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Objective To evaluate the influences of various field-defining method of Varian accelerator on radiation dosimetry parameters, and provide theoretical basis for the beam modeling of the treatment planning system ( TPS ) . Methods The percentage depth dose ( PDD ) , the off-axis ratio ( OAR ) and the total scattering factors ( Scp ) of radiation fields were measured in three different conditions, including collimators (JAW), multileaf collimator(MLC) and JAW +MLC. The measured data was analyzed and compared with each other. Results The PDD of central axis was marginally influenced by three field-defining method. In both directions, the MLC-defined field sizes were larger by a maximum of 2. 9 mm ( left-right) or 1. 7 mm ( gun-target) than the JAW-defined ones. In the left-right direction, the width of field penumbra shaped by MLC was larger than the field of the same size as defined by JAW. The result of gun-target direction was to the contrary. In both directions, the field penumbra and size displayed no significant differences as defined by JAW+MLC or JAW. Conclusions The field size, penumbra width, and the total scattering factors were influenced by field-defining method, which indicates that special attention should be paid to the dosimetric parameters of MLC during TPS beam modeling for IMRT planning.
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Objective To evaluate the influences of various field-defining method of Varian accelerator on radiation dosimetry parameters, and provide theoretical basis for the beam modeling of the treatment planning system ( TPS ) . Methods The percentage depth dose ( PDD ) , the off-axis ratio ( OAR ) and the total scattering factors ( Scp ) of radiation fields were measured in three different conditions, including collimators (JAW), multileaf collimator(MLC) and JAW +MLC. The measured data was analyzed and compared with each other. Results The PDD of central axis was marginally influenced by three field-defining method. In both directions, the MLC-defined field sizes were larger by a maximum of 2. 9 mm ( left-right) or 1. 7 mm ( gun-target) than the JAW-defined ones. In the left-right direction, the width of field penumbra shaped by MLC was larger than the field of the same size as defined by JAW. The result of gun-target direction was to the contrary. In both directions, the field penumbra and size displayed no significant differences as defined by JAW+MLC or JAW. Conclusions The field size, penumbra width, and the total scattering factors were influenced by field-defining method, which indicates that special attention should be paid to the dosimetric parameters of MLC during TPS beam modeling for IMRT planning.
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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 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.
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Objective To investigate the way to accurately delineate gross tumor volume (GTV) of high grade gliomas(HGG) for intensity modulated radiation therapy (IMRT) by using computed tomography (CT) and magnetic resonance imaging (MRI) image fusion technique. Methods CT and MRI images were fused from 19 patients. The GTV of each patient were independently delineated by one chief doctor and one resident doctor on CT and MRI image. The GTV contoured on CT (GTVCT), MRI (GTVMRI) were measured, and composite volumes (GTVCT+MRI) were the sum of CT-defined GTV and MRI-defined GTV. The differences of these volumes were compared. Results Whether chief or resident doctors delineated, all were GTVMRI ＞GTVCT(P ＜0.050). The percentages of GTVMRI on GTVCT+MRI were (98.57±7.00)% by chief doctors, and (97.84±10.00)% by resident doctors. Compared the difference between GTVCT and GTVMRI in postoperative patients and preoperative patients, P =0.046, and the difference between chief doctors and resident doctors was statistically significant for GTV defined by CT (P =0.020), but not by MRI and composite image (P ＞0.050).Conclusion The GTV of HGG patients must be delineated on both CT image and MRI image, including using CT and MRI image fusion. But the composite volumes(GTVCT+MRI) should be the sum of CT-defined GTV and MRI-defined GTV. Especially for the postoperative patients,delineating GTV should be taken more attention. And the GTV should be delineated by doctors with full experiences.