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Background and Objective：The32P isotope topical applicator is a simple skin brachytherapy, in clinical hasbeen widely used in the population including infants and young children, but itssafety has been controversial. Research on body injury and impact with isotopetopical applicator treatment were mainly in adults, is quite scarce for infant and youth;Moreover, almost researchs were limited in local organizations and, for distant tissuesof the body organs were little studied, which limited clinical significance.Further, in order to study the safety of32P isotope applicator, used in infants andyoung children, Reference to the clinical32P isotope applicator treatment, we establishthe SD pups32P applicator model, detecting the appearance and the DNA damage oforganization for local skin and distant tissues and organs damage of infant SD rats.Experiment method：1. Establishment of animal model:Reference to clinical methods,32P applicators which were simplely made from32Psolution and filter paper, paste on back skin of5-7days age SD rats. Control groupwas with saline solution instead of32P solution.2. Western blotting was used to detect DNA damage response protein ATM, H2AX,P53:Different radiation activity （0μCi,5μCi25μCi125μCi） were used to handle in6h\24h\96h,respectively. Total protein was extracted from target organs andtissues,then local skin and distant skin （from the applicator edge0.5cm） and spleentissue DNA damage response protein phosphorylation overall level was detected bywestern blotting in order to explore local and distant tissues DNA damage level ofthe infant SD rats by the applicator.3. Comet assay was used to detect spleen tissue DNA damage levelThe experimental results：1. Change of local skin appearance and distant tissues32P applicator（1） After24h, to medium and large doses, with the dose increased local skin color gradually turn red, and even pale;（2） Processing for96h and then observe a half months, the local fur growth ofeach dose group was significantly suppressed, and the radiation dermatitis emerge,which showed a dose-dependent relationship,and The control group did not showinjury in the performance.;（3） Processing for96h and then observe a months, a local fur each dose grouphad recovered in some degree, but there are still deformation of rat back in thehigh-dose group, and other complications in some rat such as perineal ulceration,hind limb paralysis, envn death.The control group did not show injury in theperformance;（4） Processing for96h in high-dose group, repeat next month to observe3months, there are the more serious perineal ulcers, paralysis of the lower limbs,limited mobility, and part of the mice died after3months.2, Change of local skin ATM, P53protein expression levels by32P applicator:（1） ATM altered expression levelsa) ATM the PATM expression level of each dose group was significantly higherthan those in the control group （P <0.05）.b) ATM phosphorylation ratio （pATM/ATM） were significantly higher than thatin the control group （P <0.01） and with the dose increased ATM phosphorylation ratioincreased in a dose-dependent manner （P <0.01）.（2） Change of p53expression levelsa) Compared with the control group, each dose group P53phosphorylation ratio（PP53/P53）, were significantly increased （P <0.05）.b) Processing for6h， p53phosphorylation ratio of each dose group was nosignificant difference （P>0.05）;processing for24h,the applicator activity in the rangeof0-25μCi，PP53/P53increased in a dose-dependent manner （P <0.01）, andcontinue to increase dose to125μCi, p53phosphorylation ratio does not significantlyhigher; processing for24h, PP53/P53increased in a dose-dependent manner（P<0.01）.3, Western blotting was used to detect the distant skin ATM expression:a) Compared with the control group, ATM, PATM expression were elevated obviously （P <0.05）.b)After processing for6h, ATM phosphorylation ratio was significantly higher （P<0.05） from125μCi; after24h\96h, ATM phosphorylation ratio level wassignificantly higher than the control group, and showed significant dose-dependentrelationship （P <0.01）.4. SD rats spleen DNA damage by32P applicator（1） Comet assay resultsa) OTM of each dose group have increased in different levels （P <0.05） than thesaline group （control）.b) after processing for6h\24h, in the range of0-25μCi, With the intensity ofthe radiation dose increased,OTM increased （P <0.05）; after96h, OTM increasedupward trend with the dose incresed.（2） Western blotting detected H2AX, P53changea) Compared with the control group, P53, phosphorylation of p53, H2AXphosphorylation of H2AX expression of each dose group were significantly increased（P <0.05）.b) Each dose group H2AX phosphorylation ratio （pH2AX/H2AX） weresignificantly higher （P <0.05）, and with the increasing dose showed upward trend;after96hours,（pH2AX/H2AX） were significantly higher （P <0.01）, and in0μCi-25μCi range show in dose-dependent manner （P <0.05）, continue to be increased to125μCi slightly decline instead.c) Except5μCi in6h group, all P53phosphorylation ratio is higher than thecontrol （P <0.05）, after96h, significantly higher than that in the control group （P<0.01）, and increased with the dose increased （P <0.01）.Conclusion：1.32P applicator not only causes the SD rats applicator local skin damage, but alsocauses the distant skin and spleen damage:（1） SD rats local skin DNA damage by32P applicator, shows activity （dose rate）dependence, the degree of damage increases with the radiation intensity.（2） The increase of the dose rate of action is the main factors which causes thethe distant skin damage. （3） At the lower dose rate and after shorter duration of action,32P applicator willcause the SD pups spleen DNA damage; with increasing the the action time willincrease DNA damage, and with increasing applicator dose rate, will significantlyincrease the severity of the injury.2. The experiment suggested,32P application therapy in clinical care should be takento use, in infants and young groups, its security is particularly noteworthy, and largerdose rate long applicator should be avoided in order to minimize the body of localand distant damage.
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