Testing CBCT Image Quality Assurance Using Process Capability Indices

Purpose or Objective: A process capability index uses both the process variability and the process specifications to determine whether the process is capable. The process capability index (PCI) is a value which is considered as one of the quality measurements tool. In practice, process capability indices (PCIs) are used as a means of measuring process reproducibility potential and erformance. This work applied PCI to establish the control limits of the stability of image quality parameters of Varian on-board imaging (OBI). In addition, we evaluate the efficiency of the QA process by using the process capability performance measurement index (Cpm).

Material and Methods: The CATPHAN 600 phantom was used to evaluate the image quality parameters. Measurement on the image quality parameters where done using cloud-based image Analysis software (image owl) that provides analysis of Varian truebeam cone beam CT Ver. 2.5.10.0 DICOM images of the Catphan® phantom. High quality head Full-Fan acquisition and Pelvis Half-Fan acquisition modes were evaluated for noise, spatial Resolution, HU constancy and geometric distortion.

Results: A statistical analysis of the output constancy check was performed using JMP 14 Data analysis software. The Cpm calculated to evaluate QA of the capabilities and suitability of the CBCT image quality. The Cpm values are: noise 1.02, spatial resolution 1.1, HU constancy 1.03, geometric distortion 1.14

Conclusion: PCI is useful to quantifiably demonstrate the stability of the basic image quality parameters recommended by TG-142 for the Varian OBI imaging system. The results from this study showed stability over time for all image quality tests and processes indicate good quality because the capability index values are larger than 1. This tool can assist in improving the safety and consistency of the IGRT process.