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Objective:To develop a verification platform based on Monte Carlo (MC) for independent dose verification of volumetric modulated arc therapy (VMAT) plans.Methods:The head model including collimator of Varian TrueBeam linear accelerator was constructed by using EGSnrc/BEAMnrc, and the independent dose verification platform for the patients’ VMAT plans was built based on the head model and an in-house code. The percent depth dose (PDD) curves and off-axis ratios for different field sizes, the dose distribution of two irregular fields and three VMAT plans of the head and neck, chest, and pelvis were simulated using the platform. The simulated results of the PDD curves and the off-axis ratios of different field sizes were compared with the blue water measurement results. The difference between the irregular fields and the actual ArcCHECK measurements was also investigated. Besides, the differences among the MC simulated dose, TPS calculated dose and the ArcCHECK measured dose were analyzed by several methods, such as γ analysis and dose-volume histogram to verify whether the platform could be independently employed for dose verification.Results:The MC simulated results of PDD curves and off-axis ratios from 4 cm×4 cm to 40 cm×40 cm were in good agreement with the measured results. And the γ passing rates between the MC simulation and the ArcCHECK measurement for the irregular fields were above 98.1% and 99.1% for 3%/2 mm and 3%/3 mm, respectively. For VMAT plans of three patients, the γ results between the MC simulated dose and ArcCHECK measured dose were better than 93.8% and 95.9% under the criteria of 3%/2 mm and 3%/3 mm respectively. At the same time, the γ passing rates of nasopharyngeal, lung, and rectal cancers were 95.2%, 98.6% and 98.9% based on 3D γ analysis using TPS calculated dose and MC simulated dose under the criteria of 3%/3 mm; the passing rates of these three were 90.3%, 95.1% and 96.7% for 3%/2 mm, respectively.Conclusions:The simulation results of the MC-based verification platform developed in this study show a good agreement with the actual measurement results, and the simulation results are closer to the real dose distribution using the patients’ data. The preliminary results demonstrate that the platform can be used for accurate independent dose verification of VMAT plans.
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Intestinal dysfunction can be induced under infection,trauma or stress. The intestinal mu＿cosal barrier injury is a common pathophysiological process in critically ill patients. The bowel is one of the earliest and most severely affected organ under severe infection and tissue hypoxia＿ischemia. Intestinal dam＿age leads to a large number of bacterial flora shift,resulting in intestinal infection,intestinal endotoxemia and intestinal sepsis. In recent years, gastrointestinal barrier function has attracted people′s attention, which is closely related to the prognosis of critically ill patients. This article described the normal intestinal barrier function,the effects of trauma and stress on intestinal barrier function, bacterial group migration, and the effects of endotoxin translocation on the body and its prevention and treatment.
ABSTRACT
Intestinal dysfunction can be induced under infection,trauma or stress. The intestinal mu-cosal barrier injury is a common pathophysiological process in critically ill patients. The bowel is one of the earliest and most severely affected organ under severe infection and tissue hypoxia-ischemia. Intestinal dam-age leads to a large number of bacterial flora shift,resulting in intestinal infection,intestinal endotoxemia and intestinal sepsis. In recent years,gastrointestinal barrier function has attracted people′ s attention,which is closely related to the prognosis of critically ill patients. This article described the normal intestinal barrier function,the effects of trauma and stress on intestinal barrier function,bacterial group migration,and the effects of endotoxin translocation on the body and its prevention and treatment.
