Abstract
The nonphysical wedge is a modality that uses computer-controlled jaw motion to generate wedge-shaped dose distributions. There are Varian enhanced dynamic wedges (EDWs) and Siemens virtual wedges (VWs). We recently commissioned dynamic wedges on both Varian and Siemens LINACs. The beam data, acquired with a Wellhöfer chamber array and a Sun Nuclear profiler, are used for modeling in the ADAC Pinnacle system. As recommended by ADAC, only a limited number of beam data is measured and used for beam modeling. Therefore, the dose distributions of dynamic wedges generated by Pinnacle must be examined. Following the commissioning of the dynamic wedges, we used 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 differences more than 3% 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 quality assurance tests that are necessary to ensure acceptable consistency between the delivered dose and the associated treatment plan when dynamic wedges are applied. PACS numbers: 8753 Dq, 87.53.Xd
Highlights
One of the advantages offered by modern LINACs is the ability to dynamically vary the jaw position during treatment to generate wedge-shaped dose distributions
Using dynamic jaws to generate dose distributions equivalent to those produced by physical wedges placed in a static field was first proposed in the 1970s.(1) Since the clinical implementation of the nonphysical wedge has been discussed by a number of investigators.[2,3,4,5,6,7,8,9]
Varian uses the segmented treatment table (STT), which governs the position of the jaws with respect to the number of delivered monitor units (MUs)
Summary
One of the advantages offered by modern LINACs is the ability to dynamically vary the jaw position during treatment to generate wedge-shaped dose distributions. Using dynamic jaws to generate dose distributions equivalent to those produced by physical wedges placed in a static field was first proposed in the 1970s.(1) Since the clinical implementation of the nonphysical wedge has been discussed by a number of investigators.[2,3,4,5,6,7,8,9]. The large range of field shapes and wedge angles introduces a new challenge for commissioning nonphysical wedges on modern treatment-planning systems. The delivery of wedge-shaped radiation therapy requires that the related components of the LINAC hardware and software be functioning correctly and that the RTP system has the ability to accurately model and calculate dose. We compared the data from the Pinnacle RTP system with the mea-
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