基于支持向量机算法的乳腺癌放射治疗自动化光束布置。
Automated beam placement for breast radiotherapy using a support vector machine based algorithm.
机构信息
Department of Electrical and Computer Engineering, Polytechnic Institute of New York University, Brooklyn, NY, USA.
出版信息
Med Phys. 2012 May;39(5):2536-43. doi: 10.1118/1.3700736.
PURPOSE
To develop an automated beam placement technique for whole breast radiotherapy using tangential beams. We seek to find optimal parameters for tangential beams to cover the whole ipsilateral breast (WB) and minimize the dose to the organs at risk (OARs).
METHODS
A support vector machine (SVM) based method is proposed to determine the optimal posterior plane of the tangential beams. Relative significances of including/avoiding the volumes of interests are incorporated into the cost function of the SVM. After finding the optimal 3-D plane that separates the whole breast (WB) and the included clinical target volumes (CTVs) from the OARs, the gantry angle, collimator angle, and posterior jaw size of the tangential beams are derived from the separating plane equation. Dosimetric measures of the treatment plans determined by the automated method are compared with those obtained by applying manual beam placement by the physicians. The method can be further extended to use multileaf collimator (MLC) blocking by optimizing posterior MLC positions.
RESULTS
The plans for 36 patients (23 prone- and 13 supine-treated) with left breast cancer were analyzed. Our algorithm reduced the volume of the heart that receives >500 cGy dose (V5) from 2.7 to 1.7 cm(3) (p = 0.058) on average and the volume of the ipsilateral lung that receives >1000 cGy dose (V10) from 55.2 to 40.7 cm(3) (p = 0.0013). The dose coverage as measured by volume receiving >95% of the prescription dose (V95%) of the WB without a 5 mm superficial layer decreases by only 0.74% (p = 0.0002) and the V95% for the tumor bed with 1.5 cm margin remains unchanged.
CONCLUSIONS
This study has demonstrated the feasibility of using a SVM-based algorithm to determine optimal beam placement without a physician's intervention. The proposed method reduced the dose to OARs, especially for supine treated patients, without any relevant degradation of dose homogeneity and coverage in general.
目的
开发一种基于切线束的全乳放射治疗自动束位设置技术。我们旨在寻找切线束的最佳参数，以覆盖整个左侧乳房（WB）并使风险器官（OARs）的剂量最小化。
方法
提出了一种基于支持向量机（SVM）的方法来确定切线束的最佳后平面。将包括/避免感兴趣体积的相对显著性纳入 SVM 的成本函数中。找到将整个乳房（WB）和包含的临床靶区（CTVs）与 OARs 分开的最佳 3-D 平面后，从分离平面方程中推导出切线束的机架角度、准直器角度和后切缘大小。与医生手动设置束位获得的治疗计划相比，评估自动方法确定的治疗计划的剂量学指标。该方法可以通过优化后多叶准直器（MLC）位置进一步扩展到使用 MLC 阻挡。
结果
分析了 36 例（23 例俯卧位和 13 例仰卧位）左侧乳腺癌患者的计划。我们的算法平均将接受>500 cGy 剂量的心脏体积（V5）从 2.7 减少到 1.7 cm3（p=0.058），并将接受>1000 cGy 剂量的同侧肺体积（V10）从 55.2 减少到 40.7 cm3（p=0.0013）。没有 5 毫米浅层的处方剂量（V95%）的 WB 体积接受率（V95%）下降了 0.74%（p=0.0002），而 1.5 厘米边界肿瘤床的 V95%保持不变。
结论
本研究证明了使用基于 SVM 的算法在没有医生干预的情况下确定最佳束位设置的可行性。该方法降低了 OAR 的剂量，特别是对于仰卧位治疗的患者，同时总体上没有任何相关的剂量均匀性和覆盖度的降低。
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