Objective To study the effect of leaf movement speed on the setup error of multileaf collimator (MLC) in RapidArc mode,and to improve quality assurance and verify the reliability of RapidArc.Methods Referring to the PicketFenceStatic_M120.dcm and PicketFenceRA_Ml20.dcm files,the Tilt tests with different adjacent leaf speed were designed and setup errors of MLC were obtained by analyzing electronic portal imaging device images.Results In the Tilt tests,the setup errors gradually increased from gapl 1 to gapS0 in both static gantry mode and RapidArc mode.With a gantry angle of 270°,gap41 had the maximum setup error of-0.55 mm.In the RapidArc mode,gap46 had the maximum setup error of-0.67 mm.The deviation of gap width was no greater than 15％ in any mode.There was no significant difference in deviation pattern of gap width between four modes with different gantry angles.The same gaps in different stripes showed a consistent trend in gap width.The RapidArc mode had a larger variation in percentage deviation of gap width than the static gantry mode.Conclusions The setup error increases with the increase in the speed of MLC leaf.The variation in the leaf speed has no significant impact on the gap width.There is no correlation between the leaf speed and the deviation of gap width.Four different gantry angles give similar deviation patterns of gap width,suggesting that the deviation of gap width is related to the leaf rather than the gantry angle.The RapidArc mode has a greater impact on the gap width than the fixed gantry mode.

Objective To compare the dose distribution of the three-dimensional conformal radiotherapy(3D-CRT)and 5-field or 7-field intensity modulated radiation therapy(IMRT), and to explore the value of IMRT in preoperative radiotherapy for rectal cancer.Methods Ten rectal cancer patients treated with preoperative combination radiotherapy and chemotherapy were enrolled in this study. 3D-CRT plan and the 5.field or 7-field IMRT plans were performed for each patient.The conformal index (CI),heterogeneity index(HI)of the planning target volume(PTV)and the dose of normal organs of 3D-CRT plan(3D-CRTp)and the 5-field or 7-field IMRT plans(IMRT5fp or IMRT7fp)were analyzed with the dose-volume histogram.Results The CI values of PTV were 0.91,0.87 and 0.78 in IMRT7fpIMRT5fp and 3D- CRT but with IMRT7fp>IMRT5fp>3D-CRTp(t=-5.69、-8.91,P<0.01),respectively.The HI values of PrV were 1.09,1.08 and 1.05 in IMRT5fp,IMRT7fp and 3D- CRTp but with IMRT5fp >IMRT7fp>3D- CRTp(t=3.41、-6.89,P<0.01),respectively.The ratio of dose volume were 0.08,0.10 and 0.19(t=2.79、3.52,P<0.05)in IMRT7fp,IMRT5fp and 3D- CRTp on the small intestine V50,with 0.07,0.10 and 0.19(t=2.58、3.40,P<0.05)in IMRT7fp,IMRT5fp and 3D-CRTp on the bladder V50 and 0.01,0.01 and 0.05(t=3.00、3.17,P<0.01)in IMRT7fp,IMRT5fp and 3D- CRTp on the fomoral head V45.The ratio of dose volume were 0.31 and 0.38(t=3.91,P<0.01)in IMRT7fp and IMRT5fp on the bone marrow V50,with 0.07 and 0.10 in IMRT7fp and IMRT5fp on bladder V45.Conclusions IMRT plan is superior to 3 D- CRT plan in dose conformal degrees of PTV with preoperative radiotherapy of rectal cancer and can significantly protect the normal tissues.The 7-field IMRT plan might be the optimal plan for dose conformal degree and dose uniformity compared with 5-field IMRT.

