Click here to


Are you sure ?

Yes, do it No, cancel

A Data Driven Retrospective Analysis of Couch Tolerances On Patients Positioned Using the Elekta Hexapod

R George*, N Kirby , D Saenz , University of Texas Health Science at San Antonio, San Antonio, TX


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: After patients are positioned using the Elekta Hexapod, the couch coordinates are compared to coordinates from the patient’s first fraction and unless they are within a tolerance table, require manual override from the therapists to treat. If tolerances are too small, therapists will need to frequently override, which could eventually lead to them unintentionally overriding something else. The purpose of this study was to provide clinically feasible tolerance levels that reduced the total number of overrides.

Methods: Couch coordinates relating to patient positioning information from 30 different patients, including a total of 833 treatment fractions, were acquired and analyzed. Standard deviations of the vertical, lateral, and longitudinal couch parameters were calculated, which were then used to devise tolerances such that the total number of overrides was reduced. The initial number of overrides at a 3 cm uniform vertical, lateral and longitudinal tolerance was evaluated and then iteratively the tolerances were varied (increased) such that there was a lower number of overrides. The initial goal was to reduce the number of total overrides to 5%.

Results: Initial data showed that couch parameters were being overridden 48% of the time. A uniform tolerance of 7 cm was required to achieve the 5% goal. Alternatively, a tolerance table of 7 cm for vertical, 6 cm for lateral, and 3 cm for longitudinal only yielded a 9% override

Conclusion: Trying to achieve a 5% override percentage required larger than desired tolerances. The asymmetric tolerances achieved only a 9% override frequency, while greatly reducing the volume allowed by the uniform 7 cm tolerance table.


Cone-beam CT


TH- Dataset analysis/biomathematics: biostatistics and clinical trial design

Contact Email