Quality control of cone-beam computed tomography (CBCT) systems is an essential part of quality assurance to periodically check that quality requirements are met, reduce uncertainties and errors and reduce the likelihood of accidents and incidents. Radiation exposure levels must be measured to ensure that patient doses associated with CBCT examinations are kept as low as reasonably achievable consistent with the required diagnostic information. The main purpose of this document is to present procedures for quality control of CBCT systems used for dental, radiotherapy, interventional radiology and guided surgery applications.
The ‘Quality control in cone-beam computed tomography’ is the second of the series on quality control protocols. The European Federation of Organizations for Medical Physics (EFOMP) published the first document on ‘Quality Controls in digital mammography’ in 2015. These books are freely available online at efomp.org and can be used as both, in-depth working guides to everyday practice and an up-to-date reference sources for medical physicists engaged in quality control of medical imaging systems.
This book is the result of the experience and knowledge of an international group of leading medical physics experts and an excellent illustration of the synergy that can be achieved when every team member works at their best and collaboratively follows the whole process through its completion.
The aim of the guideline presented in this article is to unify the test parameters for image quality evaluation and radiation output in all types of cone-beam computed tomography (CBCT) systems. The applications of CBCT spread over dental and interventional radiology, guided surgery and radiotherapy. The chosen tests provide the means to objectively evaluate the performance and monitor the constancy of the imaging chain. Experience from all involved associations has been collected to achieve a consensus that is rigorous and helpful for the practice.
The guideline recommends to assess image quality in terms of uniformity, geometrical precision, voxel density values (or Hounsfield units where available), noise, low contrast resolution and spatial resolution measurements. These tests usually require the use of a phantom and evaluation software. Radiation output can be determined with a kerma-area product meter attached to the tube case. Alternatively, a solid state dosimeter attached to the flat panel and a simple geometric relationship can be used to calculate the dose to the isocentre. Summary tables including action levels and recommended frequencies for each test, as well as relevant references, are provided.
If the radiation output or image quality deviates from expected values, or exceeds documented action levels for a given system, a more in depth system analysis (using conventional tests) and corrective maintenance work may be required.