Plaque Simulator implements a default Quality Assurance QA_Check point located 6.0 mm from the plaque face (concave surface) on the central axis (CAX) of a plaque. The QA_Check point is roughly equivalent to the COMS 5 mm prescription point. This point was selected because it is nearly always within the solid angle of primary exposure of every seed in every plaque model. The QA_Check results are summarized on page 2 of the treatment plan document with a green background and are detailed in the QA Document which provides all of the information needed to manually duplicate the calculation.
The standard QA document treats all seeds as isotropic point sources in an infinite homogeneous water environment which greatly simplifies the calculation and facilitates manual duplication. The related QA_Point is located at the same coordinates as the QA_Check but it is calculated using the same dosimetric settings and corrections as the Rx point. The two calculations will differ by a few percent for EP plaques and may differ by up to 15% for plaques with silicone seed carriers.
An independent calculation can be performed for the QA_Check point by hand directly on the QA Document, by copying the QA Document data into a spreadsheet, or from scratch using the COMS or EP seed center coordinates which are available as labels in the Plaque window and/or in Plaque Simulator user guide. For example, in the plaque coordinate reference frame, the check point is located at X,Y,Z coordinates of (6.0,0.0,0.0), the center of the central seed of a COMS plaque is at (-1.4,0.0,0.0), and center of the central seed of an EP plaque (e.g. EP917) is at (-0.4,0.0,0.0).
For a more comprehensive verification of Plaque Simulator's dose calculations you can export an .iqa6 file for the companion PSQACheck application. By preference setting default, PS will automatically create an .iqa6 file in the patient folder whenever the treatment planning document group is printed to a .pdf file.
PSQACheck is a cross-platform application (introduced with PS6 version 6.8.0) that calculates dose to the QA_Check point (or any point) in an infinite homogenous water environment but, unlike the standard QA document, PSQACheck also includes verification of your physics data, radionuclide decay for the scheduled implant time, 3D linear source location and orientation, TG43 linear source and anisotropy functions and so on. Versions of PSQACheck for both MacOS and MS Windows PCs and a few sample files may be found in the Plaque Simulator Data/(Hidden Support Files)/(Quality Assurance)/PSQA Check application/ folder. Using this application you can run your dosimetry verifications on a completely independent computer from that used for PS6 treatment planning.