Objective To investigate of the accuracy and feasibility of independent check for intensity-modulated radiotherapy (IMRT).Methods Inputing the linear accelerator Varian 600C/D physical data to IMsure ( a independent checking software) and constructing a calculation model.Use of IMsure to calculate the point dose and fluence of 25 cases IMRT treatment plans which have been calculated by Eclipse treatment planning system (TPS),and do a actual measurement of these plans by Matrixx at the same time.IMsure,TPS calculation results and measurement results of Matrixx were compared.Results Select Matrixx's center probe as a reference point,to TPS calculated results as the standard,then the average difference of the IMsure calculation and Matrixx measurement were ( -0.13 + 1.24)％ (t =0.20,P =0.840 ) and ( - 0.18 ± 1.45 ) ％ ( t =0.86,P =0.400 ),respectively.Compared IMsure with 3 mm/3 ％and 2 mm/2％ standard respectively,the average γ rate of TPS were (98.7 ±2.8)％ and (94.9 ±7.2)％ ;compared matrixx measurement results,the average γ rate of TPS were ( 99.0 + 2.0 ) ％ and ( 93.2 ±6.9) ％.The results show that the difference of the point dose and the γ rate of dose distribution by Matrixx measurement and IMsure calculation was no statistically significant difference ( t =1.54,P =0.126 ).Conclusions Independent checking software can be used in the treatment planning system to acceptance and initial clinical tests.In routine,a independent checking software as IMsure may do a pre-verificaton of IMRT treatment plan,or even partially replace of the actual measurement if the adequate conventional quality assurance do well,thus reducing the daily measurements.

Objective To investigate the differences between Monte Carlo (MC) calculated doseto-water (Dw) and dose-to-medium (Dm) for lung cancers treated with intensity-modulated radiotherapy (IMRT).Methods A total of 10 lung carcinoma patients with 5-field IMRT treatment plans were stratified sampling randomly selected for this study,which were performed on Monaco treatment planning system (TPS) with MC algorithm.Using the patients' own CT images as quality assurance (QA) phantoms,two kinds of QA plan were calculated,one was the Dm,and another was the Dw plan.Dose volume histogram (DVH) parameters and the subtraction of two plans were used to evaluate the spatial distribution of the difference between the Dm and Dw.Results Differences between dose-volume indices computed with Dm and Dw for the PTV65 and PTV50 doses (D50％,D98％ and D2％) were-0.3％,-0.2％,0.3％ and 0.1％,-0.6％,0.4％,respectively,of which the D50％ of PTV65 and D98％ of PTV50 had statistical difference (t =-2.536,-3.776,P ＜ 0.05).For normal tissues,spinal cord,heart,lung and esophagus,the D50％ differences between Dm and Dw were 0.3％,1.1％,-0.2％ and -0.1％,of which the Dm of spinal cord and heart were slightly lower than the Dw (t =2.535,3.254,P ＜ 0.05).For the D2％ of the normal tissues,the differences were 0.3％,-0.6％,-0.7％ and 0.6％,the differences were statistically significant (t =2.311,-4.105,-3.878,6.214,P＜0.05).All the differences were within 2％.Meanwhile planned subtraction analysis showed the differences between the Dm and Dw varied very much with the other body parts of the patient,especially for bone tissues,and the two doses were significant difference (＞ 5％).Conclusion In the course of clinical application,the relative differences between Dm and Dw for lung cancers MC calculations should be noted when considering the dose limitations of bone tissue.

Objective To study the impact of the resolution of reference dose distribution and evaluated dose distribution to Gamma rate in the verification of IMRT. Methods Designed four fields, the resolution of dose distribution calculated in water phantom and exported from TPS are 1 ,2,3 ,4,5,6 mm. To calculate Gamma index by IBA's OmniPro-I'mRT software in different sampling resolution. Results When the resolution of evaluated dose distribution was fixed, the change of reference dose distribution's resolution has little effect on Gamma rate (5％ to IMRT field) ;When the resolution of reference dose distribution was fixed , the Gamma rate increased as the evaluated dose distribution's resolution ( ＞ 1 mm) raise ( the Gamma rate increase ( 15. 2 ±6. 2) ％ ( t = 11. 99 ,P < 0. 01 ) and ( 14. 9 ± 5. 5) ％ ( t = 13. 24 , P ＜ 0. 01 ) while the resolution of evaluated dose distribution changed from 6 mm t0 3 mm and from 3 mm to 1 mm　respectively) .Conclusions To use Camma method for verification of IMRT, the measured data can be as a reference dose distribution without　interpolation;the computed data by TPS can be as a evaluated dose distribution and it is more appropriate for the resolution of 1 mm.

Objective To explore the accuracy of high definition computed tomography angiography (HDCTA)in the evaluation of coronary in-stent restenosis.Methods 93 patients with 159 implanted coronary stents who underwent both HDCTA and CAG were included in the study.The sensitivity,specificity,positive predictive value (PPV),negative predictive value (NPV)and diag-nostic accordance rate of HDCTA were calculated.The imaging quality was analyzed by visual estimation.Possible factors that in-fluenced the diagnostic accuracy of HDCTA were evaluated,which included stent location,stent diameter and heart rate in the pa-tients with left anterior descending branch stents.Results Restenosis was found in 21 stents by CAG and 19 stents by HDCTA.The false positive and false negative were 5 and 3,respectively.Sensitivity,specificity,PPV,NPV and diagnostic accordance rate were 90.5%,96.4%,79.2%,98.5% and 95.6% respectively.The image quality was 4 score in 75 stents (47.1%),3 score in 33 (20.8%),2 score in 27 (17%),≤1 score in 24 (15.1%).The image quality of proximal segments,large stents (≥3.0 mm)and slow heart rate (<66 beast per minute)was significantly better than that of distal segments,small stents (<3.0 mm)and fast heart rate (≥6 6 beast per minute).Conclusion HDCTA is a convenient,efficient and non-invasive method for follow-up after im-plantation of the coronary artery stents.

