Objective To investigate the impact of planning parameter settings on plan quality and delivery efficiency of VMAT for nasopharyngeal carcinoma with two treatment planning systems (TPS),as references for clinic plan optimization. Methods 25 patients with nasopharyngeal carcinoma were selected and planned for SIB?VMAT treatment. The same planning aims were used in the two kinds of TPS ( TPS?1 and TPS?2). Multiple planning parameters were set for plan optimization. Dose distribution to the target volumes and organs at risk,monitor unit ( MU) and delivery time were compared. Paired t?test or one?way ANOVA was used for the data which was in accordance to normal distribution;otherwise, nonparametric Wilcoxon signed rank test or nonparametric Friedman test was used. Results More segments lead to better plan quality and less MU but longer delivery time ( Minor impact was observed when segment number was larger than 120) in TPS?1,while it had little impact on both plan quality and delivery efficiency in TPS?2. Comparing to single?arc plans,dual?arc VMAT achieved no significant benefit in plan quality but had more MU and longer delivery time in TPS?1 ( P= 0?000 ) . However, dual?arc VMAT plans had better dose distribution in TPS?2, decreased the maximum and mean dose for spinal cord in 3?9% and 13?7%respectively (P=0?000,0?000).Changing the settings of maximum or minimum dose rate did not affect the plan quality in both of the tested TPSs. Increasing the maximum or minimum dose rate reduced the delivery time but the latter increased the number of MU ( P=0?000,0?000) . Conclusions VMAT plan quality and delivery efficiency is affected significantly and differently by planning parameter settings for two TPSs. Trial test should be conducted for different TPS to determine the optimal parameter settings.

Objective To study corrective method for displacement in the procedure of electronic portal imaging device (EPID)-based intensity-modulated radiotherapy dose valuation by studying the relative mechanical displacement of different vendor EPID (aS1000,Varian; aS500,Varian; iViewGT,Elekta).Methods A 5 cm × 5 cm field was set up to acquire portal images for three kinds of EPID,then a in house software was used to analysis the portal images.The relative displacement was acquired via analyzing a series of comparation between center positions of gantry angle ranging from 0° to 360° and gantry angle at 0°.Results In the lateral direction,the maximum relative displacement of EPID with aS1000,S500 and iViewGT were (-0.23 ±0.17) mm,(2.94±0.17) mm and (0.35 ±0.09) mm,respectively.In the longitude direction,the displacements were (-4.16 ± 0.20) mm,(-4.15 ± 0.25) mm and (-1.66 ±0.11) mm,respectively.As to longitude direction,the displacements could be well fitted with the usage of quadruplicate empiric function.Conclusions There is a significant difference at the aspect of relative displacement between different vendors EPID at different gantry angles.And the displacement in the longitude direction is obviously larger than in the lateral direction.The relative displacement should be corrected when applying EPID to the intensity-modulated radiotherapy dose verification at different gantry angles.

Objective To study preliminary the accuracy of clinical target volume (CTV) and internal target volume (ITV) automatically generated by an in-house deformable registration software on fourdimensional CT (4DCT),and evaluate its feasibility of clinical application.Methods Clinic treated one lung cancer patient and one liver cancer patient were selected for the study.CTV was delineated by radiation oncologist according to a single respiratory phase image of 4DCT scanning,and then deformed to the other phases and generated the CTVdefm on each phase image.Differences between the CTVdefm and CTVmanu were then compared.A composite ITVcopm was created by overlapping all the CTVdefm of 10 phases and compared with the ITVMIP which was contoured on the maximum intensity projection (MIP) CT images,including the shape,volume and geometric center position of the ITV contour.Results For the tested lung case,average volume difference between the CTVdefm and CTV was (-2.59 ± 5.02)％ for the all 10 phases,and the vector departure of the two ITV centers was (1.04 ± 0.89) mm.The ITVcomp almost completely matched the ITVMIP on the tested liver case with a volume difference smaller the 1％ and only 1.4 mm vector departure between their geometric centers.Conclusion The validity of the CTVdefm and ITVcomp gained from automatic deformation of manual delineation reference based on 4DCT images were preliminary evaluated and proved to be good enough for clinic planning.

Objective In order to explore the ways of reflecting the dose distribution in the implementation of the of IMRT (intensity modulated radiation therapy),a 2D diode array (2D-DA) was used in verifying the composite dose distribution of IMRT plans in the way of multi-gantry-angle composite (MGAC).Methods IMRT quality assure (QA) plans of 27 patients,based on the 2D-DA and solid water phantom,were designed and verified in two ways of single-gantry-angle composite (SGAC) and MGAC verifications.The comparison and analyzation of the dose distributions of the TPS calculation and the measurement of the 2D-DA were done.Results (1) When the beam central axes were not superposed with the detectors'plane of the 2D-DA,the verification passrate of SGAC and MGAC planar dose distribution of 27 patients'IMRT plan were 94.56%±4.28% and 94.81%±3.80% (the criteria:rvalue,3 ram/3%),respectively.There was no statistical difference between the results of two sets (t =-0.213,P＞0.05).(2) When one of the beam central axes was superposed with the detectors'plane of the 2D-DA,the verification passrate of MGAC planar dose distribution were 79.72%±12.77%.Conclusions Using the 2D-DA with a proper phantom,there was no statistical difference in the SGAC and MGAC verifications of IMRT plans when the beam central axes were not superposed with the detectors'plane.However,the MGAC dose distribution can provide more about the clinical dosimetry,and the errors in the implementation of the of IMRT were easier located.

