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Purpose: A Monte Carlo Dose (MCD) engine coupled with a Virtual Source Model (VSM) will be incorporated into the IMPAC‐MOSAIQ system for use as a dose QA tool. The VSM is an efficient accelerator head model that requires commissioning of the source parameters using a series of measurements. The commissioning measurements, procedures, and verification of results will be described. Method and Materials: A series of in‐air measurements is used along with a limited number of in‐water measurements to determine the parameters required to characterize a particular linac. The in‐air measurements are used to determine the primary source strength, primary source size, and secondary source size. In addition, the shape of the off‐axis profiles is determined through use of the Pade approximation. The in‐water measurements are used to determine the spectral shape and amount of electron contamination from a series of monoenergetic kernals. A series of in‐water verification measurements is then used to confirm accuracy of the characterization through MCD verification calculations of in‐water profiles. After verification of the commissioned parameters, the model is ready for use as a dose QA tool for comparison to 3D DICOM dose exported from the treatment planning software. Results: Good agreement is seen between output factors and profiles for a series of field sizes for the multiple machine types studied. Conclusion: Multiple machine types can be commissioned for use with the VSM in order to facilitate dose QA using a Monte Carlo dose engine. Conflict of Interest: The authors are employees of Elekta. |
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