Gamma-Ray Source

gamma-ray source [′gam·ə ‚rā ‚sȯrs]

(nucleonics)

A quantity of radioactive material that emits gamma radiation and is in a form convenient for radiology.

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Gamma-Ray Source 

(medicine), or radium (cobalt) “gun,” an apparatus for remote gamma therapy, mainly for malignant tumors. The gamma-ray source uses a directed beam of gamma rays with variable cross section. The device is equipped with a shielding container (head) made of lead, tungsten, or uranium, which holds the radiation source (usually ⁶⁰Co, less frequently ¹³⁷Cs; radium was formerly used). A port in the head, equipped with a diaphragm, makes it possible to produce an exposure field of the required shape and size and to cut off the radiation beam when the source is not operating.

There are long-focus and short-focus types of gamma-ray source. The short-focus type, in which the distance from the source to the patient’s skin is less than 25 cm, is intended for the irradiation of tumors no deeper than 3-4 cm and usually uses sources with an activity of up to 100 curies. The long-focus type, in which the distance between source and skin is 70-100 cm, is used to irradiate deep-lying tumors. The radiation source in this type is usually ⁶⁰Co with an activity of several thousand curies; they create the necessary dosage distribution. A distinction is made between long-focus gamma-ray sources for stationary and moving irradiation; in the latter the radiation source can either rotate around one axis, making a complete turn or oscillating over a specified angle (rotary sources), or it can rotate simultaneously about three mutually perpendicular axes, describing a spherical surface (rotary-convergent sources). With moving irradiation the dosage absorbed is concentrated at the focus that requires therapy, while avoiding injury to healthy tissues.

Gamma-ray sources are installed in rooms whose walls are made of special materials that protect surrounding areas from the gamma radiation.

REFERENCES

Ruderman, A. I., and M. Sh. Vainberg. Fizicheskie osnovy distantsionnoi rentgeno- i gamma-terapii. Moscow, 1961.
Luchevaia terapiia s pomoshch’iu izluchenii vysokoi energii. Edited by I. Becker and G. Schubert. Moscow, 1964. (Translated from German.)

V. G. VIDENSKII