Department of Radiation Oncology, Tom Baker Cancer Center and University of Calgary, 1331 29 Street NW, Calgary, Alberta, Canada.
Radiat Oncol. 2010 Jun 10;5:52. doi: 10.1186/1748-717X-5-52.
Fiducial markers and daily electronic portal imaging (EPI) can reduce the risk of geographic miss in prostate cancer radiotherapy. The purpose of this study was to estimate CTV to PTV margin requirements, without and with the use of this image guidance strategy.
46 patients underwent placement of 3 radio-opaque fiducial markers prior to prostate RT. Daily pre-treatment EPIs were taken, and isocenter placement errors were corrected if they were > or = 3 mm along the left-right or superior-inferior axes, and/or > or = 2 mm along the anterior-posterior axis. During-treatment EPIs were then obtained to estimate intra-fraction motion.
Without image guidance, margins of 0.57 cm, 0.79 cm and 0.77 cm, along the left-right, superior-inferior and anterior-posterior axes respectively, are required to give 95% probability of complete CTV coverage each day. With the above image guidance strategy, these margins can be reduced to 0.36 cm, 0.37 cm and 0.37 cm respectively. Correction of all isocenter placement errors, regardless of size, would permit minimal additional reduction in margins.
Image guidance, using implanted fiducial markers and daily EPI, permits the use of narrower PTV margins without compromising coverage of the target, in the radiotherapy of prostate cancer.
基准标记和日常电子射野影像验证（EPI）可降低前列腺癌放射治疗中靶区外扩的风险。本研究旨在评估在不使用和使用这种图像引导策略的情况下，CTV 至 PTV 的边缘要求。
46 例患者在接受前列腺 RT 前放置了 3 个放射性不透射线的基准标记。每天进行治疗前 EPIs，如果左右轴或上下轴的等中心位置误差>或=3mm，或者前后轴的等中心位置误差>或=2mm，则进行校正。然后进行治疗中 EPIs 以估计分次内运动。
不使用图像引导时，每天需要 0.57cm、0.79cm 和 0.77cm 的左右、上下和前后轴边缘，以获得 95%的CTV 完全覆盖概率。使用上述图像引导策略，这些边缘可以分别减少到 0.36cm、0.37cm 和 0.37cm。无论大小，校正所有等中心位置误差都可以进一步最小化边缘的缩小。
使用植入的基准标记和每日 EPI 的图像引导，可以在不影响靶区覆盖的情况下，在前列腺癌的放射治疗中使用更窄的 PTV 边缘。
