An investigation and comparison of effective factors on variations of Honsfield numbers in CT scanners

Abstract

Objectives:This study was conducted to evaluate effective factors in variation of amount of Handsfield numbers in different CT scanners, considering the importance of CT number equivalence in diagnostic programs and cancer treatment by radiotherapy. Providing the better functional solutions for CT calibration, improving the quality of diagnostic and therapeutic programs, the emphasis on accepted tolerance and controlling the errors resulted from dose calculated by treatment planning systems were studied.Methods:The process performed on raw data obtained during the calibration procedure on ten CT scanners in different radiotherapy centers in IRAN. This quality control tests performed by a selected approved Iranian company.Results: This research focused on CT Number correctness and accuracy tests section in calibration procedure. The factors influencing the variation of Honsfield numbers in CT scans were evaluated by analyzing the obtained data. Data are compared with other factors that cause to alter Handsfeld CT number and reported in previous researches.Creating an error and changing the numbers of CTs causes change in the CT density curve and ultimately effects on treatment plan and the received patient dose. Therefore, it should minimize the error rate by evaluating the effective factors of the TPS. The main factors affecting on Honsfield numbers are: photon energy, the characteristics of materials in phantoms used for calibration of the systems, physical phantom shape and diameter, patient/phantom position and image reconstruction algorithm.Conclusion: It is strongly recommended that a well-documented assessment program is required to ensure Honsfield numbers changes in the confined range of treatments.

Keywords

• computer tomography
• hounsfield numbers
• ct simulation system
• ct numbers
• ct quality control
• electron density