Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Radiother Oncol. 2011 Mar;98(3):340-6. doi: 10.1016/j.radonc.2010.11.010. Epub 2011 Feb 4.
To investigate application of pre-treatment established correlations between bladder-filling changes and cervix-uterus displacements in adaptive therapy.
Thirteen cervical cancer patients participated in this prospective study. Pre-treatment, and after delivery of 40 Gy, a full bladder CT-scan was acquired, followed by voiding the bladder and acquisition of 4 other 3D scans in a 1h period with a naturally filling bladder (variable bladder filling CT-scans, VBF-scans). For the pre-treatment VBF-scans, linear correlations between bladder volume change and displacements of the tip of the uterus (ToU) and the center of mass (CoM) of markers implanted in the fornices of the vagina relative to the full bladder planning scan were established. Prediction accuracy of these correlation models was assessed by comparison with actual displacements in CT-scans, both pre-treatment and after 40 Gy. Inter-fraction ToU and marker-CoM displacements were derived from the established correlations and twice-weekly performed in-room bladder volume measurements, using a 3D ultrasound scanner.
Target displacement in VBF-scans ranged from up to 65 mm in a single direction to almost 0mm, depending on the patient. For pre-treatment VBF-scans, the linear correlation models predicted the mean 3D position change for the ToU of 26.1 mm±10.8 with a residual of only 2.2 mm±1.7. For the marker-CoM, the 8.4 mm±5.3 mean positioning error was predicted with a residual of 0.9 mm±0.7. After 40Gy, the mean ToU displacement was 26.8 mm±15.8, while prediction based on the pre-treatment correlation models yielded a mean residual error of 9.0 mm±3.7. Target positioning errors in the fractioned treatments were very large, especially for the ToU (-18.5mm±11.2 for systematic errors in SI-direction).
Pre-treatment acquired VBF-scans may be used to substantially enhance treatment precision of cervical cancer patients. Application in adaptive therapy is promising and warrants further investigation. For highly conformal (IMRT) treatments, the use of a full bladder drinking protocol results in unacceptably large systematic set-up errors.
研究在自适应治疗中，在预处理时建立膀胱充盈变化与宫颈-子宫位移之间的相关性的应用。
本前瞻性研究纳入了 13 例宫颈癌患者。在预处理时，以及在 40Gy 后，进行了充盈膀胱的 CT 扫描，然后排空膀胱，并在 1 小时内自然充盈膀胱（可变膀胱充盈 CT 扫描，VBF 扫描）进行了另外 4 次 3D 扫描。对于预处理 VBF 扫描，建立了膀胱容积变化与植入阴道穹窿的标记物的子宫顶端（ToU）和质心（CoM）相对于全膀胱计划扫描的位移之间的线性相关性。通过与预处理和 40Gy 后的实际位移进行比较，评估这些相关性模型的预测准确性。在分次治疗中，根据建立的相关性和每周两次的室内膀胱容积测量，使用 3D 超声扫描仪，得出了 ToU 和标记物-CoM 的分次间位移。
在 VBF 扫描中，靶标位移在单个方向上的范围从高达 65mm 到几乎为 0mm，具体取决于患者。对于预处理 VBF 扫描，线性相关模型预测 ToU 的平均 3D 位置变化为 26.1mm±10.8mm，残余误差仅为 2.2mm±1.7mm。对于标记物-CoM，预测的平均定位误差为 8.4mm±5.3mm，残余误差为 0.9mm±0.7mm。40Gy 后，ToU 平均位移为 26.8mm±15.8mm，而基于预处理相关性模型的预测结果平均残余误差为 9.0mm±3.7mm。分次治疗中的靶标定位误差非常大，尤其是对于 ToU（SI 方向的系统误差为-18.5mm±11.2mm）。
预处理时获得的 VBF 扫描可显著提高宫颈癌患者的治疗精度。在自适应治疗中的应用具有很大的前景，值得进一步研究。对于高度适形（调强放疗）治疗，使用全膀胱饮水方案会导致不可接受的大系统设置误差。
