The Application Research Of VMAT

Part1. The dosimetric difference in the dose distribution ofintensity-modulated radiotherapy for whole pelvic lymph node incervical cancer patientsBackground and Objective: In recent years, Intensity-modulated Arc radiotherapy（IMAT） have been utilized to further improve dose conformity and spare normal tissue inpatients with esophageal carcinoma. Volumetric modulated single and double arc therapywith a RapidArc has been shown to result in higher dose conformity to complex shapedtumor regions and tighter constraints on limits of radiation to organs at risks, whilereducing monitor units and treatment time in patients with esophageal carcinoma. To studythe dosimetric difference of whole pelvic lymph node radiotherapy among RapidArc andintensity-modulated radiation therapy （IMRT） plans applying different energy x-ray incervical cancer patients with multiple pelvic lymph node metastases.Methods: Twelve cases of cervical cancer who underwent radical surgery anddemonstrated multiple pelvic lymph node metastases were treated with radiotherapy. Threeplans were generated for each case:7-filed IMRT, one-arc RapidArc（RA1=358°）andtwo-arc RapidArc（RA2=716°）. For each plan,6MV and15MV X-Ray were appliedrespectively. The dosimetric differences were compared among different plans.Results: All plans could meet the clinical requirement. The CI, HI and EVI of IMRTand RA2were better than RA1with significantly difference （P<0.05）, while the differencesbetween IMRT and RA2were not significant. There were no significant differences werefound in irradiation dose of organs at risk except for small bowel V₄₀（IMRT<RA2<RA1,P<0.05）. And dose distribution of the same plan approach applying different energydiffered no significantly.Conclusions: Compared to IMRT, there were no significant dosimetric benefits werefound except treatment time and monitor unit in radiotherapy for whole pelvic lymph node applying RaidArc; the6MV X-ray should be applied chiefly if IMRT or RapidArc wereused. Part2. Dosimetric study for thoracic esophageal carcinomaradiotherapy:RapidArc Combined with Active BreathingCoordinatorBackground and Objective: In recent years, Intensity-modulated Arc radiotherapy（IMAT） have been utilized to further improve dose conformity and spare normal tissue inpatients with esophageal carcinoma. Volumetric modulated single and double arc therapywith a RapidArc has been shown to result in higher dose conformity to complex shapedtumor regions and tighter constraints on limits of radiation to organs at risks, whilereducing monitor units and treatment time in patients with esophageal carcinoma.Respiration-induced internal organ motion and deformations during RT limit itsspatial accuracy in patients with thoracic esophageal carcinoma. Currently, deep inspirationbreath-hold （DIBH）, achieved using an active breathing control device （ABC）, allows forthe temporary and reproducible immobilization of internal thoracic structures byimplementing a breath hold at a predefined lung volume. As a result, this study aimed tocompare and analyze the dosimetric parameters of intensity-modulated arc therapy（RapidArc） combined with active breathing coordinator in the thoracic esophagealcarcinoma radiation therapy.Methods:10cases treated in our radiotherapy center were selected for this study.Patients received training on the use of ABC underwent CT simulation with moderate deepinspiration breath-hold （mDIBH） and free breathing （FB）. Based on the distinct CT, twotreatment plans were generated, RapidArc combined with ABC （RA-ABC） and FB forfixed-gantry IMRT （IMRT-FB）. The dosimetric parameters from DVH which werecompared between RA-ABC and IMRT-FB plan included planning target volume （PTV）,mean dose to normal tissue and the percentage of volume which received radiation dose noless than xGy （Vx）.Results: All patients tolerated a specified time of breath-holding and all plans couldmeet the clinical requirement. PTV decreased from376cm³in FB situation to260cm³using ABC. Total lung volume was5964.6cm³and3838.8cm³, respectively for mDIBH and FB patients，while heart volume were524.4cm³and642.7cm³respectively. The D2%,D98%, CI and HI of IMRT-FB were slightly better than RA-ABC without significantlydifference （P>0.05）. For RA-ABC plans, there were significant decrease in irradiation doseof total-lung’s V₂₀, V₃₀, V₄₀, V₅₀and mean lung dose （P<0.05）. For RA-ABC plans, overallMUs, total control points and overall deliver time were significant decreased （P<0.05）.Conclusions: Application of RapidArc combined with ABC in thoracic esophagealcarcinoma decreased irradiated lung volume, and probably would improve dose escalation.