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Objective@#To investigate the effect of simple artifacts on the calculation of radiation dose in actual clinical operations by the aid of artificially caused CT artifacts.@*Methods@#The phantom was scanned using CT before and after replacing the titanium alloy component. Then, the CT values were measured at different distances before and after replacement. After correcting the CT value of the titanium alloy region to the CT value of the water phantom, the doses to the phantom were calculated by using Varian′s AAA algorithm, AXB algorithm and Pinnacle system′s CCC algorithm. The absolute dose values at different distances were furtherly analyzed.@*Results@#Varian system was consistent with Pinnacle system in evaluating the CT values. When the CT value deviated by less than 30 HU for a uniform phantom, the dose deviations of the three different algorithms were within 6.0 %-12.0 % at a distance of 0.5 cm from the body surface, and less than 1.0% at a distance of more than 1.5 cm from the body surface. When the CT value deviated by 15 HU for the lung phantom, both Varian′s AAA algorithm and Varian′s AXB algorithm showed about 1.0% dose deviation. However, the CCC algorithm of the Pinnacle system had a significant difference (5.0%) in dose values under the same conditions.@*Conclusions@#CT artifacts have noticeable effects on the calculation of radiation dose and change tissue dose distribution which may result in insufficient or excessive exposure doses.
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Objective To design water-equivalent plastic scintillator detector for the measurement of absorbed dose in tumor radiotherapy.Methods The concentration of ZrO2to be doped in polystyrene was estimated according to the empirical formula,and then the Monte Carlo program Geant 4(GEometry And Tracking 4)was used to simulate the energy deposition and transport process of X-rays with different energies in water,solid water RW34(composed of 2.1 wt％TiO2doping polystyrene)and different concentrations of ZrO2particles doped in polystyrene.The dose and attenuation coefficients were compared among different materials at different depths of water.Results The doses at different depths and the attenuation coefficient of polystyrene(doped with about 0.4 wt％ZrO2nanoparticles)were much more consistent with those of water and even exhibit much better water-equivalence than RW34.Conclusions The simulation results provide the basis for the development of water-equivalent scintillator.
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Objective To investigate the application of a self-made positioning device in CT-MRI image fusion in patients with laryngeal tumor,as well as the precision of image fusion and the changes in target volume delineation after fusion.Methods A total of 10 patients with laryngeal cancer were enrolled,and a self-made positioning device was used to collect CT and MRI images in a fixed position.These images were fused by mutual information combined with manual fusion.The precision of image fusion was assessed by the positional deviation of internal and external markers and degree of gross tumor volume (GTV) overlap (PCT-MRI) between CT and MRI images.GTV was contoured based on CT images (VCr),MRI images (VMRI),and fused images (VCT+MRI).The overlapped volume of VCT and VMRI(VCT-MRI) Was calculated,and the target volume was analyzed and compared.Results The positional deviations of three external markers in the three directions were 0.996±0.222 mm,1.146±0.291 mm,and 1.368±0.298 mm (P=0.000),respectively,while those of the internal markers were 0.476±0.151 mm,0.561±0.083 mm,and 0.724± 0.125 mm (P=0.000),respectively.VCT,VMRI,VCT+MRI,and VCT-MRI were 26.355±7.876 cm3,33.556± 7.407 cm3,40.036±7.627 cm3,19.875±8.588 cm3(P=0.000),respectively.PCT-MRI was 73.7％±9.8％.Conclusions The self-made positioning device can improve the consistency of position during the collection of CT and MRI images,and fused CT-MRI images can provide more information and improve the precision of target volume delineation.
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Objective To study the clinical application of Compass (R) system,a novel 3D quality assurance system for the verification of esophageal carcinoma intensity-modulated radiotherapy (IMRT) plan.Methods 12 esophageal carcinoma IMRT plans were optimized with Eclipse 8.6 treatment planning system (TPS),and then Compass (R) reconstructed 3D dose distributions with the patient anatomy.Comparison was performed among the reconstructed and calculated with TPS,Dose-volume parameters (γ pass rate、average dose deviation) to the planning target volume (PTV) and critical structures were quantitative valuated.Furthermore two-dimensional dose verification were performed use MatriXX,γ pass rate were evaluated with 3％/3 mm criteria.Results The γ pass rate of actual gantry angle was found generally declined seemingly compared with 0 degree gantry angle in two dimensional verification,difference was statistically significant (P =0.018-0.001).In 3D dose verification,the γvolume of PTV were exceed 93％,the deviation of D95,D50,D2 were less than 3％;The γvolume of lungs and heart were exceed 95％,the average dose deviation were less than 3％;The γ pass rate of spinal cord and trachea were exceed 98％.The independent check verified more conformed with the TPS calculated.Dose deviations appeared in the radiation field edge area.Conclusions 3D dose verification can provide more information to comprehensively evaluate the plan which is benefit for evaluating the clinical value of verification.
