| Objective: Measuring the setup errors in Three-dimensional conformal radiation therapy(3D-CRT) of lung cancer using Cone- Beam ComPuted TomograPhy, finding a reasonable margin from the Clinic Target Volume(CTV)to the Planning Target Volume(PTV).Methods: 51 cases of untreated lung cancer were enrolled into this study from January.2009 to December.2010, fastening all patients with thermoplastic elastomer, processing the simulation with the same posture, 64 spiral CT machine scanning the CT image by 64 spiral CT machine, and planning CT images were gained,which were transmitted to the treatment planning system(Precise PLAN Release 2.16three-dimensional therapy planning system,3D-TPS ), the doctor contoured the GTV (gross tumor volume), CTV(Clinic Target Volume),PTV( Planning Target Volume )and the organs at risk(OAR). The Physicist made the planing ,according to the doctor requests, sand the planing to IGRT。After copleting radiotherapy setup in linear accelerator,we captured patients'XVI using KV Cone- Beam ComPuted Tomography. .And we used image processing tools to compare the KV Cone- Beam ComPuted Tomography image data and the plan CT data. ,then gained patients , position errors in theleft-right(LR) , superior-inferior(SI)and anterior-posterior(AP)three directions were≤2mm,the irradiation would be implemented,if the error of any one direction was≥2mm,we would correctived it online. Patients usually received KVCBCT scans at the first 3 times,and then one time a week, Patients who were treated by hypo -fractionated radiotherapy received KVCBCT scans everyday. All the Positioning errors data were analyzed using SPSS13.0 computer statistical software.The differences of the positioning errors between before and after treament were analyzed using an paired T test , P<0.05said the differences were statistically significant .Result:51 patients were eligible for the analysis. There were 35 males and 16 females.The age was ranged from41 to 83 years old.The 51 patients received a total of 570 KV CBCT scans.there were 306 scans before couch correction ,and were 264 scans after couch correction. The detection of set-up deviation were -0.88cm—1.75cm in left-to-right direction,-1.79cm -1.01cm in superior-to-inferior direction,and-0.93cm -0.63cm in anterior-to-posterior direction. The detection rates of deviation of≤2mm in three directions were12% before couch correction. Among the 306scans before couch correction ,the detection rates of deviation of≤2mm were 30.2% in left-to-right direction, 21.2%in superior-to-inferior direction,and46.6%in anterior–to - posterior direction. Among the 306scans after couch correction ,the detection rates of deviation of≤2mm were 96. 9% in left-to-right direction, 95.7%in superior-to-inferior direction,and97.6%in anterior-to-posterior direction. The detection rates of deviation of≤2mm in three directions were 95% after couch correction. The systematic error was -1.7mm ,and the random error was 2.4 mm before couch correction in left-to-right direction. The systematic error was 1.5mm ,and the random error was3.2mm before couch correction in superior-to-inferior direction. The systematic error was -1.3mm ,and the random error was2.0mm before couch correction in anterior-to-posterior direction. The systematic error was 1.2mm ,and the random error was 1.7mm after couch correction in left-to-right direction. The systematic error was -1.4mm ,and the random error was3.1mm after couch correction in superior-to-inferior direction. The systematic error was -0.9mm ,and the random error was1.8mm after couch correction in anterior-to-posterior direction. We analyzed the set-up errors befored and after couch correction and the results showed that the error after adjustment was significantly reduced than before. P<0.05,the difference was statistically significant. According to the espression which was proposed by VanHerk,the scope of CTV-PTV expansion mean 2.5∑+0.7σ,so that the minimum dose Of 90% of the clinical target voluneis more than 95% the prescription dose,and then we would get the set-up errors befored couch correction size of theCTV-PTV margin of patients with lung cancer in left-to-right, superior-to-inferior, anterior-to-posterior direction was respectively5.27mm,8.75mm,4.98mm,the set-up errors after couch correction size of theCTV-PTV margin of patients with lung cancer in left-to-right, superior- to -inferior,anterior-to-posterior direction was respecti- vely 2.53mm,3.22mm,2.14mm.Then we would get the set-up errors after couch correction size of theCTV-PTV margin of patients with lung cancer in left-to-right, superior-to-inferior, anterior-to-poste- rior direction was reduced 2.74(52%)mm,5.53(63%)mm,2.84(57%)mm than before.Conclusions: We can gain the three-dimensional imaged of every patient by KV Cone- Beam ComPuted Tomography, so that we would corrective the set-up errors in every treatment. After the KV Cone- Beam ComPuted Tomography error correction ,the set-up errors in three-dimensional directions can be controlled less than 2 mm. According to the espression which was proposed by VanHerk,the scope of CTV-PTV expansion mean 2.5∑+0.7σ,so that the minimum dose Of 90% of the clinical target voluneis more than 95% the prescription dose,and then we would get the set-up errors after couch correction size of theCTV-PTV margin of patients with lung cancer in left-to-right, superior-to-inferior, anterior-to-poste- rior direction was reduced 2.74(52%)mm,5.53(63%)mm, 2.84(57%)mm than before. |
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