Cone-Beam CT Image-Guided Radiotherapy (CBCT-IGRT)

Overview

Cone-beam CT image-guided radiotherapy (CBCT-IGRT) acquires a volumetric CT image immediately before or during each radiation treatment fraction using a kV or MV X-ray source mounted on the treatment gantry. The resulting image is registered to the planning CT to verify and correct patient and tumour positioning before beam delivery. In pancreatic SBRT, CBCT-IGRT enables daily verification of fiducial marker position and soft-tissue tumour location, supporting the tight PTV margins required for high-dose hypofractionated treatment.

Used by

• CBCT-IGRT is described as a standard image-guidance component of the linac-based SBRT technical workflow reviewed in nine prospective trials of locally advanced pancreatic cancer; enables daily positional correction with fiducial markers to maintain tight PTV margins (2–5 mm) and protect adjacent OARs (duodenum, stomach, small bowel). PMID:27826200

Notes

• Typical workflow: acquire CBCT immediately before each SBRT fraction, register to planning CT using bony anatomy and/or implanted fiducials, apply couch corrections, then deliver treatment.
• Paired with 4D-CT simulation and endoscopic fiducial placement for comprehensive motion management in pancreatic SBRT.
• CBCT soft-tissue contrast is lower than diagnostic CT; fiducial markers are used as surrogate landmarks for the tumour centre.
• On-board imaging dose contribution (1–3 cGy per CBCT) is negligible relative to SBRT prescription doses (33 Gy / 5 fx).

Sources

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