Per-site build sheet · Vacuum Cushions
The cushion family covers lung, liver, kidney, spine and pelvic SBRT plus the auxiliary H&N IMRT and MR-linac transfer use cases. This page is the per-site build sheet — size + bead grade + motion-management + CTV-to-PTV margin — anchored against AAPM TG-101 / TG-178 and the RTOG SBRT protocol framework.
Cushion size
XL (160 × 80 cm) or Whole-body
Bead grade
High-density SBRT-grade
Motion management
4D-CT-derived ITV or breath-hold gating
CTV-to-PTV margin
CTV-to-PTV 5 mm typical per AAPM TG-101 after motion management
Chain: Cushion conforms at 4D-CT simulation; locks ITV-derived patient shape; baseplate indexes the cushion at the same couch position every fraction.
Cushion size
XL (160 × 80 cm)
Bead grade
High-density SBRT-grade
Motion management
Breath-hold gating (DIBH or end-expiration); occasional 4D-CT
CTV-to-PTV margin
CTV-to-PTV 5 mm with DIBH; 7 mm with 4D-CT-only
Chain: Cushion locks the breath-hold patient shape; DIBH gate reproduces internal anatomy at the same external breath-hold posture; setup transfers across fractions.
Cushion size
L (120 × 80 cm) or XL
Bead grade
High-density SBRT-grade
Motion management
Free-breathing with spine-rigid setup
CTV-to-PTV margin
CTV-to-PTV 1–2 mm at the vertebra; 3 mm at the cord (RTOG 0631 framework)
Chain: Cushion conforms to the supine spine-aligned patient; cord-sparing SBRT delivery needs sub-mm reproducibility — cushion plus indexed baseplate plus daily CBCT verification.
Cushion size
L (120 × 80 cm)
Bead grade
High-density SBRT-grade
Motion management
Free-breathing; bladder / rectal protocol
CTV-to-PTV margin
CTV-to-PTV 5 mm typical for nodal / bone SBRT
Chain: Cushion conforms to buttocks and posterior pelvis; bladder / rectal protocol locks internal anatomy; setup chains cushion + indexed baseplate + knee-foot support.
Cushion size
S (60 × 50 cm) under head + thermoplastic mask
Bead grade
Standard polystyrene
Motion management
Free-breathing
CTV-to-PTV margin
CTV-to-PTV 3 mm typical
Chain: Cushion supports cervical-spine curvature; mask locks the shell on top; baseplate indexes the cushion + mask assembly. Cushion is auxiliary to mask but improves comfort + setup reproducibility.
Cushion size
Site-appropriate (S–XL)
Bead grade
MR-compatible non-ferromagnetic bead
Motion management
Real-time MR cine + intra-fraction adaptation
CTV-to-PTV margin
Site-specific per MR-linac protocol; typically tighter PTV margin enabled by daily adaptive planning
Chain: MR-compatible cushion + MR-compatible baseplate. Same conformal hold and indexed pitch as the conventional setup but with no B0-field perturbation. MR-sim setup transfers to MR-linac at the same reproducibility as CT-sim to conventional linac.
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