COBALT 60 TELETHERAPY SOURCES - CONTINUOUS CONTROL THROUGHOUT THEIR LIFE CYCLE

摘要

Teletherapy is a method of treatment of cancer in which the radiation from a source is focused on the cancerous tissue from a distance. Cobalt metal is irradiated in the form of pellets of 1 mm dia X 1mm ht in the nuclear reactor to produce ~(60)Co by the nuclear reaction ~(60)Co(n,γ)Co. Teletherapy sources (output 100-170 RMM) are fabricated by doubly encapsulating these pellets with specific activity greater than 9.25 TB1q/gm (250 Ci/gm) in stainless steel capsules. The sources are loaded in the teletherapy machines installed at the hospitals. When the source output reaches to less than 40 RMM(88.8 TBq/2400 Ci), treatment is not recommended as the time of treatment increases considerably. At this stage fresh sources are loaded in the teletherapy machines. These decayed sources require continuous monitoring till they are disposed in the well guarded national waste management facilities. The decayed sources are reused by cutting open the capsules to recover pellets for fabrication of sources for laboratory irradiators and further encapsulated in the source pencils to use as industrial sources. These methods allow the ~(60)Co for another two half lives and hence the activity to be disposed will be reduced by 75 %. In India, both of these methods are being followed to effectively utilize the ~(60)Co and to reduce the quantity to be disposed as active waste.The decayed teletherapy sources if left unattended may cause serious security concerns. Teletherapy sources in the hospital are under control, the laboratory and the industrial sources are in the control of the competent authority. After the use in the irradiators the sources will be transferred to the waste management agency. Thus continuous control is established for the teletherapy sources during its use, reuse in the laboratory and irradiators and further in the waste management agency.