What is simulation prior to conventional external beam radiotherapy (EBRT)?

Updated: Aug 17, 2020
  • Author: Isamettin Andrew Aral, MD, MS; Chief Editor: Edward David Kim, MD, FACS  more...
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Simulation is a process during which the patient is prepared for therapy. The patient is placed in the treatment position, and the radiation field or fields are marked. Simulation for conventional EBRT relies on fluoroscopy and plain radiography. These less sophisticated techniques are generally considered acceptable because the treatment borders (margins) are more inclusive than those used in 3-dimensional conformal therapy (3D-CRT) and intensity-modulated radiotherapy (IMRT). CT-based simulation is increasingly popular for 3D-CRT and IMRT.

Localization of the target and the adjacent normal tissue is critical in the planning of both conventional therapy and 3-dimensional treatment. For conventional therapy, the patient is placed in the supine position. Radiographs of the anteroposterior (AP), posteroanterior (PA), left lateral, and right lateral fields are obtained. Typically, treatment fields are shaped with corner blocks only, and borders are based on bony landmarks.

Normal tissue is delineated by using radiopaque contrast materials in the rectum and bladder. Retrograde urethrography is performed to establish the inferior margin of the prostate. Blocking of normal structures is indicated in most cases; however, custom blocking is not always necessary.

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