ABSTRACT
Objective To investigate the radiobiological effects of radiation with different dose rates on human nasopharyngeal carcinoma cell line CNE-2 treated with or without a poly ADP-ribose polymerase (PARP) inhibitor,olaparib.Methods The concentration of olaparib used to treat cells equaled to the inhibition concentration IC10 of olaparib to CNE-2 cells.The CNE-2 cells were divided into acute radiotherapy (RT) group,fractionated radiotherapy (FRT) group,olaparib + RT group,and olaparib + FRT group.All groups were exposed to radiation of 0,1,2,3,5,7,and 10 Gy at a dose rate of 3 Gy/min.The delivery time for each dose point was 4 min in RT and 30 min in FRT.The colony forming assay was used to evaluate the survival of CNE-2 cells at each dose point.The multi-target,single-hit model was used to fit the cell survival curves and the parameters,D0,Dq,and SF2,were calculated.At dose points of 0.1,and 2 Gy,western blot was used to determine the expression of PARP-1 in the RT group and the FRT group and γH2AX in each group.Immunofluorescence was used to evaluate the γH2AX focus formation.A single factor analysis of variance was used to compare the 4 groups,and two two compared with SNK-q test.Results The IC10 value of olaparib to CNE-2 cells was 4.0 μmoL/L.At dose points of 1 and 2 Gy,the PARP-1 expression was significantly higher in the FRT group than in the RT group (P=0.029,0.022),while the γH2AX focus number was significantly smaller in the FRT group than in the other three groups (all P＜0.05);compared with the RT group,the D0,Dq,and SF2 values in the FRT group were increased by 11.67％,15.78％,and 23.61％,respectively;compared with the FRT group,the D0,Dq,and SF2 values in the Olaparib+ FRT group decreased by 11.19％,6.44％,and 13.26％,respectively;there were no significant differences in above indices between the RT group,the Olaparib+RT group,and the Olaparib+FRT group.Conclusions For the same radiation dose,fractionation reduces the relative dose rate and weakens the radiobiological effects.lowdose olaparib can compromise the single strand break repair induced by the decline of the relative dose rate in a fractionated irradiation mode,which promotes the formation of double-strand break and improves the radiobiological effects.
ABSTRACT
Objective To study the dosimetric characteristics of thermoluminescent dosimeter (TLD).Methods A total of 350 pieces of TLD 2000 type TLDs having the same sensitivity within ± 3.0％ were selected.The TLDs were irradiated to study the repeatability and dosage effect of TLDs by using 6 MV X-rays and 125I seeds.In order to study the dose response,the TLDs were irradiated at different dosages by using 137Cs (662 keV γ-rays),125I seeds and 6 MV X-rays.In order to study the energy response,the TLDs were exposed to the same dose,from 125I seeds,137Cs and X-rays(48,65,83,118,250 keV and 6 MV).Results The maximum deviations of the repeatability were 2.7％ and 4.0％ for 6 MV X-rays and 125I seeds,respectively,and there was no effect of dose rate observed.The dose response of TLDs to 137Cs and 125I seeds were linear.For 6 MV X-rays,the linear response was within the range of 0.74-10 Gy and non-linear range was beyond 10 Gy.The energy response to 125I seeds,48,65,83,118,250 keV and6 MV X-rays,relative to the energy response of 137Cs,were 1.70,1.25,1.08,0.99,0.91,0.96 and 1.22,respectively.Conclusions TLD 2000 has a good repeatability and linear dose response for 137Cs,125I seeds and 6 MV X-rays with no dose rate effects,but the dose response is energy dependent.
ABSTRACT
Objective To analyze the dose rate effect and potentially lethal damage repair in DNA double strand break repair deficient murine cells (SCID) irradiated by ? ray. Methods The wild type(CB.17+/+) and SCID cells were exposed to ? ray at high and low dose rates. The high dose rate exposure was fractionated into two equal doses at 24?h intervals. The survival rates of irradiated cells were calculated by clony forming analysis. Results When ? ray was given to wild type(CB.17+/+) cells in two fractions at 24?h intervals, the survival rate was significantly higher than that when the same total dose was given singly. In contrast, there was no difference in the survival rates between the single and fractionated exposure in SCID cells. SCID cells were more sensitive than CB.17+/+ cells to both low and high dose rates ? ray exposure for cell killing. The survival rate by low dose rate exposure was significantly higher than that by high dose rate exposure, not only in CB.17+/+ cells but also in SCID cells. Conclusions SCID cells are deficient in repairing ? ray induced double strand breaks. There is dose rate effect in both SCID and CB.17+/+ cells.