Influence of momentum acceptance on range monitoring of 11C and 15O ion beams using in-beam PET
Influence of momentum acceptance on range monitoring of 11C and 15O ion beams using in-beam PET
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DOI：
10.1088/1361-6560/ab8059
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发表时间：
2020-06-21
影响因子：
3.5
通讯作者：
Yamaya, Taiga
中科院分区：
文献类型：
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作者：
Mohammadi, Akram;Tashima, Hideaki;Yamaya, Taiga
在重离子治疗中，需要监测一次离子在肿瘤中的停止位置，以实现有效治疗并防止正常组织的过量暴露。正电子发射离子束，如 (11)C 和 (15)O，已被建议用于使用束内正电子发射断层扫描 (PET) 成像进行重离子治疗的范围验证，该成像能够以高信噪比可视化离子停止位置。我们之前已经证明了束内 PET 成像用于 (11)C 和 (15)O 离子束范围验证的可行性，并在模拟中观察到束停止位置和剂量峰值位置之间的轻微偏移，具体取决于初始束能量扩散。在这项研究中，我们重点通过PET系统对(11)C (210 MeV u(-1))和(15)O (312 MeV u(-1))正电子发射离子束的布拉格峰位置和最大检测到的正电子发射碎片位置之间的偏移进行实验确认，动量接受度分别为5%和0.5%。为此，我们测量了深度剂量，并使用聚甲基丙烯酸甲酯 (PMMA) 模型对具有不同动量接受能力的两束光束进行了束内 PET 成像。对于 5% 和 0.5% 的动量接受度，(15)O 离子束照射的 PMMA 模型中布拉格峰位置和 PET 峰位置之间的偏移分别为 1.8 mm 和 0.3 mm。对于5％和0.5％的动量接受，(11)C离子束的两个峰位置之间的偏移分别为2.1mm和0.1mm。我们观察到两个光束的动量接受率为 5% 时布拉格峰和 PET 峰位置之间存在较大的偏移，这与我们之前研究中报告的模拟结果一致。还使用改进的微剂量动力学模型（mMKM）和蒙特卡罗模拟根据计算的相对生物有效性（RBE）值估计生物剂量。在治疗应用中应谨慎使用动量接受率为 5% 的光束，以避免当剂量远端衰减位于治疗体积之外时，对肿瘤以外的正常组织施加额外剂量。
In heavy-ion therapy, the stopping position of primary ions in tumours needs to be monitored for effective treatment and to prevent overdose exposure to normal tissues. Positron-emitting ion beams, such as(11)C and(15)O, have been suggested for range verification in heavy-ion therapy using in-beam positron emission tomography (PET) imaging, which offers the capability of visualizing the ion stopping position with a high signal-to-noise ratio. We have previously demonstrated the feasibility of in-beam PET imaging for the range verification of(11)C and(15)O ion beams and observed a slight shift between the beam stopping position and the dose peak position in simulations, depending on the initial beam energy spread. In this study, we focused on the experimental confirmation of the shift between the Bragg peak position and the position of the maximum detected positron-emitting fragments via a PET system for positron-emitting ion beams of(11)C (210 MeV u(-1)) and(15)O (312 MeV u(-1)) with momentum acceptances of 5% and 0.5%. For this purpose, we measured the depth doses and performed in-beam PET imaging using a polymethyl methacrylate (PMMA) phantom for both beams with different momentum acceptances. The shifts between the Bragg peak position and the PET peak position in an irradiated PMMA phantom for the(15)O ion beams were 1.8 mm and 0.3 mm for momentum acceptances of 5% and 0.5%, respectively. The shifts between the positions of two peaks for the(11)C ion beam were 2.1 mm and 0.1 mm for momentum acceptances of 5% and 0.5%, respectively. We observed larger shifts between the Bragg peak and the PET peak positions for a momentum acceptance of 5% for both beams, which is consistent with the simulation results reported in our previous study. The biological doses were also estimated from the calculated relative biological effectiveness (RBE) values using a modified microdosimetric kinetic model (mMKM) and Monte Carlo simulation. Beams with a momentum acceptance of 5% should be used with caution for therapeutic applications to avoid extra dose to normal tissues beyond the tumour when the dose distal fall-off is located beyond the treatment volume.