Objective To study the dosimetry characteristics of 9 equal spaced fields and 9 fields with beam angle optimization (BAO) process for cervix uteri.Methods 12 cervix uteri cancer patients CT Images were transferred into Eclipse planning system.Each patient,the 9 equal spaced fields and 9 fields by BAO process were IMRT plan designed with the same CT image.Make a evaluation of dose distribution for target volume and OARs,and paired t test for them.Results Comparing to 9 equal spaced fields IMRT plan,the quality of 9 fields IMRT plan with BAO process the the PTV V95％ was 99.31％ vs 99.42％,P =0.020,at the same time V105％,V110％,Dmax,D got 60.54％ vs 47.92％,P =0.013;7.14％ vs 0.37％,P =0.000;56.62 Gy vs 55.47 Gy,P =0.000;53.29 Gy vs 52.72 Gy,P =0.000,the CI and HI was 0.85 vs 0.89,P =0.000 ;0.10 vs 0.13,P =0.000.For organs at risk,bladder V40 was increased by 4.7 ％ (P =0.013) ;the D40 of rectum was 0.5 Gy higher (P =0.004) ; the small bowel's DVH showed that V40 and Dmax increased by 0.6％ (P =0.015) and 1.4 Gy (P =0.000),D of bone marrow were raised separately by 1.3 Gy (P =0.000),the spinal cord's dose D0.1 cm3 was also increased by 2.0 Gy (P =0.000).Conclusion The quality of 9 equal spaced fields IMRT plan will be better than those achieved by BAO process optimized plans.

Objective To investigate dosimetric advantage of fixed field intensity-modulated radiotherapy (FF-IMRT),volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) for cervix uteri cancer.Methods CT datasets of ten patients with cervix uteri cancer were enrolled in the study.FF-IMRT,VMAT and HT plans were designed on Eclipse and HT treatment planning system.Plans were optimized with the aim to assess OAR while enforcing highly conformal target coverage.Institutional dose-volume constraints used in cervix uteri cancer were kept the same for three techniques.The different of three plan was play by single factor analysis of variance and compared to two groups by LSD method.Results All FF-IMRT,VMAT and HT resulted in equivalent target coverage but HT had an improved homogeneity index (P =0.000) and conformity index (P =0.000),or PTV of 105％ prescription dose (47.12％,45.83％ and 0.05％,P=0.000) and lowest Dmax dose (54.53 Gy,53.65 Gy,52.69 Gy,P=0.000).Compared with FF-IMRT and VMAT,the bladder V40 and Dmax of HT were lowest (50.01％,46.84％,42.98％,P=0.001 and 54.49 Gy,52.96 Gy,52.78 Gy,P=0.000),with the rectum V40 lowest (54.61％,48.34％,46.78％,P =0.006),the intestine Dmax lowest (54.53 Gy,53.65 Gy,52.66 Gy,P =0.000) and marrow Dmax lowest (54.51 Gy,54.44 Gy,52.13 Gy,P=0.000).But the delivery MU per fraction were highest (1429.20 MU,617.80 MU,7002.04 MU,P =0.000).Conclusions HT technology is feasible for clinical applications in cervical uteri cancer and can be used as a new method to promote.

Objective To explore the measurement method of the treatment dose of the patient with Diode for photon beam in radiotherapy,and to validate the treatment dose by comparing with the treatment planning system (TPS).Methods Experiments of the reproducibility,dose rate dependence,non-linearity dose response,and calibration factor in 60Co γ and 6 MV X beams were carried out with Diode on the surface of solid phantom and in water phantom.According to the needs of clinic treatment,different conditions were chosen to observe the dose changes with the angle of incidence,energy response,distance of source to skin,field size,wedge angle,block and tray using ionization chamber and water phantom.The Diode was placed on the surface of the solid phantom to obtain the correction factors.The doses of the chest,abdomen,and head and neek were verified with the Alderson phantom and Diode.Diode doses of the pelvis,head and neck at 14 points on the patient were measured.Results The Diode was irradiated at the points of the Alderson phantom,such as AP,RL and LL of the pelvis,with and without wedges,RL and LL junction of the neck and chin,with and without mask,the maximum relative deviation of doses was within ± 3% between Diode and TPS.The Diode was placed in different locations on the patient,including chest,abdomen and head and neck.The relative maximum deviation of doses was within ±5% between Diode and TPS.Conclusions The Diode method is reliable for measuring the exposure doses of the patient in radiotherapy.

