Therapeutic use of Phosphorus-32

Phosphorus-32 (³²P) is a radioactive isotope of phosphorus with mass number as 32. It has a half life of 14.3 days and emits beta-particles. In the chemical form of Sodium hydrogen phosphate, ³²P is used in the treatment of leukemia (a type of blood cancer) and polycythemia (abnormal high count of erythrocytes in blood due to a variety of causes). It is also used for relief from pain in the patients affected by metastatic cancer of bone and the patient needs not to be hospitalized for such treatment. The doses range from 1 mCi to 10 mCi. In the colloidal form the radioisotope is used in the body cavities in the same manner as Gold-198 (¹⁹⁸Au) and the patient may need hospitalization for such therapy.

Phosphorus-32 (³²P) could also used in the differential diagnosis of tumors of the eye. A dose of 500 microCurie (mCi) to 750 microCurie (mCi) needs to be administered intravenously and after an hour, two hours and 4 hours, the radioactive concentration is measured in the diseased eye and the normal eye. If the tumor is malignant, the involved eye would take up more ³²P. The investigation may be performed on an out patient basis taking all the aseptic precautions by an eye specialist. It is worth to remember that after 10 half lives (143 day) this radioactive would almost exhaust in its content of radioactivity.

What is the use of Iodine-131 in Medical Practice?

There are two main uses of Iodine-131 (¹³¹I) in medicine or medical practice.

1. Diagnostic application in some procedures


2. Therapy for thyroid disorders or thyroid cancer

The Iodine-131 (¹³¹I) has a radioactive half life of 8.1 days and its radiations are beta particles(b^- particles) and gamma rays (g-rays). This is most widely used radioisotope in the management of hyperthyroidism and thyroid cancer and thyroid function related diagnostic procedures. There are half a dozen investigations associates with the thyroid function which involve the oral or intravenous administration of a few microCuries (mCi) of ¹³¹I. Subsequent study of the patient, either by the direct measurement of ¹³¹I deposited in the thyroid gland through measurement of ¹³¹I excreted in the urine of the patient or by assessment of radioactivity in the blood samples drawn at different time intervals after the administration of ¹³¹I. The part of the ¹³¹I retained or excreted depends on the normal, hyperthyroid or hypothyroid conditions. The uptake or excretion of ¹³¹I exhibits a diagnostic parameter. After absorption of ¹³¹I by the thyroid gland the iodine is elaborated into the thyroid hormone which is discharged in the blood. The hyperactive gland produces too much hormone which would be detected in the blood samples taken at 24 to 96 hours after the administration of radioactive iodine (¹³¹I). The measurement of the iodine content is computed from the counts of radioactivity detected in the blood samples. The radioactivity is measured as gamma rays (g-rays) by a Geiger Muller counter or it may be measured as beta particles (b-particles) by a Scintillation counter at a 'Hot Laboratory'.

The therapeutic use of Iodine-131 (¹³¹I) could be culminated through optimal doses of this radioisotope with reference to the thyroid disorder and the age and weight of the patient. There are specialized clinics at the authorized medical centers having facilities for the Nuclear Medicine and associated research.

Penetration Power Of Radiation Energies

The penetration power of the radiation energy is related to the type of radiation. The radioactive chemicals emit radiation in the form of particles or rays and the penetration power of these particles or rays in the tissues of our body varies due to variation in the energy of these particles or rays. The alpha (α) particles can not penetrate more than a few micrometers in our body tissue, and are of little practical importance in medicine. The beta negative (β^-) and beta positive (β⁺) particles have penetrating power varying from 100 to 500 micrometers (mm) as in case of radiations of Carbon-14 (¹⁴C) and Sulphur-35 (³⁵S) to over a centimeter (cm) as in case of Yttrium-90 (⁹⁰Y) radioisotope. The beta negative (β^-) particles from Gold-198 (¹⁹⁸Au), Gold-199 (¹⁹⁹Au) and Iodine (Iodine-125, 130, 131, 132 etc) have a penetration power in tissues ranging from 1 to 3 millimeters (mm). The gamma rays (g-rays) are like x-rays and are usually very penetrating. The energy range of gamma rays (g-rays) is almost equal to that from 40 kilovolt (KV) to 3 megavolt (MV) x-ray machines. Negative beta (b^-) particles may or may not have accompanying gamma rays (g-rays). The gamma rays (g-rays) emitted by a particular radioisotope would always have the same penetrating power or energy. The positrons or positive beta (b⁺) particles in addition to possible gamma rays (g-rays) are always accompanied by 50 KV x-rays.

