MRI-based treatment plan simulation and adaptation for ion radiotherapy using a classification-based approach.
MRI-based treatment plan simulation and adaptation for ion radiotherapy using a classification-based approach.
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DOI：
10.1186/1748-717x-8-51
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发表时间：
2013-03-06
期刊：
影响因子：
--
通讯作者：
Greilich S
中科院分区：
文献类型：
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作者：
Rank CM;Tremmel C;Hünemohr N;Nagel AM;Jäkel O;Greilich S
为了在离子放射治疗中受益于肿瘤的高度适形照射，需要复杂的治疗计划和模拟。本研究的目的是调查的潜力，MRI的离子放射治疗计划模拟和适应使用分类为基础的方法。首先，体素组织分类应用于从MR图像获得伪CT数，使用多达8个对比度。在三个体模的交叉验证研究中评价了适当的MR序列和参数。其次，使用基于MRI的伪CT和参考CT优化离子放射治疗计划，并在参考CT上重新计算。最后，模拟目标偏移，并在伪CT上优化适应偏移的治疗计划，并与没有计划调整的参考CT优化进行比较。伪CT值的推导导致81 - 95 HU范围内的平均绝对误差。最显着的偏差出现在空气和不同的组织类之间的边界，起源于部分体积效应。使用伪CT进行优化的离子放射治疗计划的模拟显示，与参考CT优化相比，靶体积的远端区域中的PTV平均剂量偏差仅为1.4 - 3.1%。适应于靶体积偏移并在伪CT上优化的计划显示出与在参考CT上优化的非适应计划相当的靶剂量覆盖范围。我们能够证明，虽然不存在物理关系，但使用纯统计分类方法的基于MRI的伪CT值推导是可行的。大的误差出现在密质骨类，并来自一个不完善的区别骨和其他组织类型的MRI。在治疗计划的模拟中，证明了这些偏差与在两个方向上2 mm的靶体积移位的不确定性相当，这表明特别是自适应离子放射疗法的应用是有趣的。
In order to benefit from the highly conformal irradiation of tumors in ion radiotherapy, sophisticated treatment planning and simulation are required. The purpose of this study was to investigate the potential of MRI for ion radiotherapy treatment plan simulation and adaptation using a classification-based approach. Firstly, a voxelwise tissue classification was applied to derive pseudo CT numbers from MR images using up to 8 contrasts. Appropriate MR sequences and parameters were evaluated in cross-validation studies of three phantoms. Secondly, ion radiotherapy treatment plans were optimized using both MRI-based pseudo CT and reference CT and recalculated on reference CT. Finally, a target shift was simulated and a treatment plan adapted to the shift was optimized on a pseudo CT and compared to reference CT optimizations without plan adaptation. The derivation of pseudo CT values led to mean absolute errors in the range of 81 - 95 HU. Most significant deviations appeared at borders between air and different tissue classes and originated from partial volume effects. Simulations of ion radiotherapy treatment plans using pseudo CT for optimization revealed only small underdosages in distal regions of a target volume with deviations of the mean dose of PTV between 1.4 - 3.1% compared to reference CT optimizations. A plan adapted to the target volume shift and optimized on the pseudo CT exhibited a comparable target dose coverage as a non-adapted plan optimized on a reference CT. We were able to show that a MRI-based derivation of pseudo CT values using a purely statistical classification approach is feasible although no physical relationship exists. Large errors appeared at compact bone classes and came from an imperfect distinction of bones and other tissue types in MRI. In simulations of treatment plans, it was demonstrated that these deviations are comparable to uncertainties of a target volume shift of 2 mm in two directions indicating that especially applications for adaptive ion radiotherapy are interesting.