Variability in target delineation of cervical carcinoma: A Korean radiation oncology group study (KROG 15-06)

Purpose
To determine inter-observer variability in target volume definition of cervical cancer in radical and adjuvant radiotherapy (RT) settings.
Methods
Eight physicians contoured CTVs of 2 patients underwent definitive and postoperative RT. Each volume was analyzed using the individual/median volume ratio and generalized conformity index (CIgen). And center of mass (COM) of each contour was calculated. Expert agreement was quantified using an expectation maximization algorithm for Simultaneous Truth and Performance Level Estimation (STAPLE).
Results
For definitive RT, the individual/median volume ratio ranged from 0.51 to 1.41, and CIgen was 0.531. Mean 3-dimensional distances of average to each COM were 7.8 mm. For postoperative RT setting, corresponding values were 0.65–1.38, 0.563, and 5.3 mm. Kappa value of expert agreement was 0.65 and 0.67, respectively. STAPLE estimates of the sensitivity, specificity, and kappa measures of inter-physician agreement were 0.73, 0.98, and 0.65 for the definitive and 0.75, 0.98, and 0.67 for the adjuvant radiotherapy setting. The largest difference was observed in the superior-inferior direction, particularly in the upper vagina and the common iliac area.
Conclusion
As there was still some variability in target delineation, more detailed guidelines for target volume delineation and continuing education would help to reduce this uncertainty.

研究目的
明确根治性放疗（radical radiotherapy, RT）与辅助放疗（adjuvant radiotherapy, RT）场景下，宫颈癌靶体积勾画的观察者间变异程度。

研究方法
共8名医师对2例分别接受根治性放疗与术后放疗的患者的临床靶体积（Clinical Target Volume, CTV）进行了勾画。针对每一例勾画轮廓，分别采用个体体积/中位体积比值与广义适配指数（generalized conformity index, CIgen）开展分析，并计算每个勾画轮廓的质心（center of mass, COM）。采用基于期望最大化算法的同时真值与性能水平估计算法（Simultaneous Truth and Performance Level Estimation, STAPLE）量化专家共识度。

研究结果
对于根治性放疗场景，个体体积/中位体积比值范围为0.51~1.41，CIgen为0.531，各勾画轮廓的质心与平均勾画的三维距离均值为7.8 mm。对于术后放疗场景，对应数值分别为0.65~1.38、0.563与5.3 mm。医师间专家共识的Kappa值分别为0.65与0.67。经STAPLE算法估算的医师间一致性灵敏度、特异度与Kappa指标：根治性放疗组分别为0.73、0.98与0.65，辅助放疗组分别为0.75、0.98与0.67。医师间勾画差异在头脚方向最为显著，尤其集中于阴道上段与髂总淋巴引流区。

研究结论
鉴于宫颈癌靶区勾画仍存在一定变异，制定更为细致的靶体积勾画指南并开展继续教育，将有助于降低此类不确定性。