Quantity of radioactive material is always expressed in terms of radioactive disintegrations per second. The major unit of expression of radioactivity represents 37 billion (37 x10⁹) disintegrations per second and is called Curie (Ci). One thousandth (¹/₁₀₀₀) part of a Curie is called milliCurie (mCi) and one thousandth (¹/₁₀₀₀) part of a milliCurie is called microCurie (mCi). Brief description of these units is as below:

1. Curie (Ci): 37x10⁹ disintegrations per second


2. milliCurie (mCi): 37x10⁶ disintegrations per second


3. microCurie (mCi): 37x10³ disintegrations per second

There are quite many radioisotopes used in medical practice as a therapy and also in medical diagnostic procedures. The quantities of radioactive materials used in therapy are in milliCuries (mCi) and those used in diagnostic procedures is in microCuries (mCi).

What Is Radioactive Decay Or Half Life Of A Radioisotope

Radioactive isotopes or radioisotopes of an element are always in the process of nuclear disintegration in order to acquire the stable form. The major unit of radioactivity is Curie (Ci) which means 37x10⁹ disintegrations per second. One thousandth (¹/₁₀₀₀) part of a Curie is called milliCurie (mCi) and one thousandth (¹/₁₀₀₀) part of a milliCurie is called microCurie (mCi). Other units of the radioactivity will be discussed in some other article. The radioactive chemical is being expressed in terms of radioactivity it possessed at the time (0 hour) of evaluation and labeling. Every radioisotope undergoes decay or nuclear disintegration at a uniform rate and the time after which it loses the half of its activity is called its Half Life.

Radioactivity is linked to per unit mass or volume of radioactive chemical. The radioactive Half Life could be a few hours, days or many years. For example ²⁴Na has a Half Life of 15 hours, ¹²⁵I has a Half Live of 60 days, ⁶⁰Co has a Half Live of 5.2 years and ¹⁴C has a Half Live of 5730 years. If 1gram of a radioactive chemical has 2Ci radioactivity at 0-hour, it would be reduced to 50% (1Ci) after the completion of 1st Half Life, 25% after completion of 2nd Half Life, 12.5% after the completion of 3rd Half Life and 6.25% after the completion of 4th Half Life and goes on reducing to 50% on the completion of successive Half Lives as depicted below, through the Radioactivity Decay Graph.

However the mass or volume of the radioisotope would not under go any change with the reduction in radioactivity due to passage of time and completion of successive Half Lives one after the other. Preparation of Radioactivity Decay Graph is must for the radioisotope users to workout the radioactivity at a particular time or date with respect to the Half Life of a radioisotope.

How The Structure Of Matter Is Associated With Radioactivity

We know that the matter is made up of elements. The smallest part of any element is its atom. Atoms are composed of a positively charged nucleus containing protons (positively charged subatomic particles) and neutrons (inert particles), and around the nucleus, there are orbital electrons (negatively charged subatomic particles). In 1896 Bacquerel discovered the phenomenon of radioactivity in the atoms of some elements. The mass of an atom is represented by its nucleus that is the sum of protons (positively charged subatomic particles) and neutrons (inert particles) in the nucleus. Each element has been allotted a chemical symbol and its atomic number is fixed. The number of electrons is always equal to the number of protons in the nucleus of an atom and this number stands for the atomic number of an atom. Mass of an electron is ¹/₁₈₀₀ of the mass of a proton on atomic scale. The atoms in some of the elements have natural variation in mass number and that made them unstable or radioactive.

Isotopes: Atoms of a particular element not have to be exactly alike in terms of mass number. In such atoms the things that must be alike are the number of protons (positively charged subatomic particles) in the nucleus or the nuclear charge and the number of orbital electrons (negatively charged subatomic particles). But the number of neutrons (inert particles) may vary and hence atomic mass may vary in a narrow range. Atoms of the same element with same atomic number but with different number of neutrons (inert particles) are called isotopes. A single chemical symbol of an element is not sufficient to represent an isotope. The chemical symbol along with a superscript at the upper left or right, depicting the mass number and lower left depicting the atomic number, represents an isotope; however, it is not necessary to mention atomic number to depict an isotope, as ⁵¹Cr represents an isotope of Chromium. Each element has a unique atomic number but the mass number may vary depending on the number of the isotopes of that element. An element generally has only one stable isotope.

Radioactivity: Majority of the elements found naturally have stable atoms. The atoms of the elements never change unless they are attacked with subatomic particles from outside; however, some of the atoms in some heavy elements are inherently unstable. The unstable atoms are called radioactive isotopes or radioisotopes. The nucleus of the radioactive atom or radioisotope undergoes disintegration with the ejection of tiny particle accompanied by electromagnetic radiation. After disintegration the rest of the material of the nucleus rearranges itself and becomes the nucleus of a different element.