Personal Monitoring of Radiation Professionals

All persons associated with commercial, diagnostic or therapeutic use of radioisotopes or radiochemicals, x-rays or other sources of radiation could be labeled as radiation professionals or radiation workers. Excessive exposure to radiation beyond the maximum permissible dose (MPD) for a person of a particular age may lead to serious healthy problems. The maximum permissible dose [MPD=(N-18)x5=?Rads; where N stands for the age in years] to the whole body, at any age is equal to 5 times of the number of years beyond 18 years. The MPD in consecutive three months should not exceed 3 rads. The accumulated MPD is also the MPD for the head and the trunk of a person associated with the handling and use of radiochemicals or radioisotopes or operating radiation equipments.

The dose received by any individual is ascertained by various types of monitoring procedures. The most commonly used are film badges and small ionization chambers. The film badges and small ionization chambers are supplied and monitored by many commercial firms.

Film Badges:

The film badge is a small packet of photographic film which is sensitive to radiation; or it may be containing two pieces of photographic films of different sensitivities. A part of these films is covered by one or more metal filters to resist the beta radiation and the other part is open to the beta radiation exposure. For x-rays a different type of film and filter is employed in the film badge. The film badge is worn by the person while handling the radiochemicals or operating radiation equipments. The darkening of the film of the film badge is related to the radiation dose received by a worker. Under the open window it gives the effect of beta radiation and under the filter the effect of gamma radiation or high energy x-rays.

Small Ionization Chambers:

The ionization chambers used for the personal monitoring are small instruments about the size and shape of a fountain pen. These are also called "pocket dosimeters". Before putting to use these are charged with electric pulse from a special charger. The charging transfers the electrical charge to the insulated wire inside the pocket dosimeter. The principle of the functioning of an ionization chamber or pocket dosimeter is that on exposure to the radiation the charge on the insulated wire inside it would decrease.

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.