Intraoperative cone-beam CT for guidance of head and neck surgery: Assessment of dose and image quality using a C-arm prototype

• Published in: Medical physics (Lancaster) 2006-10, Vol.33 (10), p.3767-3780
• Main Authors: Daly, M. J., Siewerdsen, J. H., Moseley, D. J., Jaffray, D. A., Irish, J. C.
• Format: Article
• Language: English
• Subjects: Anatomy; biomedical equipment; Biophysical techniques (research methods); C-arm; Computed radiography; Computed tomography; computerised tomography; COMPUTERIZED TOMOGRAPHY; Cone beam computed tomography; cone-beam CT; Dose-Response Relationship, Radiation; dosimetry; Evaluation Studies as Topic; EYES; flat-panel detector; Fluoroscopy; Fluoroscopy - methods; Head and Neck Neoplasms - diagnostic imaging; Head and Neck Neoplasms - surgery; head and neck surgery; Humans; Image analysis; IMAGE PROCESSING; Image Processing, Computer-Assisted; Image quality; image reconstruction; image resolution; image-guided surgery; imaging performance; Imaging, Three-Dimensional; intraoperative imaging; Medical image noise; Medical image quality; Medical image reconstruction; Medical imaging; NECK; Non‐ionizing radiation equipment and techniques; PHANTOMS; Phantoms, Imaging; radiation dose; RADIATION DOSES; Radiographic Image Enhancement; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry; Radiotherapy Planning, Computer-Assisted - methods; SPATIAL RESOLUTION; SURGERY; THYROID; Tomography Scanners, X-Ray Computed; Tomography, Spiral Computed - methods; Tomography, X-Ray Computed - methods
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.2349687

Cone-beam computed tomography (CBCT) with a flat-panel detector represents a promising modality for intraoperative imaging in interventional procedures, demonstrating sub-mm three-dimensional (3D) spatial resolution and soft-tissue visibility. Measurements of patient dose and in-room exposure for CBCT-guided head and neck surgery are reported, and the 3D imaging performance as a function of dose and other acquisition/reconstruction parameters is investigated. Measurements were performed on a mobile isocentric C-arm (Siemens PowerMobil) modified in collaboration with Siemens Medical Solutions (Erlangen, Germany) to provide flat-panel CBCT. Imaging dose was measured in a custom-built 16 cm cylindrical head phantom at four positions (isocenter, anterior, posterior, and lateral) as a function of kVp ( 80 – 120 kVp ) and C-arm trajectory (“tube-under” and “tube-over” half-rotation orbits). At 100 kVp , for example (“tube-under” orbit), the imaging dose was 0.059 (isocenter), 0.022 (anterior), 0.10 (posterior), and 0.056 (lateral) mGy/mAs, with scans at ∼ 50 and ∼ 170 mAs typical for visualization of bony and soft-tissue structures, respectively. Dose to radiosensitive structures (viz., the eyes and thyroid) were considered in particular: significant dose sparing to the eyes (a factor of 5) was achieved using a “tube-under” (rather than “tube-over”) half-rotation orbit; a thyroid shield ( 0.5 mm Pb-equivalent) gave moderate reduction in thyroid dose due to x-ray scatter outside the primary field of view. In-room exposure was measured at positions around the operating table and up to 2 m from isocenter. A typical CBCT scan ( 10 mGy to isocenter) gave in-air exposure ranging from 29 mR ( 0.26 mSv ) at 35 cm from isocenter, to < 0.5 mR ( < 0.005 mSv ) at 2 m from isocenter. Three-dimensional (3D) image quality was assessed in CBCT reconstructions of an anthropomorphic head phantom containing contrast-detail spheres ( 11 – 103 HU ; 1.6 – 12.7 mm ) and a natural human skeleton. The contrast-to-noise ratio (CNR) was evaluated across a broad range of dose ( 0.6 – 23.3 mGy ) . CNR increased as the square root of dose, with excellent visualization of bony and soft-tissue structures achieved at ∼ 3 mGy ( 0.10 mSv ) and ∼ 10 mGy ( 0.35 mSv ) , respectively. The prototype C-arm demonstrates CBCT image quality sufficient for guidance of head and neck procedures based on soft-tissue and bony anatomy at dose levels low enough for repeat intraoperative imaging, with total dose