Analytical Method for Determination of Wedge Factors Dependency of Field Size and Depth for 6mv & 18mv Photon Beams In Siemens Primius Plus Accelerator

Shields with variable thickness (physical wedge) is used in radiotherapy for eliminating hot spots and create a uniform dose distribution beam. In this regard, determining a factor for calculating the attenuation of beam by using the wedge is important in order to compensate for the dose of the treatment. This study aims to use a semi-experimental method and convert it to computer software for determining the wedge factor and enlarging treatment planning system (TPS) in radiotherapy department. Subjects and Relative dosimetry of accelerator Primus plus of Ahvaz Golestan hospital radiotherapy department was performed for with wedge and without wedge fields at the reference depth (10 cm), by ionization chambers (CC13/SN-6186 & 6187) that was calibrated in atomic energy organization of Iran (SSDL center). The wedge factors were calculated for square fields with wedge angles 15,30,45 and 60. Finally, an analytical equation for wedge factor is defined. By this equation the attenuation coefficient of wedge can be obtained. With these results the wedge factor in all depths¬ of phantom, therapeutic fields and photon energy (6 and 18 MV) is determined. Therefore, using TBL Curve ver5 and MATLAB they were converted in to a computer software. By using TBL Curve ver5 software an analytical equation for different depths of wedged fields in photon energies 6 and 18 MV with accuracy (r2› 0/995) is obtained, that can determine the wedge factor with accuracy less than 5% compared to measurement. Based on this research determination of wedge factor for all field size at any depth, energy and for each physical wedge is available even for any case which the measuring of wedge factor is not possible. Linear accelerator, wedge factor, physical wedge, radiotherapy, treatment planning system