Optimizing lens and organ dose evaluation in head CT examinations using monte carlo simulation: influence of gantry tilt and scan range.

To minimize radiation exposure to the eye lens during head computed tomography examinations, we performed a high-precision Monte Carlo simulation using the particle and heavy ion transport code system to investigate the effects of gantry tilt angle and scan range on the dose to the lens and other radiosensitive organs. Utilizing a source model with a 2 mm beam width, we visualized the sharp dose peak and the subsequent gradually attenuating tail in the dose distribution to the lens, quantitatively demonstrating that even minor adjustments in the tilt angle or slice position can markedly impact the lens dose. The tilt angle was defined relative to the orbitomeatal line; an upward tilt of +5˚ or more reduced the lens dose by up to 87%. Additionally, a -35˚ downward tilt substantially reduced the lens dose, which is attributed to the presence of high-attenuation tissues in the x-ray path. For organs such as the salivary glands, thyroid, and oral mucosa, scan range adjustments affect the effective dose, with up to a 1.5-fold difference observed depending on whether the eyeballs were included in the scan. These findings underscore the critical importance of a precise protocol design, including the gantry tilt and slice range, in minimizing radiation exposure to multiple organs and provide valuable insights into radiation protection and protocol optimization.