The Damage Rule Of Immune Organ, Kidney And Thyroid Gland, And PET/CT May Be Used To Rapidly Evaluate The Damage After Total Body Irradiation

BackgroundWith a large consume of nonrenewable resource. Nuclear is playing an important role in the process of industrialization, it offered the welfare for all aspects of our lives. However, the incidents, such as the atomic bombings of Hiroshima and Nagasaki, Three Mile Island accident, the Chernobyl Nuclear Accident and Fukushima Nuclear Accident have caused tremendous losses in the lives and properties of the people. Therefore, the researchers of all the world make a sustained effort for radiation protection, however, the management of radiation protection is remainly basis on the interaction between living tissue and ionizing radiation and the accurate measurement of doses. At present, the study are focus on the irradiated individual dosimetry in order to meet prompt, reasonable and effective medical treatment after a mass-casualty accidents. The traditional methods, such as peripheral blood lymphocyte counting, the dicentric chromosome assay, premature chromosome condensation and the micronucleus assay are very labor-intensive and time-consuming processes. However, some new methods, such as genetic techniques (Somatic mutations glycophorin A/hypoxanthine guanine phosphoribosyl transferase), gene expression assays and protein biomarkers (g-H2AX, C-reactive protein), being study. Therefore, it is very important to explore a new method that reflect the tissue damage and may be more simple, accurate, high-through.ObjectiveThe purpose of this study was mainly to investigate the damage rule of immune organ, kidney and thyroid gland and whether the PET/CT may be used to rapidly evaluate the damage after total irradiationMaterials and methodsAll animal experimental protocols were in agreement with the guidelines established by the Institute and approved by the Institutional Review Board at the Southern Medical University Animal Care and Use Committee (License number SCXK (Yue)2006-0015). Adult uncastrated male Tibetan minipigs (weighing21.16±5.54kg, supplied by the Center for Laboratory Animals, Southern Medical University, Guangzhou, China) were maintained under standard laboratory conditions with a12-h light and12-h dark cycle; they were allowed free access to feed and water.Forty-eight anesthetised (Sumianxin II:0.15mL/kg) Tibetan minipigs were divided into one control group and five experimental groups and placed in a phantom for fixation of postures to subject the animals to radiation exposure by an8-Mv X-ray (isocentric) linear accelerator (Precise System Treatment, ELEKTA, Sweden). The irradiation was carried out at the Cancer Centers of the Armed Police Hospital of Guangdong following the protocol described elsewhere. Animals in the experimental groups (n=9in each group) received a single-fraction total body irradiation (TBI) dose of2,5,8,11and14Gy, respectively. In the control group (n=3), the animals without received TBI. Physical dose within the chamber was assessed using direct-reading dosimeters (Arrow-Tech, Inc., Rolla, ND, USA). The dose rate was fixed as255cGy/min for all the treatment groups. The Tibetan minipigs were observed at three different time points (6,24and72h) after radiation exposure. Spleen, thymus and lymph node tissues and blood samples were also collected for histological examination(light and electron microscrope), apoptosis and blood analysis.We chose the five radiation doses (namely,2,5,8,11and14Gy), each radiation dose has its own medical significance in humans. Radiation doses ranging from2to14Gy cause damage mainly to the haematopoietic system, the immune system and the gastrointestinal tract. In a scenario following a large nuclear event, different doses need different types of medical intervention. Subjects receiving below2Gy exposure cause no acute health effects and therefore need no supportive care. At approximately2-5Gy, these doses can be roughly doubled through the use of antibiotics, platelet and cytokine treatment. At a dose of approximately5-8or8-11Gy, bone-marrow transplantation is a useful option. There is usually lethal exposure above11Gy (14Gy) because of lethal gastrointestinal damage. Therefore, we believe that a dosimetry method that can rapidly and accurately distinguish doses ranging from2and11Gy is of utmost importance because people receiving these exposure doses all need immediate medical attention. We also select three observation time points (6,24and72h) post-irradiation, because the spleen responds rapidly and is very sensitive to TBI according to previous research (within hours post-irradiation). In addition, the latent period (from radiation exposure to symptom onset) is a critical time for medical intervention and the symptoms of ARS (acute radiation syndrome) can often appear within hours to weeks.Positron-emission tomography, in combination with computed tomography using 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG PET/CT), is a non-invasive diagnostic technique that utilises the biochemical metabolic differences between benign and malignant tissues; and it has achieved an established role in staging, restaging during treatment monitoring and prediction of response or non-response in many malignancies. However, varying