Inclusion of geometrical uncertainties in radiotherapy treatment planning by means of coverage probability
Inclusion of geometrical uncertainties in radiotherapy treatment planning by means of coverage probability
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DOI：
10.1016/s0360-3016(98)00468-4
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发表时间：
1999-03-01
影响因子：
7
通讯作者：
Visser, AG
中科院分区：
文献类型：
--
作者：
Stroom, JC;de Boer, HCJ;Visser, AG
目的：根据ICRU-50的建议，放射治疗过程中肿瘤位置的几何不确定性通常被包括在治疗计划中，方法是在临床靶体积（CTV）上增加一个边界以产生计划靶体积（PTV）。我们已经开发了一种自动计算该边界的方法。特定患者组的几何不确定性通常可以通过患者组中系统偏差分布的标准偏差（Sigma）来表征并且通过随机偏差分布的平均标准偏差（σ），可以在治疗室坐标系中的3D矩阵中表示要规划的患者的CTV，其中体素值在CTV内部为1并且在CTV外部为0，该矩阵与平移和旋转的适当概率分布的卷积产生具有覆盖概率（CP）的矩阵，覆盖概率（CP）被定义为CTV覆盖的每个点的概率，PTV然后可以被选择为对应于某个等概率水平的体积。对系统偏差和随机偏差进行单独计算，选择等概率体积，系统偏差对CTV中剂量分布的影响可以通过计算系统偏差的CP矩阵的剂量直方图来估计，产生所谓的剂量概率直方图（DPD），A DPD代表患者组中所有系统偏差的平均剂量体积直方图（DVH）。随机偏差的后果可以通过剂量分布与随机偏差的概率分布的卷积来计算。在DPH计算中使用卷积剂量矩阵可获得关于几何不确定性对CTV中剂量影响的完整信息，结果：该模型被证明是快速和准确的前列腺癌，宫颈癌和肺癌的情况下，CTV到PTV边缘大小，确保至少95%的剂量，（平均）99%的CTV，对于所有三种情况似乎等于约2 σ +0.7 σ。由于旋转偏差包括在内，所得到的利润率可以是各向异性的，如前列腺癌的情况下，结论：已经开发了一种方法，用于计算CTV到PTV利润率的基础上的假设，CTV应充分照射的概率很高。(C)1999 Elsevier Science Inc.
Purpose: Following the ICRU-50 recommendations, geometrical uncertainties in tumor position during radiotherapy treatments are generally included in the treatment planning by adding a margin to the clinical target volume (CTV) to yield the planning target volume (PTV), We have developed a method for automatic calculation of this margin.Methods and Materials: Geometrical uncertainties of a specific patient group can normally be characterized by the standard deviation of the distribution of systematic deviations in the patient group (Sigma) and by the average standard deviation of the distribution of random deviations (sigma), The CTV of a patient to be planned can be represented in a 3D matrix in the treatment room coordinate system with voxel values one inside and zero outside the CTV, Convolution of this matrix with the appropriate probability distributions for translations and rotations yields a matrix with coverage probabilities (CPs) which is defined as the probability for each point to be covered by the CTV, The PTV can then be chosen as a volume corresponding to a certain iso-probability level. Separate calculations are performed for systematic and random deviations, Iso-probability volumes are selected in such a way that a high percentage of the CTV volume (on average > 99%) receives a high dose (> 95%), The consequences of systematic deviations on the dose distribution in the CTV can be estimated by calculation of dose histograms of the CP matrix for systematic deviations, resulting in a so-called dose probability histogram (DPH), A DPH represents the average dose volume histogram (DVH) for all systematic deviations in the patient group. The consequences of random deviations can be calculated by convolution of the dose distribution with the probability distributions for random deviations. Using the convolved dose matrix in the DPH calculation yields full information about the influence of geometrical uncertainties on the dose in the CTV,Results: The model is demonstrated to be fast and accurate for a prostate, cervix, and lung cancer case, A CTV-to-PTV margin size which ensures at least 95% dose to (on average) 99% of the CTV, appears to be equal to about 2 Sigma + 0.7 sigma for three all cases. Because rotational deviations are included, the resulting margins can be anisotropic, as shown for the prostate cancer case,Conclusion: A method has been developed for calculation of CTV-to-PTV margins based on the assumption that the CTV should be adequately irradiated with a high probability. (C) 1999 Elsevier Science Inc.