Department of Radiation Oncology, University Medical Center Mannheim, University Heidelberg, Germany.
Strahlenther Onkol. 2011 Jul;187(7):406-15. doi: 10.1007/s00066-011-2198-6. Epub 2011 Jun 27.
For reirradiation of spinal column metastases, intensity-modulated radiation therapy (IMRT) reduces the dose to the spinal cord, while allowing longer treatment times. We analyzed the potential of volumetric modulated arc therapy (VMAT) to reduce treatment time and number of monitor units (MU).
In CT datasets of 9 patients with spinal column metastases, the planned target volume (PTV) encompassed the macroscopic tumor including the spinal cord or medullary cone, respectively. The prescribed dose for the target was 40 Gy, but median spinal cord dose was intended to be < 26 Gy. We compared a posterior (3D-PA) static field technique, a two-field wedge technique (3D-wedge) and 5-/7-beam IMRT with VMAT. Conformity index (CI), homogeneity index (HI40), dose volume histogram (DVH) parameters, treatments delivery time (T), and MU were analyzed. Dosimetry was validated with EDR2-film/ionization chambers.
PTV coverage was insufficient for 3D-conformal radiotherapy (3D-CRT) when spinal cord tolerance was respected. The IMRT approach provided excellent results but has the longest treatment time. VMAT produced dose distributions similar to IMRT with shorter treatment times (VMAT: mean 4:49 min; IMRT: mean 6:50 min) and fewer MU (VMAT: 785; IMRT: 860). Reduced conformity and increased homogeneity for VMAT when compared to IMRT were observed. An absolute deviation between measured and calculated dose of +0.70 ± 3.69% was recorded. γ-Index analysis showed an agreement of 91.33 ± 3.53% for the 5%/5 mm criteria.
For this paradigm, VMAT produces high quality treatment plans with homogeneity/conformity similar to static IMRT, shorter treatment times, and fewer MU. Verification measurements showed good agreement between calculation and delivered dose, leading to clinical implementation.
对于脊柱转移瘤的再照射，强度调制放射治疗（IMRT）降低了脊髓的剂量，同时允许更长的治疗时间。我们分析了容积调强弧形治疗（VMAT）缩短治疗时间和减少监测单位（MU）数量的潜力。
在 9 例脊柱转移瘤患者的 CT 数据集，计划靶区（PTV）包括宏观肿瘤，包括脊髓或圆锥，分别。目标的规定剂量为 40 Gy，但中位脊髓剂量的目的是<26 Gy。我们比较了一种后（3D-PA）静态场技术、两野楔形技术（3D-楔形）和 5/7 束 IMRT 与 VMAT。适形指数（CI）、均匀性指数（HI40）、剂量体积直方图（DVH）参数、治疗时间（T）和 MU 进行了分析。剂量学用 EDR2 胶片/电离室进行验证。
当尊重脊髓耐受时，3D 适形放疗（3D-CRT）的 PTV 覆盖率不足。IMRT 方法提供了优异的结果，但治疗时间最长。VMAT 产生的剂量分布与 IMRT 相似，但治疗时间更短（VMAT：平均 4:49 分钟；IMRT：平均 6:50 分钟），MU 更少（VMAT：785；IMRT：860）。与 IMRT 相比，VMAT 的一致性和均匀性降低。测量和计算剂量之间的绝对偏差为+0.70±3.69%。γ指数分析表明，对于 5%/5 mm 标准，符合率为 91.33±3.53%。
对于这种方案，VMAT 产生了高质量的治疗计划，具有与静态 IMRT 相似的均匀性/适形性、更短的治疗时间和更少的 MU。验证测量显示计算和输送剂量之间具有良好的一致性，从而实现了临床应用。
