Peripapillary Tumor Tutorial

Peripapillary Tumor

Note: this case study assumes that you are already familiar with the basics of creating and importing the images that Plaque Simulator expects for image based planning.

In this case study a peripapillary (ie adjacent to the optic disc) tumor with a button-shaped central mass surrounded by low elevation retinal extension is modeled using a fundus image collage, planar CT reconstructions and basal dimensions from ultrasound measurements.

Axial CT Reconstruction

Open the axial multiplanar reconstruction (MPR) created in OsiriX.
Calibrate the image (e.g. 40 mm).
Adjust the eye modeling tool to fit the eye.

Equatorial CT Reconstruction

Open the equator multiplanar reconstruction (MPR) created in OsiriX.
Calibrate the image.
Adjust the eye modeling tool to fit the eye.

Sagittal CT Reconstruction

Open the sagittal multiplanar reconstruction (MPR) created in OsiriX.
Calibrate the image.
Adjust the eye modeling tool to fit the eye.

Tumor-Merdian CT Reconstruction

Open the tumor-meridian multiplanar reconstruction (MPR) created in OsiriX.
Calibrate the image.
Adjust the eye modeling tool to fit the eye.
Adjust the tumor tool to mark the approximate location of the tumor.

Tumor-Coronal CT Reconstruction

Open the tumor-coronal multiplanar reconstruction (MPR) created in OsiriX.
Calibrate the image.
Adjust the eye modeling tool to fit the eye.

Ultrasound images

Open the ultrasound image(s).
Note the tumor dimensions.
Height 5.5 mm from the inner sclera.
Base 12.2 x 11.4 mm.

Fundus photograph

Open the fundus image.
Calibrate the image.
Set the fundus collage menu for 5 pictures.
Position collage center markers 2-5.
The ultrasound measurements indicated that below the retina, low altitude tumor may be extending from the base of the button shaped mass. Extending the collage with 2 or 3 additional photos covering the medial side of the tumor button would have been useful.

Model the tumor

In the Retinal Diagram window:

Open the Std. tumor sheet.
Adjust the radial, circumferential and height controls to match the ultrasound measurements (e.g. 12.2 x 11.3 x 5.5 mm).
Adjust latitude and longitude such that the proposed standard tumor (tinted orange) overlays the tumor mass and its posterior edge aligns with the posterior edge of the tumor where it overhangs the optic disc in the fundus collage.
Click OK to exit the sheet.
The main tumor mass, as seen in the ultrasound images, is button-shaped but it is surrounded by what appears to be retinal detachment and broad low altitude sub retinal extension along the inner sclera. This tumor is best modeled using the peak shape control due to its extensive base. Using the peak shape will give the best match to the tumor appearance in the CT images. Click the Peak button (it's located near the upper left of the window).
Creating a standard tumor will always center the tumor apex.
Set the cursor to drag-apex mode (in the toolbar controls along the top of the window) and then reposition the tumor apex marker over the apex of the button shaped mass as illustrated.

In the Planar Dosimetry window:

Adjust the window layout for two panes side-by-side.
In this layout, the meridian plane will always be on the left and the coronal plane on the right. The window's controls affect the currently active pane (except for the rotation controls which are pane independent). To select the active pane, click the cursor in the pane. The active pane is framed by a thin black box and its lower right corner is filled in black. In this example the meridian (left) pane is active.
Optionally set the pane size to about 400x400 pixels. This can be done by dragging the bottom-right corner of the window or by using the window size control at the lower left.
Activate the left (meridian) pane (by clicking in it) and overlay the tumor-meridian image by clicking the T-Mer control in the Overlay controls group along the right side of the window.
Activate the right (coronal) pane (by clicking in it) and overlay the tumor-coronal image by clicking the T-Cor control in the Overlay controls group along the right side of the window.
Use the meridian rotation controls to rotate the meridian plane to match the tumor-meridian image. The projection of the meridian plane onto the coronal plane is a pale dashed line in the right (coronal) pane of the window. The dashed line should overlay the purple axis of the OsiriX tumor-coronal reconstruction in the right pane.
Use the coronal translation controls to translate the coronal plane to match the location of the tumor-coronal image. The projection of the coronal plane onto the meridian plane is a pale dashed line in the left (meridian) pane of the window. The dashed line should overlay the blue axis of the OsiriX tumor-meridian reconstruction in the left pane.

