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myQA iON - Dose Analysis

  • Updated

The Configuration tab is only visible when a Configuration manager is logged in. Here the user can:

  • Edit the Beam Model Dictionaries
  • Edit or clone the Hounsfield Units (HU) to Density Files
  • Customize the PDF Report

 

SciMoCa (RT only)

 

 

Beam Model Dictionary

  • Login using a Configuration manager account.
  • Under Settings > Configuration go to Dictionaries.
  • Click Edit to open the selected dictionaries dialog.
  • Change the defaults (1) depending on the treatment machine, beam energy, beam model ID, and any other corrections provided with the beam model information.
  • Click Save.

 

Adjust MLC offset and dose calibration values 

  • Click Edit on the beam model.
  • Locate the "LeafOffsetCorrection" and "DoseCalibrationCorrection" tags (2) and update the values accordingly for the desired treatment machine and energy.

 

Cyberknife configuration

Please ensure that the Cyberknife data has been properly configured in both the Beam model dictionary
and the Cyberknife collimator file.

  • Open the Beam model dictionary and ensure that the Cyberknife data has been entered.
  • Click Save to save the changes in the Beam model dictionary and close the window.
  • Open the Cyberknife Collimator dictionary and ensure that the Cyberknife data has been entered
    correctly. 
  • Click Save to close. 

 

HU to Density files

HU information from patient CT images must be converted into density information for processing by the MC engine.

  • Under Settings > Configuration go to HU density files.

  • Click Edit.
    A minimum of two rows of values need to be saved. The valid range of values is:

    • -1000 to 6000 for HU
    • 0 to 4.8 g/cm3 for Mass Density
    • 0 to 4.8 g/cm3 for Relative Electron Density 

    Example: HU to density file edit

  • Click Save.
     

Insert a new HU to density file 

  • Under Settings > Configuration go to HU density files and click Clone.
  • Enter a new name in the Name field and choose from Mass Density or Electron Density in the drop down menu of the Type field.
  • Replace the HU and Density values in each line and click Save to save and create a new HU to density file.

 

MCSquare (PT only) 

HU to Density files 

The calibration data consists of two curves per scanner; HU to mass density and HU to material.

Example: HU to density curve

IMPORTANT NOTICE:
The HU to density file only accepts integer numbers.

HU to mass density:

  • The HU to mass density conversion model must be defined by a list of HU values with their corresponding mass density values (in g/cm³).
  • The MC simulation interpolates intermediate values in order to convert all voxels of the CT image into a 3D map of the patient mass densities.

HU to material:

  • The HU to type of materials conversion model must be defined as a list of pairs of HU values and material ID (IDs 39 to 62 in the example below).
  • Each HU value corresponds to lower limit of the range of HU representing a specific material. For example, a voxel with HU values in the range [-950; -120] will be represented by the material ID 40 (Schneider_Lung) in figure below.
  • All materials available for the MC simulation can be found in the Materials folder. This is not accessible directly in myQA iON and will be provided separately if asked.

 

How to Update Calibration Data 

Calibration Curves

Both calibration curves must be updated by the user in order to match the scanner on site.

In general, the TPS only requires a single curve (HU to density) but if the user used the stoichiometric method (as described in Schneider et al. Phys. Med. Biol. 41 (1996) 111–124), they should be able to update both curves needed for the MC algorithms.

There are a few drawbacks with the stoichiometric calibration:

  • The HU to SPR (Stopping Power Ratio) function is non-injective: some materials having the same SPR can have different HU values
  • The inserts used for the calibration are based on human tissue.

Please note that additional materials (water phantoms, dosimetry devices, metal, etc) are excluded from
the calibration. For those reasons, when computing a plan in a non-human CT (e.g., water phantom,
dosimetry device) it is highly recommended to create a new scanner folder with a specific calibration curve
containing the needed materials (water, Plexiglas, etc.). 

 

Materials list

The list cannot be updated by the user in myQA iON. Trying to match TPS and MC materials is not recommended, as it will remove the independence between the two methods.

 

Overrides

During the planning phase, the dosimetrist can override the density of some structures. The TPS usually exports the override information in the structure set associated to the CT. This information is considered during a pre-processing phase before the data is sent to a MC algorithm for dose computation. The workflow is as follows:

  • Extract the REL_MASS_DENSITY or Rel_STOP_RATIO of the ROI(s) in the RT Structure Set.
  • Revert the CT calibration curve to convert the REL_MASS_DENSITY or Rel_STOP_RATIO in the equivalent HU.
  • Override the ROI with the new HU.
  • Provide the new CT to MCSquare.

Please note, overrides are managed through global and local parameters.