Establishment Of The Technology Platform Of OBI-based Image-Guided Radiation Therapy

The clinical applications of image-guided radiation therapy (IGRT)technology are to detect and minimize the patient’s position and anatomicaldifferences between the actual treatment and the treatment plan.However,thesafety and effect is the premise of IGRT for the clinical applications.The thesisbegan with the study on establishing quality assurance(QA) procedures of theIGRT system.The major QA programs,implementation methods and testingfrequency of daily QA, monthly QA and annual QA were analyzed anddiscussed.Based on the created QA,the thesis explored the clinical applicationsof using cone beam CT (kVCBCT) images.Image quality, stability and volume precision in kVCBCT are the key tothe success of IGRT.It is necesary to systematically study it.The methods of thestudy were: The image quality evaluation phantom was repeatedly scanned. Aconventional simulator CT images was used as a benchmark and results relatedto the low contrast resolution, spatial resolution, uniformity and image noisewere compared with the CBCT using the commercial treatment planningsystem.The comparison of image quality, long-term stability and volumeprecision was analyzed.One of the study’s purposes was to quantitativelyevaluate the image quality, stability and volume precision of the on-boardkVCBCT on the linear accelerator.It is difficult to acquire the actual dose received by means of IGRT.Thegoal of dose-guided radiation therapy (DGRT) is to optimize the plan forsubsequent treatment according to the exact dose of the actual treatment.It is ahot also difficult topic inernationally.The methods of the study were:Hounsfield unit (HU) values and profile along the two orthogonal lines ofimage quality evaluation phantom in kVCBCT images were compared to thosein the conventional CT.The kVCBCT CT value-density calibration curve wasestablished.The intensity modulated radiotherapy plans were created on theconventional CT images and copied to kVCBCT images.The dose distributionwas recalculated by means of the kVCBCT value-density calibration curve inthe treatment planning system.The dosimetric comparisons were performed between the kVCBCT and conventional CT plans on the phantom and10esophageal cancer patients.Another purpose of the study was to investigate thedose calculation accuracy and feasibility of using kVCBCT for esophagealcancer radiotherapy for carrying out the technical platform of IGRT and DGRT.The study showed that⑴t herewere no differences observed betweenconventional CT and kVCBCT in spatial resolution.However, in terms of the lowcontrast resolution, uniformity and image noise, the conventional CT images weresuperior to the kVCBCT ones.In valid scan range of the kVCBCT, reconstructedprecision was promising.There was no significant time trend in the image quality.⑵Thedosimetric differences were small between the kVCBCT-based and conventionalCT-based plans, and the dose distribution comparison showed good agreements.Therefore, the following conclusions can be drawn.The image quality ofkVCBCT is inferior to the conventional CT.However, tumor and soft tissues are visiblein the kVCBCT images.The image stability and reconstructed precision issatisfying.The accurate dose calculation based on kVCBCT for esophageal cancer isfeasible.The kVCBCT images can be used for monitoring the dosimetric changes duringthe treatment.