Online adaption approaches for intensity modulated proton therapy for head and neck patients based on cone beam CTs and Monte Carlo simulations
Online adaption approaches for intensity modulated proton therapy for head and neck patients based on cone beam CTs and Monte Carlo simulations
复制标题
DOI：
10.1088/1361-6560/aaf30b
复制
发表时间：
2019-01-01
影响因子：
3.5
通讯作者：
Paganetti, H.
中科院分区：
文献类型：
--
作者：
Botas, P.;Kim, J.;Paganetti, H.
为了开发一种基于快速蒙特卡罗剂量计算和锥束CT(CBCT)成像的强度调制质子治疗(IMPT)在线计划自适应算法，对平均6次CBCT扫描的头颈部癌症患者进行研究。为了使治疗计划适应新的患者几何形状，将轮廓传播到CBCT，并通过CT和CBCT之间的可变形图像配准计算向量场(VF)。在自适应规划算法中，波束在其远端衰减处跟随VF移动，并在CBCT中进行光线跟踪以调整其能量，创建几何适应的规划。研究了四种几何自适应模式：无约束几何移位(Free)、等中心移位(ISO)、距离移位(RS)和等中心移位和距离移位(ISO-RS)。在评估几何自适应后，利用MC生成的影响矩阵自动调整选定波束子集的权重，以满足原始计划要求。所有的Beamlet计算都是在GPU(图形处理单元)上运行的快速蒙特卡洛算法完成的。仅几何适应仅适用于微小的解剖变化。权重调整适配适用于每个分数，Free和Iso模式的性能相似，并且优于两个距离移位器模式。在体重调节的自由模式下，平均V95和V107分别为99.4+/-0.9和6.4%+/-4.7%。每个分数的计算时间接近于5min，但进一步的任务并行化可以将其减少到与患者建立后的传递适应相似的1-2min，并开发了一种在线适应算法，显著提高了分数间几何变化的治疗质量。该算法的临床实施将允许在治疗前立即进行分娩适应，从而允许计划IMPT的利润率降低。
To develop an online plan adaptation algorithm for intensity modulated proton therapy (IMPT) based on fast Monte Carlo dose calculation and cone beam CT (CBCT) imaging.A cohort often head and neck cancer patients with an average of six CBCT scans were studied. To adapt the treatment plan to the new patient geometry, contours were propagated to the CBCTs with a vector field (VF) calculated with deformable image registration between the CT and the CBCTs. Within the adaptive planning algorithm, beamlets were shifted following the VF at their distal falloff and raytraced in the CBCT to adjust their energies, creating a geometrically adapted plan. Four geometric adaptation modes were studied: unconstrained geometric shifts (Free), isocenter shift (Iso), a range shifter (RS), or isocenter shift and range shifter (Iso-RS). After evaluation of the geometrical adaptation, the weights of a selected subset of beamlets were automatically tuned using MC-generated influence matrices to fulfill the original plan requirements. All beamlet calculations were done with a fast Monte Carlo running on a GPU (graphics processing unit).Geometrical adaptation alone only worked with small anatomy changes. The weight-tuned adaptation worked for every fraction, with the Free and Iso modes performing similarly and being superior than the two range shifters modes. The mean V95 and V107 were 99.4 +/- 0.9 and 6.4% +/- 4.7% in the Free mode with weight tuning. The calculation time per fraction was similar to 5 min, but further task parallelization could reduce it to similar to 1-2 min for delivery adaptation right after patient setup.An online adaptation algorithm was developed that significantly improved the treatment quality for inter-fractional geometry changes. Clinical implementation of the algorithm would allow delivery adaptation right before treatment and thus allow planning margin reductions for IMPT.