Magnitude of observer error using cone beam CT for prostate interfraction motion estimation: effect of reducing scan length or increasing exposure
Magnitude of observer error using cone beam CT for prostate interfraction motion estimation: effect of reducing scan length or increasing exposure
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DOI：
10.1259/bjr.20150208
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发表时间：
2015-01-01
影响因子：
2.6
通讯作者：
Dearnaley, David P.
中科院分区：
文献类型：
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作者：
McNair, Helen A.;Harris, Emma J.;Dearnaley, David P.
目的：锥形束CT（CBCT）实现软组织与计划CT的配准，用于放射治疗中的位置验证。本研究的目的是确定使用标准CBCT协议进行前列腺位置验证的观察者间误差（IOE），以及与标准成像协议相比，减少CBCT扫描长度或增加曝光的影响。CBCT图像使用新的7 cm长图像和标准曝光获得（1644 mAs），标准12 cm长图像（1644 mAs），部分2（12），7 cm长图像，更高曝光（2632 mAs），部分3（7 H），31例接受放射治疗的前列腺癌患者。8名观察员（2名临床医生和6名放射技师）配准了图像。提供了准则和培训。使用Kruzkal-Wallis检验比较IOE的平均值。Levene的测试被用来测试的IOE和独立的前列腺position.Results的方差的差异：没有显着差异被发现在任何方向上的IOE之间的每个图像协议。平均绝对IOE在前后方向上最大。IOE的标准差（SD）在三种图像协议中的每一种的左右方向上最小。IOE的SD仅显著小于前后（AP）方向上的独立前列腺运动（分别为1.8和3.0 mm：p=0.017）。在RL、SI和AP方向上，95%、77%和96%的图像的IOE在独立前列腺运动的1 SD内。结论：减少CBCT扫描长度和增加曝光对IOE没有显著影响。为了减少成像剂量，可以考虑减少CBCT扫描长度，而不会增加前列腺配准的不确定性。CBCT验证前列腺放疗的精度受IOE的影响，应在实施前进行量化。知识的进步：本研究显示了在CBCT实施前量化IOE大小的重要性。
Objective: Cone beam CT (CBCT) enables soft-tissue registration to planning CT for position verification in radiotherapy. The aim of this study was to determine the interobserver error (IOE) in prostate position verification using a standard CBCT protocol, and the effect of reducing CBCT scan length or increasing exposure, compared with standard imaging protocol.Methods: CBCT images were acquired using a novel 7cm length image with standard exposure (1644 mAs) at Fraction 1 (7), standard 12 cm length image (1644 mAs) at Fraction 2 (12) and a 7cm length image with higher exposure (2632 mAs) at Fraction 3 (7H) on 31 patients receiving radiotherapy for prostate cancer. Eight observers (two clinicians and six radiographers) registered the images. Guidelines and training were provided. The means of the IOEs were compared using a Kruzkal-Wallis test. Levene's test was used to test for differences in the variances of the IOEs and the independent prostate position.Results: No significant difference was found between the IOEs of each image protocol in any direction. Mean absolute IOE was the greatest in the anteroposterior direction. Standard deviation (SD) of the IOE was the least in the left-right direction for each of the three image protocols. The SD of the IOE was significantly less than the independent prostate motion in the anterior-posterior (AP) direction only (1.8 and 3.0 mm, respectively: p=0.017). IOEs were within 1 SD of the independent prostate motion in 95%, 77% and 96% of the images in the RL, SI and AP direction.Conclusion: Reducing CBCT scan length and increasing exposure did not have a significant effect on IOEs. To reduce imaging dose, a reduction in CBCT scan length could be considered without increasing the uncertainty in prostate registration. Precision of CBCT verification of prostate radiotherapy is affected by IOE and should be quantified prior to implementation.Advances in knowledge: This study shows the importance of quantifying the magnitude of IOEs prior to CBCT implementation.