Experimental realization of dynamic fluence field optimization for proton computed tomography
Experimental realization of dynamic fluence field optimization for proton computed tomography
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DOI：
10.1088/1361-6560/ab9f5f
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发表时间：
2020-10-07
影响因子：
3.5
通讯作者：
Dedes, G.
中科院分区：
文献类型：
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作者：
Dickmann, J.;Sarosiek, C.;Dedes, G.
质子计算机断层扫描 (pCT) 在生成质子治疗治疗计划所需的相对阻止本领 (RSP) 空间图方面具有高精度和剂量效率。通过注量调制 pCT (FMpCT)，可以实现规定的噪声分布，从而可以在采集过程中采用特定于对象的动态调制注量来减少成像剂量。对于 FMpCT 采集，我们将图像分为感兴趣区域 (ROI) 和非 ROI 体积。在质子治疗中，ROI 体积将涵盖所有治疗束。然后，优化算法计算动态调制的注量，以实现 ROI 内的低规定噪声和其他地方的高规定噪声。它还会生成计划的噪声分布，即通过蒙特卡罗模拟计算得出的该注量的预期噪声图。通过使用强度调制笔形光束网格采集 pCT 图像，可以实现优化的注量。在这项工作中，我们连接了临床质子束线的控制系统，以提供优化的注量。使用三个模型，我们获得了具有均匀能量密度、恒定噪声处方和 FMpCT 任务的图像。将图像噪声分布和注量图与相应的计划分布以及处方进行比较。此外，我们提出了一种校正方法，可以消除由于使用具有空间变化能量分布的笔形光束采集而产生的图像伪影，这在临床操作中是看不到的。将 FMpCT 扫描的 RSP 准确性与均匀扫描进行比较，发现与标准 pCT 扫描相当。虽然我们确定了未来实验采集的技术改进，特别是与意外的笔形光束尺寸减小和注量模式失准相关的技术改进，但与计划噪声的一致性令人满意，我们得出结论，针对特定图像噪声处方进行优化的 FMpCT 在实验上是可行的。
Proton computed tomography (pCT) has high accuracy and dose efficiency in producing spatial maps of the relative stopping power (RSP) required for treatment planning in proton therapy. With fluence-modulated pCT (FMpCT), prescribed noise distributions can be achieved, which allows to decrease imaging dose by employing object-specific dynamically modulated fluence during the acquisition. For FMpCT acquisitions we divide the image into region-of-interest (ROI) and non-ROI volumes. In proton therapy, the ROI volume would encompass all treatment beams. An optimization algorithm then calculates dynamically modulated fluence that achieves low prescribed noise inside the ROI and high prescribed noise elsewhere. It also produces a planned noise distribution, which is the expected noise map for that fluence, as calculated with a Monte Carlo simulation. The optimized fluence can be achieved by acquiring pCT images with grids of intensity modulated pencil beams. In this work, we interfaced the control system of a clinical proton beam line to deliver the optimized fluence. Using three phantoms we acquired images with uniform fluence, with a constant noise prescription, and with an FMpCT task. Image noise distributions as well as fluence maps were compared to the corresponding planned distributions as well as to the prescription. Furthermore, we propose a correction method that removes image artifacts stemming from the acquisition with pencil beams having a spatially varying energy distribution that is not seen in clinical operation. RSP accuracy of FMpCT scans was compared to uniform scans and was found to be comparable to standard pCT scans. While we identified technical improvements for future experimental acquisitions, in particular related to an unexpected pencil beam size reduction and a misalignment of the fluence pattern, agreement with the planned noise was satisfactory and we conclude that FMpCT optimized for specific image noise prescriptions is experimentally feasible.