Room: AAPM ePoster Library
Purpose: proton therapy systems worldwide started implementing onboard kV cone-beam computed tomography (CBCT) for treatment volume localization and visualization of soft tissues. Intensity modulated proton therapy in conjunction with improved volumetric imaging techniques will help assessing not only target localization but changes in beam path length as well—not to mention the capability of enabling a robust adaptive therapy program. Routine quantitative assessment of various image quality parameters such as geometric accuracy, spatial resolution, uniformity, Hounsfield unit (HU) consistency of various materials, contrast to noise ratio (SNR) etc., are pivotal as CBCT systems are prone to scatter, beam hardening and setup alterations.
Methods: CBCT quality assurance program for the IBA Proteus®PLUS system were developed based on AAPM task group 142 & 179 guidelines. Radiological Imaging Technology, Inc. (RIT) software was employed for the analysis and reporting of the CBCT QA data and The Phantom Laboratory (CATPHAN®600) phantom was used to measure these various image quality parameters on a monthly basis.
Results: CBCT QA baselines used for each treatment rooms were acquired separately over a period using a commonly acquired clinical preset at our institution. Figure: 1 shows the positioning of the CATPHAN phantom in the proton gantry. Figure: 2 and 3 show the RIT software employed for CBCT analysis and the monthly CBCT QA reporting template presenting institutional baselines. In this study, the long term stability (over 2 years of CBCT QA data) for three proton gantry, kV CBCT systems will be presented along with some of the challenges associated with the IBA systems scatter correction techniques and preset specific tuning process.
Conclusion: study was conducted to evaluate the long term stability of basic image quality parameters for the kV CBCT systems on an IBA proton gantry system based on TG 142 & TG 179 recommendations and vendor suggested tolerance limits.