Plaque Simulator implements a 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 equivalent to the COMS 5 mm prescription point. 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 QA_Check treats all seeds as isotropic point sources in water which greatly simplifies the calculation and enables 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).