Wedge Angle Confirmation in Computer Controlled Wedge Field

Abstract

Wedge is a beam amending devices that causes an advanced decrease in the intensity across the beam resulting in a tilt of the isodose curves from their normal positions. The use of a 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 the virtual wedge angles from the machine setup angles in Siemens’ ONCOR Linear accelerator (Linac) and compare it with published data of different linear accelerators as a function of beam energy and field sizes. This experiment was carried out on Siemens’ ONCOR impression linear accelerator. The doses at different depths were measured by using the 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, 15, and 20 cm². The selected virtual wedge angles for our study are 15, 30, 45, and 60 degrees. This work was 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 LDA99 detector for the virtual wedge profile was used. The wedge angle was calculated for the 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 were analyzed. The variations increase with field size and wedge angle but decrease with beam energy. Variation is under 3% which is acceptable before treatment planning.