The tutorial involves a very large tumor that extends from the ora to the optic disc. This case was selected for the tutorial because it illustrates treatment planning using primarily CT and ultrasound. You will gain experience:
Plaque Simulator fuses images and measurements derived from CT (or MR), fundus camera photographs and ultrasound studies to build a three dimensional model of each patient's eye and tumor. A simulation session begins by preparing these images for import into Plaque Simulator. Note: this tutorial does not use fundus images.
Full size versions of the screen captures in this tutorial can be viewed by simply clicking on the pictures. Use the 'back' button of your browser to return to the tutorial after downloading the full size picture.
Please familiarize yourself with the basics of image based planning for eye plaques by following the links below before proceeding with this tutorial.
After the images have been prepared, they will be imported into Plaque Simulator, typically as .jpg files, and calibrated. A 3D model of the eye will be created and the tumor location and altitude entered. Please review these links before proceeding with this tutorial.
Please familiarize yourself with the Basic, Posterior and Anterior tutorials before proceeding with this tutorial.
The sample images used in this tutorial can be found in Plaque Simulator Patients/(Tutorials)/PS6/Large Tutorial which should have been installed in the Documents folder of the logged-in PS user as part of your original installation or update of Plaque Simulator.
From the File menu:
From the Plan menu:
If the Image window is not visible or frontmost, make it the frontmost window by clicking the cursor in its window or by selecting Images from the Window menu (in the menu bar at the top of the screen).
In the Image window
Hold down the Option button on the keyboard while clicking the Axial button in the MPR controls group to load multiple images.
Drag the ruler tool to measure the tumor height (e.g. 11.42 mm) and the circumferential base chord dimension (e.g. 17.5 mm) as it appears in the tumor-coronal plane.
Drag the ruler tool to measure the tumor height (e.g. 11.43 mm) and the radial (meridian) base dimension (e.g. 17.53 mm) in the meridian plane. Note that the tumor height measurement depends upon the location of the tumor apex, the angle at which the imaging plane passes through the tumor and the curvature of the sclera below the tumor. As a result, the meridian plane is generally the most reliable image for measuring the tumor height.
Drag the ruler tool to measure the tumor height (e.g. 11.4 mm) and the nominal base dimension (e.g. 17.5 mm). The tumor height measurement is consistent with the CT measurement, the tumor base may be larger or retinal detachment.
In the Retinal Diagram window
The objective of this step is to verify that the tumor location, shape, size and apex as created in the Retinal Diagram window is consistant with the tumor as it appears in the MPR images. Cross-sections of the tumor in the meridian and coronal dosimetry planes are tinted brown. The brown tinted regions should closely overlay the tumor in the MPR images. If the model and MPR do not overlay, further refinement of the model may be necessary.
In the Planar Dosimetry window
The Standard Tumor sheet always returns the tumor apex to a point directly above the geometric center of the elliptical tumor base. Observe that the apex of this tumor needs to be shifted anteriorly to better model the tumor and the measurements. Set the Retinal Diagram window cursor mode to drag apex in the toolbar and then nudge the tumor a bit anteriorly along the meridian plane projection until the tumor matches in the Planar Dosimetry window.
After moving the tumor apex slightly anterior the standard model and the CT images match nicely.
In the Plaque Loading window
From the Plaque menu select Plaque Files.
From the Plaque Files menu select the EP2340NP file.
The EP2340NP 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 EP2340NP plaque was selected because:
In the Retinal Diagram window:
Auto-centered, eyelets balanced
In the planar dosimetry window the anterior edge of the plaque lifts slightly from the sclera due to the oblate curvature of the anterior eye but it is such a small amount that we will ignore it for this tutorial. You could optionally tilt the plaque a degree around its Y axis.
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 EP2340NP plaque file was opened, the dose calculation modifiers in the Prescription window's toolbar were automatically set to:
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 July 2, 2014.
Organize your windows so the Plaque window and the Retinal Diagram window are both visible alongside one another.
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.
1. In the Prescription (Rx) window
2. In the Implant Calculator window
The 'P1 Central AXis table' now lists the dose at the Rx point (tumor #1 apex at 11.4 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 2.03 mCi at the time of implant.
In the Isodose window
From the Dosimetry menu:
The EP2340NP plaque is very broad and the fast slot-only collimation ray-tracing approximation does not completely account for shallow angle radiation that crosses the plaque just above its face. To illustrate this, in the left column, the dose calculation uses the fast approximation that just ray-traces the immediate slot and ignores the shell. In the right column is the slower, complete ray-trace collimation calculation that also includes the shell. Indicated times also include calculation of the retinal surface.
On the right is a composite isodose overlay of the two collimation calculations. The differences between the two versions are exemplified by the 30 and 40 Gy isodose lines outside the eye at the edge of the plaque. Within the eye the two calculations yield identical results, with a calculation time difference of 1.7 vs 26.5 secs.
This example illustrates that the fast collimation approximation for EP slotted plaques that bypasses ray-tracing the entire shell is adequate for typical treatment planning purposes. The remainder of this tutorial is based on the fast collimation approximation.
In the RDAH Document window
In the Patient Setup window
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.
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.
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.