ABSTRACT
Objective To explore the effect of the Jaw‐tracking with RapidArc(JT‐RapidArc) plans for upper thoracic e‐sophageal cancer .Methods Treatment planning was designed by using RapidArc and JT‐RapidArc techniques for 11 consecutive patients .The dose‐volume histogram parameters of PTV and the organs at risk ,conformity index(CI) ,heterogeneity index(HI) , low dose volume of normal tissue (B‐P ) and monitor units (MU ) were compared between the different techniques . Results Compared with the RapidArc plan ,JT‐RapidArc had increased coverage of PTV1(64) D98 and HI(P0 .05) .Plans with JT‐RapidArc had lower Lung(V5 ,V10 , V13 ,V20 ,V30 ,Dmean ,P0 .05) .JT‐RapidArc plans increaseed the MU by 1% (349 ± 29 vs .345 ± 16 ,P>0 .05) as compared with RapidArc plans .Conclusion All of the plans had met the requirements of clinical dosime‐try .JT‐RapidArc plans as compared with RapidArc plans ,showing better part of target coverage ,part of lung and heart and B‐P sparing ,which MU was slightly increased .
ABSTRACT
Objective To compare the dosimetric differences of volumetric modulated arc therapy (VMAT) for preoperative radiotherapy of rectal cancer using 6MV X-ray flattening filter-free (FFF) and flattening filter (FF) modes.Methods FF-VMAT and FFF-VMAT plans were designed for 15 rectal cancer patients with preoperative radiotherapy by planning treatment system (Eclipse 10.0),respectively.Prescription dose of PTV was 50 Gy in 25 fractions.When the plans were normalized to 50 Gy to 95 ％ of PTV,the dose volume histogram (DVH),target and risk organ doses,conformity indexes (CI),homogeneity indexes (HI),low dose volume of normal tissue (B-P),monitor units (MU) and treatment time (TT) were compared between the two kinds of plans.Results FF-VMAT provided the lower Dmean,V105,HI (P ＜ 0.05),and higher CI (P ＜ 0.05) compared with FFF-VMAT.Small intestine (D5),Bladder (D5,Dmean V40,V50),L-femoral head (V40),R-femoral head (Dmean) were lower in FF-VMAT than those in FFF-VMAT (P ＜ 0.05).FF-VMAT had higher B-P (V5) compared with FFF-VMAT (P ＜ 0.05).FF-VMAT reduced the monitor units (MU) by 21％ (382±53 vs 483±26,P ＜ 0.05),as well as the treatment time (TT) in FF-VMAT was no significant difference compared with that in FFF-VMAT [(148±4) s vs (146±3) s,P ＞ 0.05)].Conclusions The qualities of FF-VMAT and FFF-VMAT plans were comparable and both clinically acceptable.When comparing two plans,FF-VMAT showed better target coverage and some of OARs sparing.The MUs of FFF-VMAT were higher than those of FF-VMAT,yet were not delivered within the same time.
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Objective: To evaluate the radiation protection and performance test for the 192Ir brachytherapy apparatus. Methods: According to the national standard, radiation protection and its various properties of the 192Ir brachytherapy apparatus were tested. The radiation leakage dose of the 192Ir brachytherapy apparatus and the radiation scattered dose of the surrounding environment were tested with the ion chamber survey meter 451P. The activity of 192Ir radiation source was calibrated with the well chamber HDR1000 Plus. Results: The radiation leakage and scattered dose of the 192Ir source storage device and the surrounding environment are far below the national standard. The deviation of the activity calibration for 192Ir source is-2.07%, accordance with national standard±5%. Conclusion: Radiation protection and its various properties of the 192Ir brachytherapy apparatus should be regularly monitor for assuring the quality of the brachytherapy.
ABSTRACT
Objective To perform a routine quality assurance procedure for Truebeam multi-leaf collimator (MLC) using MLC quality assurance (QA) phantom,verifying the reliability of MLC during the treatment.Methods MLC QA phantom was a specialized phantom for multi-leaf collimator QA,and contained five radio-opaque spheres that were embedded in an L-shape.The phantom was placed isocentrically on the Truebeam treatment couch for the tests.A quality assurance plan was settled up in the Eclipse v10.0 so that the fields for acquiring the necessary images could be created.The images were acquired by the electronic portal imaging device (EPID),and imported into the PIPSpro software for the analysis.The tests were delivered once a week for six weeks to verify consistency of the delivery,and the images were acquired in the same manner each time.Results For the leaf position test,the average position error was (0.21 ± 0.02) mm.The leaf width was measured at the isocenter,and the average error was (0.04±0.02) mm for the leaf width test.Multi-Port test showed the dynamic leaf shift error,the average error was (0.26 ± 0.04) mm.For the leaf transmission test,the average inter-leaf leakage value was 1.0％ ± 0.14％.Conclusions The MLC system of Truebeam could operate very well and the QA phantom is a useful test tool for the MLC QA.