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Objective:To conduct a comparative analysis of the radiation damage to zebrafish embryos and the associated biological mechanism after ultra-high dose rate (FLASH) and conventional dose rate irradiation.Methods:Zebrafish embryos at 4 h post-fertilization were exposed to conventional and FLASH irradiation (9 MeV electron beam). The mortality and hatchability of zebrafish after radiation exposure were recorded. Larvae at 96 h post-irradiation underwent morphological scoring, testing of reactive oxygen species (ROS) levels, and analysis of changes in oxidative stress indicators.Results:Electron beam irradiation at doses of 2-12 Gy exerted subtle effects on the mortality and hatchability of zebrafish embryos. However, single high-dose irradiation (≥ 6 Gy) could lead to developmental malformation of larvae, with conventional irradiation showing the most significant effects ( t = 0.87-9.75, P < 0.05). In contrast, after FLASH irradiation (≥ 6 Gy), the ROS levels in zebrafish and its oxidative stress indicators including superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) were significantly reduced ( t = 0.42-15.19, P < 0.05). There was no statistically significant difference in ROS levels in incubating solutions after conventional and FLASH irradiation ( P > 0.05). Conclusions:Compared to conventional irradiation, FLASH irradiation can reduce radiation damage to zebrafish embryos, and this is in a dose-dependent manner. The two irradiation modes lead to different oxidative stress levels in zebrafish, which might be a significant factor in the reduction of radiation damage with FLASH irradiation.
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Objective:To compare the radiation chemistry effects on water molecules after ultra-high dose rate (FLASH) and conventional irradiation.Methods:Both FLASH and conventional irradiation were applied to ultrapure water, with the hydroxyl radical yield in the homogeneous phase detected using electron paramagnetic resonance (EPR) and the hydrogen peroxide (H 2O 2) yield in the diffusion phase analyzed uuxing fluorescence probe. The liposome model was then established to investigate the radiation chemistry effect of FLASH and conventional irradiation in inducing lipid peroxidation. Results:Radiation chemistry reactions were observed in water molecules after irradiation. In the homogeneous phase, the yield of free radicals using FLASH irradiation is similar to those from conventional irradiation ( P>0.05). In the diffusion phase, the amount of H 2O 2 produced by FLASH irradiation was significantly lower than those from conventional irradiation ( t=0.49-12.81, P<0.05). The liposome model confirmed that conventional irradiation could significantly induce lipid peroxidation through the radiation chemistry effect in water molecules as compared with FLASH irradiation ( t=0.31-11.73, P<0.05). Conclusions:The radiation chemistry effect in water molecules after FLASH irradiation was significantly lower than that from conventional irradiation. This could be one of the mechanisms of FLASH effect.
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Objective:To compare the effects on DNA strand break induced by ultra-high dose rate (FLASH) electron beam and conventional irradiation, and investigate whether FLASH effect was correlated with a reduction of radiation response.Methods:Aqueous pBR322 plasmid was treated with FLASH (125 Gy/s) and conventional irradiation (0.05 Gy/s) under physioxia (4% O 2) and normoxia (21% O 2). Open circle DNA and linear DNA were detected by agarose gel electrophoresis, and the plasmid DNA damage was quantified with an established mathematical model to calculate the relative biological effect (RBE) of DNA damage. In some experiments, Samwirin A (SW) was applied to scavenge free radicals generated by ionizing radiation. Results:Under physioxia, the yields of DNA strand breakage induced by both FLASH and conventional irradiation had a dose-dependent manner. FLASH irradiation could significantly decrease radiation-induced linear DNA compared with conventional irradiation ( t=5.28, 5.79, 7.01, 7.66, P<0.05). However, when the aqueous plasmid was pretreated with SW, there was no difference of DNA strand breakage between FLASH and conventional irradiation ( P>0.05). Both of the yields of open circle DNA and linear DNA had no difference caused by FLASH and conventional radiotherapy at normoxia, but were significantly higher than those under physioxia. In addition, the yields of linear DNA and open circle DNA induced by FLASH irradiation per Gy were (2.78±0.03) and (1.85±0.17) times higher than those of conventional irradiation, respectively. Conclusions:FLASH irradiation attenuated radiation-induced DNA damage since a low production yield of free radical in comparison with conventional irradiation, and hence the FLASH effect was correlated with oxygen content.
