Medical Physicist's Notes · TruPose™
Halcyon, Ethos and Radixact ship with translation-only or single-rotation couches. The SGRT camera reports the residual pitch / roll / yaw delta in degrees, in real time — but without a robotic couch you can read the delta and not act on it. The peer-reviewed dose-coverage cost of that gap is up to 5 % PTV loss (Dhabaan 2012); TruPose closes it with three colour-coded knobs at the base of the neck.
Where TruPose plugs into the existing setup chain on a bore-class linac. The SGRT delta is the trigger; the three knobs are the actuator; the couch translations are unchanged.
CBCT alignment
Standard kV-CBCT registration to the planning CT — translations and (where the couch supports it) the single rotation are applied automatically. This is the 3DoF / 4DoF starting point on Halcyon, Ethos and Radixact.
TruPose
TruPose is on the couch; no action yet.
SGRT surface match
SGRT camera locks onto the patient surface and reports residual pitch / roll / yaw deltas in degrees. On a bore-class linac without a robotic couch, these deltas are visible but un-actionable by the couch alone.
TruPose
TruPose is on the couch; deltas displayed.
TruPose rotational zero
Therapist reads the SGRT delta on the monitor, turns the matching colour-coded knob (pitch / roll / yaw) until the SGRT reads zero. ±4.0° on each axis — more than four times the published worst-case residual yaw (~1°, Dhabaan 2012).
TruPose
Three knobs turned; SGRT delta zeroed.
SGRT confirm + beam-on
SGRT confirms the surface match held during the knob adjustments. Intra-fraction motion is monitored continuously by the SGRT loop; the published correction-active envelope (Liu 2015) is 98.5 % of fraction time inside 0.4 mm / 0.2°.
TruPose
Locked. Beam-on.
SGRT-rotational-delta workflow framework: AAPM TG-147 (Willoughby 2012); 4DoF-vs-6DoF dose comparison: Dhabaan A et al., J Appl Clin Med Phys 13(6):3850 (2012).
Four findings from the peer-reviewed 6DoF positioning literature. None of them name TruPose — together they describe the residual-error envelope and dosimetric cost that a bore-class 6DoF setup has to clear.
Dhabaan 2012 — 4DoF-only PTV-coverage loss
PMC5718543When pitch and roll corrections were omitted (4DoF only), PTV-coverage loss reached 5 % depending on target geometry. 28 patients / 38 targets / 63 fractions of frameless cranial SRS.
Dhabaan 2012 — residual rotational error after 6DoF
PMC5718543Mean residual rotational error after 6DoF correction was < 0.3° on any axis; max observed yaw residual was ~1°. Max translational residual was 1.2 mm in the longitudinal direction.
Liu 2015 — time within tolerance, corrected vs uncorrected
PMC4433479With rotational correction active, treatment time within 0.4 mm / 0.2° was 98.5 % across 20 experiments in 7 volunteers. Without correction, the same tolerance was only held for 10.7 % of treatment time.
Wilbert 2010 — first clinical 6DoF positioning
PMC2890022Semi-robotic 6DoF positioning achieved 1.6 ± 0.8 mm clinical inter-fraction repositioning (3D vector, 7 patients) and 0.6 ± 0.4 mm intra-fraction rigidity — the first published bore-class 6DoF envelope.
±4.0° per axis — over four times the published worst-case residual.
Dhabaan 2012 measured the maximum residual yaw rotation at ~1° after 6DoF correction across 63 fractions. TruPose's per-axis range gives the therapist room to clear the worst case without re-imaging.
Source: Dhabaan A et al., J Appl Clin Med Phys 13(6):3850 (2012). PMC5718543.
Scope of this page
TruPose is not named in Dhabaan 2012, Wilbert 2010, Liu 2015 or TG-147. Those papers and the practice guideline define the bore-class 6DoF positioning envelope that any rotational-correction device must serve, and we cite that envelope. Treat this page as a fit-to-evidence argument for a manual rotational adjuster, not a head-to-head device comparison.
Sources cited on this page
TruPose™ Head Adjuster
Sibling posts in the TruPose family.