3 Main Purposes of Radioisotopes in Medical Science

The following points highlight the three main purposes of radioisotopes in medical science. The purposes are: 1. Experimental 2. Diagnostic 3. Therapeutic.

Purpose # 1. Experimental:

(i) The research work needs radioisotopes to investigate absorption, mobilization, stor­age, and distribution of different sub­stances in the body.

(ii) The substance under investigation is ‘tagged’ with a radioactive isotope which acts as a tracer substance. The tracer sub­stance is detected in the body by the ra­diation it emits. The best method used for the detection of the radioactive isotope is Geiger-Muller counter and the less sensi­tive is auto-radiograph method.

(iii) The absorption, mobilization, and trans­port of iron have been studied by the use of radio-active iron (Fe⁵⁹).

(iv) Iodine clearance of blood is calculated by radio-active iodine (I¹³¹).

(v) The radio-active phosphorus (P³²) has been used for studying the formation of antibody in the reticulo-endothelial sys­tem.

Purpose # 2. Diagnostic:

(i) The volume of fluid compartments of the body is measured by radioactive isotopes.

(ii) Thyroid function is determined by the use of radio-iodine (I¹³¹).

(iii) The radioactive cobalt (Co⁶⁰) is used for diagnosing pernicious anemia.

(iv) The radioactive sodium (Na²⁴) has been used for circulator}’ studies and diagnosis of arterial diseases.

(v) The diagnosis for the localisation of brain tumours has been done by the use of ra­dioactive di-iodo-fluorescein.

Purpose # 3. Therapeutic:

(i) The isotopes which are selectively taken up by certain tissues and emit mainly β- rays without causing any damage to the surrounding healthy tissues are only used for this purpose.

The most important ra­dio-isotopes for the purpose are radio-iodine (I¹³¹), radio gold (Au¹⁹⁸), and radio- phosphorus (P³²).

(ii) The radioactive (I¹³¹) as a solution of Nal¹³¹ is administered in the body after a light breakfast.

The effect of a dose is observed within 3 to 4 weeks and maximum effect within 3 to 4 months.

The second dose, if required, is given at the interval of 2 to 3 months. It acts by emitting β- and γ- radiations.

This is used in the treatment of hyperthyroidism and thyroid cancers. The usefulness of I¹³¹ depends on the capacity of the thyroid gland to capture and con­centrate iodine from the blood stream.

Nal¹³¹, in a very high dose, is used in the treatment of congested heart failure or an­gina pectoris.

I¹²⁵ is more convenient than I¹³¹ because its half-life is 7 times greater than that of I¹³¹, the half-life of I¹²⁵ is 57.4 days, whereas the half-life of I¹³¹ is 8.04 days.

I¹²⁵ can be stored for more periods with losing lesser activity and this causes lesser damage to the gland because it does not emit P-radiation.

(iii) Radioactive phosphorus (P³²) is adminis­tered in the form of sodium phosphate, either orally or intravenously.

It emits p-radiation and its half-life is 14.3 days. Its end product is S³². P³² is distributed to all tissues of the body as it has high meta­bolic role.

When administered, it is rap­idly taken up by multiplying cells, bone marrow, spleen, and lymph nodes.

It is used in the treatment of various types of cancers. Especially, it is used in poly­cythemia vera and chronic lymphatic leukemia.

(iv) Radioactive gold (Au¹⁹⁸) emits β- and γ-rays and its half-life is 2.69 days. Its end product is Hg¹⁹⁸. It is chemically and bio­logically inert.

It is deposited in tissue area when injected in the body. It produces local irradiation since very little of it en­ters the blood.

The p-rays emitted by it are completely trapped by tissues. It is used in the treatment of malignant pleural and peritoneal effusions.

(v) Radioactive cobalt (Co⁶⁰) is the most im­portant isotope in clinical medicine. It emits both P- and y-rays and its half-life is 5.3 years.

It can be used as a substitute for sodium in interstitial surface. It has been found to be cheaper and does not require any closed container.