Return to the Retinal Diagram window and, if necessary, fine-tune the tumor shape, location and apex so as to overlay the tumor as seen in the meridian and coronal planes.

Select a plaque

In the Plaque Loading window

From the Plaque menu select Plaque Files.

From the Plaque Files menu select the EP930P file.

The EP930P is a large diameter 2nd generation EP plaque. The 'NP' at the end of the file name indicates that the plaque is notched and the file includes an embedded picture of the face of the plaque.

The EP930P plaque was selected because:

The shape and size are a good physical and dosimetric fit for this large, tall tumor.
The collimating slots for the radionuclide sources create a fairly steep dose gradient outside the tumor perimeter and help reduce scleral hotspots near the center of the plaque.

Position the plaque under the tumor

In the Retinal Diagram window:

You can manually drag and rotate a plaque on the diagram by setting the cursor to drag-plaque mode.
Click within the projection of the plaque perimeter on the retina to drag. The control and command keys rotate the plaque while dragging.
Click the Center button in the Plaque controls group
to automatically center the plaque under the tumor base and rotate the plaque so as to balance the suture eyelets at equal distances from the limbus. Balancing the eyelets is not required, but it does slightly simplify surgical placement. Drag the plaque slightly anterior to better fit the notch to the nerve sheath.
The small arrows at the corners of the rotation control rotate the plaque CW and CCW in 1 or 90 degree increments.
Rotate the plaque CCW to achieve a symmetric fit of the notch to the nerve as illustrated.
Set the planar Planar Dosimetry window to two pane side-by-side display. Activate the meridian plane by clicking in the pane. Use the overlay controls to overlay the merdian plane on the T-Meridian image. Activate the coronal pane by clicking in it and then overlay the coronal plane on the T-Coronal image.
In the Retinal Diagram window set the cursor to drag-apex mode.
Click within the apex icon and drag the tumor apex until the tumor shape matches the MPR images in the planar dosimetry window.
In the Plaque Offset Diagram window tilt the plaque 2 degrees about its Y axis to better simulate its position after being sutured to the eye which is slightly oblate anteriorly.

Centered, eyelets balanced, tumor apex adjusted, plaque tilted anteriorly.

Enter prescription

In the Prescription window we will set the prescription (Rx) dose, the Rx point, dose calculation modifiers, and the implant and removal dates and times.
Note: subsequent planning activities are simplified by establishing the Rx at this stage of the planning process, but the Rx can be revised at any time.

When the EP930P plaque file was opened, the dose calculation modifiers in the Prescription window's toolbar were automatically set to:
ModifiersEP

Linear, anisotropic source
No silicone seed carrier
Gold flourescence corrections enabled
No air scatter correction
No shell collimation (Note: shell collimation is redundant for Eye Physics plaques such as the EP930 where virtually all collimation occurs at the slot edges close to the seed rather than at the perimeter of the plaque shell. In this case, disabling the shell collimation modifier accelerates the collimation ray tracing computation.)
Slotted collimation enabled
Do NOT change these modifier settings until and unless you are VERY familiar with PS.

For this tutorial, we will begin with a Rx of 85 Gy to the tumor apex to be delivered in 168 hours (1 week) with the implant scheduled for 10 AM on August 20, 2014.

Set the Rx units to Gy.
Set the Rx dose to 85 Gy..
In the insertion controls group set the implant date and time to 10AM on Aug. 20, 2014.
In the removal controls group click the 1 Week button.

