Per-site chain · SBRT Immobilization System
The ten-component SBRT chain ships complete, but per-site the active layers differ. Lung SBRT engages the wing-board T-grip and respiratory belt; liver adds the belly bridge; pelvic adds the knee bridge; spine adds the elevation cushion. This page is the per-site build sheet and the AAPM TG-101 / RTOG margin target each workflow plans for.
Target
Peripheral lung nodule; 4D-CT-derived ITV
CTV-to-PTV margin
CTV-to-PTV 5 mm typical after 4D-CT motion management (AAPM TG-101)
Active chain configuration
Platform + T-vacuum cushion + wing-board T-grip + carbon-fibre headrest + respiratory belt
Notes: Wing-board T-grip is critical — both arms above head to clear lateral beam paths. Belly bridge typically not engaged (no compression for peripheral lung). Respiratory belt sets 4D-CT phase binning baseline.
Target
Central / hilar lung nodule with cord, oesophagus, great-vessel proximity
CTV-to-PTV margin
CTV-to-PTV 3–5 mm with DIBH; OAR-driven margin reduction
Active chain configuration
Platform + T-vacuum cushion + wing-board T-grip + headrest + respiratory belt + DIBH gating
Notes: Central lung sites need tighter motion management — typically DIBH gating instead of ITV. Belt + SGRT (if available) confirm reproducible breath-hold. The cushion locks the breath-hold posture.
Target
Liver primary or metastasis; DIBH preferred
CTV-to-PTV margin
CTV-to-PTV 5 mm with DIBH; 7 mm with 4D-CT only
Active chain configuration
Platform + T-vacuum cushion + belly bridge + wing-board T-grip + headrest + respiratory belt
Notes: Belly bridge engaged — typical SI motion drops from 15–25 mm free-breathing to 5–10 mm with compression. DIBH gate (or 4D-CT for non-DIBH-capable patients) sets the breath-hold patient shape; cushion locks it.
Target
Renal cell or adrenal metastasis; DIBH or 4D-CT
CTV-to-PTV margin
CTV-to-PTV 5 mm with DIBH or compressed 4D-CT
Active chain configuration
Platform + T-vacuum cushion + belly bridge + wing-board T-grip + headrest + respiratory belt
Notes: Same configuration as liver. Belly compression typically more effective on kidney (less diaphragmatic coupling); the chain is unchanged but the SI-motion reduction is larger.
Target
Pelvic nodal or bone SBRT; free-breathing
CTV-to-PTV margin
CTV-to-PTV 5 mm with daily CBCT verification
Active chain configuration
Platform + T-vacuum cushion + knee bridge + knee+feet cushion + headrest
Notes: Knee bridge is the dominant axis — locks femoral rotation < 2° and pelvic tilt < 3°. Cushion locks buttock and posterior pelvic shape. Wing-board T-grip and respiratory belt typically not engaged (free-breathing workflow).
Target
Vertebral SBRT; cord-sparing dose-fall-off requirement
CTV-to-PTV margin
CTV-to-PTV 1–2 mm at vertebra; 3 mm at cord (RTOG 0631 framework)
Active chain configuration
Platform + T-vacuum cushion + elevation cushion + carbon-fibre headrest + indexing bar
Notes: Spine SBRT needs sub-mm reproducibility for cord-sparing. Elevation cushion sets the spine-aligned posture; cushion locks the spine outline; indexing bar locks the platform position. Daily CBCT confirms.
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