Electron FLASH Delivery at Treatment Room Isocenter for Efficient Reversible Conversion of a Clinical LINAC.
Electron FLASH Delivery at Treatment Room Isocenter for Efficient Reversible Conversion of a Clinical LINAC.
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DOI：
10.1016/j.ijrobp.2021.01.011
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发表时间：
2021-07-01
影响因子：
7
通讯作者：
Gladstone, David J.
中科院分区：
文献类型：
--
作者：
Rahman, Mahbubur;Ashraf, Ramish;Zhang, Rongxiao;Bruza, Petr;Dexter, Chad A.;Thompson, Lawrence;Cao, Xu;Williams, Benjamin B.;Hoopes, P. Jack;Pogue, Brian W.;Gladstone, David J.
在本研究中，开发了程序来实现临床直线加速器 (LINAC) 的高效可逆转换，并将超高剂量率 (UHDR) 电子束或常规束传送到治疗室等中心进行 FLASH 放射治疗。通过将 X 射线目标从光束路径中缩回、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，LINAC 被转换为在 20 分钟内提供 UHDR 光束。使用 Gafchromic 胶片和光激发光剂量计 (OSLD) 在不同射野尺寸的固体水体模中测量剂量率、表面和深度剂量分布。脉冲控制器通过散射辐射信号对脉冲进行计数，并门控预设脉冲计数的传输。基于快速光电倍增管的切伦科夫探测器以 2 ns 采样率测量每个脉冲束输出。转换回临床模式后，测量所有临床委托能量的常规光束输出、平坦度、对称性、射野大小和能量。直径1cm、直径1.5的圆形视野和钳口大开视野等角点处的表面平均剂量率分别为238±5、262±5和290±5Gy/s。梁的径向对称性分别在2.4%、0.5%和0.2%以内。胶片和OSLD同时照射的剂量在1%以内。 PMT 显示 LINAC 在输出稳定之前需要前 4-6 个脉冲内的斜坡上升时间，并且其稳定性在 3% 以内。在治疗室的等角点处实现了 10 MeV UHDR 光束。光束输出是可重复的，但需要进一步研究上升时间，相当于~1 Gy，需要剂量监测。 UHDR 光束可以照射小型和大型受试者，以在经过最小修改的临床环境中研究潜在的 FLASH 放射生物学效应，并且可以通过减少源到表面的距离来进一步增加剂量率。
In this study, procedures were developed to achieve efficient reversible conversion of a clinical linear accelerator (LINAC) and deliver ultra-high dose-rate (UHDR) electron or conventional beams to the treatment room isocenter for FLASH radiotherapy. The LINAC was converted to deliver UHDR 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-rate, surface and depth dose profiles were measured in solid water phantom at different field sizes with Gafchromic film and optically stimulated luminescent dosimeter (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. The surface average dose rate at the isocenter for a 1 cm in diameter, 1.5 in diameter circular fields, and jaws wide open field was 238±5, 262±5, and 290±5 Gy/s, respectively. The radial symmetry of the beams was within 2.4%, 0.5%, and 0.2% respectively. The doses from simultaneous irradiation of film and OSLD were within 1%. The PMT showed the LINAC required ramp up time in the first 4–6 pulses before the output stabilized and its stability was within 3%. 10 MeV UHDR beams were achieved at the isocenter of the treatment room. The beam output was reproducible but requires further investigation of the ramp up time, equivalent to ~1 Gy, requiring dose monitoring. The UHDR beam can irradiate both small and large subjects to investigate potential FLASH radiobiological effects in minimally modified clinical settings and dose-rates can be further increased by reducing the source to surface distance.
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作者：
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