Waghorn Benjamin J, Shah Amish P, Rineer Justin M, Langen Katja M, Meeks Sanford L
Department of Radiation Oncology, UF Health Cancer Center at Orlando Health, 1400 South Orange Avenue MP 730, Orlando, Florida 32806, USA.
Radiat Oncol. 2014 Feb 5;9:46. doi: 10.1186/1748-717X-9-46.
Intrafraction motion during step-and-shoot (SNS) IMRT is known to affect the target dosimetry by a combination of dose blurring and interplay effects. These effects are typically managed by adding a margin around the target. A quantitative analysis was performed, assessing the relationship between target motion, margin size, and target dosimetry with the goal of introducing new margin recipes.
A computational algorithm was used to calculate 1,174 motion-encoded dose distributions and DVHs within the patient's CT dataset. Sinusoidal motion tracks were used simulating intrafraction motion for nine lung tumor patients, each with multiple margin sizes.
D95% decreased by less than 3% when the maximum target displacement beyond the margin experienced motion less than 5 mm in the superior-inferior direction and 15 mm in the anterior-posterior direction. For target displacements greater than this, D95% decreased rapidly.
Targets moving in excess of 5 mm outside the margin can cause significant changes to the target. D95% decreased by up to 20% with target motion 10 mm outside the margin, with underdosing primarily limited to the target periphery. Multi-fractionated treatments were found to exacerbate target under-coverage. Margins several millimeters smaller than the maximum target displacement provided acceptable motion protection, while also allowing for reduced normal tissue morbidity.
已知步进式射野（SNS）调强放疗期间的分次内运动通过剂量模糊和相互作用效应的组合影响靶区剂量学。这些效应通常通过在靶区周围添加边界来处理。进行了定量分析，评估靶区运动、边界大小和靶区剂量学之间的关系，目的是引入新的边界处方。
使用一种计算算法在患者的CT数据集中计算1174个运动编码的剂量分布和剂量体积直方图。使用正弦运动轨迹模拟9例肺肿瘤患者的分次内运动，每个患者有多个边界大小。
当超出边界的靶区最大位移在上下方向小于5mm且前后方向小于15mm时，D95%下降不到3%。对于大于此值的靶区位移，D95%迅速下降。
在边界外移动超过5mm的靶区可导致靶区发生显著变化。当靶区在边界外移动10mm时，D95%下降高达20%，剂量不足主要局限于靶区周边。发现多次分割治疗会加剧靶区覆盖不足。比靶区最大位移小几毫米的边界提供了可接受的运动保护，同时也能降低正常组织的并发症。
