The PSQACheck Application for Plaque Simulator Version 6.8.0 and later

This tutorial was last revised: 2/14/2021
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What is PSQACheck?

PSQACheck provides a cross-platform, independently calculated verification of several aspects of PS6 dosimetry:

  1. PS6's TG43 physics data.
  2. Source coordinates and orientation.
  3. Source calibration and decay for the treatment schedule.
  4. Dose calculation to a reference point, usually located 6mm above the plaque center.
  5. Runs on either the primary treatment planning system or any other computer (MacOS or MS Windows PCs).

Installing PSQACheck

To manually install on any MacOS computer, simply copy it to the Applications folder of whichever computer you want to run it on.

Note: on MacOS, the support files of an application are organized into a special structure referred to as a bundle (a.k.a. package) which is essentially a folder, but it is presented to the user as if it were a single file. On MacOS applications can be launched by simply double-clicking their bundle icon. The icon seen on MacOS entitled is actually a MacOS bundle. You can see the contents of a bundle/package from the MacOS Finder by selecting Show Package Contents from the contextual menu that appears when right-clicking the icon. is an independently coded (Xojo), cross-platform, quality assurance application for Plaque Simulator (PS) that you can run on your computer. Included with the PS installer (6.8.0 and later) are versions of compiled for both MacOS and MS Windows 64 bit operating systems. The MacOS version is a universal binary that runs natively on both x86 and Apple Silicon architectures.

The PS installer will automatically place a copy of in your Plaque Simulator Folder.


To install on a MS Windows computer, copy the PSQACheck folder found in Plaque Simulator Folder/Plaque Simulator Data/(Hidden Support Files)/(Quality Assurance)/PSQA Check application/For Windows 64 bit/ to your PC. You can even place the entire folder on the Windows desktop if you like. The Windows version of the application is named PSQACheck.exe and must be launched from its enclosing PSQACheck folder in which all of its linked libraries reside.


Example plan


The plan features one intensity modulated seed at the apex of the notch and several empty seed placeholders near the anterior rim of the plaque.

For this tutorial, a treatment plan using a model 1824 notched plaque has been created. The planned insertion date is Feb 17th, 2021 with a 1 week implant duration. The plan features one intensity modulated seed at the apex of the notch and several empty seed placeholders near the anterior rim of the plaque. The dose Rx is 85 Gy to the apex of a 5 mm tall peripapillary tumor.

The tumor apex is near, but not precisely above the plaque center. The QA point will be PS6's default which is a point located at 6 mm from the concave face along the plaque's central axis. A plaque's coordinate system origin is located on its the concave face near its center of cylindrical symmetry with the X axis being the "central" axis of the plaque as illustrated above.

The basic PS6 treatment plan documentation includes a simple QA document that performs an independently coded TG43 point source calculation suitable for validating with a pocket calculator, but it shares the same physics files with the primary PS6 dosimetry calculations and runs on the same planning computer. For a more comprehensive QA check, the provides an independently coded (Xojo), cross-platform, quality assurance application for Plaque Simulator that you can run on any MacOS or MS Windows computer. The requires a physics file and a treatment configuration file exported from PS6. The exported treatment configuration file will be automatically created whenever a treatment plan .pdf file is saved, and can also be manually created via the Export menu accessed from the menubar's File menu. These are both .xml files that can be inspected with a text editor. DocumentExportPSQAMenu


The tumor apex is near, but is not situated along the plaque's central axis.




The 1st page of the treatment plan that documents the Rx and surgical logistics of the treatment.


This document is the seed loading map that IsoAid uses to assemble the plaque.


This is the point source QA document that usually accompanies treatment plans. It employs a simple point source approximation suitable for computing using a pocket calculator.

Initializing PSQACheck

The PSQACheck application is designed to be extremely easy to use via a drag & drop user interface. The first time you launch PSQACheck you will need to prime its physics configuration. This is most easily done by launching PSQACheck and then dropping a copy of one of Plaque Simulators .phys6 bundles(e.g. I-125 (IAI-125A).iphys6) onto the PSQACheck application. The current state of PSQACheck's physics configuration is automatically saved to a startup preferences file whenever the application quits, and is restored from that file when the application is next launched. If you change the physics configuration, you can manually save the changes to a private .psqa binary file, to an .xml file, or to the application preferences. To restore a prior physics configuration, simply drag any of these physics files (.phys6, .psqa or .xml) back onto the application window.


