Esik O, Bortfeld T, Bendl R, Németh G, Schlegel W
National Institute of Oncology, Department of Radiotherapy, Budapest, Hungary.
Strahlenther Onkol. 1997 Apr;173(4):193-200. doi: 10.1007/BF03039288.
Three-dimensional inverse treatment planning with modulated beams was applied for dosimetric optimization of a lengthy (22 cm) and complex (concave-convex) shaped planning target volume (PTV) in the cervical and upper mediastinal regions.
The planning was done for 9 coplanar beams spaced evenly at 40 intervals. Properties of 15 MV photons from a linear accelerator were simulated. The optimization of the fluence modulation profiles for each beam was based on a definition of the desired/permitted relative dose levels in the PTV and organs at risk, and a definition of the strengths of the constraints to achieve these objectives.
An adequate dose delivery to the PTV and protection of the spinal cord are completely achievable. The dose delivered to the lungs is clinically acceptable with respect to the risk of radiation-induced pneumonitis. For reasons of physics, no further decrease in the radiation burden on the lungs can be attained with X-rays without compromising the PTV coverage. The radiation burden on some critical part of normal tissues was effectively reduced by application of a dummy organ at risk.
The inverse planning is an effective method for conformal radiotherapy of large tumors as well. However, the power of the technique is insufficient when the tolerance dose of the neighbouring normal tissue is too low and its volume effect is high. Although requiring further operator interactions, introduction of dummy organs at risk may be of help in reducing the radiation burden on normal tissues.
应用调强束三维逆向治疗计划对颈段和上纵隔区域一个长（22厘米）且形状复杂（凹凸形）的计划靶区（PTV）进行剂量优化。
对9个共面束进行计划，束间间隔40度均匀分布。模拟了直线加速器产生的15兆伏光子的特性。每个束的注量调制曲线优化基于PTV和危及器官中期望/允许的相对剂量水平的定义，以及实现这些目标的约束强度的定义。
完全可以实现向PTV的充分剂量传递以及对脊髓的保护。就放射性肺炎风险而言，传递到肺部的剂量在临床上是可接受的。由于物理原因，在不影响PTV覆盖的情况下，用X射线无法进一步降低肺部的辐射负担。通过应用一个虚拟危及器官，有效降低了正常组织某些关键部位的辐射负担。
逆向计划也是大肿瘤适形放疗的有效方法。然而，当邻近正常组织的耐受剂量过低且其体积效应较高时，该技术的效能不足。尽管需要进一步的操作者交互，但引入虚拟危及器官可能有助于减轻正常组织的辐射负担。