degrees of18F-FDG uptake are found in normal tissues and in benign processes where F-FDG is used as a marker of glycolysis, moreover,18F-FDG does not specifically accumulate in malignancy. Previous studies have confirmed that18F-FDG evaluation can detect inflammatory and infectious processes that remain undetected during routine anatomical imaging. The study use this technique for research18F-FDG uptake difference in different tissue under physiology-pathological changes after different dose total body irradiation so as to deduce the relationship between tissue, dose and18F-FDG uptake.ResultsGeneral condition:All the animals survived the irradiation procedures and were preserved during the observation period after exposure to total body irradiation. It caused loss of appetite, sluggish, erythema, weak in spirits and a decrease in activity of Tibetan minipig. However, with an increase in the radiation dose, the time to onset of vomiting and diarrhea appears earily, body surface area of erythema also become more large.Counts of peripheral blood:the average WBC counts appeared to temporarily increase at6h post-irradiation, reach maximum value (12.98±0.23) at2Gy exposure; followed by a sharp decline with an increase in the radiation doses and prolongation of observation time points, reach minimum value (1.28±0.25) at72h after14Gy exposure. There were significant differences in the white blood cell (WBC) counts at24and72h after different dose exposure when tested using the one-way ANOVA test (A post hoc)(P<0.01). However, the average lymphocyte counts appeared to sharply decline with an increase in the radiation doses, reach minimum value at72h after14Gy exposure. There were significant differences in the lymphocyte counts at72h after different dose exposure when tested using the one-way ANOVA test (A post hoc)(P<0.01)..Standard uptake value (SUV):Using the one-way ANOVA and repeated measures test, the mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.740P=0.665, there were significant different between irradiated groups (F=107.445, P=0.000) and between four time points (F=306.379, P=0.000), there were no significant different between control group and experimental group before TBI (F=0.375, P=0.856), there is interactive effect between dose and time points (F=32.894,P=0.000) and the significant effect was six hour after11Gy TBI.Linear regression analysis to assess Spearman’s correlation coefficient between spleen SUV and radiation dose at6,24and72h after TBI. The dose ddi not follow Gaussian distributions, and the correlation coefficient was r=0.94P<0.01,0.91P<0.01,0.82P<0.01, respectively. At6h post-irradiation, spleen SUV showed a clear and significant positive correlation with the radiation dose.Splenic PET/CT imaging:The normal splenic uptake was generally of a low grade, in addition to being diffuse. with an increase in the radiation dose at6h post-irradiation, there was a gradual increase in18F-FDG uptake of the spleen. The18F-FDG uptake of the spleen increase with an increase in the radiation dose at24and72h but not obvious.Standard uptake value (SUV) of both kidneys:the mauchly’s test of sphericity was refused by hypothesis which Statistics was W=0.400P=0.081(left), W=0.387P=0.071(right), there were significant different between irradiated groups (left: F=225.289, P=0.000; right:F=114.942, P=0.000) and between four time points (left: F=195.210,P=0.000, right:F=188.081, P=0.000), there is interactive effect between dose and time points (left:F=44.008, P=0.000; right: F=42.223, P=0.000) and the significant effect was72hour after14Gy TBI. Both kidneys PET/CT imaging:The normal both kidneys uptake was generally of a low grade, in addition to being diffuse. With prolonging of observed time points in the14Gy group, the value of FDG uptake were increased more markly of bilateral renal parenchyma, which were also found at24and72hours in the11Gy group. But there were low FDG uptake in the2,5,8Gy and control group.Light and electron microscope:Under the observation of light microscope, After2-14Gy radiation, the pathological changes of immune tissue (spleen, thymus and lymph node) lymphocytes underwent similar three pathological stages,the starting phase of death (apoptosis and necrosis) at6h post-irradiation, eliminating phase of debris at24h post-irradiation; exhausted phase of lymphocytes at72h post-irradiation. These changes were obvious at thymic cortex, splenic white pulp and germinal center of lymph nodes, the normal architecture of the lymph node is obliterated at24and72h after14Gy exposure.Under the observation of transmission electron microscope, RER and Golgi complex dilatation, nuclear swelling or pyknosis appeared in the lymphocyte of thymus, spleen and lymph node, nuclear condensation and fragmentation, chondriosome swell and ridge disappearance could be observed at6h after different dose total body irradiation, with an increase of radiation dose, lymphocyte apoptosis increase, phagocytic activity of macrophages also increase; the lymphocyte decrease at24h after different dose total body irradiation, the number of phagocytes become more and more, three to seven apoptotic lymphocyte or debris could be observed around phagocytes, with an increase of radiation dose, necrosis become more obvious, we could see spotty or lamellar