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Related Concept Videos

Adjusting a Traverse01:12

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In the site survey of a four-sided traverse, internal angles are essential to ensure geometric accuracy. The survey revealed that the sum of the measured internal angles was 359 degrees and 48 minutes, which is 12 minutes less than the expected 360 degrees. This discrepancy signals an error likely arising from measurement inaccuracies during the fieldwork.To rectify this error, the adjustment process involved distributing the 12-minute shortfall equally across the four internal angles. By...
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Implication of CT table sag on geometrical accuracy during virtual simulation.

John R Zullo1, Rajat Kudchadker, Richard Wu

  • 1Radiation Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. jrzullo@mdanderson.org

Medical Dosimetry : Official Journal of the American Association of Medical Dosimetrists
|November 6, 2007
PubMed
Summary

CT scanner table sag can cause significant patient positioning errors during radiation therapy simulation. Measuring and correcting for this mechanical limitation is crucial for accurate radiation oncology treatment delivery.

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Area of Science:

  • Medical Physics
  • Radiological Imaging
  • Radiation Oncology

Background:

  • Computed tomography (CT) scanners are essential for radiation oncology treatment simulation.
  • Accurate patient positioning during simulation is critical to minimize radiation dose to normal tissues.
  • CT scanner table sag, a mechanical limitation, can compromise patient positioning accuracy.

Purpose of the Study:

  • To quantify the extent of vertical displacement (sag) in various CT scanner tables under clinical weight loads.
  • To compare table sag across different CT scanner models and manufacturers.
  • To highlight the implications of table sag on radiation therapy simulation accuracy.

Main Methods:

  • Clinically representative weight loads were applied to different CT scanner tables.
  • Table sag was measured at various extension positions from the table base.
  • Measurements were conducted on tables from multiple manufacturers and models.

Main Results:

  • Table sag varied significantly, ranging from approximately 0.7 mm to 6.6 mm.
  • Sag differences were observed not only between manufacturers but also between tables of the same model.
  • The degree of sag was dependent on table extension and applied weight.

Conclusions:

  • CT scanner table sag is a prevalent issue that can lead to isocenter localization and patient positioning errors.
  • Implementing scanner-based laser offset corrections is recommended for patient virtual simulation.
  • Regular measurement of table sag under load during CT simulator commissioning is essential.