under construction this 1st week of September 1999 Link to: Home / Reactors
This site is intended for non-technical persons interested in learning more about the application of radioactive materials in medicine. The contribution this page adds to the WWW is an overall view of the subject with a focus on production instead of the "users and usees." A sister page of this page can be found at Nordion but is a cursory description from the prospective of a single commercial distributor and therefore has a very narrow scope. A patient education website is provided by Varian.
Nuclear medicine is the application of radioactive substances, specifically radioisotopes, for:
studying and understanding biological processes,
viewing internal biological structures and processes for diagnosis of abnormal conditions, and
selectively destroying diseased cells, primarily cancer tumors.
Who uses radioisotopes?
Various applications are supervised and administered by degreed, trained and certified professionals in tens of thousands of laboratories, hospitals and clinics in virtually every region of the country. In most cases, degreed trained and certified technicians conduct the tasks. Specifically,
research is supervised by PhD's in laboratories,
diagnosis is supervised by MD's in hospitals or clinics, and
therapy is supervised by MD's in hospitals or clinics.
The ultimate beneficiary is the public. It is estimated that more than 50% of the population will directly benefit from the application of nuclear diagnosis and therapy techniques in their lifetimes. Indirect benfits from the understanding of biological processes already extend to the entire population.
Why are radioisotopes used?
Radioisotopes are used because of the penetrating and ionizing characteristics of the radiations emitted from decaying atoms.
For research, radiations can pass through tissue and be detected external to the body uniquely signaling atomic events without destroying the tissue which is common in chemical analytical methods. Furthermore, the sensitivity of nuclear methods enables far less disruption of normal biological processes in the study of living individuals.
For diagnosis, penetrating radiations can produce exact images of internal structures without invasive surgery and the accompanying complications.
For therapy, while radiations delivered to diseased cells disrupt normal cells moderately just as surgery and chemotherapy, developing techniques will increase radiation effectiveness while further reducing the effect on normal cells. We are currently seeing that radiotherapy will be nominally superior to chemotherapy and invasive surgery.
How are radioisotopes used?
Radiopharmeceuticals: Radioisotopes are chemically attached to protein molecules to create radiopharmeceuticals. Various proteins are managed differently by the body. Proteins are selected which concentrate in the target organ. The US national laboratory leading the research effort in radiopharmeceuticals is Brookhaven National Lab where work is being done in the development of the pharmeceutical portion of radiopharmeceuticals.
Brachytherapy sources: are not pharmeceuticals but are implanted solid gold Au-198 and irridium Ir-192 seed implants (under construction). An example of a brachytherapy source distributor is International Isotopes, Inc. of Texas.
Boron Neutron Capture Therapy: BNCT utilizes neutron beams created by non-power nuclear reactors. The neutron beams are aimed into the target organ (currently being tested on a form of cancer of the glial cells on the brain stem, glioblastoma) which has been prepared with a boron laden pharmeceutical which concentrates in the malignant glial cells. Boron has a very high ability to absorb neutrons and when so done releases an alpha particle. The alpha particles travel into the sensitive genetic molecules (chromosomes) and cause ionization damage to the genetic molecules thereby killing the cell. Brookhaven National Lab is also the lead laboratory for the development of BNCT.
Imaging: The use of penetrating radiations for imaging is nothing new. X rays supplied by electronic sources have been used routinely for most of this century. But techniques have become increasingly sophisticated in order to expand radiographic capabilities in an effort to visualize an ever increasing list of internal maladies. When the radiopharmeceuticals concentrate within the selected organ, then images of the size, shape and location of the organ can be made by determining the origin of each detected radiation released from the pharmeceutical. Tc-99 is used in over 90% of the medical imaging applications. Tc-99 is produced by reactors. Other isotopes are produced by either reactors or accelerators for specialized imaging applications. Several good applications of organ imaging are thyroid, bone, heart, and kidney scans.
