University of Nebraska Medical Center, Omaha, Nebraska, USA.
Varian Medical Systems, Palo Alto, California, USA.
J Appl Clin Med Phys. 2024 Feb;25(2):e14159. doi: 10.1002/acm2.14159. Epub 2023 Sep 21.
Radiotherapy delivered at ultra-high-dose-rates (≥40 Gy/s), that is, FLASH, has the potential to effectively widen the therapeutic window and considerably improve the care of cancer patients. The underlying mechanism of the FLASH effect is not well understood, and commercial systems capable of delivering such dose rates are scarce. The purpose of this study was to perform the initial acceptance and commissioning tests of an electron FLASH research product for preclinical studies.
A linear accelerator (Clinac 23EX) was modified to include a non-clinical FLASH research extension (the Clinac-FLEX system) by Varian, a Siemens Healthineers company (Palo Alto, CA) capable of delivering a 16 MeV electron beam with FLASH and conventional dose rates. The acceptance, commissioning, and dosimetric characterization of the FLEX system was performed using radiochromic film, optically stimulated luminescent dosimeters, and a plane-parallel ionization chamber. A radiation survey was conducted for which the shielding of the pre-existing vault was deemed sufficient.
The Clinac-FLEX system is capable of delivering a 16 MeV electron FLASH beam of approximately 1 Gy/pulse at isocenter and reached a maximum dose rate >3.8 Gy/pulse near the upper accessory mount on the linac gantry. The percent depth dose curves of the 16 MeV FLASH and conventional modes for the 10 × 10 cm applicator agreed within 0.5 mm at a range of 50% of the maximum dose. Their respective profiles agreed well in terms of flatness but deviated for field sizes >10 × 10 cm . The output stability of the FLASH system exhibited a dose deviation of <1%. Preliminary cell studies showed that the FLASH dose rate (180 Gy/s) had much less impact on the cell morphology of 76N breast normal cells compared to the non-FLASH dose rate (18 Gy/s), which induced large-size cells.
Our studies characterized the non-clinical Clinac-FLEX system as a viable solution to conduct FLASH research that could substantially increase access to ultra-high-dose-rate capabilities for scientists.
放射治疗在超高剂量率（≥40Gy/s）下进行，即 FLASH，有可能有效地扩大治疗窗口，并极大地改善癌症患者的治疗效果。FLASH 效应的潜在机制尚不清楚，能够提供这种剂量率的商业系统也很少。本研究的目的是对一种用于临床前研究的电子 FLASH 研究产品进行初步验收和调试测试。
瓦里安公司（加利福尼亚州帕洛阿尔托）对一台医用直线加速器（Clinac 23EX）进行了改造，增加了一个非临床 FLASH 研究扩展模块（Clinac-FLEX 系统），该系统能够以 FLASH 和常规剂量率提供 16MeV 电子束。采用光致发光剂量计、放射化学胶片和平行板电离室对 Flex 系统的验收、调试和剂量学特性进行了测试。对辐射情况进行了调查，认为现有的防护拱顶已足够。
Clinac-FLEX 系统能够在等中心处提供约 1Gy/脉冲的 16MeV 电子 FLASH 束，并在直线加速器龙门架的上部附件上达到超过 3.8Gy/脉冲的最大剂量率。16MeVFLASH 和常规模式下 10×10cm 施源器的百分深度剂量曲线在最大剂量的 50%范围内相差不超过 0.5mm。它们各自的曲线在平坦度方面吻合良好，但对于大于 10×10cm 的射野，曲线会有差异。FLASH 系统的输出稳定性显示剂量偏差小于 1%。初步的细胞研究表明，与非 FLASH 剂量率（18Gy/s）相比，FLASH 剂量率（180Gy/s）对 76N 乳腺正常细胞的细胞形态影响要小得多，后者会诱导大尺寸细胞。
我们的研究将非临床 Clinac-FLEX 系统描述为一种可行的解决方案，可用于进行 FLASH 研究，这将极大地增加科学家获得超高剂量率能力的机会。