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Objective To study how to design the treatment plan to reduce the influence of respiratory movement and the dose of heart and lung as few as possible,to improve the dosage distribution in the target area after radical mastectomy of breast cancer.Methods Twelve patients with breast cancer after radical mastectomy were selected.A dose of 50 Gy with 2 Gy every day and 5 times per week was prescribed.Based on the treatment planning system (TPS),4-field intensity modulated radiotherapy (4FIMRT) and hybrid intensity modulated treatment planning 2-field conformal radiotherapy (2FCRT) + 4FIMRT were designed respectively.The two plans were compared from the aspects of target conformity index (CI),the homogeneity index (HI) and exposure dose volume delivered to organ at risk.Results According to the hybrid plan of 2FCRT + 4FIMRT,HI was 1.08±0.01,which was superior to that from 4FIMRT (1.11±0.01,t =9.587,P ＜ 0.05).While CI was 0.74±0.08,based on the plan of 2FCRT+4FIMRT,which was slightly lower than that from 4FIMRT (0.80±0.03,t =2.497,P ＜ 0.05).Considering the dose volumes on ipsilateral lung in two plans,the values of V5,V10,Dmean of 2FCRT+4FIMRT plan were significantly less than those of 4FIMRT plan.V5,V10,Dmean from the former plan were 13 ％,23 ％,7 ％ less than those from the latter plan (t =6.002,P ＜ 0.05;t =6.826,P ＜ 0.05;t =3.645,P ＜ 0.05).Meanwhile,Dmean of contralateral lung,Dmean of heart,Dmean and V5 of contralateral breast from the 2FCRT +4FIMRT plan were all lower than those of 4FIMRT plan.Those differences between two plans were statistically significant (P ＜ 0.05).Differences of V20 and V30 of ipsilateral lung,and V30 of heart between two plans did not make sense by the statistics analysis (P ＞ 0.05).Conclusion Hybrid radiotherapy theoretically reduces the influence of respiratory movement,improves the uniformity of target dose and lowers the risk of complications of radiation therapy on breast cancer.
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Objective To explore the influence of dose rate reference control level on the design of accelerator shielding.Methods According to the standards of GBZ 126-2011,GBZ/T 201.1-2007 and GBZ/T 201.2-2011,two different shielding calculation methods,based on the dose rate reference control level and week dose control level,were used to calculate and compare the thickness of accelerator room shielding.Results Under the same condition of maximum weekly workload,the obtained results were different when the calculated dose rate reference control value was larger than dose rate reference control level (2.5 μSv/h).The maximum difference of shielding thickness reached 64 cm.Meanwhile,considering dose rate reference control level,the different accelerator rates could lead to different radiation shielding thickness.Conclusions The dose rate at reference point must be first calculated before calculating shielding thickness.The calculation should be made on the premise that dose rate reference control level is met.
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Objective To test the accuracy of a three-dimensional dose verification system CompassR,which reconstructing dose distribution based on measurements and independent dose calculation,and to evaluate the feasibility of its application in clinical intensity-modulated radiotherapy (IMRT) quality assure.Methods A set of square-wave chart patterns of 2 cm,1 cm and 0.5 cm gaps was designed and 11 completed IMRT lung plans were selected for the test.EDR2 film and the ionization chamber were used for test and verifying of plane dose distribution and some special points dose of CompassR.The IMRT phantom plans were verified by CompassR with three-dimension based on anatomical information.Parameters including the volume γ pass rate and the average dose deviation were tested using dose volume histograms.Results In square-wave chart patterns test,the dose distribution reconstructed and calculated by CompassR coincided with the measurement using film.The γ pass rates (3％/3 mm,2％/2 mm) exceeded 90％.When the width of field is 0.5 cm,the γ pass rate was a little lower on account of the penumbra zone.Compared to the dose distribution profile which was measured by film,the maximum deviations of the dose distribution profile which was reconstructed and calculated by CompassR were 3.21％ and 2.70％.The absolute dose deviation of specific point in the IMRT plans was less than 3％,the maximum deviation occurred in the lung.Compared to film,the averageγpass rates on the isocenter plain in IMRT plan were (94.65 + 1.93)％ (3％/3 mm) which was reconstructed by CompassR.In three-dimensional dose verification,the volume γ pass rates of targets and risk organs were not less than 90％,and the deviation of average dose was less than 1％.Conclusions Accuracy of the tested system satisfies the demand of IMRT dose verification.CompassR could provide information of volumetric dosimetry and anatomical location of dose error,which is benefit for evaluating the clinical value of verification result.
