Wikström Kenneth, Nilsson Kristina, Isacsson Ulf, Ahnesjö Anders
Department of Medical Physics, Uppsala University Hospital , Uppsala , Sweden.
Acta Oncol. 2014 Feb;53(2):268-77. doi: 10.3109/0284186X.2013.802836. Epub 2013 Jun 20.
Optical surface detection has attractive features as a mean in radiotherapy for patient positioning tasks such as set-up, monitoring and gating. To aid in hitting radiotherapy targets the correlation between detected surface displacements and internal structure displacements is crucial. In this study, we compare set-up displacements derived from a body surface laser scanning (BSLS) system to displacements derived from bone registrations with a cone beam computed tomography (CBCT) system in order to quantify the accuracy and applicability of BSLS for fractionated treatments in the pelvic region.
Displacements from concurrent BSLS and CBCT registrations were compared for 40 patients treated in the pelvic region for a total of 170 set-ups. Surface data captured by BSLS at the first treatment fraction (BSLSref) was used as main reference for the BSLS system, while bony structures from the planning CT were used as a reference for the CBCT method. As comparison, the patient outline extracted from the planning CT was used as BSLS reference (CTref). The displacements detected by the CBCT system (skin-marks-only) was also used for comparison.
The mean differences (± 1 SD) between the BSLS and CBCT displacements were -0.01 (± 0.17) cm, 0.00 (± 0.21) cm and 0.01 (± 0.17) cm in the lateral, longitudinal and vertical directions, respectively. The median length of the difference was 0.26 cm (0.24-0.29 cm, 95% CI). The median of the difference between CBCT and BSLS displacements based on CTref was 0.37 cm (0.30-0.39 cm) and the median for skin-marks-only was 0.38 cm (0.34-0.42 cm).
The BSLS system is a good supplement to the CBCT system for accurate set-up for fractions when no CBCT is deemed necessary for pelvic targets. Inter-fractional skin movement in relation to bone was estimated to be 0.2 cm in the lateral (X), longitudinal (Y) and vertical direction (Z), respectively.
光学表面检测作为放射治疗中患者定位任务（如摆位、监测和门控）的一种手段具有吸引人的特性。为了有助于命中放射治疗靶点，检测到的表面位移与内部结构位移之间的相关性至关重要。在本研究中，我们将体表激光扫描（BSLS）系统得出的摆位位移与锥束计算机断层扫描（CBCT）系统通过骨配准得出的位移进行比较，以量化BSLS在盆腔区域分次治疗中的准确性和适用性。
对40例在盆腔区域接受治疗的患者共170次摆位时同时进行的BSLS和CBCT配准得出的位移进行比较。BSLS在首次治疗分次时采集的表面数据（BSLSref）用作BSLS系统的主要参考，而计划CT中的骨结构用作CBCT方法的参考。作为比较，从计划CT中提取的患者轮廓用作BSLS参考（CTref）。CBCT系统检测到的位移（仅皮肤标记）也用于比较。
BSLS和CBCT位移在横向、纵向和垂直方向上的平均差异（±1标准差）分别为-0.01（±0.17）cm、0.00（±0.21）cm和0.01（±0.17）cm。差异的中位数长度为0.26 cm（0.24 - 0.29 cm，95%可信区间）。基于CTref的CBCT和BSLS位移之间差异的中位数为0.37 cm（0.30 - 0.39 cm），仅皮肤标记的中位数为0.38 cm（0.34 - 0.42 cm）。
当盆腔靶点无需CBCT时，BSLS系统是CBCT系统用于准确分次摆位的良好补充。相对于骨的分次间皮肤运动在横向（X）、纵向（Y）和垂直方向（Z）上估计分别为0.2 cm。
