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Radioactive Isotopes in Nuclear Medicine
Radiopharmeceuticals & Nuclear Medicine
Although radiation is shown to be harmful at certain levels in humans the utilization of this elemental phenomenon has been in use as a specialized medicinal practice since its development by John Lawrence in 1936. From this time the field of nuclear medicine has expanded and become more effective and is providing new potential as we move further into our understanding of nuclear science.
The basic idea behind nuclear medicine is to use isotopes directly or attached to a molecule absorbed by a targeted organ or area of tissue to produce imaging of the area in a non-invasive manner and allow targeted treatment through radiation therapy to affected regions of the body. To date the most widely used type of radiation in nuclear medicine is gamma radiation. This type of radiation emits a single energy in that it is free from beta-emissions allowing for more precise imaging. (gsu.edu, 2012) The most commonly used tracer in nuclear medicine is “molybdenum-99m/technetium-99m” due to its short half-life allowing for quick removal from the body. (NAP, 2007). The use of gamma radiation emitting isotopes not only allows for imaging but for targeted radiation therapy.
The concept behind targeted radiation therapy is the use of radiation emitting isotopes attached to certain relevant molecules such as sugar that will be absorbed by the targeted region of the body yet contain a high enough amount of radiation to be lethal to the targeted cells. In particular x-rays and gamma rays are used to shrink tumors and kill cancer cells by destroying their DNA. There are two major types of radiation delivery. External-beam radiation therapy utilizes a machine to deliver the radiation externally from the body. The other is the use radioactive substances such as iodine placed in the blood stream, this called Systematic Radiation Therapy (Cancer.gov, 2012).
The process leading up to treatment can be very involved as it can include “CAT scans, Magnetic resonance imaging (MRI), positron emission tomography (PET) and even ultrasound scans” (Cancer.gov, 2012). Importance is placed on determining precisely where the radiation needs to be administered, the best mode of delivery and consistent accurate following of the treatment plan. Because eradiation is toxic to humans the dosage has to be closely ministered and regulated to ensure that an over exposure does not occur. Although radiation therapy can target and destroy cancerous cells it also has potential to harm otherwise healthy cells in the surrounding area. This has been shown to have both short term and long term effects. In particular salivary glands can sustain permanent damage during radiation treatment to the head or neck area. To combat this, the drug Amifostine was developed and approved by the FDA as a suitable radioprotector and when administered during treatment protects the tissue from absorbing radiation and thus protecting the cellular health of the area (Cancer.gov, 2012).
As different forms of cancer are the cause of most deaths in today’s society research and development in the field of treatment for these diseases has taken a great leap through the use of nuclear medicine yet as with all things there is potential for harm. The major advantage of this technology is its ability to help diagnose and create specified treatment plans for disease in the body. The greatest limitation is it toxicity to human tissue resulting in a limitation not only in the amount safely prescribed by also limitations in that areas of the body are not able to be treated with radiation therapy multiple times.
