Fiorino C, Reni M, Bolognesi A, Cattaneo G M, Calandrino R
Servizio di Fisica Sanitaria, H.S. Raffaele, Milano, Italy.
Radiother Oncol. 1998 Jun;47(3):285-92. doi: 10.1016/s0167-8140(98)00021-8.
Accurate contouring of the clinical target volume (CTV) is a fundamental prerequisite for successful conformal radiotherapy of prostate cancer. The purpose of this study was to investigate intra- and inter-observer variability in contouring prostate (P) and seminal vesicles (SV) and its impact on conformal treatment planning in our working conditions.
Inter-observer variability was investigated by asking five well-trained radiotherapists of contouring on CT images the P and the SV of six supine-positioned patients previously treated with conformal techniques. Short-term intra-observer variability was assessed by asking the radiotherapists to contour the P and SV of one patient for a second time, just after the first contouring. The differences among the inserted volumes were considered for both intra- and inter-observer variability. Regarding intra-observer variability, the differences between the two inserted contours were estimated by taking the relative differences in correspondence to the CT slices on BEV plots (antero-posterior and left-right beams). Concerning inter-observer variability, the distances between the internal and external envelopes of the inserted contours (named projected diagnostic uncertainties or PDUs) and the distances from the mean inserted contours (named mean contour distances or MCDs) were measured from BEV plots (i.e. parallel to the CT slices).
Intra-observer variability was relatively small (the average percentage variation of the volume was approximately 5%; SD of the differences measured on BEV plots within 1.8 mm). Concerning inter-observer variability, the percentage SD of the inserted volumes ranged from 10 to 18%. Differences equal to 1 cm in the cranio-caudal extension of P + SV were found in four out of six patients. The largest inter-observer variability was found when considering the anterior margin in the left-right beam of P top (MCD = 7.1 mm, 1 SD). Relatively high values for MCDs were also found for P bottom, for the posterior and lateral margins of P top (2.6 and 3.1 mm, respectively, I SD) and for the anterior margin of SV (2.8 mm, 1 SD). Relatively small values were found for P central (from 1.4 to 2.0 mm, 1 SD) and the posterior margin of SV (1.5 mm, 1 SD).
The application of larger margins taking inter-observer variability into account should be taken into consideration for the anterior and the lateral margins of SV and P top and for the lateral margin of P. The impact of short-term intra-observer variability does not seem to be relevant.
准确勾画临床靶区（CTV）是前列腺癌成功进行适形放疗的基本前提。本研究的目的是调查在我们的工作条件下，观察者内和观察者间在勾画前列腺（P）和精囊（SV）时的变异性及其对适形治疗计划的影响。
通过让五位训练有素的放射治疗师在CT图像上勾画六例先前接受适形技术治疗的仰卧位患者的P和SV，来研究观察者间变异性。通过要求放射治疗师在首次勾画后立即再次勾画一例患者的P和SV，来评估短期观察者内变异性。对于观察者内和观察者间变异性，均考虑所勾画体积之间的差异。对于观察者内变异性，通过在BEV图（前后和左右射野）上对应CT层面计算相对差异来估计两次勾画轮廓之间的差异。对于观察者间变异性，从BEV图（即平行于CT层面）测量所勾画轮廓的内部和外部包络之间的距离（称为投影诊断不确定性或PDU）以及与平均勾画轮廓的距离（称为平均轮廓距离或MCD）。
观察者内变异性相对较小（体积的平均百分比变化约为5%；在BEV图上测量的差异标准差在1.8mm以内）。关于观察者间变异性，所勾画体积的标准差百分比范围为10%至18%。在六例患者中有四例患者的P + SV的头脚方向延伸差异达1cm。在考虑P顶部左右射野的前缘时发现最大的观察者间变异性（MCD = 7.1mm，1个标准差）。对于P底部、P顶部的后缘和侧缘（分别为2.6和3.1mm，1个标准差）以及SV的前缘（2.8mm，1个标准差），也发现MCD值相对较高。对于P中央（1.4至2.0mm，1个标准差）和SV的后缘（1.5mm，1个标准差），发现值相对较小。
在制定适形放疗计划时，应考虑到观察者间变异性，在SV和P顶部的前缘及侧缘以及P的侧缘适当扩大安全边界。短期观察者内变异性的影响似乎不大。
