Journal of Medical Physics
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Year : 2004  |  Volume : 29  |  Issue : 2  |  Page : 55-60

Analysis Of Clinical Teletherapy Gamma Beams From Radiotherapy Machines



Correspondence Address:
S Sathiyan


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The mega voltage photons interacting with the patient results in the production of scattered photons, secondary electrons and neutrons. These secondary particles lead in the deterioration of primary beam to a certain extent in terms of radiation flux and energy and it is relevant for radiation protection considerations of the patient during treatment. In this study an experimental method was used to estimate the quantum of flux due to primary and secondary photons, as well as recoil electron from the telecobalt beams by introduction of various intervening materials. The components of the Cobalt-60 output beam at different distances from the source position were studied in detail. At 50 cm distance from the source position, the recoil electron flux contribution is 13.8 %, 5.1 %and 4.7 %for depleted Uranium, tungsten and lead collimators respectively. At 80 cm distance the recoil electron contributes less than 2 % of the total flux. The effect of introduction of 5 mm Perspex plate in the beam will increase the flux of the recoil electron from 5.1 % to 17 %at 50 cm distance from the source and it is insignificant beyond 80cm. The recoil electron contribution is significantly less in tale Caesium beam compared to telecobalt beam. The outcome of this study helps in taking appropriate measures to reduce the less penetrating components In the useful beam.


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