Brain Tumor and Treatment with Gamma Knife

Gamma rays (g-rays) are like high energy x-rays and can be focused with electromagnetic lenses like electron beam. Gamma knife is a new development in the field of Biomedical Engineering for the surgical interventions. Gamma knife in any way does not look like your kitchen knife, but it refers to a customized beam of gamma rays (g-rays). The conventional surgical procedures for the removal of a brain tumor may need a lot of expertise and experience for a neurosurgeon. The conventional neurosurgical procedures also need utmost precision while chopping of a brain tumor. The gamma knife has made it possible to retard the growth of a brain tumor through non-invasive procedure. The well focused gamma rays (g-rays) at the pre-investigated tumor site in the brain put a full stop on the metabolic activity of tumor cells. Though the technique is called gamma knife radio surgery; the brain tumor is not removed physically but dried and destroyed in situ. The patient needs not to be anaesthetized for gamma knife radio surgery and imaging. There are very few centers in the world equipped with the gamma knife radio surgery facility for the brain tumors.

Diagnostic and Therapeutic uses of Radioisotopes of Cobalt

Three radioisotopes of Cobalt used in medical practice are Cobalt-57 (⁵⁷Co), Cobalt-58 (⁵⁸Co), and Cobalt-60 (⁶⁰Co). Cobalt-60 (⁶⁰Co) has a half life of 5.27 years and it emits gamma rays (g-rays). Half life of Cobalt-57 (⁵⁷Co) is 270 days and that of Cobalt-58 (⁵⁸Co) is 71 days only. It is important to note that the radioisotopes with shorter half life are always good for diagnostic use whereas with longer half life are good for radiotherapy or radiation therapy. Cobalt-60 (⁶⁰Co) is a preferred source of radiation for radiotherapy at present; though earlier it was in dual use. Cobalt-57 (⁵⁷Co) and Cobalt-58 (⁵⁸Co) are preferred for diagnostic applications due to shorter half life.

Use of Cobalt-57 and Cobalt-58 in Diagnosis:

The most common use of Cobalt-57 (⁵⁷Co) or Cobalt-58 (⁵⁸Co) is in the diagnosis of pernicious anemia (fetal anemia caused by vitamin B-12 deficiency due to poor absorption of vitamin B-12 by small intestine due to intrinsic factor defect). Cyanocobalamin (vitamin B-12) and hydroxycobalamin labeled with ⁵⁷Co or ⁵⁸Co are commercially available for diagnostic use. The dose is 0.5 microCurie (mCi) to 2 microCurie (mCi). The administration is oral after 24 hours of fasting and the patient is not allowed to eat for 2 hours following the administration of vitamin B-12 labeled with radioisotope. The patient does not need hospitalization for this investigation. The excretion of radioactive is measured in the 24 hour urine specimen of the patient after the administration of radioactive labeled vitamin B12.

Use of Cobalt-60 in Therapy:

The gamma rays (g-rays) emitted by Cobalt-60 (⁶⁰Co) are like high energy x-rays. The radiotherapy or radiation therapy is helpful in some types of cancers. The patients are usually hospitalized for radiotherapy with Cobalt-60 (⁶⁰Co). The exposure time is worked out by the Radiation Physicist. Smaller radiation sources of Cobalt-60 (⁶⁰Co) are called seeds and needles, and are used for intra-cavity and intra-interstitial radiation therapy. The seeds or needles of Cobalt-60 (⁶⁰Co) are removed from the body cavities or interstitial tissue after the optimal time of exposure. The large sources of Cobalt-60 (⁶⁰Co) are used for 'teletherapy' or external radiation like high energy x-rays.

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).

What Is Meant By Radioactive Disintegration

Radioactive disintegration is a process of nuclear disintegration of a radioisotope in its effort to achieve a stable nucleus. We know that in the naturally available radioactive elements there are only two kinds of particles which could be ejected from its atoms:

1. The alpha (a) particle, which is really the nucleus of a Helium atom (⁴He) and carries away 4 mass particle and 2 atomic particles.
   
   _ZX^A - ₂a⁴ = _Z-2X^A
   
   Here X represents chemical symbol, Z is atomic number and A is mass number.
   
   
2. The other particle which could be ejected is beta (b) particle, which is an electron. It does not however, comes from an orbit, but from a neutron, which under certain circumstances, dissociates into a proton and an electron. The electron is not tolerated in the nucleus and is ejected immediately, but an extra positive charge (neutron replaced by a proton) is left in the nucleus. The new atom now has the same mass but the atomic number one higher than the old or previously possessed by it.
   
   _ZX^A - _-1b⁰ = _Z+1X^A

Uranium, Thorium and Radium are the best known naturally occuring radioactive elements. In 1934 it was documented that it was possible to create isotopes and radioisotopes by bombarding the stable elements with high energy subatomic particles. Except Hydrogen and Helium more than two isotopes have been created from every element by artificial manipulations. There are 21 isotopes of Iodine ranging from ¹¹⁹I to ¹³⁹I and out of these 20 are radioactive isotopes or radioisotopes except ¹²⁷I.

The artificially created radioactive isotopes or radioisotopes have the same radiations as those of natural ones. Some of them also emit protons or beta⁺ (b⁺) particles.

_ZX^A - ₊₁b⁰ = _Z-1X^A

Radioactive disintegration of radioisotopes results in the emission of only one type of above mentioned particles and radiation like x-rays called gamma (g) rays. The atoms of any particular radioactive element are destined to emit the same kind of radiation till its total disintegration; there is no way to switch on to any other type of radiation.