CT Simulation

     CT simulation features a state of the art CT scanner with a localization package, patient marking system and a virtual simulator capable of producing real-time digitally reconstructed radiographs (DRRs).  In its most sophisticated application, CT simulation is a process that allows the clinician to perform a virtual simulation on a CT dataset obtained for an individual patient.  The simulation is based entirely on the patient's unique anatomy.  It is a volumetric simulation taking into account every curve and angle of the individual. There is complete information available regarding the size, shape, location, and position of the patient’s anatomy.  The tumor can be accurately outlined and the beam(s) of radiation can be set to the center of this volume. It is this focus on patient uniqueness that establishes CT simulation as the necessary tool for conformal radiation therapy and allows for minimization of normal tissue volume treated.  

     CT simulation allows for display of the patient’s anatomy in the three conventional axes of axial, sagittal, and coronal, but it also allows for enhanced visualization of anatomy along the beam axis. In addition, through the use of multimodality imaging packages the primary CT dataset can be linked to a MR, PET, SPECT, or secondary CT scan to achieve an even higher level of visualization.  With CT simulation the link to precise treatment planning becomes a smooth transition.  

Emory's CT Simulation System

     There are three main components to Emory's CT simulator system: the GE Lightspeed CT scanner, an integrated laser system for patient marking and localization, and the GE AdvantageSim virtual simulator capable of producing real-time digitally reconstructed radiographs (DRRs).  The system offers high-resolution imaging and short examination time for the full range of oncologic procedures including volumetric localization, simulation and verification for conformal, high-precision and stereotactic radiotherapy planning. Click here to see the components of the CT simulation system.

     With these components a complete 3-D dataset can be obtained, the tumor and other structures delineated, a radiation anatomical target determined, the patient marked, fields simulated and shaped, digitally reconstructed radiographs printed, and radiation treatment fields on the virtual patient’s skin can be seen. This method is superior to conventional simulation using an X-ray tube system. Click here to see the four-step process of Emory CT simulation.

Digitally Reconstructed Radiographs (DRRs)

     DRRs are the next generation of radiation therapy planning images which provide radically improved visualization of soft tissue and bony anatomy.  DRRs mimic images produced by an X-ray simulator by tracing rays through a CT dataset. The superior visualization of DRRs is achieved through the use of an image compositing algorithm which provides for the definition of up to four separate tissue classes. Each class is assigned a separate opacity which modulates the attenuation of rays through the CT-based patient anatomic model. DRRs provide anatomic detail in a projection geometry that cannot be achieved in a conventional simulation setting.

Examples of CT Simulation

     The first picture below illustrates CT simulation of the breast.  The second shows the radiation fields and internal structures for CT simulation of the prostate.