Dose to Plan Comparison (IMRT QA)

• This step-by-step example assigns a dose map with a treatment plan using gamma map to quantify the differences.
• This instruction set is using the images of the RapidArc example what is part of the installation.

Assign Dose Map

Add a “Dose to plan comparison” object to your case.

At least one valid dose map object must be available in the case. The dose map should have fiducials assigned to allow an image registration.

By default the first available dose map in the case is assigned. One can select from the “Dependence - Dose map” combo box any available dose map in the case as shown below.

Assign Treatment Plan

• A treatment plan in FilmQA Pro consists of an image, a dose scaling range and the isocenter information.

To load the Treatment plan, right click the “Data—Treatment plan” icon ..

... and select one of the following 4 options:

• “Open treatment plan” - opens file with Treatment Planning System proprietary format (e.g. BrainLab, Pinnacle, TomoTherapy file formats, more available!). Data files include all plan data including dose range and isocenter.
• “Open image from file” - opens file including a single image (e.g. tif, png, more available). In most cases this requires to enter both dose range and isocenter manually.
• “Open image from Dicom file” - opens DICOM file include one or multiple images or slices of a 3D cube. User defined plane can be interpolated from a 3D cube. Data files include all plan data including dose range and isocenter—this is the most common way to import a treatment plan. ·
• “Paste CSV data as image” - loads treatment plan data from Windows clip board when copied as CSV table in another application (e.g. from Excel spread sheet). This requires to enter both dose range and isocenter manually.

See also Available Images Formats in FilmQA Pro.

If the isocenter is Not assigned, FilmQA Pro assumes the image center is the isocenter of the plan.

In case of the RapidArc example, the treatment plan is stored as tif file, i.e. use the “Open image from file” option to load the plan.

The example screen should look like shown below.

Image Registration

Select the “Tool - Image comparer” in the case data selector to start the image comparer. The fiducials assigned in the dose scan are fitted automatically to the coordinates of the isocenter. The fiducial fit can be also invoked using the “Fiducial fits” button as shown below.

The isocenter fit requires that the dose map is roughly assigned, i.e. flipping and 90° rotations must be correct so that the quadrants have the right orientation. Use the button to select rotation and flipping as shown below.

Rotate and flip the dose map prior to the registration. The rotation is carried out first, then the flipping.

Other registrations methods are available.

The example screen should look like shown below.

Comparison Results

Use the rotation and step pad underneath the center image to adjust dose map position

The step size can be changed by toggling the button—right click this button for more step size options.

The “Δ fiducial” block shows the average offset between isocenter and fiducials in x and y direction as well as the absolute distance—right click for additional options.

An efficient way to find the dose map position that maximizes passing rate is displaying the isolines of both images (select “Isomap” tab) and adjusting the dose map position with small steps.

For the RapidArc example a passing rate of ~97% at 2% / 2 mm (99.9% at 3% / 3 mm) can be reached as shown above.

The comparison map parameter are displayed at the right lower part. For the gamma function the parameter are as follow:

• Tolerance: Gamma tolerance value. Button underneath allows to select options for the gamma calculation (see below)
  
  including:
  • Relative tolerance: Tolerance relative to local dose value
  • Tolerance relative to maximum: Global gamma
  • Tolerance to user defined value: User selectable absolute tolerance
  • Maximum relative search radius: Radius relative to distance criterion the algorithm keeps searching to find a distance to agreement value
  • Gamma search: Mode to end gamma search
• Distance: Gamma distance value. Button underneath allows to select gamma function type.
  • Gamma relative error: Gamma out put is “Gamma normalized” * Tolerance.
  • Gamma angle: 0° gamma is dominated by dose offset, 180° gamma dominated by DTA. If gamma is dominated by DTA, the passing rate can be improved by adjusting image position.
  • Gamma normalized: Gamma = sqrt(Delta^2 + DTA^2) where
    Delta = |Reference - Client| / Tolerance
    DTA = |Location(Reference) - Location(Client = Reference)| /Distance
    Gamma in normalized form as defined in paper by Low, Harms, Mutic, Purdy in Med. Phys. 25(1998)„5, p. 656.
• Min. Threshold: Minimum threshold to cut off lower dose values. Either relative in % or absolute in Gy—use button underneath to toggle.
• Default value: Default value for the gamma function used when Distance to Agreement search fails (no matching values is found).

Generate Report

If the final results are displayed a report can be generated, just select the “report” tab to display the corresponding report as shown below

Click button to update all report settings to current setting of all tabs (right click button for additional options).

Click button to save report as pdf file or the button to print the report.

 

Watch demonstration movie