Objective To study the dosimetric comparison of split field and fixed jaw techniques for large IMRT target volumes in the rectum cancer.Methods CT images of fifteen patients with rectum malignancies and regional target volumes were transferred into Eclipse planning system.SFT plan and FJT plan were performed on an Eclipse TPS using beam data generated for linear accelerator.A standard beam arrangement consisting of seven coplanar fields was used in both techniques.Institutional dose-volume constraints used in rectum cancer were kept the same for both techniques.Target and organs at risk were evaluated.Results PTV95 in FJT plan coverage was lower (t =-2.24,P ＜ 0.05).Dmean in FJT plan was increased (t =2.54,P ＜ 0.05),but Dmax was not different.HI in FJT plan became inferior (t =3.09,P ＜0.05),while CI was not different.There was no difference in dose distribution among bladder,femoral head and cauda equina.The value of V5 of small intestine increased in FJT plan (t =4.76,P ＜0.05),and the values of V20 and V50 of bone marrow were better than those in SFT plan (t =-2.66,-3.36,P＜0.05),while Dmax was higher than that in SFT plan (t =3.30,P ＜ 0.05).The value of V20 of body was higher in FJT plan than that in SFT plan (t =2.48,P ＜0.05).The number of MU was significantly lower in FJT plan than that in SFT plan (t =-9.38,P ＜0.05).The average segments in FJT plan decreased by 39.4％ compared with SFT plan (t =-6.46,P ＜ 0.05).Verification rate in FJT plan group was better than that in SFT plan (t =10.46,P＜0.05),and the treatment time was shortened from 12 to 6 min.Conclusions Compared to SFT technique,patients with rectal cancer who were treated with FJT could get better dose of target and organs,which can meet the clinical treatment requirements.The technique could shorten the treatment time and reduce the treatment MU.It also could increase the number of patients to be treated,reduce their waiting time and reduce the difficulty of QA.

Objective To compare the dosimetric difference in planning target volume(PTV)and organ at risk(OAR)with conventional and the three-dimensional treatment planning for limlted-stage small cell lung cancer.Methods Ten patients with limited-stage small cell lung cancer were chosen in the present study.Two treatment planning were designed twice respectively with the Cadplan R 3.1.2 treatment planning system for each patient in two-course.The total radiation dose was 50 Gy.The dosimetric parameters were assessed with dose volume histograms in PIT and OAR.Results For the first course,the dose homogeneity indices(HI)of PTV1,conformal indices(CI)of PTV2,contralateral lung V3o and eontralateral mean lung dose in the three-dimensional treatment planning were better than that in the conventional treatment planning.For the second course,the HI,CI and mean dose of PTV1,CI and mean dose of PTV2 in the three-dimensional treatment planning were better than that in the conventional treatment planning.Conclusions By comparison with conventional treatment planning,the three-dimensional conformal treatment planning could meet the demands of dosimetrie requirements well for limited-stage small cell lung cancer with three-dimensional conformal radiotherapy,but with no significant dnsimetric differences in the OAR.