necrosis area after14Gy exposure; apoptotic lymphocyte could not be observed at72h post-irradiation, with an increase of radiation dose, thymus, spleen and lymph node tissue become more lack, RER and chondriosome become more vacuolization. More animals showed no significant gross morphologic changes in the low dosage (2,5and8Gy) of the experiment. Areas of congestion and petechial hemorrhages were noted in the high dosage (11and14Gy). Definite abnormalities were present at24hours after high dosage under light microscopy, especially in the group receiving14Gy, there were acute congestion, inflammatory cells infiltration in renal interstitium, the formation of tube cast and the degeneration and necrosis of tubular cells, no obvious glomerular changes were noted except for congestion and endotheliocytic swelling of vessel. In contrast to the findings described above, under the electron microscope distinct changes were seen at6hours of11Gy. The obvious heterochromatin of the glomerular epithelial cells, endotheliocytic and focal fusion of foot processes were be seen. This became more marked with increase of observed time and dosage. The tubules manifested focal degenerative changes in the cytoplasm and nucleus as early as6hours after8Gy, consisting of the chromatin condensation and aggregation, dilatation of the agranular endoplasmic reticulum and the mitochondria, numerous lysosomal structures, and lipid droplets. This became more marked with increase of observed time and higher dosage.After different dose irradiation, abundant lymphocyte apoptosis ratio was found in thymus,spleen and lymph node of Tibetan minipig. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.693P=0.133, there were significant different between irradiated groups (F=251.87, P=0.000) and between three time points (F=1530.24, P=0.000), there is interactive effect between dose and time points (F=145.36, P=0.000) and the significant effect of lymphocyte apoptosis ratio of spleen was six hour after14Gy TBI. The mauchly’s test of sphericity was refused by hypothesis which Statistics was W=0.426, P=0.009, there were significant different between irradiated groups (F=1379.847,P=0.000) and between three time points (F=221.711,P=0.000), there is interactive effect between dose and time points (F=23.471, P=0.000) and the significant effect of lymphocyte apoptosis ratio of thymus was24hour after14Gy TBI. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.978P=0.883, there were significant different between irradiated groups (F=133.704,P=0.000) and between three time points (F=179.188,P=0.000), there is interactive effect between dose and time points (F=22.569,P=0.000) and the significant effect of lymphocyte apoptosis ratio of spleen was24hour after11Gy TBI.The renal function testing include BUN and Cr. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.867P=0.456, there were significant different between irradiated groups (F=54.308,P=0.000) and between three time points (F=9.527,P=0.000), there is interactive effect between dose and time points (F=7.352, P=0.000) and the significant effect of BUN was24hour after14Gy TBI. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.840P=0.384, there were significant different between irradiated groups (F=54.308,P=0.000) and between three time points (F=104.753,P=0.000), there is interactive effect between dose and time points (F=20.842, P=0.000) and the significant effect of Cr was72hour after14Gy TBI.The thyroid gland function testion include weight, FT3,FT4and TSH.The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.962P=0.808, there were significant different between irradiated groups (F=4.831,P=0.012) and between three time points (F=12.482,P=0.000), there is no interactive effect between dose and time points of weight (F=1.685, P=1.43). The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.800P=0.294, there were significant different between irradiated groups (F=11.358,P=0.000) and between three time points (F=27.565,P=0.000), there is interactive effect between dose and time points (F=2.763, P=0.02) and the significant effect of FT3was72hour after14Gy TBI. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.982P=0.897, there were significant different between irradiated groups (F=7.010,P=0.000) and between three time points (F=6.629,P=0.005), there is no interactive effect between dose and time points (F=0.689, P=0.725) of FT4. The mauchly’s test of sphericity was not refused by hypothesis which Statistics was W=0.771P=0.23, there were significant different between irradiated groups (F=10.476, P=0.000) and between three time points (F=155.801,P=0.000), there is interactive effect between dose and time points (F=22.235, P=0.000) and the significant effect of TSH was72hour after14Gy TBI.Conclusions(1):This research showed that the metabolism of18F-FDG-PET/CT may indirectly reflect radiation dose and the extent of damage. This may provides reliable basis for PET/CT used to early diagnose to acute radiation disease.(2):Immune organ is highly sensitive tissues for radiation. Apoptosis is the major death pathway of lymphocytes in2,5,8,11Gy treatment group.(3):Thyroid gland is moderately sensitive tissues for radiation, it undergo hype-phase at six hours, active phase at24hours and hypo-phase after total body irradiation.