Currently there are several methods used in nuclear medicine. Positron Emission Tomography or PET is used to create images using a radioactive substance. After injection usually done through an IV the radioactive material accumulates in the organs and tissues allowing for administers to locate disease or malfunctioning organs and tissue. The procedure is generally painless except for the injection, yet some people do experience allergic responses to the radioactive substance in the form of swelling, pain and/or redness around the injection site. The general procedure leading up to treatment which is generally on going to monitor the disease is a simple as abstaining from food for 4-6 hours before the treatment. The most common uses for this procedure is diagnose and determine the severity of different disorders such as cancer, brain disorders and heart problems (NIH.gov, 2012)
Another similar method of internal nuclear medicinal discovery is that of the Gallium Scan. The Gallium scan is much like the PET in that it uses a radioactive substance in the blood stream to local problem areas within the body. However, the substance used is a specific substance that collects in the bones, breast tissue, the bowels, spleen and liver. The major purpose of this type of treatment is to diagnose lymphoma. Unlike the PET the Gallium Scan requires no fasting before the procedure. A bowel movement however is necessary for accurate and clear imaging. There are no serious side effects associated with this procedure save for the usual redness and swelling of the injection site. Although effective in finding and diagnosing lymphoma cancer it does not detect all types of cancer. (NIH.gov, 2012)
From a more precise avenue the White Blood Cell Scan was developed to local areas in the body specifically suffering from infection and/or inflammation. The procedure consists of having blood drawn and that blood being separated to isolate the white blood cells, at which point the white blood cells are mixed with a radioactive isotope called indium-111. After several ours the cells are the reintroduced to the blood stream. After 6-24 hours the white blood cells will have accumulated in infected/affected areas allowing for the scanner to pick up the radiation emitted from the isotope and thus locate the problem area. Generally this scan takes up to 2 hours to perform in which time the patient must remain perfectly still. The most effective areas of determination are the abdomen and bones of the body. There are no preparatory needs for this procedure; however antibiotics can cause false results if accumulated in the body. (NIH.gov, 2012)
In the area of cancer treatment the Iobenguane scans (MIBG) is currently being tested as a means of combating the malignant cancers pheochromocytoma and paraganglioma. The goal is to radiate the cancerous cells enough to destroy them without harming other tissue in the area. This treatment unlike others requires a hospitalization of one week after each treatment and can have follow up treatments for up to 4 years. (BioPortfolio.com, 2012)
The Octreotide Scan is another method used in nuclear medicine to locate cancer in the body. The Octreotide scan uses radioactive ocreotide that will attach to the tumors that have receptors for it present. The radiation is then imaged by the machine to show the location of the tumors. (NCI.gov, 2012) After the injection there is a 1 hour wait before the scan can be performed. This type of scan uses gamma imaging to provide very accurate and clear imaging details. As with other procedures there is no specific preparation and/or side effects.
It is clear by the many technologies being developed that nuclear medicine has many potential health benefits, specifically in the areas of diagnosing and treating certain cancers and diseases. Although radiation exposure is harmful to human tissue the levels used in the radioactive isotopes are minimal and generally pass from the person’s body quickly with the exception of the MIBG. This area of medicine obviously hold much promise in treatment of cancerous cells, however it is an inherently limited method as it is centered on trying to balance the health benefits against the potential harm injection and/or use of radioactive material in the body can cause. The risks of utilizing this medicine in diagnoses may be small but the use of it to treat the disease is still a balancing act.
A Study Evaluating Ultratrace Iobenguane I 131(MIBG) in Patients With Malignant Pheochromocytoma/Paraganglioma, BiopOrtfolio.com, 2012. Retrieved on May26th 2012 from http://www.bioportfolio.com/resources/trial/78242/A-Study-Evaluating-Ultratrace-Iobenguane-I-131-mibg-in-Patients-With-Malignant.html
Technetium, Astrophysics, Hyperphysics, gsu.edu, 2012 Retrieved on May 25th 2012 from http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/technetium.html
Octreotide scan, Dictionary of Cancer Terms, National Cancer Institute, National Institute of Health, 2012. Retrieved on May 26th 2012 from http://www.cancer.gov/dictionary?cdrid=390304
PET scan, Medline Plus, U.S National Library of Medicine, National Institute of Health, 2012. Retrieved on May 26th 2012 from http://www.nlm.nih.gov/medlineplus/ency/article/003827.htm
Gallium scan, Medline Plus, U.S National Library of Medicine, National Institute of Health, 2012. Retrieved on May 26th 2012 from http://www.nlm.nih.gov/medlineplus/ency/article/003450.htm
WBC scan, Medline Plus, U.S National Library of Medicine, National Institute of Health, 2012.Retrieved on May 26th 2012 from http://www.nlm.nih.gov/medlineplus/ency/article/003834.htm
Advancing Nuclear Medicine through Innovation. Washington, DC: The National Academies Press, 2007, p.12. Retrieved on May 25th 2012 from http://www.nap.edu/openbook.php?record_id=11985&page=12