interpretation of in‑air output ratio of wedged fields in differentmeasurement conditions

Background: the collimator scatter factor (sc) is one of the most important parameters inmonitor unit (mu) calculation. there are several factors that impact sc values, including headstructures, backscatter in dose monitoring chambers, and wedges. the objective of this study wasto investigate the variation of sc with different buildup cap materials, wall thickness of buildupcaps, source‑to‑chamber distances (scds), ionization chambers, and wedge angles in 6 mvphoton beam. methods: in this study, copper and perspex buildup caps were made with twodifferent thicknesses for each buildup cap. measurements were performed on an elekta compactmedical linear accelerator (6 mv) using rk dosimeter with a sensitive volume of 0.120 cm3 andfarmer‑type ion chamber with a sensitive volume of 0.65 cm3. in all measurements, buildup capsand ionization chambers were positioned such as to stand vertically to the beam central axis. itwas also investigated the effect of internal wedge with different angles (30° and 60°) differentscds on sc. results: it was found in large field sizes, sc values in perspex buildup cap werehigher than copper. different scds and type of ion chamber and wall thickness of buildup capshad no significant influence on sc values. the presence of wedge influenced sc values significantly.variation of sc in wedged fields compared to open fields had a maximum deviation of 0.9% and6.8% in 30° and 60° wedge angles, respectively. conclusion: it was found that the presence ofwedges had a significant influence on sc and increases with wedge angles. as such, it should betaken into account in manual mu calculations.