Cone beam CT dose optimisation: A review and expert consensus by the 2022 ESTRO Physics Workshop IGRT working group

Image guided radiotherapy (IGRT) using kilovoltage cone-beam CT (CBCT) has become an indispensable tool to ensure the geometric accuracy of radiotherapy treatment delivery. Although significant technical advances have been made in reducing imaging dose, the repeated imaging procedures can still accumulate significant dose to healthy tissues. Despite the widespread use, we still lack clear guidance for optimisation and widely accepted frameworks for evaluating the quality and suitability of CBCT imaging protocols. To address this gap, the 2022 European Society for Radiotherapy and Oncology (ESTRO) Physics Workshop focused on image-quality and imaging-dose optimisation for IGRT using CBCT. This publication represents a review and an expert consensus of the 2022 ESTRO Physics Workshop IGRT working group. Here we aim to provide practical advice for optimising and maintaining CBCT imaging protocols to meet the needs of local procedures and patient populations. The review includes summaries of the current status of CBCT use and optimisation for IGRT in adults and paediatrics, an overview of currently available guidelines, and finally practical guidance on optimising and implementing CBCT imaging protocols for local IGRT treatments and patient populations.