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Related Experiment Videos

Two-dimensional exit dosimetry using a liquid-filled electronic portal imaging device and a convolution model

R Boellaard1, M van Herk, H Uiterwaal

  • 1Radiotherapy Department, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Huis, Amsterdam.

Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology
|August 1, 1997
PubMed
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Electronic portal imaging device (EPID) exit dose measurements using a convolution model achieve high accuracy (1.7% SD) in clinical radiotherapy. This method offers a reliable alternative to diode dosimetry for quality control.

Area of Science:

  • Medical Physics
  • Radiotherapy Dosimetry
  • Image Analysis

Background:

  • Accurate measurement of radiation dose distribution is critical in radiotherapy.
  • Electronic Portal Imaging Devices (EPIDs) offer a potential tool for in-vivo dosimetry.
  • Developing robust methods for EPID-based dose measurement is essential for quality assurance.

Purpose of the Study:

  • To evaluate the accuracy of two-dimensional exit dose measurements using an EPID and a convolution model.
  • To assess the performance of this method across various clinical scenarios, including different beam energies, phantom types, and beam modifiers.
  • To compare EPID-derived exit doses with established dosimetry techniques.

Main Methods:

  • Exit doses were calculated from portal images acquired with a liquid-filled EPID using a convolution model.

Related Experiment Videos

  • Measurements were validated against ionization chamber data for homogeneous and inhomogeneous phantoms under various beam conditions (open, wedged, 4-18 MV).
  • Accuracy was further assessed using anthropomorphic phantoms (lung, larynx) and in vivo diode measurements in clinical patient treatments.

    • Main Results:

    • The EPID convolution model achieved high accuracy, with results within 1.2% (1 SD) of ionization chamber measurements for open beams and homogeneous phantoms.
    • Accuracy slightly decreased to 1.7% (1 SD) with wedges and inhomogeneous phantoms.
    • Agreement with diode measurements in clinical settings was within 1.1% (1 SD) for patient treatments, demonstrating clinical applicability.

    Conclusions:

    • EPID-based exit dose determination using a convolution model is accurate (1.7% SD) for most clinical radiotherapy situations.
    • This EPID dosimetry method provides a viable and powerful alternative to diode dosimetry.
    • The EPID system is a valuable tool for dosimetric quality control in high-precision radiotherapy.