Kanani Abolfazl, Yazdi Mehran, Owrangi Amir M, Karbasi Sareh, Mosleh-Shirazi Mohammad Amin
Ionizing and Non-Ionizing Radiation Protection Research Center (INIRPRC), School of Paramedical Sciences, Shiraz University of Medical Sciences, Shiraz, Iran.
Signal and Image Processing Lab. (SIPL), School of Electrical and Computer Eng., Shiraz University, Shiraz, Iran.
Brachytherapy. 2022 Nov-Dec;21(6):933-942. doi: 10.1016/j.brachy.2022.07.003. Epub 2022 Aug 4.
To evaluate an iterative metal-artifact reduction (iMAR) algorithm, dual-energy CT (DECT) through virtual monoenergetic images (VMI), and a combination of iMAR and DECT for reducing metal artifact severity (AS) induced by Fletcher titanium applicators used in cervix brachytherapy, the efficacy of which are hitherto unreported.
120 kV single-energy CT (SECT) (Siemens) of BEBIG tandem applicators, varying in shape (straight or curved) and diameter (3.5 mm or 5 mm) in a custom-made water-filled phantom, and their DECT images obtained from extrapolation of 80 kVp and 140 kVp, were reconstructed using four methods: DECT through VMI±iMAR, and SECT±iMAR. The DECT images were reconstructed monoenergetically at 70, 150, and 190 keV. AS was evaluated using measured values and statistical analysis.
iMAR, DECT, and combined DECT and iMAR reduced AS (p < 0.05). DECT had a lower AS than SECT, even without iMAR (p < 0.025). SECT+iMAR was more effective than DECT-iMAR with VMI at 70 and 190 keV (p < 0.05), whereas showing no statistically significant difference at 150 keV. With DECT and iMAR combined, AS was reduced more effectively compared to the SECT+iMAR or DECT alone. It also reduced the mean interobserver uncertainty by 0.2 mm.
These findings indicate that iMAR reduces the AS caused by Fletcher titanium applicators for both SECT and DECT, a combination of iMAR and DECT is superior to either strategy alone, and at low energies, DECT+iMAR also produces similar artifact reduction. These practical strategies promise more accurate source-position and structure definitions in CT-based gynecological brachytherapy treatment planning.
评估一种迭代金属伪影减少（iMAR）算法、通过虚拟单能图像（VMI）的双能CT（DECT）以及iMAR与DECT相结合的方法，以降低宫颈近距离放射治疗中使用的弗莱彻钛施源器所导致的金属伪影严重程度（AS），其效果迄今尚未见报道。
在定制的充水模体中，对形状（直形或弯形）和直径（3.5毫米或5毫米）各异的BEBIG串联施源器进行120 kV单能CT（SECT）（西门子）扫描，并通过80 kVp和140 kVp外推获得其DECT图像，使用四种方法进行重建：通过VMI±iMAR的DECT以及SECT±iMAR。DECT图像在70、150和190 keV进行单能重建。使用测量值和统计分析评估AS。
iMAR、DECT以及DECT与iMAR相结合均降低了AS（p < 0.05）。即使不使用iMAR，DECT的AS也低于SECT（p < 0.025）。SECT+iMAR在70和190 keV时比使用VMI的DECT - iMAR更有效（p < 0.05），而在150 keV时无统计学显著差异。与单独的SECT+iMAR或DECT相比，DECT与iMAR相结合能更有效地降低AS。它还将观察者间的平均不确定性降低了0.2毫米。
这些发现表明，iMAR可降低SECT和DECT中由弗莱彻钛施源器引起的AS，iMAR与DECT相结合优于单独的任何一种策略，并且在低能量下，DECT+iMAR也能产生类似的伪影减少效果。这些实用策略有望在基于CT的妇科近距离放射治疗计划中实现更准确的源位置和结构定义。
