Hiroshima Heiwa Clinic, High-Precision Radiotherapy Center, Kawaramachi, Naka-ku, Hiroshima-shi, Hiroshima, Japan.
Devision of Radiation Oncology, Niigata University Medical and Dental Hospital, Asahimachi-dori, Chuo-ku, Niigata, Japan.
PLoS One. 2018 Nov 21;13(11):e0206673. doi: 10.1371/journal.pone.0206673. eCollection 2018.
The effect of dose-delivery time with flattening filter (FF) and flattening filter-free (FFF) photon beams based on microdosimetric kinetic model (MKM) was investigated in this study. Monte Carlo simulation with the particle and heavy ion transport code system (PHITS) was performed to calculate the dose-mean lineal energy yD (keV/μm) of FF and FFF 6 MV photon beams using the IAEA phase-space files of Varian TrueBeam linear accelerator. Human non-small cell lung cancer NCI-H460 cells were used to determine the MKM parameters under the condition that dose-delivery times with continuous irradiation were 1, 5, 10, 30, and 60 min, and the adsorbed dose was 2, 4, and 8 Gy in this study. In addition, the relative biological effectiveness (RBE) of FF and FFF photon beams were calculated for evaluating the effect of dose delivery time. The RBE of FF decreased to 99.8% and 97.5% with 5 and 60 min for 2 Gy in comparison to 99.6% and 95.1% for 8 Gy, respectively. Meanwhile, that of FFF decreased to 99.5% and 94.9% with 5 and 60 min for 2 Gy in comparison to 99.5% and 94.9% for 8 Gy, respectively. Dose-delivery time has an effect on the RBE with photon beams. In other words, the dose-delivery time should be considered during radiation therapy. Furthermore, FFF photon beams were an effective irradiation method compared to FF in dose-delivery time on account of improving clinic throughput.
本研究基于微剂量动力学模型（MKM），探讨了使用调强适形（FF）和调强适形自由（FFF）光子射束时剂量传递时间的影响。采用粒子与重离子输运代码系统（PHITS）的蒙特卡罗模拟，利用瓦里安 TrueBeam 直线加速器的国际原子能机构相空间文件，计算了 6MVFF 和 FFF 光子射束的剂量平均线性能量 yD（keV/μm）。本研究中，在连续照射剂量传递时间分别为 1、5、10、30 和 60min，吸收剂量分别为 2、4 和 8Gy 的条件下，用人非小细胞肺癌 NCI-H460 细胞测定了 MKM 参数。此外，还计算了 FF 和 FFF 光子射束的相对生物效应（RBE），以评估剂量传递时间的影响。与 8Gy 相比，FF 光子射束的 RBE 分别在 2Gy 时降低至 5min 的 99.8%和 60min 的 97.5%；同时，FFF 光子射束的 RBE 分别在 2Gy 时降低至 5min 的 99.5%和 60min 的 94.9%，而 8Gy 时的 RBE 分别为 99.5%和 94.9%。因此，光子射束的剂量传递时间会影响 RBE。换句话说，在放射治疗过程中应考虑剂量传递时间。此外，由于提高了临床通量，FFF 光子射束在剂量传递时间方面比 FF 更有效。
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