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Objective To investigate the feasibility and potential advantages of RapidArc applied to the radiotherapy of the postoperative rectal cancer.Methods 8 postoperative patients with rectal cancer were selected to be treated with a dose of 50Gy in fraction of 2Gy every time and 5 times a week.IMRT and RapidArc were used respectively to compare different target conformities,homogeneity index,dose-volume histogram data,treatment times and monitor units.Results The conformal index by RapidArc was 0.89±0.02 which was better than those by 5F-IMRT,0.87±0.02 (t =3.286,P ＜ 0.05),while the homogeneity index of target volume (1.060±0.005) and average dose [(52.55±0.76) Gy] by RapidArc were a little less than the homogeneity index of target volume (1.064±0.007) and average dose [(52.90±0.82) Gy] by 5F-IMRT (t =-1.459,-1.000,P ＞ 0.05).The exposure dose and mean dose of bladder and small bowel in high dose region by RapidArc were lower than those by 5F-IMRT,as well as bone marrow.The differences were statistical significant (P ＜ 0.05).The monitor units by RapidArc and by 5F-IMRT were (631±68) MU and (1046±146) MU,respectively (t =-5.830,P ＜ 0.05),while the mean treatment times were (78±5) s and (348±29) s,respectively (t =-26.358,P ＜ 0.05).Conclusion Compared with 5F-IMRT,RapidArc improves the target conformities and lowers the exposure dose for the organs at risk in high dose region while using fewer monitor units and less treatment time,which helps comforting patients and improving the efficiency.
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Objective To compare the dosimetric differences between two plans of RapidArc and 5F-IMRT for breast cancer radiotherapy after breast-conserving surgery.Methods Eight female patients with left-sided breast cancer after breast-conserving surgery were selected.A dose of 50 Gy in 25 fractions was prescribed for plans of RapidArc and 5F-IMRT.Target conformity index (CI),homogeneity index (HI),target coverage,exposure dose volume delivered to organ at risk were compared between two plans.At the same time,treatment delivery time and monitor units (MU) were also compared.Results The target conformity index (CI) in RapidArc plan (·0.88 ±0.03) was higher than that in 5F-IMRT plan (0.79 ±0.02,t =8.28,P ＜ 0.05).The homogeneity index (HI) in RapidArc plan 9.01 ± 0.73 was significantly lower than that in 5F-IMRT plan10.44 ± 1.08 (t =-2.73,P ＜0.05).For the dose volume delivered to the ipsilateral lung in two plans,the values of V10,V20,V30,and Dmean in RapidArc plan were lower than those in 5F-IMRT plan(t =-7.53,-7.20,-8.39,-7.80,P ＜ 0.05).However,the value of V5 in RapidArc plan was higher than that in 5F-IMRT plan (t =5.67,P ＜0.05).For the heart,the values of V5,V10 and Dmean in RapidArc plan were higher than those in IMRT plan(t =10.46,28.76,5.40,P ＜ 0.05),while the value of V30 in RapidArc plan was lower than that in 5F-IMRT plan(t =-6.12,P ＜0.05).The values of V5 in contralateral lung and breast were higher in RapidArc plan than those in 5F-IMRT plan(lung:t =21.50,P ＜0.05;breast:t =5.44,P ＜0.05).The MU in RapidArc plan was decreased by 25％,and the average treatment delivery time was saved by 60％,compared with that of 5F-IMRT plan.Conclusions During breast cancer radiotherapy after breast-conserving surgery,compared with 5F-IMRT plan,the RapidArc plan could improve the target HI,and reduce both the irradiated dose in high-dose volume and MU,and shorten the treatment time,but increased the exposed volume in low-dose volume of normal tissues.
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ObjectiveTo compare the accuracy of enhanced dynamic wedge (EDW) models of adaptive convolution algorithm (ACA) in Pinnacle3 9.0 and anisotropic analytical algorithm (AAA),and pencil beam convolution (PBC) algorithms in Eclipse7.3 treatment planning systems (TPS).MethodsTo evaluate the accuracy of the three algorithm models,we compared actual measurement values with TPS calculation values of EDW wedge factors under for different fields in which Varian-21EX 6 MV X-ray was applied,and also compared the actual dose distribution profile with that of TPS.ResultsThe deviations of EDW wedge factors of symmetry fields and asymmetric fields are within 2.8％ and 19.4％ for ACA in Pinnacle3 9.0.Meanwhile,the deviations are 1.0％ and 2.0％ for AAA,1.2％ and 3.0％ for PBC in Eclipse7.3.The deviations between measurement and calculation of all fields profile for ACA is within 3％ and within 2.7％ for AAA within 4.0％ for PBC in wedge direction.For the dose distributions,we evaluated the pass rates of three algorithms using gamma analysis.The gamma pass rates among all the three algorithms in symmetry and asymmetric fields are above 87％ and 85％ respectively.After the removal of the penumbra zone,the pass rates among all the three algorithms are above 96％ in symmetry fields,and above 95％ in asymmetric fields,respectively.Conclusions AAA and PBC algorithms in symmetric and asymmetric fields can meet the need of clinical applications.While,wedge factor of ACA should not be used in clinical due to its greater error in asymmetric fields.