Table 1.

Positioning uncertainty model for the SRT/SRS treatment with the frameless ExacTrac Brainlab system.

${\mathrm{\Delta }}_{\mathrm{M}}$	Mask systematic uncertainty	Mean of shifts from the XC data for each patient
${\sigma }_S$	Setup random uncertainty	Standard deviation of the XC data for each patients
${\mathrm{\Delta }}_{\mathrm{F}}$	IR frame systematic uncertainty	Mean of the XC data for all patients
${\mathrm{\Delta }}_{\mathrm{L}}$	Localizer systematic uncertainty	Mean of XV data
${\sigma }_{\text{XR}}$	X‐ray image quality and image registration algorithm	Standard deviation of means of XV data
${\mathrm{\Delta }}_{\mathrm{C}}$	Couch sagging	Phantom study with various couch angles and weights
${\mathrm{\Delta }}_{{\text{ISO}}_{\text{MV}}}$	Radiation isocenter	Machine Winston‐Lutz QA data
${\mathrm{\Delta }}_{{\text{ISO}}_{\text{kV}}}$	Imaging isocenter	Machine Winston‐Lutz QA data
${\mathrm{\Delta }}_{{\text{ISO}}_{\text{IR}}}$	IR optical imaging isocenter	Machine Winston‐Lutz QA data