Megavoltage image-based dynamic multileaf collimator tracking of a NiTi stent in porcine lungs on a linear accelerator.
Megavoltage image-based dynamic multileaf collimator tracking of a NiTi stent in porcine lungs on a linear accelerator.
复制标题
DOI：
10.1016/j.ijrobp.2011.03.023
复制
发表时间：
2012-02-01
影响因子：
7
通讯作者：
Keall, Paul J
中科院分区：
文献类型：
--
作者：
Poulsen, Per R;Carl, Jesper;Nielsen, Jane;Nielsen, Martin S;Thomsen, Jakob B;Jensen, Henrik K;Kjargaard, Benedict;Zepernick, Peter R;Worm, Esben;Fledelius, Walther;Cho, Byungchul;Sawant, Amit;Ruan, Dan;Keall, Paul J
To investigate the accuracy and potential limitations of MV image-based dynamic MLC tracking in a porcine model on a linear accelerator. A thermo-expandable NiTi stent designed for kV x-ray visualization of lung lesions was inserted into the bronchia of three anaesthetized Göttingen minipigs. A 4DCT scan was used for planning a 5-field conformal treatment with circular MLC apertures. A 22.5Gy single fraction treatment was delivered to the pigs. The peak-to-peak stent motion was 3-8mm with breathing periods of 1.2-4 seconds. Prior to treatment, x-ray images were used for image-guided setup based on the stent. During treatment delivery, continuous portal images were acquired at 7.5Hz. The stent was segmented in the images and used for continuous adaptation of the MLC aperture. Offline, the tracking error in beam’s eye view of the MV beam was calculated for each image as the difference between the MLC aperture center and the segmented stent position. The standard deviations of the systematic error Σ and the random error σ were determined and compared with the would-be errors for a non-tracking treatment with pre-treatment image-guided setup. Reliable stent segmentation was obtained for 11 out of 15 fields. Segmentation failures occurred when image contrast was dominated by overlapping anatomical structures (ribs, diaphragm) rather than by the stent, which was designed for kV rather than MV x-ray visibility. For the 11 fields with reliable segmentation, Σ was 0.5mm/0.4mm in the two imager directions, while σ was 0.5mm/1.1mm. Without tracking, Σ and σ would have been 1.7mm/1.4mm and 0.8mm/1.4mm, respectively. For the first time, in vivo DMLC tracking has been demonstrated on a linear accelerator showing the potential for improved targeting accuracy. The study mimicked the envisioned patient workflow of future patient treatments. Clinical implementation of MV image-based tracking would require markers designed for MV-visibility.
