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 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 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 inspect the dosimetry characteristic of a 2-D ionization chamber array and its response to oblique incident electron beam.And to discuss feasibility to using it to validate the electron arc therapy plan.Materials and methods:(1)The 2-D ionization chamber array was calibrated referring to a themble chamber,comparing the response to electron beams with incidence angle ranged from-50°to 50°.(2)Phantom test plans of 6 and 10MeV electron beam arc therapy were designed,with the beam rotation arcs of 30°,60°and 90° respectively,symmetric to the Central axis of 0°gantry angle.Dose distribution of each plan was verifled with the 2-D array.Results:(1)Measurement differences between the central detector of the array and the thimble chamber were less than 2%,under the planned oblique inddent 6/10MeV electron beam.(2)For the all test plans,dose error was less than 3%at dmax in the symmetric axis of the electron beam arcs.Off-axis dose error was less than 2%within the central 70%area of the profile in non-rotating direction,and smaller than 1.5%in the rotational direction.The measured dose distribution had good agreement with the TPS calculation in isodose curves between 100%and 20%.The gammapass rates(△D=5%,△d=5cm)were 99.98%、99.89%、99.74%、98.64%、99.16%and 99.44%respectively for 6 and 10 MeV plans with electron beam arcs of 30°,60°and 90°.Conclusion:it is practicable using the tested 2-D ionization chamber array to verify and validate the electron beam arc therapy plan.

Objective To quantify the amplitudes of lung tumor motion during free-breathing using four dimensional computed tomography (4DCT), and seek the characteristics of tumors with large motion. Methods Respiratory-induced tumor motion was analyzed for 44 tumors from 43 patients. All patients un-derwent 4DCT during free-breathing before treatment. Gross tumor volumes (GTV) on ten respiratory phases were contoured by the same doctor. The eentroids of GTVs were autoplaeed with treatment software (ADAC Pinnacle 7.4f), then the amplitudes of tumor motion were assessed. The various clinical and anatomic fac-tors associated with GTV motion were analyzed. The characteristics of tumors with motion greater than 5 mm in any direction were explored. Results The tumor motion was found to be associated with T stage, GTV size, the superior-inferior (SI) tumor location in the lung, and the attachment to rigid structures such as the chest wall, vertebrae or mediastinum. The motion over 5 mm was observed in ten tumors, which were all lo-cated in the lower or posterior half of the lung, with the greatest motion of 14.4 mm. For 95% of the tumors, the magnitude of motion was less than I 1.8 mm, 4.6 mm and 2.7 mm along the SI, anterior-poste-rior (AP) and lateral directions, respectively. Conclusions Tumor motion due to breathing is associated with tumor location, volume, and T stage. The greatest motion was in the SI direction for unfixed tumor in lower-lobe, followed by tumor in upper-lobe posterior-segment.

Objective To define individualized internal target volume (ITV) for hepatocellular car-cinoma using four-dimensional (4D) CT, and to compare the differences in target volume definition and dose distribution among 3D, 4D and respiratory-gated plans. Methods 4DCT scanning was obtained for 12 pa-tients with hepatoceUular. Gross tumor volume (GTV), clnical target volume (CTV) and normal tissues were contoured on all 10 respiratory phases of 4DCT images. The 3D, 4D and gated treatment plans were prepared for each patient using three different planning target volumes (PTVs): 1) PTV3D was derived from a single CTV plus conventional margins;2) PTV4D was derived from ITV4D, which encompassed all 10 CTVs plus setup margins (SMs);3) PTV_(Gating) was derived from ITV_(Gating), which encompassed 3 CTVs within ga-ting-window at end-expiration plus SMs. The PTV volume and dose distribution were compared among differ-ent plans. Results The PTV3D was the largest in all 12 patients, but still missed partial target volume in 5 patients when comparing with PTV4D. Both the 4D plans and the gated plans spared more normal tissues than the 3D plans, especially the hver. Without increasing normal tissue dose, the 4D plans allowed for increas-ing the calculated dose from (50.8±2.0) Gy (3D plans) to (54.7±3.3) Gy, and the gated plans could further increase the dose to (58.0±3.9) Gy. Conclusions The 4DCT-based plans can ensure optimal tar-get coverage with less irradiation of normal tissues and allow dose escalation when compared with 3D plans.Respiratory gated radiotherapy can further reduce the target volumes to spare more surrounding tissues, espe-cially for patients with large extent of respiratory mobility.

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.