Dosimetric evaluation of a treatment planning system using pencil beam convolution algorithm for enhanced dynamic wedges with symmetric and asymmetric fields

Radiation therapy treatment planning for many clinical situations requires wedgeshaped isodose distributions. The wedged dose distributions can be generated through the use of physical wedges (PWs), motorized wedges and the synchronization of jaw or multileaf collimator dynamic motion with accelerator dose output. Modern medical accelerators are usually equipped with a dynamic wedge (DW) option. The DW makes use of dynamic movement of one pair of independent jaws on a linac and generates dose distributions equivalent to those produced by a PW placed in static fields. The segmented treatment tables (STTs), which are implemented on Varian linacs, are used to control the dose rate and jaw movement for producing a set of DWs. Each STT contains information on the moving collimator position versus cumulative weighting of monitor units (MUs). The enhanced dynamic wedge (EDW), the second generation of DW for Varian linac, uses a single STT to generate all the other STTs for all field sizes and wedge angles (1). The clinical advantages of using DWs have been reported by many investigators (2-7). EDW is preferred over PW because it is not limited in length and does not create additional low energy electron and photon scatter that increases both surface and peripheral dose (8, 9). However use of DW requires more complex dosimetry and quality control procedures (10). During commissioning activity, care must be exercised to ensure that dynamic wedges are