Borsavage Jennifer M, Cherpak Amanda, Robar James L
Dalhousie University, Department of Physics and Atmospheric Science, 5820 University Ave., Halifax, Nova Scotia B3H 1V7, Canada.
Dalhousie University, Department of Radiation Oncology, 5820 University Ave., Halifax, Nova Scotia B3H 1V7, Canada.
Phys Imaging Radiat Oncol. 2020 Nov 5;16:103-108. doi: 10.1016/j.phro.2020.10.007. eCollection 2020 Oct.
A commercial 2.5 MV beam has been clinically available for beam's-eye-view imaging in radiotherapy, offering improved contrast-to-noise ratio (CNR) compared to therapeutic beams, due to the softer spectrum. Previous research suggested that imaging performance could be improved using a low-Z diamond target to reduce the self-absorption of diagnostic energy photons. The aim of this study was to 1) investigate the feasibility of two 2.5 MV diamond target beamline configurations and 2) characterize the dosimetry and planar image quality of these novel low-Z beams.
The commercial 2.5 MV beam was modified by replacing the copper target with sintered diamond. Two beamlines were investigated: a carousel-mounted diamond target beamline and a 'conventional' beamline, with the diamond target in the target arm. Planar image quality was assessed in terms of spatial resolution and CNR.
Due to image artifacts, image quality could not be assessed for the carousel-mounted low-Z target beam. The 'conventional' 2.5 MV low-Z beam quality was softer by 2.7% compared to the commercial imaging beam, resulting in improved CNR by factors of up to 1.3 and 1.7 in thin and thick phantoms, respectively. In regard to spatial resolution, the 'conventional' 2.5 MV low-Z beam slightly outperformed the commercial imaging beam.
With a simple modification to the 2.5 MV commercial beamline, we produced an improved energy spectrum for imaging. This 2.5 MV diamond target beam proved to be an advantageous alternative to the commercial target configuration, offering both superior resolution and CNR.
一种商用2.5兆伏（MV）射线束已在临床上用于放射治疗中的射野方向观成像，由于其能谱较软，与治疗射线束相比，提供了更高的对比度噪声比（CNR）。先前的研究表明，使用低原子序数的金刚石靶可减少诊断能量光子的自吸收，从而提高成像性能。本研究的目的是：1）研究两种2.5 MV金刚石靶射线束配置的可行性；2）表征这些新型低原子序数射线束的剂量学和平面图像质量。
通过用烧结金刚石替换铜靶对商用2.5 MV射线束进行改造。研究了两条射线束：一个旋转盘式安装的金刚石靶射线束和一个“传统”射线束，金刚石靶位于靶臂中。根据空间分辨率和CNR评估平面图像质量。
由于图像伪影，无法对旋转盘式安装的低原子序数靶射线束的图像质量进行评估。与商用成像射线束相比，“传统”2.5 MV低原子序数射线束的能谱软2.7%，在薄模体和厚模体中，CNR分别提高了1.3倍和1.7倍。在空间分辨率方面，“传统”2.5 MV低原子序数射线束略优于商用成像射线束。
对2.5 MV商用射线束进行简单改造后，我们得到了用于成像的改进能谱。这种2.5 MV金刚石靶射线束被证明是商用靶配置的一种有利替代方案，具有更高的分辨率和CNR。
