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 an equatorially centered tumor is so tall (9 mm) that its dome obscures a portion of the posterior hemisphere when photographed leading to potential misinterpretation of the fundus photo. Correct 3D modeling of the tumor base requires fusion with planar CT reconstructions and dimensional confirmation using ultrasound measurements.
In this wide angle, single center fundus photo, it at first appears that the posterior edge of this 9 mm tall equatorially centered tumor comes close to the fovea.
What we are actually seeing in the fundus photo is not the tumor base. The single viewpoint of this wide angle fundus camera directly in front of the eye results in the apex of this tall dome shaped tumor obscuring a portion of the posterior of the eye. Note that eyelashes are also obscuring the fundus photo in a similar manner.
Depending on the location and shape of tall tumors, a fundus collage using a camera with a narrower field of view and multiple viewpoints may provide a slightly better view of the tumor base.
The actual tumor base projected onto the retinal diagram is illustrated here. The model was created using the standard tumor sheet with dimensions based on the ultrasound measurements and location derived from the CT reconstructions. The 3D model is easily verified by overlaying the model's meridian and coronal dosimetry planes onto the tumor-meridian and tumor-coronal CT reconstructions and displaying the meridian plane in the 3D Setup window.
In the Plaque Loading window
From the Plaque menu select Plaque Files.
From the Plaque Files menu select the EP2342P file.
The EP2342P is a large diameter 2nd generation EP plaque. The 'P' at the end of the file name indicates that the file includes an embedded picture of the face of the plaque.
The EP2342P plaque was selected because:
In the Retinal Diagram window:
Centered, eyelets balanced, tumor apex adjusted, plaque tilted anteriorly.
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:
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 8 AM on August 29, 2014.
Notes:
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 9.24 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 1.39 mCi at the time of implant.
In the Isodose window
From the Dosimetry menu:
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.