Once primed with a TG43 physics configuration, the physics tab will look like this:


You can review and edit g(r) attenuation curves, F(r,angle) anisotropy curves, coefficients, source name, dose rate constant, half-life and source length. The PS unique ID is a 4 character code used by PS6 to uniquely identify every source type and should match the ID used in PS6. The G(1,90) parameter is recalculated from the source length and if labeled in green matches the value imported from the physics file.

Performing a QA check

PSQACheck implements an AAPM TG43 methodology for linear and point sources to calculate dose delivered to a point located in an infinite, homogeneous water environment.

NOTE: PSQACheck supports physics data for only one model of seed at a time and so can not deal with plaques that contain multiple models of seeds. Each seed, however, may have its own calibration date and calibration strength.

To perform a QA check, first export an xxxxxx.iqa6 file from PS6 and then either drag the file onto the PSQACheck application (or simply double click the .iqa6 file on MacOS.) If PSQACheck is on a different computer from the treatment planning system you will have to copy the .iqa6 file from the treatment planning computer to the appropriate computer. The .iqa6 files are actually .xml text files and so can be inspected using a text editor and should transfer easily between systems as email attachments or using network or USB memory stick "sneakernet" methods.



This is PSQACheck as it appears on MacOS 10.15 (Catalina).


This is PSQACheck as it appears on Windows 10.

  • Prescription for ... group

    • The plaque insertion and removal dates were selected in PS6 and are initialized from the .iqa6 file.

    • Elapsed time is calculated from these dates.

    • PS dose displays the dose calculated by PS6 at the coordinates specified in the .iqa6 file exported by PS6. These coordinates cannot be changed within PSQACheck. Dose calculated by PS will usually be lower than the dose calculated by PSQACheck because PS applies inhomogeneity corrections to account for collimation of primary radiation emitted from the source, scatter loss due to this collimation and air in front of the eye, fluorescence from absorption in the gold and ray traces photoelectric attenuation in the silicone seed carrier of COMS plaques.

    • QA dose displays the dose calculated by PSQACheck at the coordinates displayed in the QA dose calculation point group box. You can override the TG43 calculation type in the Physics tab. The default is a linear source calculation. (Note: this differs from the QA calculation provided in PS6's QA document which is always a point source approximation.)

    • PS dose / QA dose displays the ratio of these two doses. This ratio is only useful for QA purposes when the displayed coordinates are the same.

    • QA tolerance displays the threshold for which the background color tinting of the ratio field becomes green. For example, if the tolerance is 10% then the ratio highlighting will be green when the ratio PS/QA >= 0.9

  • QA dose calculation point group

    • The dose calculation point (6.00,0.00,0.00) was selected in PS6 and initialized from the .iqa6 file. The green, cyan and magenta color bars are keys to the X,Y and Z axes as rendered in the 3D view.

    • You can rotate the 3D view using the mouse cursor and display the 3D view in a resizable window by clicking the 3D Window button.

  • Sources tab

    • Each source in the .iqa6 file carries its own coordinates, calibration date and calibration strength.

    • In this example, source #13, located at the apex of the notch is highlighted and the formula for its contribution to the calculation point dose is displayed just above the multicolumn table of calculation parameters.

    • The Is a COMS plaque checkbox optionally applies a generic 10% correction as a rough estimate of I-125 attenuation in the silicone seed carrier of a COMS plaque.

    • Columns with yellow background tinting are calculated by PSQACheck from each source's coordinate and calibration.

    • Green text indicates that a calculated value is within 1% of the value calculated by PS6 as found in the .iqa6 file. Note: QA check doses in the .iqa6 file are always point source calculations whereas PSQACheck calculations may default to a linear source dose calculation so there may be small differences in the dose column.

  • Window bottom buttons

    • Page Setup - Configure the printer setup.

    • Print - Print the window to paper (or a .pdf file on MacOS)

    • New - Clears the application for an entirely new patient.

    • Clear - Clears only the current tab (physics or sources)

    • Help - Opens a help window with a summary of how to use the application.