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Radiopharmaceuticals
Definition/Introduction
Radiopharmaceuticals include a group of radioactive agents used for either diagnostic or therapeutic interventions. Although the administration of radiopharmaceuticals is often systemic, they are likely to localize to specific tissues because of their biomolecular properties, i.e., the areas of hyperintensity observed on positron emission tomography (PET) scans that indicate a high tissue metabolic demand. Radiopharmaceuticals actively emit radiation, which makes their storage more difficult than non-radioactive pharmaceuticals. Compounds used for diagnostic interventions usually either emit beta particles (positrons or electrons) or gamma rays, while compounds that emit Auger electrons or alpha particles (helium nuclei) are generally for therapeutic interventions.
Radio-imaging involves the use of incredibly low concentrations of radiotracers (sub-micro quantities). Radio-imaging is currently used to analyze tissue physiology, detect disease, and monitor treatments; however, new uses are being discovered with the advent of personalized medicine.
Radiotherapeutic agents use the radiation emitted from the nuclide to kill the target cells or serve palliative purposes. Radiation is toxic to tissues in the body: the brain, spinal cord, kidneys, and bone marrow are especially susceptible. Many radiopharmaceuticals are delivered systemically, and this means that ideally, the pharmaceuticals should selectively prefer the tumor tissue relative to normal healthy tissue. Many various specific radionuclides are in common use.[1][2]
Issues of Concern
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Issues of Concern
Technetium-99m is one of the most common radionuclides used. It is a gamma emitter that is primarily used in diagnostic imaging and has limited therapeutic utility. Its use is in imaging: the thyroid, lacrimal glands, vascular perfusion, pulmonary perfusion, bones, myocardial, etc. It is the most common radionuclide used in diagnostic investigations. Many other radionuclides are also used, including but not limited to iodine-123, iodine-131, iron-55, selenium-75, sodium-22, strontium-89, thallium-201, xenon-133, etc.[3][4]
Iodine-131 is a radioisotope that has a broad array of applications. It undergoes beta decay, and it results in mutations in the cells that it penetrates. This characteristic gives it utility in thyroid ablations (the thyroid is the only organ in the body that uses iodine), which is useful in treating various thyroid malignancies and can be used to treat refractory Graves disease. Iodine-131 results in mutations in the cells that uptake it; it is often used in large doses, as low doses can result in an increased risk of subsequent malignancies (incomplete tissue ablation). Iodine-131 is also a gamma emitter; however, due to malignancy risk, iodine-123 (a more pure gamma emitter) is used in nuclear medicine scans of the thyroid.[5][6]
Cesium-137 is a radioactive isotope of cesium that undergoes beta decay and gamma emission. The isotope is chemically unstable and quite reactive; thus, it is not routinely used in diagnostic modalities. It is primarily medically used for low-dose temporary intracavity brachytherapy.[7]
Fluorine-18 is a radioisotope of fluorine that primarily undergoes positron emission; however, it also undergoes electron capture. Fluorine-18's primary use is as a radiotracer for PET scans. Thallium has many isotopes; however, the most medically useful is thallium-201. Thallium-201 undergoes electron capture to emit X-rays and photons. This feature makes it useful in imaging studies, and it is often used in cardiac stress tests (a test used to assess myocardial perfusion). Xenon-133 is a radioisotope of xenon that undergoes Beta decay. It is an inhaled radionuclide that is used to assess pulmonary function and cerebral blood flow. Rubidium-82 is a radioisotope of rubidium that undergoes both positron and gamma emission. It is primarily administered IV to assess myocardial imaging.[8][9]
Clinical Significance
Radiopharmaceuticals are vital to healthcare. They are instrumental in imaging, and in the United States alone, millions of nuclear medicine procedures are performed annually. They are instrumental in the treatment of many malignancies and even many benign tumors.[10][11]
Designing radiopharmaceuticals is a rigorous and complicated process that relies on many different factors. Selecting the appropriate nuclide is critical, as the specific nuclide has a specific half-life and decay mode. These both impact the localization and utility of the radiopharmaceutical. Other factors, such as molecular stability, ease, and production cost, are also important factors.[12][13]
Specific radiopharmaceuticals like radium-223 are useful for treating painful bone metastases in prostate cancer patients with castration-resistant bone metastases and have been approved by the FDA for this use.[14]
Nursing, Allied Health, and Interprofessional Team Interventions
The use of radionuclides involves an interprofessional approach, and many different disciplines must work in tandem to deliver these toxic agents. Each healthcare team member must understand the critical nature of their role and what exactly it entails and provide input to ensure proper diagnostic results with no unnecessary risks to the patient. Risks include extravasation, where radiopharmaceuticals are accidentally injected into the soft tissue surrounding the vein, which can cause harm to the patient and result in inaccurate readings for treatment. These should be recorded, reported and the patient informed.
References
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