Kim Siyong, Jin Hosang, Yang Huey, Amdur Robert J
Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL 32224, USA.
Int J Radiat Oncol Biol Phys. 2009 Apr 1;73(5):1574-9. doi: 10.1016/j.ijrobp.2008.12.023.
To investigate the amount of target positioning error and evaluate its dosimetric impact during image-guided stereotactic body radiotherapy for single-fraction spine treatment.
A prescription dose of 15 Gy and five to nine coplanar intensity-modulated beams were used. The patient was immobilized with a custom-fit vacuum mold, and the target was localized with a volumetric cone-beam CT image. A robotic couch with six degrees of freedom was used for target adjustment. For evaluation a cone-beam CT image was obtained at the end of treatment. Both target positioning error and its dosimetric impact were investigated for the first 9 cases.
For cases studied, translational errors were 0.9 +/- 0.5 mm (lateral), 1.2 +/- 0.9 mm (longitudinal), 0.7 +/- 0.6 mm (vertical), and 1.8 +/- 1.0 mm (vector), and rotational errors were 1.6 degrees +/- 1.3 degrees (pitch), 0.8 degrees +/- 0.9 degrees (roll), and 0.8 degrees +/- 0.4 degrees (yaw). For the clinical target volume, D(95) (dose to 95% of target volume), D(90), D(max), and D(mean) were evaluated. Only 1 case showed significant dose variations, reaching up to 18% in D(95). The spinal cord dose was evaluated by observing D(0.1) (dose to 0.1 cm(3)), D(0.5), D(1.0), and D(max). Although 1 case showed a dose change reaching up to 30% in D(max), cord dose was within the planning tolerance limit in all but 2 cases (3% higher in one and 0.4% higher in the other).
The implemented image-guided stereotactic body radiotherapy provides precise target localization. However, despite reasonably precise spatial precision, dosimetric perturbation can be significant because of both extremely steep dose gradients and close distances between the target and the spinal cord.
研究单次分割脊柱立体定向体部放射治疗中靶区定位误差的大小，并评估其剂量学影响。
采用15 Gy的处方剂量和五至九个共面调强射束。患者使用定制的真空模具固定，靶区通过容积式锥形束CT图像进行定位。使用具有六个自由度的机器人治疗床进行靶区调整。为进行评估，在治疗结束时获取锥形束CT图像。对前9例患者的靶区定位误差及其剂量学影响进行了研究。
在所研究的病例中，平移误差为0.9±0.5 mm（横向）、1.2±0.9 mm（纵向）、0.7±0.6 mm（垂直）和1.8±1.0 mm（矢量），旋转误差为1.6°±1.3°（俯仰）、0.8°±0.9°（横滚）和0.8°±0.4°（偏航）。对于临床靶区体积，评估了D(95)（靶区体积95%的剂量）、D(90)、D(max)和D(mean)。只有1例显示出显著的剂量变化，D(95)高达18%。通过观察D(0.1)（0.1 cm³的剂量）、D(0.5)、D(1.0)和D(max)来评估脊髓剂量。尽管有1例D(max)显示剂量变化高达30%，但除2例（1例高3%，另1例高0.4%）外，所有病例的脊髓剂量均在计划耐受限度内。
所实施的图像引导立体定向体部放射治疗可提供精确的靶区定位。然而，尽管空间精度合理，但由于剂量梯度极其陡峭以及靶区与脊髓之间距离较近，剂量学扰动可能会很显著。
