A major contributing factor to proton range uncertainty is the conversion of computed tomography (CT) Hounsfield Units (HU) to proton relative stopping power (RSP). This uncertainty is elevated with implanted devices, such as silicone breast implants when computed with single energy CT (SECT). In recent years, manufacturers have introduced implants with variations in gel cohesivity. Deriving the RSP for these implants from dual-energy CT (DECT) can result in a marked reduction of the error associated with SECT. In this study, we investigate the validity of DECT calibration of HU to RSP on silicone breast implants of varying cohesivity levels. A DECT capable scanner was calibrated using the stoichiometric method of Bourque et al for SECT and DECT using a tissue substitute phantom. Three silicone breast implants of increasing gel cohesivity were measured in a proton beam of clinical energy to determine ground-truth RSP and water equivalent thickness (WET). These were compared to SECT-derived RSP at three CT spectrum energies and DECT with two energy pairs (80/140 kVp and 100/140 kVp) as obtained from scans with and without an anthropomorphic phantom. The RSP derived from parameters estimates from CT vendor-specific software (syngo.via) was compared. The WET estimates from SECT deviated from MLIC ground truth approximately +11%–19%, which would result in overpenetration if used clinically. Both the Bourque calibration and syngo.via WET estimates from DECT yielded error ≤0.5% from ground truth; no significant difference was found between models of varying gel cohesivity levels. WET estimates without the anthropomorphic phantom were significantly different than ground truth for the Bourque calibration. From these results, gel cohesivity had no effect on proton RSP. User-generated DECT calibration can yield comparably accurate RSP estimates for silicone breast implants to vendor software methods. However, care must be taken to account for beam hardening effects.

中文翻译：

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使用单能量和双能量 CT 校准技术估计硅胶乳房植入物的质子停止能力的准确性

质子射程不确定性的一个主要影响因素是计算机断层扫描 (CT) 亨斯菲尔德单位 (HU) 到质子相对停止能力 (RSP) 的转换。当使用单能 CT (SECT) 计算时，植入设备（例如硅胶乳房植入物）会增加这种不确定性。近年来，制造商推出了具有不同凝胶内聚力的植入物。从双能 CT (DECT) 导出这些植入物的 RSP 可以显着减少与 SECT 相关的误差。在这项研究中，我们调查了 HU 对 RSP 的 DECT 校准在不同内聚力水平的硅胶乳房植入物上的有效性。使用 Bourque 等人的 SECT 和 DECT 化学计量方法使用组织替代体模校准支持 DECT 的扫描仪。在临床能量的质子束中测量了三种增加凝胶内聚力的硅胶乳房植入物，以确定地面真实 RSP 和水当量厚度 (WET)。将这些与三个 CT 光谱能量的 SECT 衍生 RSP 和具有两个能量对（80/140 kVp 和 100/140 kVp）的 DECT 进行比较，这些能量是从使用和不使用拟人模型的扫描中获得的。从 CT 供应商特定软件的参数估计得出的 RSP（syngo .via) 进行了比较。SECT 的 WET 估计与 MLIC 基本事实的偏差大约为 +11%–19%，如果在临床上使用，这将导致过度渗透。来自 DECT的 Bourque 校准和syngo .via WET 估计都产生了与地面实况误差≤0.5% 的误差；在不同凝胶内聚力水平的模型之间没有发现显着差异。没有拟人模型的 WET 估计与 Bourque 校准的地面实况显着不同。从这些结果来看，凝胶内聚力对质子 RSP 没有影响。用户生成的 DECT 校准可以为硅胶乳房植入物产生与供应商软件方法相当准确的 RSP 估计。但是，必须注意考虑光束硬化效应。