Abstract：
Objective. In current clinical practice for quality assurance (QA), intensity modulated proton therapy (IMPT) fields are verified by measuring planar dose distributions at one or a few selected depths in a phantom. A QA device that measures full 3D dose distributions at high spatiotemporal resolution would be highly beneficial for existing as well as emerging proton therapy techniques such as FLASH radiotherapy. Our objective is to demonstrate feasibility of 3D dose measurement for IMPT fields using a dedicated multi-layer strip ionization chamber (MLSIC) device.Approach.Our developed MLSIC comprises a total of 66 layers of strip ion chamber (IC) plates arranged, alternatively, in thexandydirection. The first two layers each has 128 channels in 2 mm spacing, and the following 64 layers each has 32/33 IC strips in 8 mm spacing which are interconnected every eight channels. A total of 768-channel IC signals are integrated and sampled at a speed of 6 kfps. The MLSIC has a total of 19.2 cm water equivalent thickness and is capable of measurement over a 25 × 25 cm2field size. A reconstruction algorithm is developed to reconstruct 3D dose distribution for each spot at all depths by considering a double-Gaussian-Cauchy-Lorentz model. The 3D dose distribution of each beam is obtained by summing all spots. The performance of our MLSIC is evaluated for a clinical pencil beam scanning (PBS) plan.Main results.The dose distributions for each proton spot can be successfully reconstructed from the ionization current measurement of the strip ICs at different depths, which can be further summed up to a 3D dose distribution for the beam. 3D Gamma Index analysis indicates acceptable agreement between the measured and expected dose distributions from simulation, Zebra and MatriXX.Significance.The dedicated MLSIC is the first pseudo-3D QA device that can measure 3D dose distribution in PBS proton fields spot-by-spot.
摘要：
目的：
在目前的质量保证(QA)临床实践中，通过在体模中的一个或几个选定深度处测量平面剂量分布来验证强度调制质子治疗(IMT)场。以高时空分辨率测量全3D剂量分布的QA设备对于现有的以及新兴的质子治疗技术(诸如FLASH放射治疗)将是非常有益的。我们的目标是证明使用专用多层带状电离室（MLSIC）设备对IMT场进行3D剂量测量的可行性。＆＃xD;方法：我们开发的MLSIC包括总共66层带状离子室（IC）板，或者，在x和y方向。前两层各有128个通道，间距为2mm，并且以下64个层中的每个层具有8毫米间距的32个通道,这些通道每9个通道相互连接。对总共768个通道的IC信号进行积分，并以6kfps的速度进行采样。MLSIC具有总共19.2cm的水当量厚度,并且能够在25X25cm2的场尺寸上进行测量。通过考虑双高斯-柯西-洛伦兹模型，开发了一种重建算法来重建所有深度处每个点的3D剂量分布。通过对所有点求和来获得每个射束的3D剂量分布。针对临床笔形波束扫描（PBS）计划评估了我们的MLSIC的性能。＆＃xD;主要结果：＆＃xD;可以从不同深度的带状IC的电离电流测量中成功重建每个质子点的剂量分布，这可以进一步总结为光束的3D剂量分布。3D伽玛指数分析表明，在测量和计算的剂量分布之间具有极好的一致性。＆＃xD;意义：专用的MLSIC是第一个可以逐点测量PBS质子场中3D剂量分布的伪3DQA设备。
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