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Objective:To study the effects of FLASH irradiation (FLASH-RT) and conventional irradiation (CONV-RT) on gene expression profile in mouse liver, in order to provide theoretical basis of the potential mechanism of FLASH-RT.Methods:A total of 11 C57BL/6J male mice were divided into healthy control group (Ctrl group), CONV-RT group and FLASH-RT group according to random number table method. Mouse abdomen was treated with 12 Gy CONV-RT or FLASH-RT. Then the mice were killed by neck removal, and the liver tissues were collected to extract total RNA for transcriptome sequencing (RNA-Seq) that was then analyzed by bio-informatics analysis to investigate the changes of gene expression profiles. The mRNA expression levels of Stat1, Irf9 and Rela were verified by quantitative real-time PCR assay.Results:1 762 differentially expressed genes (DEGs) were identified in group FLASH-RT vs. CONV-RT. Among them, 660 genes were up-regulated and 1 102 genes were down-regulated. 1 918 DEGs were identified in groups FLASH-RT vs. Ctrl. Among them, 728 genes were up-regulated and 1 190 genes were down-regulated. 1 569 DEGs were identified in group CONV-RT vs. Ctrl. Among them, 1 046 genes were up-regulated and 523 genes were down-regulated. According to Gene Ontology (GO) analysis, these DEGs from groups FLASH-RT vs. CONV-RT were involved in various functions including defense response to virus, other organisms in cell components, adenylyltransferase activity in molecular function activity. These DEGs from group FLASH-RT vs. Ctrl were involved in various functions including defense response to other oranisms, endoplasmic reticulum chaperone complex, double-stranded RNA binding and so on. These DEGs from group FLASH-RT vs. CONV-RT were involved in several Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways including influenza A, Herpes simplex infection and so on. These DEGs from group FLASH-RT vs. Ctrl were involved in several KEGG pathways including influenza A, NOD-like receptor signaling pathway. Stat1 was likely to be activated by FLASH radiation. The quantitative real-time PCR assay showed that FLASH-RT obviously increased the mRNA expressions of Stat1, Irf9 and Rela ( t=6.62, 2.11, 1.67, P<0.05). Conclusions:FLASH-RT and CONV-RT could alter gene expression profiles in mouse liver tissues, and these DEGs are involved in multiple radiobiological functional pathways. In comparison with CONV-RT, FLASH-RT induces a low level of liver injury, which may due to hypoxia radiation resistance.
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Objective To investigate the biological effect of 125I seeds continuous low dose rate (CLDR) irradiation and 60Co γ-ray high dose rate (HDR) irradiation on H1299 cell line of non-small cell lung cancer (NSCLC). Methods H1299 cells in exponential growth were separately irradiated with 125I seeds CLDR irradiation and 60Co γ-ray HDR irradiation. The cell survival fraction was inspected with clone formation experiment, the cell cycle and apoptosis rate was determined with flow cytometry, and the expressions of Bax and Bcl-2 proteins were measured by Western blot method. Results With the irradiation dose increasing, the anti-proliferation effect of 125I seeds CLDR irradiation on H1299 cells became more remarkable than that of 60Coγ-ray HDR irradiation. When the irradiation dose reached 4 Gy, the G2/M phase percentage and the apoptotic ratio of H1299 cells in 125I seeds CLDR irradiation group were 21.77±0.31%and 13.79±0.50% respectively, which were only 18.85±0.99% and 8.79±0.22% respectively in 60Co γ-ray HDR irradiation group, the difference was statistically significant (P<0.05). In 125I seeds CLDR irradiation group the expression of Bax protein was remarkably up-regulated, while the expression of Bcl-2 protein was down-regulated. Conclusion The inhibition effect of 125I seeds CLDR internal irradiation on the proliferation of H1299 cells is more obvious than that of 60Co γ-ray HDR irradiation. In 125I seeds CLDR irradiation group, the imbalance of Bcl-2/Bax ratio may play an important role in achieving the antitumor effect.
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From May 1979 through December 1981 a total of 524 patients with carcinoma of the uterine cervix were treated by radiation therapy with curative intent. Among the 524 patients, 356 were treated with a high-dose-rate (HDR), remote-controlled, afterloading intracavitary irradiation (ICR) system using a cobalt source (Ralstron), and 168 patients received a low-dose-rate (LER) ICR using a radium source. External beam irradiation with a total dose of 40-50 gy to the whole pelvis followed by intracavitary irradiation with a total dose or 30-39 gy in 10-13 fractions to point A was the treatment protocol ICR was given three times a week with a dose of 3 gy per fraction. Five-year actuarial survival rates in the HER-ICR group were 77.6% in stage IB (N=20), 68.2% in stage II (N=182), and 50.9% in stage III (N=148). In LDR-ICR group, 5-year survival rates were 87.5% in stage IB (N=22), 66.3% in stage II (N=91), and 55.4% in stage III (N-52). Survival rates showed a statistically significant difference by stage, but there was no significant difference between the two ICR groups. Late bowel complications after radiotherapy were noted in 3.7% of the HDR-ICR group and 8.4% of the LDR-ICR group. There was no severe complication requiring surgical management. The incidence of bladder complications was 1.4% in the HDR-ICR group and 2.4% in the LDR-ICR group. The application of HDR-ICR was technically simple and easily performed on an outpatient basis without anesthesia, and the patients tolerated it very well. Radiation exposure to personnel was virtually nil in contrast to that of LDR-ICR. Within a given period of time, more patients can be treated with HDR-ICR because of the short treatment time. Therefore, the HDR-ICR system is highly recommended for a cancer center, particularly one with a large number of patients to be treated. In order to tachieve an improved outcome, however, the optimum dose-fractionation schedule of HDR-ICRand optimum combination of intracavitary irradiation with external beam irradiation should be determined through an extensive protocol study with different treatment regimens.