Importance of CBCT setup verification for optical-guided frameless radiosurgery

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Therapy

Background:

• Frameless stereotactic radiosurgery (SRS) relies on accurate patient positioning.
• Optical guidance platforms (OGP) offer real-time patient monitoring during SRS.
• Verification of OGP accuracy against imaging systems like Trilogy's On-Board Imaging (OBI) is crucial.

Purpose of the Study:

• Quantify discrepancies between OGP and OBI systems for phantom and patient setup.
• Evaluate the necessity of cone-beam CT (CBCT) for OGP patient setup.
• Compare the verification capabilities of CBCT versus orthogonal kV-kV imaging.

Main Methods:

• Utilized three phantoms (custom, Penta-Guide, RANDO) for system comparison.
• Analyzed setup data from 5 patients using OGP+CBCT and 14 patients using CBCT alone.
• Investigated a specific patient case with significant OGP-CBCT couch shift discrepancy.

Main Results:

• Phantom experiments showed CBCT and kV-kV shifts within 1 mm.
• Three of five SRS patients using OGP setup required >3 mm 3D couch corrections.
• Patient case revealed bite-block tilting as a primary cause of OGP positioning error; CBCT provided accurate corrections, while kV-kV differed with head tilt.

Conclusions:

• Bite-block tilting is a significant source of positioning error in OGP frameless SRS.
• CBCT verification is essential for accurate patient setup and couch corrections in OGP-guided SRS.
• CBCT offers superior accuracy to orthogonal kV-kV imaging, particularly when patient head position is tilted.