University Clinic for Radiotherapy and Radio-Oncology, Salzburg, Austria.
Int J Radiat Oncol Biol Phys. 2012 Aug 1;83(5):1624-32. doi: 10.1016/j.ijrobp.2011.10.009. Epub 2011 Dec 30.
We developed and evaluated a correction strategy for prostate rotations using direct adaptation of segments in intensity-modulated radiotherapy (IMRT).
Implanted fiducials (four gold markers) were used to determine interfractional translations, rotations, and dilations of the prostate. We used hybrid imaging: The markers were automatically detected in two pretreatment planar X-ray projections; their actual position in three-dimensional space was reconstructed from these images at first. The structure set comprising prostate, seminal vesicles, and adjacent rectum wall was transformed accordingly in 6 degrees of freedom. Shapes of IMRT segments were geometrically adapted in a class solution forward-planning approach, derived within seconds on-site and treated immediately. Intrafractional movements were followed in MV electronic portal images captured on the fly.
In 31 of 39 patients, for 833 of 1013 fractions (supine, flat couch, knee support, comfortably full bladder, empty rectum, no intraprostatic marker migrations >2 mm of more than one marker), the online aperture adaptation allowed safe reduction of margins clinical target volume-planning target volume (prostate) down to 5 mm when only interfractional corrections were applied: Dominant L-R rotations were found to be 5.3° (mean of means), standard deviation of means ±4.9°, maximum at 30.7°. Three-dimensional vector translations relative to skin markings were 9.3 ± 4.4 mm (maximum, 23.6 mm). Intrafractional movements in 7.7 ± 1.5 min (maximum, 15.1 min) between kV imaging and last beam's electronic portal images showed further L-R rotations of 2.5° ± 2.3° (maximum, 26.9°), and three-dimensional vector translations of 3.0 ±3.7 mm (maximum, 10.2 mm). Addressing intrafractional errors could further reduce margins to 3 mm.
We demonstrated the clinical feasibility of an online adaptive image-guided, intensity-modulated prostate protocol on a standard linear accelerator to correct 6 degrees of freedom of internal organ motion, allowing safe and straightforward implementation of margin reduction and dose escalation.
我们开发并评估了一种使用强度调制放射治疗（IMRT）中节段直接自适应校正前列腺旋转的方法。
植入的基准标记（四个金标记）用于确定前列腺的分次间平移、旋转和扩张。我们使用混合成像：在两个预处理的平面 X 射线投影中自动检测标记；从这些图像中首次重建它们在三维空间中的实际位置。相应地，在 6 个自由度中转换包括前列腺、精囊和相邻直肠壁的结构集。在几秒钟内在现场生成的类解决方案正向规划方法中，对 IMRT 节段的形状进行几何自适应，并立即进行处理。在飞行中捕获的 MV 电子门控图像中跟踪分次内运动。
在 39 例患者中的 31 例中，在 1013 个分次中的 833 个分次中（仰卧位、平板床、膝盖支撑、膀胱完全充盈、直肠排空、没有一个内部标记迁移超过 2 毫米且超过一个标记），在线孔径自适应允许在仅应用分次间校正时将临床靶体积-计划靶体积（前列腺）的边缘安全减少到 5 毫米：发现主要的左右旋转为 5.3°（平均值），平均值的标准差±4.9°，最大值为 30.7°。相对于皮肤标记的三维向量平移为 9.3 ± 4.4 mm（最大值，23.6 mm）。在 kV 成像和最后束电子门控图像之间的 7.7 ± 1.5 分钟内的分次内运动显示进一步的左右旋转为 2.5° ± 2.3°（最大值，26.9°），以及三维向量平移为 3.0 ±3.7 mm（最大值，10.2 mm）。解决分次内误差可以进一步将边缘减少到 3 毫米。
我们在标准线性加速器上演示了在线自适应图像引导、强度调制前列腺方案的临床可行性，该方案可以校正 6 个自由度的内部器官运动，允许安全且直接地实施边缘减少和剂量升级。
