Okazaki Keita, Cao Wenchao, Taleei Reza, Mourtada Firas, Li Jun, Mooney Karen, Anne Pramila Rani, Chen Yingxuan
Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
J Appl Clin Med Phys. 2025 Oct;26(10):e70248. doi: 10.1002/acm2.70248.
The integration of mobile cone-beam computed tomography (CBCT) into brachytherapy workflows offers clinical advantages such as immediate verification of applicator placement and adaptive treatment planning. These benefits require sufficient image quality to delineate applicators, target volumes, and organs at risk. A systematic evaluation of automatic exposure control (AEC) settings, radiation dose, and image quality is essential to ensure clinically acceptable imaging while minimizing patient exposure.
This study evaluates the characteristics of AEC and its impact on image quality and radiation dose in a mobile CBCT system used for brachytherapy.
The Elekta ImagingRing CBCT system was used to scan a CatPhan phantom under two imaging protocols: Medium Dose Limit (MDL) and Ultra-High Dose Limit (UHDL). This system employs a two-layer mAs modulation process, consisting of preset mA values based on body mass index (BMI) and adjusted mA based on real-time AEC. A bolus was used to simulate larger patient sizes. Real-time x-ray tube current at 10 degrees intervals was recorded. Image quality was evaluated using image noise, noise power spectrum (NPS), modulation transfer function (MTF), Hounsfield Unit (HU) linearity, uniformity index (UI), and contrast-to-noise ratio (CNR) across different protocols.
AEC effectively modulated x-ray tube current in the MDL protocol after x-ray attenuation through the scanned phantom was measured. The UHDL protocol demonstrated greater noise reduction than the MDL. MTF values were comparable between protocols, indicating preserved spatial resolution in the MDL protocol. HU linearity was consistent across all protocols, with R > 0.993.
AEC in mobile CBCT optimized radiation dose and image quality by adjusting tube current based on attenuation. The MDL protocol reduced radiation exposure while maintaining image quality, making it a viable option for verifying applicator placement and treatment planning in brachytherapy. The UHDL protocol achieved noise reduction with the maximum available tube current.
将移动锥形束计算机断层扫描（CBCT）集成到近距离放射治疗工作流程中具有临床优势，例如可立即验证施源器放置情况和进行自适应治疗计划。这些优势需要足够的图像质量来勾勒施源器、靶区体积和危及器官。系统评估自动曝光控制（AEC）设置、辐射剂量和图像质量对于确保临床可接受的成像同时使患者暴露最小化至关重要。
本研究评估用于近距离放射治疗的移动CBCT系统中AEC的特性及其对图像质量和辐射剂量的影响。
使用Elekta ImagingRing CBCT系统在两种成像协议下扫描CatPhan模体：中剂量限制（MDL）和超高剂量限制（UHDL）。该系统采用两层毫安秒调制过程，包括基于体重指数（BMI）的预设毫安值和基于实时AEC调整的毫安值。使用 bolus 模拟更大的患者体型。以10度间隔记录实时X射线管电流。使用不同协议下的图像噪声、噪声功率谱（NPS）、调制传递函数（MTF）、亨氏单位（HU）线性度、均匀性指数（UI）和对比度噪声比（CNR）评估图像质量。
在测量了通过扫描模体的X射线衰减后，AEC在MDL协议中有效调制了X射线管电流。UHDL协议比MDL表现出更大的降噪效果。各协议间的MTF值相当，表明MDL协议中空间分辨率得以保留。所有协议下HU线性度均一致，R>0.993。
移动CBCT中的AEC通过基于衰减调整管电流来优化辐射剂量和图像质量。MDL协议在保持图像质量的同时降低了辐射暴露，使其成为近距离放射治疗中验证施源器放置和治疗计划的可行选择。UHDL协议使用最大可用管电流实现了降噪。