Notes:

The insertion and removal calendar buttons open the Calendar dialog where you can set date and time with an expanded user interface.
The initial state of the 'P1 Central AXis table' is zero because the plaque is currently empty.
The background of the 'Rx point' field is red because the Rx has not been satisfied.
The background of the 'time' field is green because the implant duration is within the bounds that were set in PS preferences. Implant durations between 4 and 7 days (96 to 168 hours) are typical.

Create a new radionuclide inventory entry

From the Plaque window click the Source button to open the radionuclide inventory window.
To create a new entry in the inventory database click the Show only radio button to enable physics model selection.
Select a seed physics model from the menu. In this example model IAI-125A (IsoAid) has been selected. This physics model is designed for source strength to be entered in units of mCi as described in the Physics Dose Constants section.
Click the New button to create a new inventory entry.
The new entry will automatically be selected (highlighted in blue in the scrollview). It will inherit the implant date and time from the current prescription as its calibration, will be named for the current patient and will contain the number of sources in the currently active plaque (plaque #1 was earlier selected as the currently the active plaque). The source strength will be initialized to 1.0 (either mCi or U depending upon the physics settings for the model seed selected).
To select a different inventory with which to load the plaque, simply click in the list.
Click the Edit button to review or change the selected inventory entry parameters.

Load sources into the plaque

Organize your windows so the Plaque window and the Retinal Diagram window are both visible alongside one another.

In the Plaque window click the Load button to fill the plaque with the 30 sources from the currently selected radionuclide inventory (that we created in the previous step).

Note: it is often faster to fully load a plaque and then delete a few unwanted seeds than it is to load a large number of seeds one at a time.
Click the Labels button to display the source strength.
Set the Plaque window cursor to load slot mode and then remove the 9 anterior-most seeds from the plaque by clicking on them so that the seed pattern matches the shape of the tumor as seen in the retina window.

In the Retinal Diagram, the source placeholders change from brown to the color of the inventory sources (e.g. cyan) to indicate that they are occupied.

Calculate source strength

1. In the Prescription (Rx) window

Earlier we set the prescription (Rx) to deliver 85 Gy to the apex of the tumor in 168 hours.
Because this plaque is asymmetrically loaded and not centered under the tumor apex, the central axis of the plaque will not be a good representation of dose to the tumor and underlying structures. The tumor axis will be a better choice. Change the axial dose table from plaque axis to tumor axis by clicking the Customize button at the bottom of the Prescription window. In the Axis controls group of the table customization sheet click the Tumor radio button and then the OK button to exit the sheet.

The 21 sources in the plaque are currently all 1.00 mCi (at the time of implant) because that is how we initialized them when we created their inventory.
The state of the 'Tumor 1 AXis table' reflects the current plaque loading. The dose to the Rx point (tumor apex) of 56.309 Gy is less than the Rx of 85 Gy. The background color is red indicating that the Rx has NOT been fulfilled.
Click the Implant Calculator button.

to open the Implant Calculator window.

2. In the Implant Calculator window

Click the Calc. Sources button. This will rescale the source strengths in the plaque to deliver the prescription of 85 Gy to the tumor apex in 168 hours.
The Prescription (Rx) and Plaque Loading windows will update to reflect the revised source strengths of 1.510 mCi per source.

The 'P1 Central AXis table' now lists the dose at the Rx point (tumor #1 apex at 5.5 mm) as 85 Gy and the background color has changed from red to green indicating the Rx has been fulfilled.

The sources in the plaque are now 1.51 mCi at the time of implant.

Choose an isodose legend

In the Isodose window

From the Select menu choose the MyFavorite.idos6 legend file.
PS6 isodose legend files bundle instructions regarding isodose values, colors, absolute vs normalized plotting, and which isodose lines and surfaces to display.
Note: the column of checkboxes simultaneously affects all 2D isodose displays; the Retinal Diagram, the meridian and coronal Planar Dosimetry surfaces, and any 2D dosimetry surfaces being rendered in the Patient Setup window.
Note: the column of radio buttons selects one or more 3D isodose surface(s) (e.g. 85 Gy) for 3D rendering in the Patient Setup window.

