Department of Clinical Oncology, Edinburgh Cancer Centre, Edinburgh, UK.
Clin Oncol (R Coll Radiol). 2011 Nov;23(9):601-7. doi: 10.1016/j.clon.2011.04.004. Epub 2011 May 6.
The target volume for breast radiotherapy after conservative surgery for breast cancer may be affected by breathing motion. We investigated differences between conventional and four-dimensional computed tomography-based treatment planning and whether gating could improve dose volume parameters.
Ten patients with left-sided breast cancer and surgical clips at the excision site had conventional treatment planning computed tomography and four-dimensional computed tomography. Treatment plans using two tangential beams (6 MV X-rays) were optimised for target coverage and homogeneity using a field in field technique for the three-dimensional scan. This plan was applied directly to four-dimensional datasets representing individual phases of the breathing cycle and combinations thereof (average and maximum intensity projection). Optimised plans were generated for the maximum inhalation scan to study what could potentially be achieved in gated radiotherapy.
Four-dimensional computed tomography with effective doses of around 10 mSv proved to be adequate for treatment planning in all patients. The average motion of the surgical clips was 3.7 mm (range 1.7-6.5mm), which was similar to the movement of the chest wall. With a margin of 7 mm for the whole breast to planning target volume, conventional three-dimensional computed tomography-based planning was found to adequately cover the target as seen on four-dimensional computed tomography without significant differences in normal tissue sparing. Improved sparing of the heart and lung could only be achieved by reducing the posterior margin of the target volume, which may be justified if four-dimensional computed tomography is used to determine the target and its motion.
No significant benefit has been shown for the use of four-dimensional computed tomography-based planning if motion management is not implemented concurrently with a reduced posterior margin between clinical and planning target volumes.
乳腺癌保乳手术后的乳腺放射治疗靶区可能会受到呼吸运动的影响。我们研究了基于常规 CT 和四维 CT 的治疗计划之间的差异，以及门控技术是否可以改善剂量体积参数。
10 例左侧乳腺癌患者，切除部位有手术夹，进行常规治疗计划 CT 和四维 CT。使用二维切线束（6MVX 射线）对三维扫描的靶区覆盖和均匀性进行优化，采用场中场技术。将该计划直接应用于四维数据集，代表呼吸周期的各个相位及其组合（平均和最大强度投影）。为最大吸气扫描生成优化计划，以研究门控放射治疗中可能实现的目标。
所有患者的四维 CT 有效剂量约为 10mSv，可用于治疗计划。手术夹的平均运动为 3.7mm（范围 1.7-6.5mm），与胸壁运动相似。对于整个乳房到计划靶区的边界为 7mm，如果使用四维 CT 来确定靶区及其运动，则常规三维 CT 基于计划的规划可以充分覆盖靶区，而不会对正常组织的保护产生显著差异。只有通过减少靶区的后界才能更好地保护心脏和肺部，这在使用四维 CT 确定靶区及其运动的情况下可能是合理的。
如果不结合临床和计划靶区之间的后界减少来实施运动管理，则使用基于四维 CT 的计划并不能显著获益。
