Treatment planning purposes use of cone-beam computed tomography images

Objective: The aim of this thesis is to examine the images of kilovoltage cone beam Computed Tomography (kV-CBCT) obtained by Elekta Synergy X-ray Volume Imaging system (XVI) and investigate their use in patient dose planning calculations. Method: Calibration and quality control procedures had been made to improve the image quality of the kV-CBCT system. Cathphan® calibration phantom had been used for CT number calibration. 3 different plans had been created in the treatment planning system (TPS). Head and thorax CT scans obtained with GE Light Speed RT and XVI imaging system. Registered plans are implemented on the head and thorax Rando phantom sections. Absolute and relative dose comparisons had been made by using farmer type ionization chamber and 2D plane array detector. Absolute dose difference comparing the ion chamber with the TPS were found between; % 1,25- % 1,48 for 9F plan and % – 0,9 and % 1,4 for 2F plan respectively. Results: The image quality have been improved %3, after XVI system calibration procedures. There wasn't any significant difference between the MU (Monitor unit) values of the plans created by two different imaging systems. Ion chamber dosimetry and TPS absolute dose difference was found for 9F (9 field ) between 1.48 % and 1.25 % , for 2F (2 fields ) between % 1.4 and % -0.9. The results of relative dose-measuring criteria of gamma analysis were δ <1 for 3 mm DTA (Distance to agreement) % 3 DD (Dose difference). Conclusion: The same plans applied on kV- KHBT images and CT images dosimetric measurements were %2 tolerance range. Key words: kV-CBCT dose calculation; Hounsfield units (HU); kV-CBCT quality control; gamma analysis