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

TLDR

Cone‑beam CT with a flat‑panel detector provides sub‑millimetre 3‑D spatial resolution and soft‑tissue visibility, making it a promising modality for intraoperative imaging in head and neck surgery. The study reports patient dose and in‑room exposure measurements for CBCT‑guided head and neck surgery and investigates how 3‑D imaging performance varies with dose and acquisition parameters. Using a Siemens PowerMobil C‑arm modified for flat‑panel CBCT, the authors measured dose in a cylindrical head phantom at multiple positions and kVp settings, recorded in‑room exposure around the operating table, and evaluated 3‑D image quality with an anthropomorphic phantom by assessing contrast‑to‑noise ratio across a range of doses. The prototype C‑arm achieved low patient dose (e.g., 0.059 mGy/mAs at isocenter for a tube‑under orbit), significant eye sparing, moderate thyroid dose reduction with shielding, in‑air exposure up to 0.5 mGy at 1 m from isocenter, and CNR that scales with the square root of dose, yielding excellent visualization of bone and soft tissue at doses comparable to or lower than a diagnostic head CT.

Abstract

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 cylindrical head phantom at four positions (isocenter, anterior, posterior, and lateral) as a function of kVp and C‐arm trajectory (“tube‐under” and “tube‐over” half‐rotation orbits). At , 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 and 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 ( 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 from isocenter. A typical CBCT scan ( to isocenter) gave in‐air exposure ranging from at from isocenter, to at from isocenter. Three‐dimensional (3D) image quality was assessed in CBCT reconstructions of an anthropomorphic head phantom containing contrast‐detail spheres and a natural human skeleton. The contrast‐to‐noise ratio (CNR) was evaluated across a broad range of dose . CNR increased as the square root of dose, with excellent visualization of bony and soft‐tissue structures achieved at and , 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 over the course of the procedure comparable to or less than the effective dose of a typical diagnostic CT of the head.