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When should systematic patient positioning errors in radiotherapy be corrected?

Thomas Bortfeld1, Marcel van Herk, Steve B Jiang

  • 1Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA. tbortfeld@partners.org

Physics in Medicine and Biology
|December 28, 2002
PubMed
Summary
This summary is machine-generated.

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Optimizing radiotherapy patient setup involves a "no action level" protocol. This study determines the ideal correction interval (N) to minimize setup errors, finding N=4 is optimal for typical cases, with minor impact from exact N choice.

Area of Science:

  • Medical Physics
  • Radiotherapy Physics
  • Radiation Oncology

Background:

  • Patient setup errors are a significant challenge in radiotherapy.
  • Accurate patient positioning is crucial for effective radiation delivery.
  • The 'no action level' protocol aims to reduce setup errors through periodic corrections.

Purpose of the Study:

  • To determine the optimal number of fractions (N) for implementing the 'no action level' protocol.
  • To minimize the total quadratic patient setup error in radiotherapy treatments.
  • To derive a formula for N based on error components and measurement uncertainty.

Main Methods:

  • Minimizing the expectation value of the total quadratic setup error.
  • Developing a formula for N based on execution error, preparation error, and measurement error.

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  • Assuming no time trend in patient setup accuracy.

    • Main Results:

    • A simple formula for the optimal N was derived, proportional to the square root of total fractions and the ratio of execution to preparation error.
    • A formula accounting for non-negligible measurement error was also provided.
    • For typical scenarios, the optimal N was found to be 4, with a shallow optimum indicating N choice is uncritical.

    Conclusions:

    • The 'no action level' protocol can be optimized by selecting an appropriate N.
    • The derived formula provides a method for determining N to reduce radiotherapy setup errors.
    • The optimal N value of 4 offers a practical guideline for clinical implementation, with flexibility in exact selection.