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 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 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 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.

Objective To evaluate the respiratory movement of the both lungs with four-dimensional CT(4DCT), and determine the optimal respiratory phase series CT images for radiation dose calculation. Methods From November 2005 to November 2006,thirty patients with lung cancer who received 4DCT scan were enrolled,including 15 left and 15 right lung cancer cases,25 men and 5 women. The media age was 55 (35-78) years old. After 4DCT scanning, the image was treated with Advantage 4D workstation,and then transmitted into Pinnacle station( Adac 7.4). The both lungs were automatically outlined using Pinnacle station with CT recognition value of-900 to-200 Hu. Then-the same physician examined the unreasonable parts and revised them. After the delineation was completed,the volume of 10 respiratory phases of lung was obtained. Results The average respiratory phase in inspiratory and expiratory phases was 78.87%±2.71% and 26.32%±3.17% in the tumor located lung,77.55%±2.81% and 24.73%±2.55% in the healthy lung. The maximum and minimum mean volume was 106.48%±3.00% and 94.23%±2.78% in the tumor located lung,107.47%±2.43% and 93.65%±2.32% in the healthy lung. The volume at the end of inspiratory and expiratory was 106.43%±3.07% and 94.63%±2.71% in the tumor located lung, 107.37%±4.62% and 93.98%±2.34% in the healthy lung. Conclusions The series CT images scan on 20% ,30% and 80% respiratory phases are reasonable for radiation dose calculation. The maximum and minimum average lung volumes are almost equal to those at the end of inspiratory and expiratory.

Objective To observe the physique and anatomy changes in patients with nasopharyngeal carcinoma (NPC) during intensity-modulated radiotherapy (IMRT), using repeated CT images and deformable registration technique, and analyze their impact on delivery dose distribution.Methods Ten NPC patients were randomly selected from those who had received IMRT treatment.Gross tumor volume of nasopharyn (GTVnx), GTV of metastastatic lymph node (GTVnd), clinical target volume (CTV) and normal tissue or organ (OAR) were re-contoured on the in-course repeated CT images using a kind of deformable registration and auto-segmentation software according to the original planning contouring.Changes in volume of treatment targets and organs at risk were evaluated and the trends were then analyzed.Dose distributions were recalculated with repeated CT images and compared to the original plans.Results The volume of GTVnx were decreased by 6.44%,10.23% and9.72%(F=1.34,P=0.278) in the 2-,4-and 6-week after IM RT comparing with before IM RT, with 6.59%, 30.98 % and 35.13 % (F = 9.22, P =0.000) in GTVnd, 0.73%, 1.86% and 1.41% (F=0.33,P=0.722) in CTV1, -1.78%, -6.47%and -9.34% (F =16.89 ,P =0.000) in CTV2, 13.96%, 32.97% and 37.77%(F=17.17,P=0.000)in the left parotid , and 3.56% , 29.57% and 35.63% (F = 13.49 , P = 0.000) in the right parotid.The mean dose change rate of GTVnx were -0.39%, 0.08% and 0.32% (F =0.15 ,P =0.860) in the 2-,4- and 6-week after IMRT comparing with planning faction dose, with 0.53%, 1.19% and 0.69% (F=0.81,P=0.455) in GTVnd, 1.95%, 2.70% and 3.78% (F=0.61,P=0.552) in the spinal cord,0.32%, 0.81% and 0.62% (F=0.03,P=0.975) in the brain stem, 4.50%, 4.66% and 7.20% (F=0.33,P=0.725) in the left parotid, 2.20%, 7.17% and 7.12% (F= 1.24,P=0.306) in the right parotid.Conclusions The GTVnd, CTV2 and parotids shrinks obviously along with the treatment times for NPC patients during IMRT.Although changes in fraction dose of GTV, CTV, spinal cord, stem and parotids are not significant, further study with larger samples is needed.

Objective To evaluate the dosimetry of high-energy electron beams by using GafChromic EBT film. Methods The percent depth doses of electron beams of 4 MeV,6 MeV,8 MeV,10MeV, 12 MeV and 15 MeV were measured with EBT. The results were then compared with the measurements with diode detector in RFA and parallel plate chamber in water tank. Results The percent depth dose curves using EBT film had a good agreement with those using the other two detectors. Furthermore, no differences were found between up-right and tilt setup methods. When film upper edge is higher than water surface, a sharp drop of measurement results using EBT film was observed in comparison with those from diode detector in build-up region. Conclusions EBT film can be applied to measure percent depth doses of high-energy electron beams. During the EBT film measurements, the film should be tilted at the angle of 5degrees to the central axis of the field. When choosing up-right setup method, the edge of the film should be parallel to the water surface.