Research: If a process is being traced, the radiopharmeceuticals can be detected through imaging in live subjects, by monitoring extracted samples, or by analyzing tissues. Reactors produce the vast majority of radio-tracers for research. The variety of tracers is so numerous it would be meaningless to describe them.
Therapy: If the application is for therapy, then the decay of the radioactive attachment will deliver a dose of energy specifically to the targeted tumor. Radiopharmeceuticals for therapy are typically highly ionizing with low penetration. Therapy sources are produced primarily in reactors, but new developments are utilizing accelerator produced isotopes and radiations directly from accelerators.
How are radioisotopes produced?
Cylcotrons: Typically produce positron emitters by collision of accelerated protons with targets. Flourine-18 is a typical product produced by colliding protons with naturally occuring Oxygen-18 thereby knocking a neutron out of the nucleus and substituting a proton in its place. Small cyclotrons can be purchased for a small fortune and installed within a medical facility. These production facilities must be located VERY near to point of use because the short half life of the radioisotope will cause the sample activity to decrease rapidly. Longer lived accelerator produced isotopes are being distributed by International Isotopes, Inc.
Glow of Utah nuclear reactor core.
Non-power nuclear reactors: Neutrons from non-power reactor cores are used to activate isotopes. These reactors have a wide variety of designs. Currently the vast majority of the Tc-99 supply for the entire North American continent is currently distributed by Nordion from the NRU reactor in Chalk River, Ontario, Canada. A small scale plant is being modified and certified at Sandia Nat'l Labs in Albuquerque, NM and will begin production soon. The Canadians are constructing 2 new Maple reactors at Chalk River to replace the NRU reactor and begin production in Sep 1999 and May 2000. The US has been without its own reliable supply of isotopes since the CintiChem reactor in New York State was shut down in 1988. For the 10 years after the CintiChem shutdown, the US medical community has been completely at the mercy of the staff of the Chalk River plant. Because short half lived radiopharmeceuticals prevent stockpiling, when production schedule disruptions occur (ie. labor union strikes as occured during May 1998) ALL applications are indefinitely postponed until operations are resumed in Canada. This is an incredible way of treating people who are essentially helpless underneath the threat of cancer.
The University of Missouri is the leading producer of medical radioisotopes among the independent university reactors. Most of the isotopes are brachytherapy sources but the facility produces small amounts of some radiopharmeceuticals.
Another non-power nuclear reactor that is producing radiopharmeceuticals is the HIFAR facility at the Australian Nuclear Science and Technology Organisation, ANSTO. This facility has experienced the same organized labor strikes as the Chalk River facility. In addition, they are proceeding with plans to replace the 40 year old HIFAR reactor with a new reactor scheduled to go into production by the year 2005.
The radiopharmeceutical situation in the former Soviet Union is in worse condition. Belarus, for example, relies entirely on isotopes from the Ignalina power reactor in Lithuania. The customs agents on the Belarusian border are notorious for holding up shipments of isotopes and demanding ransom. Supplies are always unreliable and treatments are scheduled at a moment's notice when supplies surprisingly arrive. Its fair to say that the situation in the US is only marginally better than that in countries ravaged by severe economic depression or that in third world countries. Only small progress in the US (Sandia) has been made to remedy that situation.
Simple Definitions (under construction)
seed: wire of dimensions 0.5 mm diameter and 1-2 mm length
radiography: a 2 dimensional image produced by radiations which have passed through the subject, interacted with internal structures, and focused on a target surface where the image appears
tomography: a 3 dimensional image produced from a series of 2 dimensional images
target: a naturally occuring element carefully prepared to satisfy FDA requirements which is subjected to nuclear bombardment to induce radioactivity
Au-198: radioactive gold used for brachytherapy (implants)
Ir-192: radioactive iridium used for brachytherapy (implants)
Mo-99: radioactive molybdenum, the precursor for Tc-99
Tc-99: radioactive technicium used in the vast majority of imaging applications
I-133: radioactive iodine used in thyroid imaging and thyroid therapy
