Unsealed source radiotherapy
Encyclopedia
Unsealed source radiotherapy relates to the use of soluble
forms of radioactive substances which are administered to the body by injection
or ingestion
. Such substances are typically used for their biological properties, which are similar to their non-radioactive parent substance.
A review of the subject was published in 1999 by Wynn A. Volkert and Timothy J. Hoffman.
is an element selectively taken up by the thyroid gland
in healthy people. Thyroid disease (both benign conditions like thyrotoxicosis and malignant conditions like papillary thyroid cancer
) can be treated with radioactive iodine (iodine-131) which is then concentrated into the thyroid. Iodine-131 produces beta
and gamma
radiation. The beta radiation released destroys thyroid tissue, and any thyroid cancer that takes up iodine whilst most of the gamma radiation escapes the patient's body.
Most of the iodine not taken up by thyroid tissue is excreted
through the kidney
s into the urine
. After radioactive iodine treatment, the urine will be radioactive or 'hot', and the patients themselves will also be radioactive. Depending on the amount of radioactivity administered, it can take days to weeks for the radioactivity to reduce to the point where the patient is not a radiation danger to bystanders. There are strict radiation protection regulations governing the use of these sources.
-226 and caesium
-137 are two classic examples of isotope
s which are unsuitable for use in this type of radiotherapy.
However Radium-223, which is also a bone-seeking element, but is an alpha-emitter with a half-life of 11⋅4 days that rapidly decays to stable lead-207, and it also emits some 'imaging' photons. Radium-223 decays via radon-219 (3.9 s), polonium-215 (1.8 ms), lead-211 (36.1 min), bismuth-211 (2.1 min) and thallium-207 (4.8 min) to lead-207 (stable), and releases four alpha particles in this sequence which account for >93% of the energy released. radium-223 targets the bones with retention of its daughter isotopes in the bone matrix like Sr-89. Due to its alpha emissions, modelling of the dose deposition in relation to tumour deposits in the bone marrow suggests a substantial reduction in dose to the healthy bone marrow with 223Ra compared to beta emitters.
-213 is one of the isotopes which has been used. This is made by the alpha decay of Ac-225. The generation of one short-lived isotope from longer lived isotope is a useful method of providing a portable supply of a short-lived isotope. This is similar to the generation of technetium
-99m by a technetium cow. The actinium
-225 is made by the irradiation of radium
-226 with a cyclotron
.
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
forms of radioactive substances which are administered to the body by injection
Injection (medicine)
An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...
or ingestion
Eating
Eating is the ingestion of food to provide for all organisms their nutritional needs, particularly for energy and growth. Animals and other heterotrophs must eat in order to survive: carnivores eat other animals, herbivores eat plants, omnivores consume a mixture of both plant and animal matter,...
. Such substances are typically used for their biological properties, which are similar to their non-radioactive parent substance.
A review of the subject was published in 1999 by Wynn A. Volkert and Timothy J. Hoffman.
Iodine
For example, iodineIodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
is an element selectively taken up by the thyroid gland
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
in healthy people. Thyroid disease (both benign conditions like thyrotoxicosis and malignant conditions like papillary thyroid cancer
Thyroid cancer
Thyroid neoplasm is a neoplasm or tumor of the thyroid. It can be a benign tumor such as thyroid adenoma, or it can be a malignant neoplasm , such as papillary, follicular, medullary or anaplastic thyroid cancer. Most patients are 25 to 65 years of age when first diagnosed; women are more affected...
) can be treated with radioactive iodine (iodine-131) which is then concentrated into the thyroid. Iodine-131 produces beta
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
and gamma
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
radiation. The beta radiation released destroys thyroid tissue, and any thyroid cancer that takes up iodine whilst most of the gamma radiation escapes the patient's body.
Most of the iodine not taken up by thyroid tissue is excreted
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
through the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
s into the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
. After radioactive iodine treatment, the urine will be radioactive or 'hot', and the patients themselves will also be radioactive. Depending on the amount of radioactivity administered, it can take days to weeks for the radioactivity to reduce to the point where the patient is not a radiation danger to bystanders. There are strict radiation protection regulations governing the use of these sources.
Other unsealed sources
Other unsealed sources include:| Isotope | Use | Description |
|---|---|---|
| 131I Iodine-131 Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical... -MIBG (metaiodobenzylguanidine) |
for the treatment of phaeochromocytoma and neuroblastoma Neuroblastoma Neuroblastoma is the most common extracranial solid cancer in childhood and the most common cancer in infancy, with an annual incidence of about 650 cases per year in the US , and 100 cases per year in the UK . Close to 50 percent of neuroblastoma cases occur in children younger than two years old... |
|
| 32P Phosphorus-32 Phosphorus-32 is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31... |
for overactive bone marrow | the main place of use of phosphorus Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks... is the bone marrow |
| 89Sr Strontium-89 Strontium-89 is an isotope of strontium.It is treated by the body in a similar manner to calcium, and is preferentially deposited metabolically active regions of the bone.It is an artificial radioisotope which is used in treatment of bone cancer... & 153Sm Samarium-153 Samarium-153 is an isotope of samarium.It emits beta particles and gamma rays. It is used in Samarium lexidronam.... |
for secondary cancer in the bones | strontium Strontium Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and... and samarium Samarium Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3... behave just like calcium |
| 90Y Yttrium-90 Yttrium-90 is a medically significant isotope of yttrium.It emits beta rays of 2.3 MeV.Yttrium-90 is a decay product of Strontium-90 which makes up about 5% of the Nuclear daughter isotopes when Uranium is fissioned.... |
radiosynovectomy in the knee Knee The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as... joint |
Radium and caesium
RadiumRadium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
-226 and caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
-137 are two classic examples of isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s which are unsuitable for use in this type of radiotherapy.
- Radium has a very long physical halflife and chemically it behaves like calcium and so is concentrated in bones. It will remain within the body far too long and it would continue to irradate the bone marrow for the rest of the lifeLife expectancyLife expectancy is the expected number of years of life remaining at a given age. It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience...
of any patient.
However Radium-223, which is also a bone-seeking element, but is an alpha-emitter with a half-life of 11⋅4 days that rapidly decays to stable lead-207, and it also emits some 'imaging' photons. Radium-223 decays via radon-219 (3.9 s), polonium-215 (1.8 ms), lead-211 (36.1 min), bismuth-211 (2.1 min) and thallium-207 (4.8 min) to lead-207 (stable), and releases four alpha particles in this sequence which account for >93% of the energy released. radium-223 targets the bones with retention of its daughter isotopes in the bone matrix like Sr-89. Due to its alpha emissions, modelling of the dose deposition in relation to tumour deposits in the bone marrow suggests a substantial reduction in dose to the healthy bone marrow with 223Ra compared to beta emitters.
- Caesium acts like potassium and enters all the cells of the body, thus it does not concentrate in a single organ. As a result it is not possible to deliver a high dose to a single part of the body using cs-137. Caesium has a biological halflife of between one and four months in humans.
Experimental antibody based methods - alpha emitters
At the ITU work is being done on Alpha-Immunotherapy, this is an experimental method where antibodies bearing alpha isotopes are used. BismuthBismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
-213 is one of the isotopes which has been used. This is made by the alpha decay of Ac-225. The generation of one short-lived isotope from longer lived isotope is a useful method of providing a portable supply of a short-lived isotope. This is similar to the generation of technetium
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...
-99m by a technetium cow. The actinium
Actinium
Actinium is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902...
-225 is made by the irradiation of radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
-226 with a cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
.