A method to predict patient-specific table coordinates for quality assurance in external beam radiation therapy

Daniel L. Saenz, Nestor Rodrigo Astorga, Neil Kirby, Mohamad Fakhreddine, Karl Rasmussen, Sotirios Stathakis, Niko Papanikolaou

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Purpose: While external beam radiotherapy treatment planning determines nearly every mechanical and dosimetric parameter of the linear accelerator (LINAC), the table coordinates in all three dimensions are generally unknown until initial patient setup at the LINAC. Knowing these parameters in advance could help verify the direction of patient shifts and prevent wrong-site errors. This study aims to determine the feasibility and accuracy of table coordinate prediction for indexed immobilization devices. Methods: A total of 303 table coordinates were predicted for patients on Varian and Elekta linear accelerators with immobilization devices including Orfit mask with baseplate, wingboard, breastboard and BodyFix. Predictions were made for all three spatial dimensions except for Body Fix setups due to the lack of a radiographically apparent indexing-related landmark. Coordinates were predicted by measuring baseline table coordinates in all dimensions at specified landmark positions. Results: Predictions were accurate within 2 cm for 86% of coordinates (71% within 1 cm). Table coordinates were predicted most accurately for head and neck patients with a base plate and the most difficult prediction was in the lateral direction for breastboard patients. Conclusions: With proper indexing, table coordinates can be predicted with reasonable accuracy. The data suggest an action of level of 2 cm with certain exceptions for specific immobilization devices and directions.

Original languageEnglish (US)
Pages (from-to)625-631
Number of pages7
JournalJournal of Applied Clinical Medical Physics
Issue number5
StatePublished - Sep 2018


  • external beam radiotherapy
  • patient safety
  • quality assurance

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Radiology Nuclear Medicine and imaging


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