Nuclear Medicine Scan: Do We Need To Worry About Radiation Exposure?

29 March 2022

Radiation exposure is unavoidable nuclear medicine. The fear of "radiation" has become a concern for many people when it comes to screening and treatment, but it is actually a myth.

Are nuclear medicine scans safe? Do patients undergoing nuclear medicine examinations or treatments transmit radiation to others? What if it affects my unborn child?

The list of concerns is endless. Many cancer patients refuse to undergo nuclear medicine related scans because of their fear of nuclear radiation, and as a result, their doctors are unable to accurately locate, quantify and grade their tumours, which often leads to spending more time in finding the right treatment.

Dr Tan Teik Hin, Consultant Nuclear Medicine Physician at Sunway Medical Centre, pointed out that in the field of nuclear medicine, radiation does not mean damage to the human body.

He said that most people's perception of "nuclear" is based on the knowledge of atomic bomb explosions and leakage from nuclear power plants which caused a huge disaster to mankind. So when it comes to "nuclear", it is assumed to be harmful. 

Based on this, not only do patients have doubts about nuclear medicine scans, but their families are also often worried and apprehensive.

What is a nuclear medicine scan?

In short, what we call a nuclear medicine scan is a way to produce images by detecting radiation from the radioactive tracer given to the patient, said Dr Tan.

"It is an imaging scan in which a tiny amount of radioactive drug is introduced into the patient's body, usually by intravenous or oral administration, and is then detected by nuclear medicine scanners. It is one of the methods of medical diagnostic testing, along with what we know as X-rays and CT (computerised tomography)."

He said that there are many different kinds of radioactive substances, and that the numerous radioactive substances released by atomic bomb explosions and leaks from nuclear power plants are not the same as those commonly used in nuclear medicine scans. There is a big difference in terms of radiation.

"We live in a world of radiation in our daily lives. There is no such thing as a zero-radiation environment. For example, there is a wide range of radiation and nuclides from natural rays in the sun and soil. The use of electrical appliances such as computers and mobile phones can also expose us to certain doses of radiation."

"Radiation exposure from a long haul flight is probably much higher than undergoing a nuclear medicine scan."

The myth of nuclear phobia

Dr Tan pointed out that nuclear medicine is a completely different concept from nuclear energy and nuclear weapons. The nuclides used in nuclear medicine have a shorter life and lower energy, and the doses used are small and very safe.

"And nuclear medicine is subject to strict Ministry of Health control to ensure that the nuclides used in hospitals are kept within absolute safety limits."

"Due to atomic wars and accidents at nuclear power plants, there is a general fear of nuclear energy and even some medical staff, including those with little knowledge of nuclear medicine, suffer from nuclear phobia and this has formed barriers for them to access nuclear medicine."

"In fact, nuclides contribute greatly in many areas such as sterilisation of gloves."

Studies have shown that radiation sterilised masks, gloves and other hygiene products are more secure and the rays penetrate strongly, disinfecting evenly and thoroughly without any harmful residues.

Radiation is becoming more and more widely used in disinfection and sterilisation, especially by the nuclear industry using irradiation sterilisation technology to help produce personal protective equipment, which greatly shortened the sterilisation time at the height of the pandemic.

Which cancers can nuclear medicine diagnose?

When people seek for medical advice, doctors often recommend a radiology scan to find out the condition. X-rays, CT scans and MRIs are quite common nowadays, however when doctors recommend that patients go for a PET/CT scan at a Nuclear Medicine department, some patients become confused – what are the special features and advantages of a PET/CT scan compared to conventional imaging scans such as CT scan and MRI?

One of the aims of a PET/CT scan is to detect cancer at an early stage, even when there are no symptoms. As the name implies, PET/CT = PET (positron tomography) + CT (computed tomography), which is a combination of two parts, PET images and CT images.

Nuclear medicine mainly covers molecular imaging, targeted imaging and radionuclide therapy, said Dr Tan.

In cancer diagnosis and treatment, one of the most common molecular imaging method is FDG PET/CT scan.

"FDG PET/CT uses primarily radioactive glucose as a tracer to show cellular activity and changes to better detect early disease (cancer, infection or inflammation), cancer staging, assess disease recurrence and monitor treatment response."

He pointed out that the other two most commonly used PET/CT scans are Ga-68DOTATATE (which is used to diagnose neuroendocrine tumour and paraganglioma/pheochromocytoma) and Ga-68PSMA (which is used to diagnose prostate tumours).

"We may start using other radioactive substance for PET/CT scan this year, such as the latest Ga-68 FAPI to screen for cancer."

"As for radionuclide therapy, it is a new concept of targeted therapy, mainly for thyroid cancer, metastatic neuroendocrine tumours, pheochromocytoma, metastatic prostate tumours and liver cancer that cannot be removed surgically."

Nuclide Therapy

According to Dr Tan, radiotherapy and nuclear therapy are different concepts of cancer treatments using radiation. Radiotherapy uses the concept of external radiation, in which high-energy radiation is released by a medical equipment to destroy tumour tissue, usually locally.

"Nuclide therapy applies the concept of targeted internal radiation, where a specific radiotracer is injected, attached to the tumour cells, and radiation is released to destroy the tumour locally, usually systemically."

