for medicinal purposes.
This harnessed radioactive energy can be used for imaging, as well as therapy.
The main concern for most people with regards to the use of nuclear medicine would be the amount of radioactivity they are exposed to.
The amount of radioactivity used for medicinal purposes is by far much lower and safer, compared to those used in nuclear power plants and consumer industries, or even in the dreaded nuclear weaponry.
The effective dose from the radioactive materials used is only as high as 14 millisieverts for nuclear medicine imaging.
Patients undergoing radiological examinations such as conventional x-rays, computed tomography (CT) scans and fluoroscopy are similarly subjected to radiation exposure.
To put things in perspective, everyone is subjected to natural background radiation (approximately 2.4mSv/year) of some kind or the other, be it from soil, food, water, space etc.
In fact, there are hotspots in the world such as in Ramsar (Iran), Guarapari (Brazil), Karunagappalli (India) and Yangjiang (China) where the citizens are exposed to higher natural background radiation (up to 260mSv/year) with no documented higher risk of cancer.
What is so unique about nuclear medicine?
There are various radioactive materials used for different purposes in this branch of medicine, such as technetium-99m, fluorine-18, gallium-68, iodine-131 etc.
These radioactive materials, when used by themselves or combined with specific tracers, are useful targeted imaging or therapeutic modalities for doctors.
Iodine-131, which is used for the treatment of well-differentiated thyroid cancer is a well-known theranostic agent (coined from the words “therapy” and “diagnostic”) that not only allows doctors to treat the cancer, but also see where the disease is located at the same time.
As a matter of fact, iodine-131 has been in clinical use since the 1940s.
In nuclear medicine imaging, two main types of scanners are required: the gamma camera and the positron emission tomography (PET) camera.
The scanners identify, as well as quantify, the distribution of the injected radiotracers (chosen based on their “target” properties).
For example, imaging of bone metastases for cancers such as breast and prostate cancers, are performed using bone-seeking technetium-99m-methyl disphosphonate.
This radiotracer is very sensitive in detecting early bone metastases, from as little as 5% abnormal bone turnover, compared to 40%-50% in conventional imaging.
The small amount of injected radioactive material would decay over time and is essentially harmless to the body.
The majority of PET/CT imaging performed worldwide uses fluorine-18-fluorodeoxyglucose.
This is a glucose analog, and hence distributes within the body to areas with high glucose consumption, particularly targeting cancers that are metabolically very active.
Doctors worldwide use fluorine-18-fluorodeoxyglucose PET/CT scans in the management of cancer patients, be it for assisting in biopsy, detection of the primary cancer site, staging, restaging, evaluating response to treatment, or surveillance.
This unique radiotracer can be used for various cancers such as head and neck cancers, lymphoma, breast cancer, lung cancer, melanoma, sarcoma, liver cancer, gastrointestinal tract cancer and gynaecological cancers.
In patients with lymphoma, fluorine-18-fluorodeoxyglucose imaging helps doctors stage the cancer and plan chemotherapy.
Subsequently, it is used to evaluate the effectiveness of the therapy and help the decision on whether to continue the chemotherapy or switch the regime.
For patients with lung cancer, this imaging is useful in assisting doctors to decide whether curative surgery is a viable option or to proceed with palliative chemotherapy.
With the development of targeted therapies such as tyrosine kinase inhibitors (TKI), this imaging is also useful in aiding doctors to decide if their patients would benefit from these expensive treatments, which can save lives and cost in the long term.
Similarly, the fluorine-18-fluorodeoxyglucose PET/CT scans can also be used to evaluate the response of TKI in the treatment of patients with refractory thyroid cancer.
Other PET tracers such as gallium-68-DOTATATE and gallium-68-PSMA, are now available in Malaysia and used for neuroendocrine and prostate cancers respectively.
The use of these gallium-68 tracers not only help with the staging of the disease, but also enables doctors to determine if the patient would respond to further radioactive therapies using yttrium-90 or lutetium-177.
The ability to combine the radioactive materials with specific targeted tracers makes nuclear medicine imaging an important cancer imaging tool.
Nonetheless, the use of PET/CT scans is not only limited to cancer cases, but can also be utilised for various other conditions, such as dementia, seizures, perfusion and viability of the heart, and even for fever of unknown origin.
Treating with radioactivity
In terms of therapy, nuclear medicine (using phosphorus-32) was first used in 1936 as a treatment for leukaemia.
As previously mentioned, iodine-131 has been used to treat well-differentiated thyroid cancer for over 80 years and remains the mainstay of treatment for patients who have undergone surgery to remove the thyroid gland.
Thyroid cancer is the ninth commonest cancer affecting women in Malaysia and iodine-131 therapy is fortunately available in most states in the country.
Besides well-differentiated thyroid cancer, iodine-131 is also useful in treating Graves’ disease, solitary toxic thyroid nodule and toxic multinodular goiter.
The role of nuclear medicine in cancer therapy is increasing rapidly with the availability of treatments for neuroendocrine and prostate cancers.
Other available nuclear medicine therapies include selective internal radiation therapy (SIRT) for hepatocellular carcinoma, radiosynovectomy for haemophilic arthropathy, and bone palliation for diffuse bone metastases.
Nuclear medicine definitely has an important role to play in medicine today and is in sync with the Precision Medicine Initiative launched by the former US President Barack Obama in 2015.
Though nuclear medicine has yet to be widely known among Malaysians, easy internet access to medical facts may soon change the scenario.
As pioneer radioactivity researcher Marie Curie once said: “Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less.”