Radiation Therapy Program, Vancouver Island Centre, British Columbia Cancer Agency, Victoria, BC, Canada.
Radiat Oncol. 2006 Sep 19;1:37. doi: 10.1186/1748-717X-1-37.
A protocol of electronic portal imaging (EPI) registration for the verification of radiation treatment fields has been implemented at our institution. A template is generated using the reference images, which is then registered with the EPI for treatment verification. This study examines interobserver consistency among trained radiation therapists in the registration and verification of external beam radiotherapy (EBRT) for patients with prostate cancer.
20 consecutive patients with prostate cancer undergoing EBRT were analyzed. The EPIs from the initial 10 fractions were registered independently by 6 trained radiation therapist observers. For each fraction, an anterior-posterior (AP or PA) and left lateral (Lat) EPIs were generated and registered with the reference images. Two measures of displacement for the AP EPI in the superior-inferior (SI) and right left (RL) directions and two measures of displacement for the Lat EPI in the AP and SI directions were prospectively recorded. A total of 2400 images and 4800 measures were analyzed. Means and standard deviations, as well as systematic and random errors were calculated for each observer. Differences between observers were compared using the chi-square test. Variance components analysis was used to evaluate how much variance is attributed to the observers. Time trends were estimated using repeated measures analysis.
Inter-observer variation expressed as the standard deviation of the six observers' measurements within each image were 0.7, 1.0, 1.7 and 1.4 mm for APLR, APSI, LatAP and LatSI respectively. Variance components analysis showed that the variation attributed to the observers was small compared to variation due to the images. On repeated measure analysis, time trends were apparent only for the APLR and LatSI measurements. Their magnitude however was small.
No clinically important systematic observer effect or time trends were identified in the registration of EPI by the radiation therapist observers in this study. These findings are useful in the documentation of consistency and reliability in the quality assurance of treatment verification of EBRT for prostate cancer.
本机构已实施电子射野影像（EPI）配准方案，用于验证放射治疗靶区。该方案使用参考图像生成模板，然后将模板与 EPI 进行配准，以实现治疗验证。本研究旨在检验经过培训的放射治疗师在验证前列腺癌外照射放射治疗（EBRT）过程中进行 EPI 配准的一致性。
对 20 例接受 EBRT 的前列腺癌患者进行分析。由 6 名经过培训的放射治疗师独立对前 10 次治疗的 EPIs 进行配准。对于每一分次，生成前后位（AP 或 PA）和左侧位（Lat）EPI，并与参考图像进行配准。前瞻性记录 AP 方向上的 SI 和 RL 方向上的两个 AP 方向上的 EPI 位移测量值，以及 Lat 方向上的 AP 和 SI 方向上的两个位移测量值。共分析 2400 幅图像和 4800 个测量值。计算每个观察者的平均值和标准差，以及系统误差和随机误差。采用卡方检验比较观察者之间的差异。采用方差分量分析评估观察者引起的方差占比。采用重复测量分析评估时间趋势。
以 6 名观察者在每个图像内测量值的标准差表示，观察者之间的差异为 APLR、APSI、LatAP 和 LatSI 分别为 0.7、1.0、1.7 和 1.4mm。方差分量分析显示，观察者引起的变异性与图像引起的变异性相比较小。在重复测量分析中，仅在 APLR 和 LatSI 测量值中出现时间趋势，但幅度较小。
在本研究中，放射治疗师观察者在进行 EPI 配准时，未发现有临床意义的系统观测者效应或时间趋势。这些发现有助于记录前列腺癌 EBRT 治疗验证的质量保证过程中一致性和可靠性。