As nuclide therapy is still considered new in treatment for tumours, not many tumours can be treated with it so far. Those that have been treated with nuclide therapy include thyroid cancer, neuroendocrine tumours, pheochromocytomas, prostate tumours and liver cancer. These tumours often have a low response to chemotherapy or have high side effects, or the tumour has metastasised and cannot be treated with radiotherapy.

Weighing the need for screening

How much radiation can the body tolerate without suffering? In general, clinical practice follows the principle of "the lower the better", which involves avoiding unnecessary exposure and minimising exposure doses.

Dr Tan pointed out that X-rays, CT scan, angiography, fluoroscopy, PET/CT scan and SPECT/CT scan all contain radiation.

"We often see patients who are fine with a chest X-ray or CT scan, or even when having these scans several times or on several parts of the body. However, when it comes to a nuclear medicine scan, they often face difficulty making the decision. This is because they lack knowledge and awareness of nuclear medicine and simply believe that nuclear medicine scans are more likely than other scans to cause radiation damage to the body or cause cancer."

"Every medical scan and treatment, not necessarily nuclear medicine, actually carries some risk and side effects."

"It is important to know that nuclear medicine scans and treatments have been tested in phase 3 clinical trials and are safe. So in principle, it's not about how much radiation you can or cannot receive, but whether you need to receive unnecessary radiation."

"If a patient is in a situation where they need to be scanned or treated with a certain type of radiation so that the best treatment can be achieved, then that scan or treatment must be the primary consideration."

"For example, if a pregnant woman who has been in a car accident needs to undergo a CT scan to ensure there is no internal bleeding, then CT scan is a priority. Furthermore, if a PET/CT scan can detect early cancer or recurrence of disease better than other scans and help treat it early, then a PET/CT scan is the first choice." However, doctors usually will not ask an individual without any conditions to undergo a PET/CT scan if there are no clear symptoms or abnormal tumour markers.

Dr Tan also said that there is no basis for the belief that one should not undergo X-ray or MRI in the short term after a PET/CT scan.

He pointed out that so far, there have been no reports or cases of adverse outcomes, especially pregnant women and children, who have been exposed to patients after nuclear medicine scans or treatments.

"Keeping a distance is only a safety recommendation. However, to avoid unnecessary panic and suspicion, we usually advise patients and others to observe this measure."

Once the radiopharmaceutical is injected into the body, it is rapidly absorbed and distributed, with the excess being metabolised and excreted. Hence, two hours after the drug is administered, the radiation dose has significantly reduced and the residual dose is not significant for other people.

Strict operating procedures at the Nuclear Medicine Centre

As the amount of radiation used in nuclear imaging such as PET/CT scan is minimal and has a very short life, the radiation in the body usually drops to normal levels after a few hours and does not cause any harm to the body or others, said Dr Tan.

As for treatment, he said that residual radiation in the patient's body must be treated with appropriate safety measures, as recommended by the nuclear medicine physicist, to ensure that people in the vicinity or within its range are not affected. Although the radiation cannot be seen or touched, a physiotherapist can calculate it through medical devices to determine whether the radiation in the body has been reduced to normal levels.

He also stressed that the standard operating procedures of each nuclear medicine centre are monitored and strictly controlled by the International Atomic Energy Agency and Ministry of Health, and the risk of leakage is very low.

"Every nuclear medicine centre has strict operational procedures for leaks to ensure that if a leak happens, it will be kept within absolute safety limits."

"In addition, the radiation from the nuclides used in nuclear medicine centre is very low and has an extremely short half-life, usually dropping to normal levels after a few hours, without causing harm to others or the environment."

On the other hand, Dr Tan  also pointed out that during the pandemic, each hospital, including Sunway Medical Centre, is committed to ensure that all patients and medical staff followed the standard operating procedures set by the Ministry of Health, which was to ensure that there was no cross-contamination between patients and staff.

He said that most routine medical procedures or tests could be carried out before or after COVID-19 vaccination. People who have undergone nuclear medicine diagnosis or treatment can still receive the vaccine and so far there have been no relevant reports of conflicts between nuclear medicine scans and COVID-19 vaccines.

On the other note, according to the International Commission on Radiological Protection (ICRP) standards, a fetal radiation dose of less than 50mGy is not likely to cause congenital risk.

"All scans, including nuclear medicine scan, will not exceed this standard. For example, the dose used in a PET/CT scan falls within approximately 10mGy. However, we still advise pregnant women not to undergo unnecessary radiological imaging unless they really need it."

Dr Tan pointed out that PET/CT scan is currently a breakthrough diagnostic tool in the medical field for diagnosing diseases such as cancer, and it also plays an important role in cutting-edge medicine such as targeted therapy. The Nuclear Medicine Centre at Sunway Medical Centre is equipped with nuclear medicine equipment including PET/CT and SPECT/CT, however, not every hospital in Malaysia offers PET/CT scans and nuclide therapy, as the construction of a nuclear medicine centre requires certain conditions and approval from the Ministry of Health. Ideally, a well-equipped and comprehensive nuclear medicine centre would not only be equipped to provide nuclear medicine screening services, but also to provide nuclide therapy that is not limited to thyroid tumours.

In addition, he pointed out that there are not many nuclear medicine physicians registered in the country and that those who are registered do not mean they can practice, especially in the area of nuclide therapy.

Source: Sin Chew