What is the role of portal imaging in image-guided radiotherapy (IGRT) for the treatment of prostate cancer?

Updated: Aug 17, 2020
  • Author: Isamettin Andrew Aral, MD, MS; Chief Editor: Edward David Kim, MD, FACS  more...
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Early attempts to identify the location of the prostate before each daily treatment resulted in suboptimal target identification. A commonly used approach includes obtaining daily port films before therapy. This strategy provides limited value to the image guidance process.

Megavoltage imaging (portal imaging) of pelvic anatomy provides reasonable confidence that the patient’s fixed pelvic structures (bones) are in the same position as that observed during CT simulation; however, it does not provide information regarding the prostate’s position in reference to these bony structures. Nevertheless, it remains an accepted method for approximating target localization in the absence of more sophisticated imaging.

An evolution from this simple form of therapy occurred with the implantation of radiopaque fiducial markers into the prostatic target, which allows a soft tissue target to be localized with portal imaging technology. Imaging of the implanted fiducial markers can be obtained with either megavoltage imaging (ie, port films) or kilovoltage imaging. In the latter setting, low-energy x-ray equipment and detectors are mounted on the treatment machine.

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