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.

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.