Quantitative Verification of Dynamic Wedge Dose Distribution Using a 2D Ionization Chamber Array

The accuracy of two calculation algorithms of the Eclipse 8.9 treatment planning system (TPS)-the anisotropic analytic algorithm (AAA) and pencil-beam convolution (PBC)-in modeling the enhanced dynamic wedge (EDW) was investigated. Measurements were carried out for 6 and 18 MV photon beams using a 2D ionization chamber array. Accuracy of the TPS was evaluated using a gamma index analysis with the following acceptance criteria for dose differences (DD) and distance to agreement (DTA): 3%/3 mm and 2%/2 mm. The TPS models the dose distribution accurately except for 20×20 cm
²
field size, 60
^°
and 45
^°
wedge angles using PBC at 6 MV photon energy. For these latter fields, the pass rate and the mean value of gamma were less than 90% and more than 0.5, respectively at the (3%/3 mm) acceptance criteria. In addition, an accuracy level of (2%/2 mm) was achieved using AAA with better agreement for 18 MV photon energy.