The influences of size (90À1500 nm) and amount (1À4 wt %) of as-synthesized seed crystals on the properties of zeolite NaA membranes on alumina hollow fibers are investigated. Seeds and membranes are characterized by dynamic light scattering, X-ray diffraction, and scanning electron microscope. It is found that in order to prepare dense NaA membranes with high separation performance, for seeds smaller than 100 and 200 nm, the optimal concentrations are 1 and 3 wt %, respectively; while for large-sized seeds (>1500 nm), membranes obtained using the seed suspension with 4 wt % seed concentration still have defects. Furthermore, the influence of crystal fragments (∼50 nm) obtained by ball-milling available crystals (e.g., 1500 nm) on the formation of zeolite membrane is also studied. Based on the morphology and performance of membranes grown from different seeds, seed-assisted membrane formation process is briefly discussed.
This study aimed to evaluate whether high-energy X-rays (HEXs) of the PARTER (platform for advanced radiotherapy research) platform built on CTFEL (Chengdu THz Free Electron Laser facility) can produce ultrahigh dose rate (FLASH) X-rays and trigger the FLASH effect. Materials and methods: EBT3 radiochromic film and fast current transformer (FCT) devices were used to measure absolute dose and pulsed beam current of HEXs. Subcutaneous tumor-bearing mice and healthy mice were treated with sham, FLASH, and conventional dose rate radiotherapy (CONV), respectively to observe the tumor control efficiency and normal tissue damage. Results: The maximum dose rate of HEXs of PARTER was up to over 1000 Gy/s. Tumor-bearing mice experiment showed a good result on tumor control (p < 0.0001) and significant difference in survival curves (p < 0.005) among the three groups. In the thorax-irradiated healthy mice experiment, there was a significant difference (p = 0.038) in survival among the three groups, with the risk of death decreased by 81% in the FLASH group compared to that in the CONV group. The survival time of healthy mice irradiated in the abdomen in the FLASH group was undoubtedly higher (62.5% of mice were still alive when we stopped observation) than that in the CONV group (7 days). Conclusion: This study confirmed that HEXs of the PARTER system can produce ultrahigh dose rate X-rays and trigger a FLASH effect, which provides a basis for future scientific research and clinical application of HEX in FLASH radiotherapy.
The ultrahigh dose-rate (FLASH) radiotherapy, which is efficient in tumor control while sparing healthy tissue, has attracted intensive attention due to its revolutionary application prospect. This so-called FLASH effect has been reported in preclinical experiments with electrons, kilo-voltage X-rays, and protons, thus making FLASH a promising revolutionary radiotherapy modality. High energy X-ray (HEX) should be the ideal radiation type for clinical applications of FLASH due to its advantages in deep penetration, small divergence, and cost-friendly. In this work, we report the first implementation of HEXs with ultrahigh dose-rate (HEX-FLASH) and corresponding application of in vivo study of the FLASH effect produced by a high-current (10 mA), high-energy (6-8 MeV) superconducting linac. Joint measurements using radiochromic film, scintillator and Fast Current Transformer device validated that a maximum dose rate of over 1000 Gy/s was achieved in the mice and the mean value within several square centimeters keeps higher than 50 Gy/s within a depth of over 15 cm. The performance of the present HEX can satisfy the requirement of the FLASH study on animals. Breast cancer (EMT6) inoculated into BAL b/c mice was found efficiently controlled by HEX-FLASH. The radio-protective effect of normal tissue was observed on the C57BL/6 mice after thorax/abdomen irradiation by HEX-FLASH. Theoretical analyses of cellular response following HEX-FLASH irradiation based on the radiolytic oxygen depletion hypothesis were performed to interpret experimental results and future experiment design. This work provided the first demonstration of the FLASH effect triggered by HEX, which paved the way for future preclinical research and clinical application of HEX-FLASH.
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