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Objective To compare the difference among DNA damages in physics processes caused by protons with different energies around Bragg peak.Methods By constructing the nucleus and DNA model using Geant4 and simulating the transportation processes of protons with different energies around Bragg peak in nucleus model based on Geant4-DNA,the information of interaction points were recorded.16％ of them were picked randomly to use as the points at which protons interact with DNA.After finding out the points which broke the DNA and writing their information to new files,these new files were treated with density-based spatial clustering of applications with noise (DBSCAN),so as to analyze and calculate the difference of DNA damages caused by protons with different energies.Results With the protons with energies from 20.0 to 0.6 MeV,the numbers of damage points and damage clusters increased from 49.86 to 549.88 and from 2.92 to 82.46,respectively;the numbers of clusters with different sizes had a remarkable increase,and the number of clusters with size not less than 5 increased by 400 times.The average cluster size increased slightly.Simple single strand breaks (SSSBs),complex single strand breaks (CSSBs),simple double strand breaks (SDSBs) and complex double strand breaks (CDSBs) of DNA increased by about 8,26,24 and 64 times,respectively.The proportion of single strand breaks (SSBs) decreased from 96.69％ to 89.37％,and the double strand breaks (DSBs) increased from 3.31％ to 10.63％.Conclusions The lower proton energy would result in the more complex damage to DNA and the harder repair of DNA damage.
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Objective To evaluate the effect of intensity-modulated radiation therapy(IMRT) on parotid function in nasopharyngeal carcinoma(NPC). Methods Eighty-three NPC patients received prima-ry IMRT between 2001 and 2003. Xerostomia before radiotherapy, at the end of radiotherapy, at 6-month, 1-,2-,3-,4- and 5-year after radiotherapy were investigated, respectively. The relation between xerostomia and parotid dose distribution was analyzed. Results Of all the patients,4,31,31 and 17 had stage Ⅰ,Ⅱ,Ⅲ and ⅣA disease, respectively. Sixteen patients received chemo-radiotherapy. The median followed-up time was 65 months. The 5-year local control and regional control rate were 96% and 95% ,respectively. The 5-year overall survival rate was 80%. The mild xerostomia rate at the seven time points was 42%, 51%, 71%, 77%, 58%, 38% and 26%. The corresponding moderate xerostomia rate was 52%, 53%, 21%,8%, 3%, 2% and 2%, respectively. No serious xerostomia was observed. The mean dose of the bilateral parotid glands was 34.34 Gy. Xerostomia at 6-month after radiotherapy was positively correlated with the mean dose of the parotid glands, and D50 was the independent factor in predicting the xerostomia. Parotid function was well protected when the mean dose and D50 were no more than 33 Gy and 29 Gy,respectively. Conclusions IMRT can improve the local-regional control of NPC and protect the parotid glands from radiation-induced in-jury.
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Objective To evaluate the efficacy and safety of actovegin against acute oral mucositis through a randomized controlled multicenter trial for nasopharyngeal carcinoma(NPC) patients treated by chemo-radiotherapy. Methods From February 2006 to May 2007,a total of 161 patients with newly diagnosed stage Ⅱ-ⅣA(1992 Fuzhou Stage) NPC were randomly assigned to the prevention group,the treatment group and the control group. All patients received current chemo-radiotherapy ± neoadjuvant chemotherapy. Radiation technique and dose were similar among the three groups. Intravenous infusion of aeovegin was started when radiation started in the prevention group and when grade 2 mueositis occurred in the treatment group,which was given 30 ml daily ,5 times per week until the end of radiotherapy. Criteria of NCI CTC 2.0 and VRS were used to evaluate acute oral mueositis and pain degree,respectively. Results 154 patients were eligible for the efficacy analysis,including 49 in the prevention group,53 in the treatment group and 52 in the control group. In the prevention group and the control group, the incidence was 31% and 56% (P=0.011) for grade 3-4 mucositis,59% and 83% (P=0.009) for grade 2-3 pain. In the treatment group and the control group,the corresponding number was 38% and 60% (P=0.023) ,70% and 90%, (P=0.014). The prevention group had a lower incidence(P=0.021) and longer average interval(P=0.009) of grade 2 mucositis when comparing with the control group. No drug-related adverse event was observed. Conclusions Prophylactic or therapeutic use of actovegin by intravenous infusion can significantly reduce the severity of ehemo-radiotherapy induced oral mucositis and pain. The prophylactic use may also postpone and decrease the incidence of grade 2 mucositis,which deserves clinic application.