Department of Radiation Oncology, Brigham and Women's Hospital, Dana Farber Cancer Institute and Harvard Medical School, Boston, MA, United States of America.
Varian Medical Systems, Baden-Dattwil, Switzerland.
Phys Med Biol. 2023 Jul 10;68(14). doi: 10.1088/1361-6560/ace09a.
. Megavoltage cone-beam computed tomography (MV-CBCT) imaging offers several advantages including reduced metal artifacts and accurate electron density mapping for adaptive or emergent situations. However, MV-CBCT imaging is limited by the poor efficiency of current detectors. Here we examine a new MV imager and compare CBCT reconstructions under clinically relevant scenarios.. A multilayer imager (MLI), consisting of four vertically stacked standard flat-panel imagers, was mounted to a clinical linear accelerator. A custom anthropomorphic pelvis phantom with replaceable femoral heads was imaged using MV-CBCT and kilovoltage CBCT (kV-CBCT). Bone, aluminum, and titanium were used as femoral head inserts. 8 MU 2.5 MV scans were acquired for all four layers and (as reference) the top layer. Prostate and bladder were contoured on a reference CT and transferred to the other scans after rigid registration, from which the structural similarity index measure (SSIM) was calculated. Prostate and bladder were also contoured on CBCT scans without guidance, and Dice coefficients were compared to CT contours.. kV-CBCT demonstrated the highest SSIMs with bone inserts (prostate: 0.86, bladder: 0.94) and lowest with titanium inserts (0.32, 0.37). Four-layer MV-CBCT SSIMs were preserved with bone (0.75, 0.80) as compared to titanium (0.67, 0.74), outperforming kV-CBCT when metal is present. One-layer MV-CBCT consistently underperformed four-layer results across all phantom configurations. Unilateral titanium inserts and bilateral aluminum insert results fell between the bone and bilateral titanium results. Dice coefficients trended similarly, with four-layer MV-CBCT reducing metal artifact impact relative to KV-CBCT to provide better soft-tissue identification.. MV-CBCT with a four-layer MLI showed improvement over single-layer MV scans, approaching kV-CBCT quality for soft-tissue contrast. In the presence of artifact-producing metal implants, four-layer MV-CBCT scans outperformed kV-CBCT by eliminating artifacts and single-layer MV-CBCT by reducing noise. MV-CBCT with a novel multi-layer imager may be a valuable alternative to kV-CBCT, particularly in the presence of metal.
. 兆伏锥形束计算机断层扫描（MV-CBCT）成像具有许多优势，包括减少金属伪影和为自适应或紧急情况提供准确的电子密度映射。然而，MV-CBCT 成像受到当前探测器效率低下的限制。在这里，我们检查了一种新的 MV 成像仪，并在临床相关情况下比较了 CBCT 重建。. 一个由四个垂直堆叠的标准平板成像仪组成的多层成像仪（MLI）安装在临床直线加速器上。使用 MV-CBCT 和千伏 CBCT（kV-CBCT）对带有可更换股骨头的定制拟人骨盆体模进行成像。使用股骨头插入物作为骨、铝和钛。所有四层和（作为参考）顶层都采集了 8 MU 2.5 MV 扫描。在刚性配准后，将前列腺和膀胱的轮廓从参考 CT 转移到其他扫描，然后计算结构相似性指数测量（SSIM）。还在没有引导的情况下对 CBCT 扫描进行了前列腺和膀胱轮廓绘制，并将 Dice 系数与 CT 轮廓进行了比较。. kV-CBCT 显示具有骨插入物的最高 SSIM（前列腺：0.86，膀胱：0.94）和具有钛插入物的最低 SSIM（0.32，0.37）。与钛（0.67，0.74）相比，四层 MV-CBCT SSIM 保持不变，具有骨（0.75，0.80），优于存在金属时的 kV-CBCT。在所有体模配置中，单层 MV-CBCT 始终表现不如四层结果。单侧钛插入物和双侧铝插入物的结果介于骨和双侧钛插入物的结果之间。Dice 系数趋势相似，四层 MV-CBCT 相对于 KV-CBCT 减少了金属伪影的影响，从而提供了更好的软组织识别。. 使用四层 MLI 的 MV-CBCT 比单层 MV 扫描有所改善，接近软组织对比度的 kV-CBCT 质量。在存在产生伪影的金属植入物的情况下，四层 MV-CBCT 扫描通过消除伪影优于 kV-CBCT，而单层 MV-CBCT 则通过减少噪声优于 kV-CBCT。使用新型多层成像仪的 MV-CBCT 可能是 kV-CBCT 的一种有价值的替代方法，特别是在存在金属的情况下。
