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Related Experiment Videos

Linear accelerator output variations and their consequences for megavoltage imaging

M Partridge1, P M Evans, M A Mosleh-Shirazi

  • 1Joint Department of Physics, Institute of Cancer Research, Royal Marsden NHS Trust, Sutton, United Kingdom. mikep@icr.ac.uk

Medical Physics
|September 2, 1998
PubMed
Summary

Radiation output fluctuations in linear accelerators are measurable and can cause artifacts in megavoltage imaging. However, these variations are within specifications and do not impact patient dose during treatment.

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Imaging Technology

Background:

  • Linear accelerators (linacs) are critical in radiation therapy.
  • Accurate radiation output is essential for precise dose delivery.
  • Megavoltage imaging techniques are increasingly used for quality assurance and verification.

Purpose of the Study:

  • To experimentally investigate radiation output intensity fluctuations in a Philips SL25 linear accelerator.
  • To assess the impact of these fluctuations on megavoltage imaging applications.
  • To evaluate the utility of megavoltage imaging for accelerator quality assurance.

Main Methods:

  • Measurements of radiation output intensity were performed using an electronic portal imaging device.
  • Fluctuations were quantified during different operational phases, including beam stabilization and gantry rotation.

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  • The effects of fluctuations on portal imaging, transit dosimetry, and megavoltage computed tomography (MVCT) were analyzed.

    • Main Results:

    • Output fluctuations of +/- 0.7% (1 SD) per pulse were observed after accounting for noise.
    • Significant fluctuations occurred during beam stabilization (15%), normal operation (4.5%), and gantry rotation (9%).
    • These fluctuations can cause image artifacts in portal imaging and errors in transit dosimetry, and ring artifacts in MVCT reconstructions.

    Conclusions:

    • Megavoltage imaging is a powerful tool for accelerator quality assurance and treatment verification.
    • Observed output fluctuations are within manufacturer specifications and do not compromise total delivered dose.
    • Understanding and quantifying these fluctuations are crucial for accurate interpretation of megavoltage imaging data.