Calculate isodose distributions and the retina dose area histogram

From the Dosimetry menu:

Select Calculate 2D matrices. This calculates dose to the meridian and coronal planar surfaces, and to the retina.
Select Calculate RDAH. This calculates the Retina Dose Area Histogram.

Review 2D dosimetry

In the RDAH Document window

The X axis of the RDAH is plotted over the range 0..400 Gy. This range was set by clicking the Fixed button in the Histogram axes group of the Histogram document preferences pane.
The retina dose area histogram (RDAH) shows that the entire tumor base (brown line on the histogram) receives at least 85 Gy and about 99% of the tumor + 2 mm retinal margin surrounding the base (green line on the histogram) receives at least 85 Gy. 100% margin coverage of a peripapillary tumor is difficult using a single notched plaque. The 2 mm margin surrounding the tumor base is similar to the PTV concept, it accounts for microscopic tumor extension and uncertainty in surgical placement of the plaque.
The prescription to the apex and tumor base have all been satisfied.

Calculate 3D dosimetry

From the Dosimetry menu:

Select Calculate 3D Matrix.
Each plaque in PS6 maintains its own 3D dosimetry matrix.
In PS6 3D dose calculations are offloaded to a separate thread so that you can continue to perform non-dosimetric activities such as rotating the eye or entering patient ID information during the calculation. The 3D calculation progress can be followed in the status line just below the toolbar of the Patient Setup window. 3D calculations for some of the larger BEBIG Ru plaques can take awhile...

Review 3D model and dosimetry

In the Patient Setup window

Click the 3D Dose button to render the selected 3D isodose surface.
Optionally enable Mer. Dose and Ret. Dose.
Click the setup appearance button to open the appearance window window.
Experiment with the 3D model and the appearance controls to create pictures for the setup document.
For example, enable the Meridian Plane checkbox.

Review documents

The Treatment Plan is a 3 page document that summarizes the entire simulation. Page 1 provides a table of patient identifiers, date & time of treatment, some radionuclide, plaque and tumor properties, a facial picture of the plaque and a miniature retinal diagram showing tumor location.

On page 2 there is a table of point dose calculations along the central axis of the plaque (or tumor), at the prescription point, lens, macula, etc..., a thumbnail of the fundus image (no fundus image was used in this plan), and an optional picture. The default picture is a radiation safety survey form.

Page 3 of the treatment plan contains thumbnails of the CT or MR images used to model the eye and any ultrasound images used to measure or model the tumor dome.

The Loading Diagram document is a "road map" to the plaque. Everything needed to order or manufacture the seeds and assemble the plaque is in this document.

The Retinal Diagram document is a VERY useful "road map" to have in hand during surgery because it illustrates the tumor and plaque location, muscle insertion regions, lists the suture eyelet coordinates and the distance between the coordinates. Everything the surgeon needs to place the plaque at the planned position is in this document.

The optional 2nd page of the Retinal Diagram document is labeled in degrees CCW (instead of clock hours) in the manner of toric intraocular lens (IOL) axis marking tools such as the Duckworth & Kent Axis Marker model 9-841.
AxisMarker

The Isodose document prints the current meridian and coronal dosimetry planes.

The Histogram document prints the Retina Dose Area Histogram (RDAH). The RDAH is a metric for comparing competetive treatment plan options.

The Setup document prints the contents of the 3D Patient Setup window.

The QA document prints a table containing all of the information needed to manually duplicate Plaque Simulator's simplified (isotropic point source in water) QA check point calculation located at 6 mm on the plaque central axis.

Print documents

The Print Group button in the toolbar of the Document Preview window prints the group of documents selected by the Document group checkboxes to either paper or to a .pdf file.

To print to a .pdf file click the PDF button in the OSX printing sheet.
Select Save as PDF... from the menu.
To send a multipage .pdf print file by email you may need to create an encrypted version to satisfy HIPAA regulations and you may also need to limit the file size to under 10 MB by compressing the embedded images. Both of these tasks can be accomplished using the OSX Preview application and a custom filter. Contact Eye Physics for details.