Role Of Nuclear Medicine In Cancer

Introduction 

Nuclear medicine is a specialised branch of medicine which uses radioactive materials for diagnosis as well as therapy. It uses radiation to diagnose and treat different ailments. Nuclear medicine scans and therapy use radiopharmaceuticals or radiotracers. 

Radiopharmaceuticals are combinations of radioactive material tagged with a pharmaceutical. Technetium, Tc-99m is often called the workhorse of nuclear medicine. It is tagged with several pharmaceuticals to scan various parts of the body. 

In nuclear medicine imaging, the patient is injected with a radiopharmaceutical and after some time the patient is asked to lie under the scanning machine. Depending on the requirements, specific body parts are imaged and the reports are generated. 

There is natural environmental radiation around us at very minute levels. But, the radiation levels emitted from these radioactive materials can impact health.¹ 

So, healthcare professionals need to make a decision if the radiological procedure is beneficial for the patient's health or not. Radiation protection is based on the JOL principle.²

J (Justification): It refers to justifying the reason for use of radiological procedures. It needs to be ensured that the benefits of the radiological procedure should be more than the harm from the radioactive materials.

O(Optimisation): If the radiological procedure is justified, then dose optimisation needs to be ensured. It means that the dose should be kept As Low As Reasonably Achievable (ALARA). According to the ALARA principle, radiation exposure should be below the limits set by the governing body.

L (Limitation): The radiation dose given should be within limits. Radiation exposure limits are set for the general public as well as radiation workers. But, there are no limits set for patients undergoing diagnostic or therapeutic procedures.

Types of nuclear medicine imaging 

Nuclear medicine imaging uses radioactive materials to scan different parts of the body. Nuclear medicine imaging comprises gamma cameras, SPECT and PET scans.

Technetium, Tc-99m is tagged with different pharmaceuticals to scan different parts of the body. Some of the scans done on the gamma camera are as follows:⁴

Bone scan : Tc-99m MDP is used for whole body bone scan. This scan is done to check metastases in bones, fractures, infections, arthritis or tumours.

Renal scan: Tc-99m DMSA, Tc-99m DTPA or Tc-99m EC are used for renal scans. These can be done to check renal function or any blockages.

Heart scan: Tc-99m MIBI or MUGA scans are used for checking the heart functions, blockages in the heart, evaluating damage after a heart attack or treatment options.

Thyroid scan: Tc-99m is used to check for thyroid disorders. 

Single Photon Emission Computed Tomography (SPECT) is another imaging in nuclear medicine. SPECT scan creates 3D images of the body to diagnose various disorders.

PET-CT (Positron Emission Tomography - Computed Tomography) is a scanner that is used to diagnose cancer or evaluate the effects of therapy on cancer cells. It is a fusion imaging with a CT scan. Most PET scans are done with F-18 FDG (Fluorodeoxyglucose). FDG is similar to glucose and the cancer cells absorb a higher amount than normal cells. So, higher metabolic activity means cancerous growth in that part. 

Radioactive materials used in nuclear medicine 

Nuclear medicine uses radioactive tracers for diagnosis as well as therapeutic purposes. The following radioactive materials are used in nuclear medicine imaging as well as nuclear medicine therapy.

• Technetium Tc-99m 
• Iodine I-131 
• Iodine I-123 
• Fluorine F-18 
• Carbon C-11 
• Xenon Xe-133 
• Gallium Ga-68 
• Nitrogen N-13 
• Yttrium Y-90 
• Lutetium Lu-177 
• Radon Ra-223 
• Phosphorus P-32

Nuclear medicine in cancer diagnosis 

The radiopharmaceuticals used for nuclear medicine imaging are⁵,⁶:

• Tc-99m: As mentioned earlier, this is often referred to as the 'workhorse' of nuclear medicine. It is tagged with various pharmaceuticals to image the heart, thyroid, brain, liver, kidneys, bones etc
• I-131: Iodine is used in the diagnosis and therapy of thyroid cancers. Thyroid cancer patients undergo surgery and then they are referred for radioiodine therapy. The patient takes radioactive iodine in liquid or pill form and is kept in isolation for some time depending on the dose. Radioiodine is also used for hypothyroid patients
• F-18 FDG: Fluorine-18 is used for PET imaging. It is injected and then patients have to wait for a specific time in isolation. After that, they are imaged under the scanner. PET scanning is done to diagnose tumours, infections, brain functions, cardiac functions etc
• Xe-133: Xenon is used in scanning lung function, medically known as pulmonary ventilation scan
• I-123 MIBG: I-123 meta-iodo-benzyl-guanidine is used in adrenal medullary tumour imaging
• F-18 NaF: F-18 sodium fluoride is used to check bone metastases in cancer patients
• C-11 Choline: It is used in diagnosing prostate cancer