Objective To compare the dosimetry characteristics of volumetric intensity-modulated arc therapy (VIMAT) and fixed field intensity-modulated radiation therapy (FF-IMRT) for cervix cancer.Methods CT images of 13 patients with cervix uteri cancer were transferred into Eclipse planning system.FF-IMRT and VIMAT plans were optimized on an Eclipse treatment planning system using beam data generated for Varian trilogy linear accelerator.Planning target volume (PTV) and organs at risk were evaluated with dose-volume histogram.To appraise the difference between the techniques,the paired t-test was applied.Results Compared with the FF-IMRT plans,PTV95％ coverage of VIMAT plan group increased (t =9.84,P =0.000),PTV110％ became lower (t =-3.72,P =0.003),Dmax decreased (t =-3.51,P=0.005),and CI became worser (t=5.39,P=0.000).PTV105％,Dmean,and HI had no difference (t =-0.02,-0.60,1.13,P =0.842,0.560,0.283).V30 of the bladder was reduced by about 10％ (t =-4.99,P =0.000),and Dmean and Dmax were 1.4 Gy and 1.5 Gy lower respectively (t =-3.65,-18.03,P =0.004,0.000) ;V40 of the rectum was reduced by about 10％ (t =-2.99,P =0.012),and Dmean and Dmax were reduced by 0.6 Gy,0.8 Gy respectively (t =-2.98,-4.05,P =0.013,0.002) ;V30,V40 and V50 of the small intestine were reduced by 16％,10％ and 11％ (t =-10.85,-4.74,-8.66,P =0.000,0.001,0.000),and Dmax was reduced by 0.8 Gy (t =-9.45,P =0.000) ; V30,V40 and V50 of the bone marrow were reduced by 26％,19％ and 16％ (t =-22.10,-10.19,-4.04,P =0.000,0.000,0.002),and Dmean reduced by 1.9 Gy (t =-16.21,P =0.000) ; D5 of the left and right femoral heads were reduced by 1.6 Gy and 2.7 Gy (t =-2.89,-6.22,P =0.015,0.000).Dmax of the caudate equine was reduced by 1.5 Gy (t=-4.80,P=0.001).V20,V30,V40 and V50 of the body were reduced by 18％,18％,4％ and3％(t=-7.52,-11.75,-6.26,-6.94,P=0.000,0.000,0.000,0.000).Dmean and Dmax of the body decreased by 1.0 Gy and 0.4 Gy (t=-3.72,-3.51,P=0.000,0.005).Average machine unit (MU) decreased by 57％ (t =-40.54,P =0.000).Conclusions cervical cancer Patients with VIMAT technology can get equivalent or superior dose distribution compared with the FF-IMRT technology.And VIMAT technology could reduce MU.But the efficacy needs further clinical evaluation

Objective Performing a daily quality assure (QA) program to get variation and error range of on board imager (OBI) system,so that the OBI system can meet the needs of clinical treatment.Methods The daily QA program including: mechanical accuracy,2D/2D Shift calculations accuracy,couch motion accuracy.Results The max deviation was-0.7 mm in lcft-right (LR) dircction and 0.8 mm in superior-inferior (S1) direction in Linac& OBI isocenter accuracy check.The max deviations in 4 blades (x1,x2,y2,y1) position accuracy check were:-2.1 mm,2.2 mm,± 1.7 mm,-2.1 mm.In OBI mechanical arms position accuracy check,31％ standard data was 85.2 cm with 0 mm deviation; 69％ standard data was 85.1 cm with 1 mm deviation.In LR,SI and anterior-posterior direction,2D/2D shift calculations accuracy was 0.46 mm,1.35 mm,-0.04 mm and couch motion accuracy was-0.1 mm,0.3 mm,0.2 mm,respectively.Conclusions By performing the daily QA program,it could be found whether OBI works properly and satisfies the clinical use.The physicist can pay more attention to the parameters which change frequently,and adjust the frequency of the parameters which are stable,so that working efficiently.

Objective To investigate whether the accelerator image beam line (IBL) full scan and extend field of view(EFOV) scan mode megavoltage cone beam CT(MV CBCT) images can be used for dose calculation in adaptive radiotherapy.Methods The large aperture CT and MV CBCT were used to scan the CIRS 062M electron density modules,the CT value was established to electron density curves in the Pinnacle treatment planning system.Also,CT and MV CBCT were used to scan the head and neck,chest,abdomen and pelvis phantom.The intensity modulated radiotherapy(IMRT) plans were made with CT images and transplanted to MV CBCT images.The dose of targets and organs with their electron density curves was calculated,and two type IMRT plans with different CT images were compared.Results The dose distribution of head and neck phantom was acceptable,compared with the reference plan,the difference was within 3 ％.The dose distribution of chest and.pelvis was significantly reduced from reference plans,and the difference was 5％ and 10％ separately.This difference was beyond the scope of clinical acceptance.Conclusions MV CBCT images of accelerator IBL full scan mode in patients with head and neck site scan could be used for dose calculation in adaptive radiotherapy,chest and pelvic sites in EFOV mode scanning MV CBCT images could only be used for image guidance.