Comparison of dosimetric properties of virtual wedge and physical wedges

The authors present a direct comparison of dosimetric properties of Siemens virtual wedge (VW) and physical wedge (PW). While there is a great difference in absolute values of wedge factors, VW factors (VWFs) and PW factors (PWFs) have a similar trend as a function of field size. PWFs have stronger depth dependence than VWF because of beam hardening in PW fields. Dose profiles in the wedge direction are match very well between VW and PW except in the toe area of the 45/spl deg/ wedge with large field sizes, where PW fields have a higher peak. The authors have demonstrated that it is dosimetrically acceptable to have an initial gap up to 3 cm for VW fields when compared with PW dose profiles. While maintaining the desired wedged dose distribution, VW has an advantage of creating smaller hot spot, when compared with PW, in the toe region of 45/spl deg/ wedge fields with large field sizes. Dose profiles in the non-wedge direction shows a significant reduction in PW fields due to off-axis beam softening and oblique filtration. PW fields also have significantly higher peripheral doses than open and VW fields. VW fields have similar surface doses as the open fields while PW fields have slightly lower surface doses.