An ionizing radiation acoustic imaging (iRAI) technique for real-time dosimetric measurements for FLASH radiotherapy.
An ionizing radiation acoustic imaging (iRAI) technique for real-time dosimetric measurements for FLASH radiotherapy.
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DOI：
10.1002/mp.14358
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发表时间：
2020-10
期刊：
影响因子：
3.8
通讯作者：
El Naqa I
中科院分区：
文献类型：
--
作者：
Oraiqat I;Zhang W;Litzenberg D;Lam K;Ba Sunbul N;Moran J;Cuneo K;Carson P;Wang X;El Naqa I
FLASH放疗（FLASH-RT）是一种具有超高剂量率（> 40 Gy/s）的新型照射方式，其在保持与常规放疗（CONV-RT）相当的肿瘤细胞根除的同时增强正常组织保留的能力已显示出巨大的前景。由于其极高的剂量率，FLASH-RT的临床转化受到剂量测定设备的风险输送和当前限制的阻碍，这些设备不能实时准确地测量更深组织的剂量。这项工作的目的是调查电离辐射声成像（iRAI）作为一个有前途的图像引导模式，实时深部组织剂量测量在FLASH-RT。基本的假设是，iRAI可以使映射剂量沉积相对于周围组织与一个单一的线性加速器（直线加速器）脉冲精度在真实的时间。在这项工作中，iRAI信号响应和沉积剂量之间的关系进行了研究，以及使用的概念验证的双模态成像系统的超声和iRAI治疗波束共同定位相对于底层解剖结构的可行性。使用两个实验装置来研究iRAI用于FLASH-RT的可行性，所述iRAI使用来自改进的Varian Clinac的6 MeV电子。首先，使用单元件聚焦传感器进行实验，在明胶体模中进行一系列点测量，并将其与使用GAFchromatic胶片的独立剂量测量进行比较。其次，使用利用相控阵换能器的超声和iRAI双模态成像系统来拍摄共配准的2D iRAI信号幅度图像以及超声B模式图像，以在具有单个直线加速器脉冲精度的离体兔肝脏模型中绘制相对于周围解剖结构的剂量沉积。使用单元件传感器，iRAI测量结果显示，与GAF铬膜剂量测量结果相比，在均匀体模中，iRAI信号幅度与直线加速器每次脉冲剂量之间存在高度线性关系（r2 = 0.9998），重复性精度为1%，剂量分辨率误差小于2.5%。这些体模结果用于开发iRAI信号响应与每个脉冲输送剂量之间的校准曲线。随后，使用校正因子来说明测量条件相对于校准的偏差，生成与胶片测量一致的归一化深度剂量曲线，RMSE为0.0243。在离体兔肝脏模型上的实验表明，可以从单个直线加速器脉冲成功地生成2D iRAI图像，该图像与B型超声图像融合以提供关于射束相对于周围解剖结构的真实的时间位置的信息。这项工作表明，在FLASH-RT实时深部组织剂量测定使用iRAI的潜力。我们的研究结果表明，iRAI信号与剂量呈线性关系，可以准确地映射相对于软组织解剖结构的辐射剂量。iRAI能够在周围软组织内的任何位置测量单个直线加速器脉冲的剂量，同时在解剖学上真实的时间内识别剂量输送的位置，因此它可以成为实现安全有效的FLASH-RT临床转换的不可或缺的工具。
FLASH radiotherapy (FLASH-RT) is a novel irradiation modality with ultra-high dose rates (>40Gy/s) that have shown tremendous promise for its ability to enhance normal tissue sparing while maintaining comparable tumor cell eradication to conventional radiotherapy (CONV-RT). Due to its extremely high-dose rates, clinical translation of FLASH-RT is hampered by risky delivery and current limitations in dosimetric devices, which cannot accurately measure, in real-time, dose at deeper tissue. This work aims to investigate ionizing radiation acoustic imaging (iRAI) as a promising image-guidance modality for real-time deep tissue dose measurements during FLASH-RT. The underlying hypothesis is that iRAI can enable mapping of dose deposition with respect to surrounding tissue with a single linear accelerator (linac) pulse precision in real time. In this work, the relationship between iRAI signal response and deposited dose was investigated as well as the feasibility of using a proof-of-concept dual-modality imaging system of ultrasound and iRAI for treatment beam co-localization with respect to underlying anatomy. Two experimental setups were used to study the feasibility of iRAI for FLASH-RT using 6 MeV electrons from a modified Varian Clinac. First, experiments were conducted using a single element focused transducer to take a series of point measurements in a gelatin phantom, which was compared with independent dose measurements using GAFchromic film. Secondly, an ultrasound and iRAI dual-modality imaging system utilizing a phased array transducer was used to take co-registered 2D iRAI signal amplitude images as well as ultrasound B-mode images, to map the dose deposition with respect to surrounding anatomy in an ex-vivo rabbit liver model with a single linac pulse precision. Using a single element transducer, iRAI measurements showed a highly linear relationship between the iRAI signal amplitude and the linac dose per pulse (r2 = 0.9998) with a repeatability precision of 1% and a dose resolution error less than 2.5% in a homogenous phantom when compared to GAFchromic film dose measurements. These phantom results were used to develop a calibration curve between the iRAI signal response and the delivered dose per pulse. Subsequently, a normalized depth dose curve was generated that agreed with film measurements with an RMSE of 0.0243, using correction factors to account for deviations in measurement conditions with respect to calibration. Experiments on the ex-vivo rabbit liver model demonstrated that a 2D iRAI image could be generated successfully from a single linac pulse, which was fused with the B-mode ultrasound image to provide information about the beam position with respect to surrounding anatomy in real time. This work demonstrates the potential of using iRAI for real-time deep tissue dosimetry in FLASH-RT. Our results show that iRAI signals are linear with dose and can accurately map the delivered radiation dose with respect to soft tissue anatomy. With its ability to measure dose for individual linac pulses at any location within surrounding soft tissue while identifying where that dose is being delivered anatomically in real time, iRAI can be an indispensable tool to enable safe and efficient clinical translation of FLASH-RT.
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