Objective:To explore the influence of the selection of statistical uncertainty of control points in Monaco planning system on the dose distribution of nasopharyngeal carcinoma (NPC), aiming to provide the statistical uncertainty of single control point in Monte Carlo calculation which satisfies clinical needs.Methods:First, nine 10 cm×10 cm square fields with an equal interval of gantry angle were designed and five cases of 9-field intensity-modulated radiotherapy (IMRT) and five cases of single-arc volumetric-modulated arc therapy (VMAT) plans were randomly selected, Then, quality assurance (QA) verification plan using patient CT as QA phantom was created. Second, the grid spacing was selected as 3 mm during the calculation of dose distribution of QA plan. The statistical uncertainties of single control point were selected as 1%, 2%, 3%, 4% and 5%, respectively. Last, the deviation of dose distribution between different statistical uncertainties and 1% statistical uncertainty was analyzed.Results:For a square field and single IMRT field, the dose deviation of center point was almost 7% while the statistical uncertainty was selected 4%. For 9-field IMRT and single-arc VMAT, the dose deviation of center point was ≤ 1.5% and the average dose deviation of PTV was ≤ 0.3% when the statistical uncertainty of control points was changed from 1% to 5%. The percentage of the point dose deviation of the coronary plane of ≤ 1% was greater than 99% when the statistical uncertainty was ≤ 3% for 9-filed IMRT and 4% for single-arc VMAT.Conclusions:For the Monaco treatment planning system based on Monte Carlo calculation, the changes in the statistical uncertainty of control point from 1% to 5% exert significant effect upon the single field. In clinical application, the statistical uncertainty of control point should be ≤ 3% for 9-field IMRT and ≤ 4% for single-arc VMAT.

Objective To develop an accurate 2D dose reconstruction model using electronic portal imaging device (EPID).2D dosimetric verifications of volumetric intensity-modulated arc therapy (VIMAT)were done using the model.And the results were compared to other dosimeters.Methods The EPID-based dose reconstruction model was using convolve,deconvolve and correction function.The dose profiles which were obtained by the ion chamber were used to determine the model parameters.A total of 12 VIMAT plans for the treatment of anatomical sites of various complexities were chosen.The results obtained from EPID were compared to other dosimeters and treatment planning system (TPS).The ion chamber was used to measure the central point absolute doses.Other dosimeters were used to measure the plane dose distributions.All dosimeters measured the dose at 10 cm depth.The results were analyzed using γevaluation method.Results Regarding absolute central point doses,the ion chamber results were within 1.5％ of the EPID results.For the comparison to Seven29 and Matrixx,the average γ pass rates with 2％and 2 mm criteria were 98.9％ and 99.8％ respectively.For the dose distributions measured by EPID and calculated by TPS,the γ pass rates with 3％ and 3 mm criteria were 99.9％.Conclusions The presented results which were obtained from the comparison of measured and calculated doses show the reliability of our EPID-based dose reconstruction model.With the model,EPID can be a reliable and fast tool for IMRT plan dosimetric verification.The model expanded to the 3D dosimetric verification in the uniform phantom will be considered as the next work.

OBJECTIVETo study the correction of algorithm for Varian enhanced dynamic wedge(EDW) factors and compare the dose/monitor unit (MU) deviation measured at the central axis of EDW field with that obtained by manual calculation or using the treatment planning system.

METHODSEDW factors and dose were measured with Thimble ion chamber at 10 cm depth under the water for 6 MV and 10 MV photon on Varian linear accelerator. The corresponding calculations were done with the radiation treatment planning system. An analytic formula, namely the MU Fraction model, was used to calculate the EDW factor, which was corrected with a constant factor. The MU of conventional 2-D planning derived from manual calculating, treatment planning system, and actual measurements were compared.

RESULTSWith the measured results as the standard, the corrected manual calculation deviation of EDW factors was significantly reduced. For photon 6 MV, the maximum deviation reduced from 4.2% to 1.3% for 60° symmetry fields was, and from -4.7% to -1.8% for asymmetric fields. For photon 10 MV, the maximum deviation for all EDW fields was reduced from -3.0% to 1.1%. Comparison of the manual calculations with the measured results showed a MU deviation for symmetric fields within 2%, and more than 5% for some asymmetric fields. The deviation between the calculations of the treatment planning and the measured results was less than 1.5%.

CONCLUSIONConstant factor correction can effectively reduce the deviation of manual calculation. For MU calculation of EDW field in conventional 2-D dimensional treatment planning, the corrected results of symmetric fields meet clinical requirements. While the minimum distance between the field edge and the central axis was less than 4 cm in asymmetric fields, the corresponding special method, measurement or the treatment planning system should be used to calculate the dose/MU.