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Related Experiment Videos

A leaf sequencing algorithm to enlarge treatment field length in IMRT.

Ping Xia1, Andrew B Hwang, Lynn J Verhey

  • 1The Department of Radiation Oncology, University of California at San Francisco, Comprehensive Cancer Center, 94143-1708, USA. xia@radonc17.ucsf.edu

Medical Physics
|July 4, 2002
PubMed
Summary

A new leaf sequencing algorithm expands the usable field length for intensity-modulated radiation therapy (IMRT) by overcoming jaw overtravel limits. This advancement enables larger treatment fields in step-and-shoot IMRT delivery without compromising safety.

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Radiotherapy Technology

Background:

  • Intensity-modulated radiation therapy (IMRT) often has a reduced maximum usable field size compared to conventional treatments due to multi-leaf collimator (MLC) leaf and jaw overtravel constraints.
  • These limitations restrict the achievable treatment field dimensions, potentially impacting treatment planning and delivery efficiency.

Purpose of the Study:

  • To develop and evaluate a novel leaf sequencing algorithm for step-and-shoot IMRT.
  • To overcome the limitations imposed by jaw overtravel constraints and maximize the usable IMRT field length.
  • To assess the algorithm's performance in delivering complex intensity patterns and clinical treatment plans.

Main Methods:

  • A new leaf sequencing algorithm was developed, modifying a previous areal algorithm to incorporate jaw position constraints.

Related Experiment Videos

  • The algorithm connects intensity elements outside jaw overtravel limits with those inside, using methods like intensity level modification and alternating leaf-sequencing direction.
  • The algorithm was tested with 1000 random intensity patterns, 800 patterns with high intensity outside limits, and three undeliverable clinical plans.

    • Main Results:

    • The new algorithm successfully delivered 100% of tested intensity patterns, including those previously undeliverable.
    • It enabled the usable IMRT field length to be extended from 21 cm to 27 cm.
    • The average number of segments remained comparable to the existing areal algorithm for random patterns, but significantly increased for challenging patterns where the areal algorithm failed.

    Conclusions:

    • The developed leaf sequencing algorithm effectively addresses jaw overtravel limitations in MLC-based IMRT.
    • This approach significantly enhances the usable field size for step-and-shoot IMRT delivery on commercial linear accelerators.
    • The algorithm offers a viable solution for delivering larger and more complex IMRT treatment fields.