Yoganathan S A, Maria Das K J, Subramanian V Siva, Raj D Gowtham, Agarwal Arpita, Kumar Shaleen
Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
School of Physics, Bharathidasan University, Tiruchirappalli, Tamil Nadu, India.
J Cancer Res Ther. 2017 Oct-Dec;13(6):994-999. doi: 10.4103/0973-1482.220353.
The aim of this work was to evaluate the various computed tomography (CT) techniques such as fast CT, slow CT, breath-hold (BH) CT, full-fan cone beam CT (FF-CBCT), half-fan CBCT (HF-CBCT), and average CT for delineation of internal target volume (ITV). In addition, these ITVs were compared against four-dimensional CT (4DCT) ITVs.
Three-dimensional target motion was simulated using dynamic thorax phantom with target insert of diameter 3 cm for ten respiration data. CT images were acquired using a commercially available multislice CT scanner, and the CBCT images were acquired using On-Board-Imager. Average CT was generated by averaging 10 phases of 4DCT. ITVs were delineated for each CT by contouring the volume of the target ball; 4DCT ITVs were generated by merging all 10 phases target volumes. Incase of BH-CT, ITV was derived by boolean of CT phases 0%, 50%, and fast CT target volumes.
ITVs determined by all CT and CBCT scans were significantly smaller (P < 0.05) than the 4DCT ITV, whereas there was no significant difference between average CT and 4DCT ITVs (P = 0.17). Fast CT had the maximum deviation (-46.1% ± 20.9%) followed by slow CT (-34.3% ± 11.0%) and FF-CBCT scans (-26.3% ± 8.7%). However, HF-CBCT scans (-12.9% ± 4.4%) and BH-CT scans (-11.1% ± 8.5%) resulted in almost similar deviation. On the contrary, average CT had the least deviation (-4.7% ± 9.8%).
When comparing with 4DCT, all the CT techniques underestimated ITV. In the absence of 4DCT, the HF-CBCT target volumes with appropriate margin may be a reasonable approach for defining the ITV.
本研究旨在评估多种计算机断层扫描（CT）技术，如快速CT、慢速CT、屏气（BH）CT、全扇束锥形束CT（FF-CBCT）、半扇束CBCT（HF-CBCT）以及平均CT，用于勾画内部靶区体积（ITV）。此外，将这些ITV与四维CT（4DCT）的ITV进行比较。
使用带有直径3 cm靶标插入物的动态胸部体模模拟三维靶标运动，获取十个呼吸数据。使用商用多层CT扫描仪采集CT图像，使用机载成像仪采集CBCT图像。平均CT通过对4DCT的10个时相进行平均生成。通过勾勒靶球的体积为每个CT勾画ITV；4DCT的ITV通过合并所有10个时相的靶标体积生成。对于BH-CT，ITV通过CT时相0%、50%以及快速CT靶标体积的布尔运算得出。
所有CT和CBCT扫描确定的ITV均显著小于4DCT的ITV（P < 0.05），而平均CT和4DCT的ITV之间无显著差异（P = 0.17）。快速CT的偏差最大（-46.1% ± 20.9%），其次是慢速CT（-34.3% ± 11.0%）和FF-CBCT扫描（-26.3% ± 8.7%）。然而，HF-CBCT扫描（-12.9% ± 4.4%）和BH-CT扫描（-11.1% ± 8.5%）产生的偏差几乎相似。相反，平均CT的偏差最小（-4.7% ± 9.8%）。
与4DCT相比，所有CT技术均低估了ITV。在没有4DCT的情况下，具有适当边界的HF-CBCT靶标体积可能是定义ITV的合理方法。
