Digitizing the Tumor

The Retinal Diagram (aka funduscopic diagram) window is used to enter the height of the tumor apex and to digitize the tumor perimeter and (optionally) other landmarks such as blood vessels on the retinal surface. The recommended method is to digitize a calibrated fundus image. If you don't have a fundus collage, or the tumor is too anterior to photograph, you can still draw the tumor directly on the diagram based on size and location estimates derived from ultrasound and CT or MR imaging.

To dispose of an existing tumor perimeter, click the Clear button next to the Tumor button. You can move the entire tumor to any location on the diagram by placing the cursor into tumor drag mode and simply clicking within the tumor and dragging. The perimeter will circumferentially warp as appropriate to acount for radial position on the polar diagram. You can also control the shape of the tumor by draging the apex marker.

The following tutorial illustrates digitization of a posteriorly located tumor using a fundus collage and subsequent circumferential warping of the tumor and collage for correct mapping onto the polar retinal diagram.

Prepare the fundus collage
  • In the Image window, open and calibrate a fundus photo collage as shown here.
  • The fundus collage is used to digitize the location, appearance, and perimeter of the tumor base on the retinal surface with respect to retinal landmarks that can also be identified in CT imaging space.
  • Two landmarks that are readily identifiable in fundus photography are the optic disc and macula. The location of the optic disc can be closely estimated in 3D CT (or MR) imaging space by reconstructing a meridian plane which bisects the eye and passes through the center of the optic nerve. This meridian plane, by definition, will also pass through the posterior pole of the eye. The posterior pole can be closely estimated in the fundus photos because the macula is adjacent to the pole.
  • Therefore, in order to accomplish the fundus-CT fusion, the fundus collage MUST contiguously include as much of the tumor as can be photographed as well as the macula and optic disc.

Open the retinal diagram window

Retina window set to Left eye with plaque, coordinate, and muscle displays disabled.

Add fundus collage to the retinal diagram
  • If a calibrated fundus photo collage has been prepared, the Photo button in the Retinal Diagram tumor controls group will be functional.
  • If the Photo button is disabled (ie dimmed) it means either you haven't yet calibrated the fundus image, you never opened a fundus image in the Image window or you accidentally put it into the wrong image buffer.
  • Click the Photo button to add the collage to the diagram.
  • The slider item in the contextual menu of the Photo button adjusts the transparency of the collage background. The expected color of the collage background is black.
  • Plaque Simulator will have automatically selected the approriate eye (ie left or right) based on the orientation of the fundus collage calibration ruler.
  • The optic disc in the photo should now be centered within the orange circle in the diagram and the posterior pole in the photo should be at the center of the diagram.

Prepare to digitize tumor perimeter
  • In the toolbar select tumor #1.
  • In the footer controls group click the Zoom In button ZoomIn to enlarge and center the tumor in the window.
  • If muscle attachments are being displayed, in the tools control group click the Muscle button to disable display of muscles. Disabling muscle overlays gives you an unobstructed view of the tumor.
  • In the tumor controls group click the Clear button to delete the current tumor and then the Tumor button to begin tumor digitization. The cursor will change to a pencil PencilCursor16x16 when positioned within the limbus circle of the diagram.

Digitize the tumor perimeter RDContourSequence
  • In the tumor controls group click the Tumor button to begin tumor digitization.
  • Move the cursor to an easily recognizable and convenient starting point on the tumor perimeter.
  • Depress the mouse button, and begn tracing the perimeter of the tumor.
  • Continue either clockwise or counter-clockwise. Counter clockwise is illustrated.
  • Once tumor digitization has begun, you may optionally depress the mouse button continuously as you trace the perimeter, or you may release the button and digitize points individually by clicking on them. Digitization will continue until the polygon defining the tumor perimeter is closed.
  • The perimeter polygon will automatically close when the cursor returns to the starting point.
  • Alternatively, you can stop digitizing just short of the starting point and press the spacebar on the keyboard to autocomplete the polygon.

Circumferentially warp the tumor and collage
  • For proper display on the polar retinal diagram, the pixels of the fundus collage must be circumferentially warped as a function of radial distance from the pole. Plaque Simulator (PS) defaults to doing this after the tumor has been digitized in order to preserve maximum image quality during the digitization process.
  • Distortion of the original image is insignificant near the center of the retinal diagram, but becomes noticable at the equator and is very significant for locations in the anterior hemisphere.
  • Once digitization of the tumor perimeter is complete, PS warps the tumor perimeter (if Auto Correct Tumor in the Diagram menu is enabled) and offers to warp the fundus collage for proper display on the retinal diagram.
  • If you are finished with all retinal digitizations answer yes, otherwise you can manually warp the photo collage at a later time.
  • The warped tumor and fundus collage look like this.

Enter the apex height
  • By default, a 2 mm margin is automatically generated surrounding the tumor base. You can change the margin when setting the tumor apex height.
  • In the tumor controls group, click the Apex button and enter the tumor apex height as measured from ultrasound studies.
  • Also in the tumor controls group, select the shape of the tumor (Peak, Dome or Mushroom).
  • The tumor apex defaults to the geometric center of the tumor base. You can move it elsewhere by enabling apex cursor mode and dragging it.

Confirm digitization using CT images
  • In the Image window, align the Eye tool on the meridian (T-Mer) and coronal (T-Cor) images that pass through the tumor apex.
  • In the Planar Dosimetry window, apply the T-Mer image to the meridian plane and the T-Cor image to the coronal plane. The brown tinted tumor cross-sections should overlay the tumor in the CT images.

Note: for low altitude tumors such as this example (2.2 mm) it is advisable to set the Rx point at an altitude of about 4 to 5 mm in order to assure dosimetric coverage of the 2 mm margin surrounding the base.


Blood vessels and landmarks
  • You may optionally digitize blood vessels or other anatomic landmarks. PS6 can calculate retina dose area histograms of landmarked regions. Click the LandMk button in the tumor controls group to start landmark entry.
  • A new landmark segment will begin every time you depress the stylus or mouse button over the diagram, and will continue until you release it. Landmarks are NOT automatically warped following digitization and will be three dimensionally accurate only if traced in the vicinity of the posterior pole or after the fundus image has been warped following tumor digitization.
  • Click the LandMk button in the tools group again to terminate landmark entry.
  • To remove selected landmarks, place the cursor in select mode
    and click on one or more landmarks in the diagram. Selected landmarks will become highlighted. To dispose of all landmarks use the LandMk button contextual menu to Select All.
    LandmarkOptionsMenu Then click the Clear button next to the LandMk button.
  • Landmark properties are set in a properties sheet which is accessed from the contextual menu of the LandMk button.

Concave tumors and base margins

Plaque Simulator's current auto-margin function is only able to properly expand spherical polygons that have convex perimeters.

For tumors with concave perimeters, such as illustrated on the right, you can manually edit the base margin to maintain the desired (e.g. 2 mm) spacing.


  • To edit the tumor margin, place the cursor in margin mode
    and drag the margin control handles to maintain the 2 mm margin.