The Mary Hillman Jennings
Radiation Oncology Center

Radiographic Simulator

The Simulator is a radiographic device that allows the radiation oncologist to map out the intended treatment volume prior to treatment delivery.

The Simulator duplicates the geometric setup of the treatment unit. This allows treatment fields that are measured on the Simulator to be reproduced accurately on the linear accelerator. The digital readouts, like field size, gantry angle, collimator angle, and table angle, are identical to those on the Linac so that any measurements and data collected during simulation can be reproduced on the treatment unit.

• Most patients start the treatment planning process in the Simulator room. For patients receiving conformal therapy, the radiation therapists construct immobilization shells out of thermoplastic or foaming agents to assist in reproducibility and accuracy during treatment. After the shell is made, the patient is radiographed to establish landmarks to be used during CT scanning.
  
  
• After the patient has the CT scan and their treatment plan has been generated, the patient is simulated using the field geometry developed from the treatment plan. Radiographs are taken of the intended treatment fields, and detailed measurements are taken for dosimetric purposes, as well as for daily set-up on the Linac.
  
  
• When the simulation is complete, the central axis and outline of the treatment port is marked on the patient. These marks help the radiation therapists line the patient up accurately for daily treatment.
  
  
• The radiation oncologist marks the position of beam-shaping devices on the radiographs so that the therapists can make lead-alloy beam blocks, or digitize the field shape into the Linac's multi-leaf collimation system.

Patients frequently require several simulations during a course of treatment to define new treatment parameters. Most often this includes a reduction in the size of the treatment port in response to the shrinking of the tumor, or to block critical structures as their tolerance dose is reached.

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