Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands.
Biomedical Engineering, Department of Cardiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands; Department of Physics, KU Leuven Campus Kulak, Kortrijk, Belgium; Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium.
Ultrasound Med Biol. 2022 Jan;48(1):149-156. doi: 10.1016/j.ultrasmedbio.2021.09.009. Epub 2021 Oct 8.
The potential of proton therapy to improve the conformity of the delivered dose to the tumor volume is currently limited by range uncertainties. Injectable superheated nanodroplets have recently been proposed for ultrasound-based in vivo range verification, as these vaporize into echogenic microbubbles on proton irradiation. In previous studies, offline ultrasound images of phantoms with dispersed nanodroplets were acquired after irradiation, relating the induced vaporization profiles to the proton range. However, the aforementioned method did not enable the counting of individual vaporization events, and offline imaging cannot provide real-time feedback. In this study, we overcame these limitations using high-frame-rate ultrasound imaging with a linear array during proton irradiation of phantoms with dispersed perfluorobutane nanodroplets at 37°C and 50°C. Differential image analysis of subsequent frames allowed us to count individual vaporization events and to localize them with a resolution beyond the ultrasound diffraction limit, enabling spatial and temporal quantification of the interaction between ionizing radiation and nanodroplets. Vaporization maps were found to accurately correlate with the stopping distribution of protons (at 50°C) or secondary particles (at both temperatures). Furthermore, a linear relationship between the vaporization count and the number of incoming protons was observed. These results indicate the potential of real-time high-frame-rate contrast-enhanced ultrasound imaging for proton range verification and dosimetry.
质子治疗改善肿瘤靶区剂量适形性的潜力目前受到射程不确定性的限制。最近提出了可注射过热纳米液滴用于基于超声的体内射程验证，因为这些液滴在质子辐照下会蒸发成超声响应的微泡。在之前的研究中，在辐照后对含有分散纳米液滴的体模进行了离线超声成像，将诱导的蒸发轮廓与质子射程相关联。然而，上述方法无法对单个蒸发事件进行计数，并且离线成像无法提供实时反馈。在这项研究中，我们使用在 37°C 和 50°C 下辐照含有分散全氟丁烷纳米液滴的体模时使用线阵进行高帧率超声成像克服了这些限制。随后帧的差分图像分析使我们能够对单个蒸发事件进行计数，并以超过超声衍射极限的分辨率对其进行定位，从而能够对电离辐射与纳米液滴之间的相互作用进行时空量化。发现蒸发图与质子（在 50°C 时）或次级粒子（在两个温度下）的停止分布准确相关。此外，观察到蒸发计数与入射质子数量之间存在线性关系。这些结果表明，实时高帧率对比增强超声成像在质子射程验证和剂量测定方面具有潜力。
