Journal of Medical Physics
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Year : 1999  |  Volume : 24  |  Issue : 1  |  Page : 21-24

Effect Of Shielding On Virtual Source Position For Electron Beams From A Clinic-1800 Linear Accelerator

Correspondence Address:
M Ravikumar

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Source of Support: None, Conflict of Interest: None

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In the present study, the virtual point source positions were determined for field sizes defined by standard electron cones and cerroband field inserts for various electron energies. Ionometric measurements were carried out with a0.6 cm3 Farmer type ion chamber at dm= in a polystyrene phantoms. The virtual source positions obtained by inverse square law method were observed to change with the beam energies and the applicator sizes. It was also observed that the Virtual Source-to-Surface Distances O/SSD) are greater for the field sizes defined by the cerroband inserts in the standard 20 cm x 20 cm applicator for all energies. These observed variations in virtual source positions are due to the change in electron scatter for different energies and beam sizes. When the cerroband cut-outs are introduced close to the chamber, the scattering conditions are likely to get altered, resulting in change in the virtual source position.

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