Aim: The use of computer controlled wedge system is an important segment of radiotherapy and increases the uniformity of dose in the target volume. The aim of this study is to verify thevirtual wedge angles from the machine setup angles in Siemens ONCOR Linear accelerator (Linac) and comparewithpublisheddataofdifferentlinearacceleratorsasafunctionofbeamenergyandfield sizes.

Method and material:This experiment was carried out on Siemens ONCOR impression linear accelerator (Linac). The doses at different depth were measured by using CC13 ion chamber. During our work the source to surface distance was kept 100 cm. The square field sizes on which we worked were 10 cm2, 15cm2 and 20 cm2.The selected Virtual wedge angles for our study are 15°, 30°, 45°and60°.This work is carried out for both photon energies 15 MV and 6 MV, tissue equivalent water phantom IBA blue water phantom inside which all the observations were taken. The LDA 99 detector for virtual wedge profile was used. The wedge angle were calculated forthe Siemen’s given formula. The variation in wedge angle from machine setup angle and published data as a function of beam energy and field sizes wereanalyzed.

Results:The variation increases with field size and wedge angle but decreases with beam energy.

Conclusion: Deviations are under 3% which are acceptable before treatment planning.