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.

Role of Gold-198 in Arresting the Growth of Cancer

The radioisotope of gold (Gold-198, ¹⁹⁸Au) has a Half Life of 2.7 days and its radiations are beta particles (b-particles) and gamma rays (g-rays). In the form of colloidal suspension ¹⁹⁸Au is used as the cancer therapy. The most common use of ¹⁹⁸Au is in the treatment of ascites (accumulation of fluid in the peritoneal cavity) and pleural effusion due to metastasis of cancer in the serous surface of cavities. Only the medical practitioners associated with nuclear medicine, administer such therapy. The dose for the treatment of pleural effusion is 25 - 75 mCi and for the treatment of ascites, the dose is 50 - 150 mCi. The patient needs to be hospitalized for the first few days during the course of treatment with the radioisotope.

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).