电子FLASH输送在治疗室等中心用于临床LINAC的有效可逆转化
Electron FLASH Delivery at Treatment Room Isocenter for Efficient Reversible Conversion of a Clinical LINAC
摘要：
目的：在本研究中，开发了实现临床直线加速器（LINAC）的有效可逆转换并将电子闪光（eFLASH）或传统射束输送到治疗室等中心的程序。材料和方法：通过从射束路径撤回X射线靶，将转盘定位在空端口上，并在治疗控制台中选择10 MV光子束能量，将LINAC转换为在20分钟内输送eFLASH射束。采用Gafchromic胶片和OSLD，在固体水模体中测量了不同深度处的每脉冲剂量和平均剂量率。脉冲控制器通过散射辐射信号对脉冲进行计数，并对预设脉冲计数的输送进行门控。基于快速光电倍增管的切伦科夫探测器在2 ns采样率下测量每脉冲光束输出。转换回临床模式后，测量所有临床调试能量的常规射束输出、平坦度、对称性、射野大小和能量。结果：在等中心点，每个脉冲的剂量为0.86 +/- 0.01 Gy（平均剂量率为310 +/- 7 Gy/s）。胶片和OSLD同时照射的剂量均在1%以内。PMT显示LINAC在输出稳定之前需要大约5个脉冲，并且对于以3分钟间隔进行的测量，其长期稳定性在3%以内。剂量、平坦度、对称性和光子能量与基线相比没有变化，并且在恢复为常规射束后在公差范围内（分别为1%、3%、2%和0.1%）。结论：10 MeV的FLASH光束在治疗室的等中心实现。射束输出是可再现的，但需要进一步研究前5个脉冲中的斜升时间，相当于<100 cGy。eFLASH光束可以在最小修改的临床设置中照射小型和大型受试者，并且可以通过减小源到表面的距离来进一步增加剂量率。
英文摘要：
Purpose: In this study, procedures were developed to achieve efficient reversible conversion of a clinical linear accelerator (LINAC) and deliver electron FLASH (eFLASH) or conventional beams to the treatment room isocenter. Material & Methods: The LINAC was converted to deliver eFLASH beam within 20 minutes by retracting the x-ray target from the beam's path, positioning the carousel on an empty port, and selecting 10 MV photon beam energy in the treatment console. Dose per pulse and average dose rate were measured in a solid water phantom at different depths with Gafchromic film and OSLD. A pulse controller counted the pulses via scattered radiation signal and gated the delivery for preset pulse count. A fast photomultiplier tube-based Cherenkov detector measured per pulse beam output at 2 ns sampling rate. After conversion back to clinical mode, conventional beam output, flatness, symmetry, field size and energy were measured for all clinically commissioned energies. Results: Dose per pulse of 0.86 +/- 0.01 Gy (310 +/- 7 Gy/s average dose rate) were achieved at isocenter. The dose from simultaneous irradiation of film and OSLD were within 1%. The PMT showed the LINAC required about 5 pulses before the output stabilized and its long-term stability was within 3% for measurements performed at 3 minutes intervals. The dose, flatness, symmetry, and photon energy were unchanged from baseline and within tolerance (1%, 3%, 2%, and 0.1% respectively) after reverting to conventional beams. Conclusion: 10 MeV FLASH beams were achieved at the isocenter of the treatment room. The beam output was reproducible but requires further investigation of the ramp up time in the first 5 pulses, equivalent to <100 cGy. The eFLASH beam can irradiate both small and large subjects in minimally modified clinical settings and dose rates can be further increased by reducing the source to surface distance.
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