The accuracy of dynamic wedge dose computation in the ADAC Pinnacle RTP system

Abstract

Non-physical wedge is a modality that uses computer controlled jaw motion to generate wedge shaped dose distributions. There are Enhanced Dynamic Wedges (EDW) of the Varian accelerators and Virtual Wedges (VW) of the Siemens.
Recently we have commissioned dynamic wedges on both Varian and Siemens accelerators. The beam data, acquired with Wellhofer chamber array and Sun Nuclear profiler, are used for the modeling in the ADAC Pinnacle system. As recommended by ADAC, only a limited number of beam data are measured and used for the beam modeling. Therefore, the dose distributions of dynamic wedges generated by Pinnacle have to be examined.
Following the commissioning of the dynamic wedges, we use Pinnacle to generate a number of dose distributions with different energies, wedge angles, field sizes and depths. The computed data from Pinnacle are then compared with the measured data.
The deviations of the output factor in all square and rectangular fields, are mostly within 2.0% for both EDW and VW. For asymmetric fields, the deviations are within 3 %. However, exceptions of more than 3 % differences have been found in a larger field and large wedge combinations. The precision of the beam profiles generated by Pinnacle is also evaluated. As a result of this investigation, we present a scope of QA test that is necessary to ensure an acceptable consistency between the delivered dose and the associated treatment plan when dynamic wedges are applied.