Bollet Marc A, McNair Helen A, Hansen Vibeke N, Norman Andrew, O'Doherty Una, Taylor Helen, Rose Mark, Mukherjee Rahul, Huddart Robert
Academic Unit of Radiotherapy & Oncology, The Royal Marsden NHS Trust, Sutton, United Kingdom.
Int J Radiat Oncol Biol Phys. 2003 Nov 15;57(4):1122-30. doi: 10.1016/s0360-3016(03)01379-8.
To evaluate the precision of using digitally reconstructed radiographs (DRRs) of either 3 mm or 6 mm slice separation vs. using simulator images for the setup verification of patients receiving CT planned conformal radiotherapy to the prostate. To calculate the transfer error between CT and simulator.
Twenty patients were CT scanned (3 mm slice spacing/width). DRRs were generated for both 3 mm (DRR 3) and 6 mm (DRR 6) separations. DRRs and a simulator image of an anterior and a lateral field were used as reference images. Five observers matched each of the reference images to treatment images using the Theraview "Target check" facility. It was assumed that poorer images would lead to a loss of precision of field placement estimations (FPE) between observers. The study was designed to detect a difference greater than 1.5 mm(2) in the precision of image placement. The transfer error was the mean difference in the setup error derived from the DRRs and the simulation films.
The precision of evaluations for simulator films and 3 mm DRRs were similar. There was a trend for the DRR 6 mm to achieve less precise results which was greatest for craniocaudal examinations (variance: simulator 1.5 mm(2), DRR6 2.8 mm(2), p = 0.17), but this did not reach statistical significance. A range of transfer errors was identified, with standard deviations ranging from 1.7 to 4.2 mm. There was evidence of a significant systematic bias in anterior craniocaudal (1.3-1.9 mm, p < 0.004) and anterior posterior (-1.9 mm, p = 0.027).
The precision of setup evaluations using DRRs is similar to that achieved by using simulator fields when planning conformal prostate radiotherapy. The use of DRRs could reduce systematic errors introduced in the planning process.
评估使用层厚为3mm或6mm的数字重建射线影像（DRR）与使用模拟定位机影像进行前列腺CT计划适形放疗患者摆位验证的精度。计算CT与模拟定位机之间的转移误差。
对20例患者进行CT扫描（层厚/层间距为3mm）。分别生成层厚为3mm（DRR 3）和6mm（DRR 6）的DRR。将DRR以及前后野的模拟定位机影像用作参考影像。5名观察者使用Theraview“靶区检查”工具将每个参考影像与治疗影像进行匹配。假定较差的影像会导致观察者之间野位置估计（FPE）精度降低。该研究旨在检测影像放置精度中大于1.5mm²的差异。转移误差是指由DRR和模拟定位片得出的摆位误差的平均差值。
模拟定位片和3mm DRR的评估精度相似。6mm DRR有得出不太精确结果的趋势，在头脚方向检查中最为明显（方差：模拟定位片1.5mm²，DRR6 2.8mm²，p = 0.17），但未达到统计学显著性。确定了一系列转移误差，标准差范围为1.7至4.2mm。有证据表明在前头脚方向（1.3 - 1.9mm，p < 0.004）和前后方向（-1.9mm，p = 0.027）存在显著的系统偏差。
在计划适形前列腺放疗时，使用DRR进行摆位评估的精度与使用模拟定位机野的精度相似。使用DRR可减少计划过程中引入的系统误差。
