Phosphorous is not found in its elemental form in nature. It is commonly found in a combination with other elements within the earth’s crust, as well as in plants, animals and rocks.
Phosphorus is an essential living element for plants (Fig 1.3), animals and even humans. These living organisms need phosphorus to build bones and teeth, these organisms also use it to build their cells and to build and store energy. There are about 700g of phosphorous in a typical 65 kg person and around 80 percent of this phosphorus is stored in the bones and teeth. Phosphorous is an important mineral in our diet, foods such as cheese, eggs, bread and meat are great sources of phosphorous.
Phosphorous is also a factor in DNA and RNA, as the chemicals are able to carry genetic information in cells. The main uses of Phosphorous is in matches and in bombs designed to set their targets on fire. Phosphorous mixtures are generally used in fertilizers, detergents and toothpastes. Some of these mixtures are then used to kill harmful insects.
There are about ten different forms of the element, but they fall into three main major categories; white, red and black.
White phosphorous is by far the more chemically reactive one out of the three. It is best if it is kept underwater. It easily combines with most elements and it can ignite freely upon exposure to air, letting off white fumes. It is extremely poisonous, and when exposed in sunlight it can turn into red phosphorus, which does neither glow or burn in air. Red phosphorus is not poisonous and it is found on the head of a match stick (Fig 1.5) the striking surface. Black Phosphorous has a flaky texture like graphite and is made by exposing white phosphorous to high pressure. It is also the least reactive form of phosphorous.
Phosphorus -32, is one of the many radioactive isotopes of Phosphorous. The nucleus of phosphorous -32 holds 15 protons and 17 neutrons. This is one extra neutron than the most common isotope of phosphorus i.e. Phosphorous -31. Phosphorus -32 only exists in small amounts on Earth, as it has a short half-life of 14.29 days, meaning it decays quickly. As seen in Phosphorous -32 atom diagram (Fig 1.6) the green neutron (coloured differently to the other neutrons) is the extra neutron that the isotope has gained, from the original Phosphorous atom. (Fig 1.7 and 1.8)
A stable isotope does not emit radiation whereas an unstable isotope goes through the process of radioactive decay. But Phosphorous -32 is an unstable isotope because it has a 1:1 ratio. Generally radioactive elements have more neutrons than protons but some elements are quite stable with more neutrons. There is instability in the nuclear forces due to an excess of neutrons.
Phosphorus-32 is used and found in many areas of medicine, biochemistry and molecular biology. Phosphorus is also used as a tracer in nuclear medicine, it is used to identify tumors in the body. This is because cancerous cells have a tendency to accumulate more phosphate than normal cells. Tracing from the outside of the body to identify the accurate location of the possible tumors.
The tumours are traced by a small quantity of radiopharmaceutical being injected, swallowed or inhaled into the body. The pharmaceutical part acts like a chemical that the body normally uses, so the body tissues “take up” the radiopharmaceutical. The radioactive part gives off radiation that then is detected by a special device. The device used depends on the organ or tissue being reviewed. It may be a gamma camera or a positron emission tomography (PET) scanner or probe (Fig 1.9). These devices record the gamma rays given off, and then a computer uses this data to make an image. There are 4 different types of nuclear medicine images:
• Dynamic – a sequence of images that captures the movement or activity (blood flow to an organ)
• Planar (static)- a 2 dimensional vision that shows one image at a time
• Whole Body – 2 dimensional photos of front and back views
• SPECT (single photon emission computed tomography- a 3 dimensional view, which shows the process of the organ bein studied
The scanning procedure can take between 15 minutes to a few hours to complete, this can depend on the part of the body that is being scanned. Some of the procedures may requie patients to fast for a period of time.
The radiation that has be emitted by the phosphorus can be used for therapeutic and diagnostic purposes. Phosphorous-32 emits the radiation of beta decay. Through phosphrous-32 doing this it decays into Sulfur-32 (See Fig 2.0) When the energy is being released it it at the rate of 1.709 MeV of energy. When getting this procedure done;
Dose rate for 1 mCi of P-32 over 1cm-sq of skin
– At 10cm: 22 rads/hr
– At 1 cm: 200 rads/hr
– At surface of skin: 2,000 rads/hr
The cost of the radiation therapy per patient can vary depending on the area being treated and the amount of times it is treated. It has been estimated that it will cost beteen $7300 -$10300 for Breast cancer, $7500- $11,100 for lung cancer and $11,300 – $25,500 for Prostate cancer (R.Nelson 2015- Cost of Variations for Radiotherapy). The cost of ovarian cancer treatment can range from $20,000 or more for surgery up to $200,000 or more for treatment with surgery and chemotherapy for advanced cancer. Phosphorous-32 has been considered as a possible chemotherapy manager that can treat dispersed ovarian cancer. Phosphorous-32 is a widely used radioisotope for cancer detection and treatment, mainly for eyes and skin cancer.
Phosphorous-32is also used as treatment for some blood disorders, including one called Polycythemia Vera (PV). PV means that your bone marrow makes too many red blood cells. The radioactive isotope is absorbed by the bone marrow and gives a dose of radiation, which temporarily lowers the production of blood cells. The radioactive phosphorous is injected into your bloodstream through a small tube that is put into your vein. This simple, painless treatment only normally takes a few minutes and is similar to having a blood test. The patient can go home straight afterwards, without having to be hospitalized.
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