Lohr F, Schramm O, Schraube P, Sroka-Perez G, Seeber S, Schlepple G, Schlegel W, Wannenmacher M
Department of Clinical Radiology, Radiologische Klinik, University of Heidelberg, Germany.
Radiother Oncol. 1997 Nov;45(2):199-207. doi: 10.1016/s0167-8140(97)00111-4.
Simulation of 3D-treatment plans for head and neck malignancy is difficult due to complex anatomy. Therefore, CT-simulation and stereotactic techniques are becoming more common in the treatment preparation, overcoming the need for simulation. However, if simulation is still performed, it is an important step in the treatment preparation/execution chain, since simulation errors, if not detected immediately, can compromise the success of treatment. A recently developed PC-based system for on-line image matching and comparison of digitally reconstructed radiographs (DRR) and distortion corrected simulator monitor images that enables instant correction of field placement errors during the simulation process was evaluated. The range of field placement errors with non-computer aided simulation is reported.
For 14 patients either a primary 3D-treatment plan or a 3D-boost plan after initial treatment with opposing laterals for head and neck malignancy with a coplanar or non-coplanar two- or three-field technique was simulated. After determining the robustness of the matching process and the accuracy of field placement error detection with phantom measurements, DRRs were generated from the treatment planning CT-dataset of each patient and were interactively matched with on-line simulator images that had undergone correction for geometrical distortion, using a landmark algorithm. Translational field placement errors in all three planes as well as in-plane rotational errors were studied and were corrected immediately.
The interactive matching process is very robust with a tolerance of <2 mm when suitable anatomical landmarks are chosen. The accuracy for detection of translational errors in phantom measurements was <1 mm and for in-plane rotational errors the accuracy had a maximum of only 1.5 degrees. For patient simulation, the mean absolute distance of the planned versus simulated isocenter was 6.4 +/- 3.9 mm. The in-plane rotational error in both planes was <3 degrees with one exception. Three large field placement errors (two patients with 11.5 and 16.0 mm distances of the planned versus simulated isocenter, respectively and one patient with a 7 degree rotational error) were detected and, as with the smaller errors, were immediately corrected.
On-line image matching of treatment planning CT-derived DRRs and distortion corrected treatment simulator images is a precise and reliable method to reduce field placement errors in the simulation of complex 3D-treatment plans for head and neck malignancy and thus enhances accuracy in the first step of the treatment preparation/execution chain. However, out-of-plane rotational errors could not be assessed and assumedly they are comparatively small since due to rigid fixation, detected in-plane errors were small.
由于头颈部恶性肿瘤的解剖结构复杂，对头颈部恶性肿瘤进行三维治疗计划的模拟很困难。因此，CT模拟和立体定向技术在治疗准备中越来越普遍，从而无需进行模拟。然而，如果仍然进行模拟，这是治疗准备/执行链中的重要一步，因为模拟误差若未立即检测到，可能会影响治疗的成功。对最近开发的基于PC的系统进行了评估，该系统用于在线图像匹配以及数字重建X线片（DRR）与失真校正模拟器监测图像的比较，能够在模拟过程中即时校正射野放置误差。报告了非计算机辅助模拟时射野放置误差的范围。
对14例患者进行了模拟，这些患者要么进行了原发性三维治疗计划，要么在对头颈部恶性肿瘤采用共面或非共面两野或三野技术进行初始对侧野治疗后进行了三维增强计划。在用体模测量确定匹配过程的稳健性和射野放置误差检测的准确性之后，从每位患者治疗计划CT数据集中生成DRR，并使用地标算法将其与已进行几何失真校正的在线模拟器图像进行交互式匹配。研究了所有三个平面中的平移射野放置误差以及平面内旋转误差，并立即进行了校正。
当选择合适的解剖地标时，交互式匹配过程非常稳健，容差<2mm。体模测量中平移误差的检测精度<1mm，平面内旋转误差的检测精度最高仅为1.5度。对于患者模拟，计划等中心与模拟等中心的平均绝对距离为6.4±3.9mm。除一例例外，两个平面内的平面内旋转误差均<3度。检测到三个较大的射野放置误差（两名患者计划等中心与模拟等中心的距离分别为11.5和16.0mm，一名患者有7度的旋转误差），与较小误差一样，这些误差也立即得到了校正。
治疗计划CT衍生的DRR与失真校正的治疗模拟器图像的在线图像匹配是一种精确且可靠的方法，可减少头颈部恶性肿瘤复杂三维治疗计划模拟中的射野放置误差，从而在治疗准备/执行链的第一步提高准确性。然而，无法评估平面外旋转误差，并且由于刚性固定，检测到的平面内误差较小，推测平面外旋转误差相对较小。
