WE‐EF‐207‐05: Monte Carlo Dosimetry for a Dedicated Cone‐Beam CT Head Scanner

Abstract

Purpose:Cone‐Beam CT (CBCT) is an attractive platform for point‐of‐care imaging of traumatic brain injury and intracranial hemorrhage. This work implements and evaluates a fast Monte‐Carlo (MC) dose estimation engine for development of a dedicated head CBCT scanner, optimization of acquisition protocols, geometry, bowtie filter designs, and patient‐specific dosimetry.Methods:Dose scoring with a GPU‐based MC CBCT simulator was validated on an imaging bench using a modified 16 cm CTDI phantom with 7 ion chamber shafts along the central ray for 80–100 kVp (+2 mm Al, +0.2 mm Cu). Dose distributions were computed in a segmented CBCT reconstruction of an anthropomorphic head phantom with 4×10⁵ tracked photons per scan (5 min runtime). Circular orbits with angular span ranging from short scan (180° + fan angle) to full rotation (360°) were considered for fixed total mAs per scan. Two aluminum filters were investigated: aggressive bowtie, and moderate bowtie (matched to 16 cm and 32 cm water cylinder, respectively).Results:MC dose estimates showed strong agreement with measurements (RMSE<0.001 mGy/mAs). A moderate (aggressive) bowtie reduced the dose, per total mAs, by 20% (30%) at the center of the head, by 40% (50%) at the eye lens, and by 70% (80%) at the posterior skin entrance. For the no bowtie configuration, a short scan reduced the eye lens dose by 62% (from 0.08 mGy/mAs to 0.03 mGy/mAs) compared to full scan, although the dose to spinal bone marrow increased by 40%. For both bowties, the short scan resulted in a similar 40% increase in bone marrow dose, but the reduction in the eye lens was more pronounced: 70% (90%) for the moderate (aggressive) bowtie.Conclusions:Dose maps obtained with validated MC simulation demonstrated dose reduction in sensitive structures (eye lens and bone marrow) through combination of short‐scan trajectories and bowtie filters.Xiaohui Wang and David Foos are employees of Carestream Health