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.

To produce the reverse transcriptase of moloney murine leukemia virus (MMLV-RT) through gene recombination, MMLV-rt gene was amplified by polymerase chain reaction (PCR) with specifically designed primers bearing restriction enzyme sites. Five mutation sites increasing the solution of the target protein were introduced through Site-directed mutation. After verification by sequencing, the gene was cloned into the expression vector pET15b to construct the recombinant plasmid pET15b-MMLV-rt. Purified MMLV-RT was obtained by affinity chromatography (Ni3+-NTA beads). Molecular weight and purity of MMLV-RT were analyzed with SDS-PAGE. Enzyme activity was characterized with RT-PCR. We successfully constructed the recombinant plasmid pET15b-MMLV-rt and obtained the MMLV-RT fusion protein with 6His on the N-terminus. Recombinant protein was purified through Ni3+-NTA beads based affinity chromatography, the purity of which was 96%. The Activity of the enzyme was high. MMLV-RT of 96% purity was obtained with the prokaryotic expression technique, which serves as the basis for mass production of this enzyme.
Animals ; Mice ; Moloney murine leukemia virus ; enzymology ; genetics ; RNA-Directed DNA Polymerase ; biosynthesis ; genetics ; Recombinant Fusion Proteins ; biosynthesis ; genetics ; metabolism ; Recombination, Genetic

Objective To study the dosimetric peculiarity of 3D intracavitary brachytherapy in the application of endometrial carcinoma comparing with traditional 2D plans. Method 39 3D brachytherapy treatment plans of 11 patients with endometrial carcinoma were retrospectively analyzed with re?planning 2D treatment plan, the dose volume histogram ( DVH) parameters such as the target dose volume parameters V150 and D90 , the 2?cc doses to organs such as bladder, small intestine, rectum and sigmoid and the total reference air kerma TRAK were analyzed. The differences between the two groups are compared by paired samples T test. Results For target with V<60 cm3 ,there is no statistically significant difference between 2D and 3D plans,the D90 is (551?17±90?33) cGy and (574?15±117?18) cGy,respectively (P=0?390). As the increase of target volume,the D90 came to be significantly different ( P=0?001) , high dose region V150 for 3D and 2D plans is (51?05±21?61) cm3 and (53?41±11?71) cm3, respectively (P=0?482). With the target volume larger than 60 cm3 ,compare to 2D plans, the 3D plan can increase the target coverage as well as OAR dose except for small intestine ( P=0?128) . In addition, with different plan mode,the BMI did not affect the crisis organ dose such as rectum, small intestine, bladder and sigmoid, the P value is 0?239, 0?198,0?744 and 0?834,respectively. Conclusions For endometrial carcinoma,compared with traditional two?dimensional plans,the 3D brachytherapy treatment plans can significantly improve the target coverage and avoiding overdose of organs, clinical curative effect and side effect still needs further observation.

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 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 determine the peripheral dose ( PD) of a Trilogy accelerator under different conditions and the feasibility of PD measurement using the semiconductor diode ionization chamber. Methods In a solid water phantom, a CC13 air?filled ionization chamber and a semiconductor diode ionization chamber were used for PD measurements with different distances (13 measurement locations within 1?31 cm) , depth ( 3, 5, 15 cm) , field sizes ( 10, 20, 30 cm) , wedge ( W15, W45, VW15, VW45) , and beam energy (6, 18 MV). The relationship of PD with PDleakage and PDscat er was determined by removing the scatter phantom. Simulating the patients with cervical cancer undergoing radiotherapy, a CIRS phantom received volumetric modulated arc therapy ( VMAT) , step?shoot intensity?modulated radiotherapy ( IMRT) , and sliding?window IMRT to measure PDs of the breast, thyroid, and lens. All the data were normalized to the isocenter. Results PD was gradually reduced with the increase in distance ( 13?41% at 1 cm from the edge to 0?25% at 31 cm from the edge) . With a fixed distance from the edge of the radiation field, there was no significant difference in PD between different depths. A radiation field with a size of 30 cm had a PD about two?fold higher than that with a size of 10 cm. PD increased with the increase in the physical wedge angle and increased by 1% compared with the open field;PD decreased with the increase in the virtual wedge angle and decreased by 2?3% compared with the open field. PD decayed from 13?35% at 1 cm to 0?23% at 31 cm under 6 MV X?ray and from 11?06% at 1 cm to 0?20% at 31 cm under 18 MV X?ray. Dscat er was dominant in the regions close to the edge of radiation field and decreased from 62?45% at 1 cm to 5?71% at 25 cm. In all measurements under 6 MV X?ray, the maximum proportion difference between CC13 ionization chamber and diode ionization chamber was less than 1%. PDs of the breast, thyroid, and lens were 6?72, 2?90, and 2?37 mGy in VMAT mode, 7?39, 4?05, and 2?48 mGy in step?shoot IMRT mode, and 9?17, 4?61, and 3?21 mGy in sliding?window IMRT mode, respectively. Conclusions For the measurement of PDs, the CC13 air?filled ionization chamber and semiconductor diode ionization chamber have good consistency and feasibility under 6 MV X?ray. In clinical practice, the understanding of the relationship of PD with different radiation conditions helps to reduce the doses to organs at risk. Shielding and protective techniques can further reduce dose deposition.