Nuclear medicine in cancer treatment 

Nuclear medicine therapy uses radioactive materials to treat cancers and other ailments. This therapy targets cancer cells and destroys them. Nuclear medicine therapies are also called radionuclide therapies. Some of the therapies used by nuclear medicine professionals are³,⁵

• I-131 therapy: I-131 therapy uses radioactive iodine I -131 to treat thyroid cancer and hyperthyroidism. Thyroid cancer patients undergo surgery to remove the cancer cells, but everything is not removed as the thyroid is very close to the parathyroid. So, the remaining cancer cells are destroyed by using radioactive I-131
• I-131 MIBG therapy: MIBG refers to meta-iodo-benzyl-guanidine. This therapy is used for the treatment of neuroendocrine tumours and neuroblastoma in infants
• Peptide Receptor Radionuclide Therapy (PRRT): PRRT is the therapy for treating gastroenteropancreatic neuroendocrine tumours (GEP- NET) which refers to NETs arising from the stomach, intestine or pancreas. For this, Lutetium-177 is tagged with DOTATATE or DOTATOC to destroy cancer cells
• Y-90 microsphere: Yttrium is used in the treatment of hepatocellular cancer

Advantages and Disadvantages 

Nuclear medicine is very beneficial in cancer diagnosis as well as treatment. As it involves the use of radioisotopes, some precautions that need to be taken by nuclear medicine professionals as well as patients. Let's check out the advantages and disadvantages (benefits vs risks) of nuclear medicine.¹,⁷

Advantages (benefits) of nuclear medicine are :

• Nuclear medicine provides high-quality images of the body which can give the specialist a detailed functional insight
• These tests can help specialists diagnose various cancers or other disorders of the body
• PET scans are useful in determining the course of treatment and whether therapy has benefitted the patient or not
• Nuclear medicine therapy is highly beneficial in destroying cancer cells and reducing pain

Disadvantages (risks) of nuclear medicine are :

• Nuclear medicine tests expose the patient to radiation. So the benefit should outweigh the risks for the procedure to be performed
• In X-rays and CT scans, the machine is the radiation source. So, the patient does not get any radiation exposure once they come out of the scanning room. But, in nuclear medicine, the patient becomes the source after radiopharmaceutical administration. So, patients have to follow some precautions even after the nuclear medicine test is completed (for a small duration of time)
• As these procedures deal with radiation, they are not safe for pregnant or breastfeeding women. In such cases, specialists decide if the benefits are more compared to the risks and then only the procedure is performed

Future of Nuclear Medicine in cancer 

Nuclear medicine has come a long way since its start. It has become an important part of oncology and medical imaging services. Developments in the field of molecular imaging have prompted experts from other fields to rely on them. Nuclear medicine is now becoming popular among cardiology, immunology, neurology etc. 

Ga-68 is gaining importance for the detection of neuroendocrine tumours and prostate cancer. 

Lu-177 is becoming the choice of specialists for the treatment of these disorders. 

Clinical trials have shown promising results from lutetium-based therapy for prostate cancer patients. 

Research is always underway for new biomarkers for therapeutic as well as diagnostic applications.⁸

Summary 

Nuclear medicine is an irreplaceable part of medical imaging services. It is used for diagnostic as well as therapeutic purposes. The patient is given a radiopharmaceutical in injection, pill or liquid form.

Radiopharmaceutical = Radioisotope + Pharmaceutical 

Radioisotope is a radioactive material that emits radiation. 

After a specified waiting time, the patient is asked to lie down under the scanner. During this time, the radioactive drug spreads in the body. Gamma rays are captured by the scanners such as gamma cameras, SPECT or PET. A nuclear medicine technologist scans and processes the images acquired from the scanner. Then, a nuclear medicine physician interprets the images and provides the results of the nuclear scan. 

As there is some amount of radiation exposure, some precautions need to be taken by staff as well as the patient. 

Nuclear medicine specialists should ensure that the radiation dose is given within the permitted limits. This should help in keeping the radiation exposure As Low As Reasonably Achievable (ALARA). 

Pregnant and breastfeeding women are advised to stay away from nuclear medicine patients and scanning areas. Nuclear medicine procedures are usually not performed on pregnant or breastfeeding women unless specified by their physician. So, nuclear medicine specialists always ask for the last menstrual period (LMP) for all the people assigned female at birth (AFAB) who are in their reproductive years before the nuclear scan.

Doctors should decide if the benefits of the procedure outweigh the risks associated. 

Nuclear medicine imaging is beneficial in detecting numerous disorders such as bone metastases, thyroid cancer, prostate cancer, lung cancer, cardiac disorders, brain disorders etc. It is also helpful in planning treatment options and evaluating the response of therapies for cancer patients. PET scanning is beneficial in checking the response of chemotherapy or radiation therapy. It can help the doctor to decide on further courses of treatment.

Nuclear medicine therapy is beneficial for thyroid cancer, prostate cancer, neuroendocrine tumours and hepatocellular cancer among others. 

Nuclear medicine is an almost painless procedure which benefits patients immensely.