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 evaluate the value of L-(methyl-11C)-labeled methionine positron emissions tomography (MET PET) and MRI in target volume delineation for postoperative radiotherapy for brain high grade glioma (HGG).Methods Thirty-seven patients with supratentorial HGG were included.Both MRI and MET PET scan were performed in the same treatment position for all patients.The consistency to determine residual tumor between MRI and MET PET was analyzed.Imaging data of MET PET and MRI were coregistered using the BrainLAB image fusion software.The extension of the volume with high uptake (VMET) on MET PET were compared quantitately with the enhancing area on MRI T1W gadolinium enhancement (VGd) and the hyperintensity area on MRI T2W (VT2).Results Both MET PET and MRI were positive for 19 patients and negative for 7 patients.The consistency between these two scans was 70.3%.MET PET was integrated with MRI in 30 patients with positive MET uptake.VMET were partially or entirely outside VGd in 29 patients and VT2 in 17 patients, whereas VGd and VT2 were partially or entirely outside VMET in all patients.The maximal distance from the margin of VMET to VGd was ≥ 2.0 cm in 50%patients and the corresponding distance of VMET to VT2 was ≥ 1.0 cm in 33% patients.Conclusions The differences are existing between MET PET and MRI in determination and identification of the location and extension of residual tumor for patients with HGG.The integration of MET PET and MRI can accurately delineate radiation target volume.

Objective To analyze the relationship between the radiation doses to mediastinal lymph nodes regions and the regional failure patterns when involved field radiation therapy (IFRT) was used for limited-stage small cell lung cancer (SCLC).Methods The mediastinal lymph node regions (group 1 to 10) of the iimited-stage SCLC patients received definitive radiotherapy were contoured in treatment planning system.The intentional or incidental radiation doses to each lymph node regions were recorded.In-field recurrence,marginal recurrence and out-of-field recurrence were respectively defined as the volume of failed lymph nodes located within the 80％ iso-dose lines,in the 80％-20％ iso-dose lines and beyond the 20％ iso-dose lines of prescribed doses.Results A total of 1 216 lymph node regions in 76 patients were contoured.The median follow-up time was 17.4 months.At diagnosis,lymph node regions with metastatic rates ＞50％ were 4R (68.7％),4L (57.9％),10R (57.9％),2R (56.6％) and 7 (51.3％).The positive lymph node regions were all subjected to prescribed doses.The lymph node regions that received incidental radiation doses of more than 3 000 cGy were:3P,4L,7,6,4R,5,2L.The median lymph node failure-free time was 9.8 months.In this study,only 1 patient developed out-of-field mediastinal lymph nodes failure.The rest of out-of-field recurrences and marginal recurrences were developed in the supraclavicular regions or contralateral hila.Conclusions When IFRT is used to treat mediastinal lymph node regions for patients with SCLC,negative mediastinal regions can be subjected to considerable incidental radiation doses.Out-of-field recurrences of the mediastinal lymph node regions are rare.This is contributed by the incidental radiation dose to these regions.

Objective To investigate the dosimetric performance of two algorithms for correcting the presence of tissue inhomogeneities,the finite site pencil beam (FSPB) and X-ray voxel Monte Carlo (XVMC) plans were implemented in the MONACO system,with the accuracy of application to clinic treatment of two algorithms were evaluated.Methods In a non-uniform artificial anthropomorphic phantom,regular open fields and intensity modulation radiated therapy (IMRT) plans of the MONACO were measured by using calibrated EBT2 films,and the dose accuracy of the two kinds of plans was analyzed by comparing the planned and measured plane dose.Results In an anthropomorphic phantom,the deviations between the calculated values by XVMC and the measured values by films were less than ± 2％.While the deviations of FSPB values between calculation and measurements was within ± 3％,except at the condition of 15 MV,10 cm ×2 cm field,the dose error in lung was up to 6.51％.The verification of individual IMRT beams based on films showed that the pass rates of calculation by XVMC and FSPB were larger than 90％ with γ criterion of 3％/3 mm and 4％/4 mm,respectively.At 3％/3 mm,the pass rates of FSPB were in the range of 80％-90％.At the same time,the pass rates of all individual fields were higher than 90％.Conclusions The accuracy of dose calculation of XVMC is better than that of FSPB when being in multi-segments and non-uniform media.The error of algorithm can be controlled within ±3％,for the calculation by XVMC.And the dose deficiency of PTV arising from algorithm can be avoided.

Objective To explore the feasibility of employing a risk category system in evaluating the treatment outcome of locoregionally advanced nasopharyngeal carcinoma (NPC) treated by intensitymodulated radiation therapy (IMRT) alone,and offering evidence for relevant perspective studies.Methods Totally 185 locoregionally advanced NPC patients were divided into high-risk and low-risk groups for evaluation and comparison.The patients who met at least one of the following criteria were defined as high-risk group and others as low-risk group:GTVnx ＞ 30 cm3;Clinical stage T4N2M0;multiple neck node metastases with 1 node size ＞4 cm,and N3 with any T stage.Results With a median follow up of 110.9 months (6.7-152.4 months),the 5-year overall survival,locoregional relapse-free survival,distant metastasis-free survival for the high-risk group vs.the low-risk group were 61.0％ vs.90.5％ (x2 =30.298,P＜0.05),78.3％ vs.91.5％ (x2 =6.352,P＜0.05)and 71.6％ vs.92.0％ (x2 =16.346,P ＜0.05).Conclusions As a simple and practicable method,the risk category system is helpful for discriminating locoregionally advanced nasopharyngeal carcinoma with different risk-group of treatment failure and in further perspective clinical research.

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.