Objective:Objective To investigate the role of radiotherapy in the treatment of refractory keloids, evaluate the self-assessment degree of satisfaction of patients and compare with the objective outcomes.Methods:A total of 144 patients (290 lesions) with refractory keloids admitted to Peking Union Medical College Hospital from 2013 to 2018 were included in this study. The median age was 28 years old (range: 15-81 years old). All lesions were subjected to electronic radiation at postoperative 24h. The regime of 5 to 7MeV electron beam radiation therapy was adopted. The total dose was ranged from 16 to 18 Gy/2f (at 1-week interval). The median follow-up time was 48 months (range: 35-91 months). Patient and Observer Scar Assessment Scale (POSAS) was used to evaluate the degree of satisfaction. Multivariate analysis was performed by Cox proportional hazards model.Results:Among 290 keloids, 52 keloids (17.9%) relapsed in 3 to 42 months from the end of radiotherapy (median 12 months). The main side effects were hyperpigmentation and local incisional extension. Univariate analysis showed that local incisional color darker than skin, pruritus, pain and young age were associated with recurrence. Multivariate analysis indicated that local incisional color darker than skin and pain were the independent prognostic factors for scar recurrence. Recurrence, hyperpigmentation and local incisional extension were the main reasons for patients′ dissatisfaction.Conclusions:Postoperative electronic radiation can achieve satisfactory efficacy in the treatment of refractory keloids. Local incisional color darker than skin and pain are the independent prognostic factors of keloid recurrence. Patient self-assessment results are not fully consistent with the objective clinical outcomes and recurrence status.

Objective To investigate how to use the ArcCHECK to complete synchronization test in helical tomotherapy(HT). Methods According to the synchronization test suggested by AAPM TG148, three aspects should be tested.(1)Gantry angle consistency:ArcCHECK device in the long axis was perpendicular to the rotation plane using virtual isocenter positioning. A delivery sequence was defined with a slice width of 2.5 cm,a pitch of 0.1,and a minimum of 40 rotations. The control sinogram was set to open the middle two leaves(No. 32 and 33)at projections centered at 0°, 120°, and 240°.(2)Couch speed uniformity:The ArcCHECK was fixed on the treatment couch by positioning the long axis in the movement direction of couch. An irradiation was done with a static gantry in the 0° position, the collimation set to 1 cm,and all MLC leaves open. A couch travel distance of 20 cm was programmed using a clinically common couch speed(0.3-0.5 mm/s for 2.5 cm treatment slice width)in the course of irradiation.(3) Synchronization of couch translation and gantry rotation:In this test,a rotational irradiation was used with the nominal 1.0 cm beam and a pitch of 1 for 13 rotations. The control sonogram was set to open all the leaves for a half rotation on the second,seventh,and twelfth rotations. The initial collected data were used as the baseline data of parameters. The subsequent measurements were compared with the baseline data using the point to point absolute dose pass rates of DD(dose difference,1%). Results The gantry angle consistency could check the correct initial angles at the beginning of the treatment and the ability to reproduce the projection every rotation.There were six parallel and straight high-dose regions in ArcCHECK software.In the couch speed uniformity test,the relative dose in the long axis in the high-dose regions was changed less than 2%. In the synchronization test of couch translation and gantry rotation,three parallel high-dose regions with the same separation spacing were present in the ArcCHECK software. The synchronization tests were done twenty-eight times in the second,seventh, and twelfth irradiation rotations and the average pass rates were 93.2%±1.5%,93.7%±1.1%,and 93.5%±1.3%,respectively. Conclusions The ArcCHECK device is a suitable alternative method for performing the synchronization test in HT due to its lower workload and costs compared with the film.

Objective To analyze the failure and processing methods of helical tomotherapy multileaf collimator (MLC) and summarize relevant maintenance experience,aiming to accurately identify the faulty parts,shorten the downtime and enhance the work time.Methods The failure data of the helical tomotherapy MLC system in the past 48 months were analyzed to identify the common faulty parts,causes and processing methods.Results During the previous 48 months,the MLC failure occurred for 20 times,11 times for air compressor failure,4 times for position verification board failure,twice for leaf driver failure,twice for cushion valve failure and once for the slip of leaf position verification rod.The MLC failure was significantly correlated with the humidity of high-pressure gas.The work time of machine exerted significant effect upon the service time of MLC parts.Conclusions The structure of the helical tomotherapy MLC system is complex.The high-intensity work increases the failure rate.The humidity of high-pressure gas affects the normal operation of the MLC equipment.The faulty parts can be identified,the downtime can be reduced and the work time can be enhanced by summarizing the experience of MLC maintenance.

Objective:An investigation on the prevention and control measures taken by radiotherapy centers of various hospitals in Beijing during the COVID-19 pandemic was conducted. The experience was summarized to provide reference for further work.Methods:Electronic questionnaires were distributed to each radiotherapy center through members of the radiation oncology therapeutics branch of Beijing medical association and members of Society of Radiotherapy Specialists (Technicians) of Beijing Medical Doctors Association. Statistical analysis was performed based on the feedback results of electronic questionnaires.Results:All forty radiotherapy centers in Beijing returned the questionnaires by the end of April 10, 2020. Except for the suspension of treatment in one center due to COVID-19 pandemic, all radiotherapy centers have taken corresponding prevention and control measures and continued to carry out radiotherapy. No COVID-19 infection of patients or medical staffs occurred during this pandemic.Conclusions:During the COVID-19 pandemic, all radiotherapy centers attach great importance to optimizing the clinical process and adopt reasonable prevention and control measures. On the basis of efficient prevention and control measures, radiotherapy is delivered to fulfill the treatment demands of cancer patients.