Stereotactic Body Radiotherapy (SBRT)
Hypofractionated ablative radiation therapy — delivers very high dose per fraction (typically 6–20 Gy) in a small number of fractions (1–5) to well-localized extracranial tumors. Principal applications: early-stage non-small-cell lung cancer, liver metastases, prostate cancer, spine metastases, oligometastatic disease, pancreatic cancer (emerging).
SBRT's clinical success depends on submillimeter spatial accuracy + motion management. A 3 mm error at 10 Gy × 5 fractions is meaningfully different from the same error at 2 Gy × 30 fractions — the dose gradient around an SBRT target is steep.
Workflow
- Simulation — CT simulation scan with 4DCT for moving targets. Contrast-enhanced when indicated; fusion with MRI / PET for contouring.
- Contouring — physician + physicist define GTV, CTV, ITV (for motion), PTV margins + OARs (organs at risk).
- Planning — VMAT or IMRT plan optimization; dose constraints per TG-101 or institutional guidelines.
- Plan QA — physicist-signed; patient-specific QA (ArcCHECK, MapCheck, portal dosimetry).
- Delivery — daily CBCT IGRT before each fraction; motion management (gating, breath-hold, tracking) as appropriate.
Typical systems
- Varian TrueBeam + RapidArc
- Varian Edge (SRS/SBRT-dedicated)
- Elekta Versa HD + HexaPOD + Symmetry
- CyberKnife (tracking-based, different geometry)
- Elekta Unity MR-Linac (for moving targets where MRI soft-tissue visualization matters)
Motion management options
- ITV (internal target volume) — plan for the full motion envelope; simplest, highest normal-tissue dose
- Breath-hold — patient + surface guidance; intermediate complexity
- Gating — beam on only during specific respiratory phase
- Tracking — CyberKnife Synchrony (tracks in real time) or Varian Calypso (electromagnetic beacons)
Clinical characteristics
- Fractions: 1–5
- Dose per fraction: 6–20+ Gy
- Room time per fraction: 30–60 min (longer than conventional IMRT due to IGRT + motion verification)
- Physicist time: significant — SBRT plans are not "set and forget"
Related
- Brain SRS (intracranial analog)
- IMRT (conventional sibling)
- VMAT / RapidArc
- TG-142
- Linear Accelerator modality