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Related Experiment Videos

Intensity-modulated radiation therapy: overlapping co-axial modulated fields.

P Metcalfe1, P Tangboonduangjit, P White

  • 1Centre for Medical Radiation Physics, University of Wollongong, NSW, Australia.

Physics in Medicine and Biology
|September 28, 2004
PubMed
Summary

Asymmetric fields in radiation therapy can treat wider head and neck tumors. However, discrepancies exist between treatment planning systems and actual dose delivery, requiring improved modeling for accuracy.

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Area of Science:

  • Medical Physics
  • Radiation Oncology

Background:

  • The Varian multi-leaf collimator (MLC) has limitations in leaf extension, posing challenges for treating large head and neck target volumes.
  • Standard width-modulated fields may not provide adequate dose coverage for these wide targets.

Purpose of the Study:

  • To evaluate the accuracy of dose calculations for asymmetric co-axial overlapping fields used to treat wide head and neck tumors.
  • To compare dose distributions predicted by the Pinnacle radiotherapy treatment planning system with those measured using film and electronic portal imaging.

Main Methods:

  • Asymmetric co-axial overlapping fields were implemented to address MLC limitations.
  • Planar dose maps from the Pinnacle treatment planning system were compared with maps reconstructed from radiographic film and electronic portal images.

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  • Linear profiles were analyzed to identify discrepancies between calculated and delivered dose distributions.

    • Main Results:

    • Film and portal images revealed small leaf-jaw matchlines at field overlap borders, which were not predicted by the treatment planning system.
    • Dose differences between reconstructed images and the planning system were approximately 2.5 cGy at d(max) in modulated fields.
    • Observed discrepancies suggest limitations in the current treatment planning system's modeling capabilities.

    Conclusions:

    • Asymmetric fields offer a viable solution for dose coverage in head and neck radiotherapy despite MLC constraints.
    • Discrepancies between calculated and delivered doses highlight the need for enhanced modeling in treatment planning systems.
    • Improved round end leaf modeling and finer dose calculation grids could minimize these discrepancies for more accurate radiation delivery.