Opportunities and challenges of upright patient positioning in radiotherapy.

Upright positioning has seen a surge in interest recently as a means to reduce radiotherapy (RT) cost, improve patient comfort, and, in selected cases, benefit treatment quality. In particle therapy, eliminating the need for a gantry can present massive reduction of upfront investment, and would drastically reduce the facility footprint. For patients with pre-existing conditions that make lying down uncomfortable, or for target sites in intimate body regions, upright RT presents a promising option toward a more comfortable, patient centred treatment. With more evidence for benefits of upright patient postures in RT emerging, several centres across the globe, mainly in particle therapy, are currently in the process of installing commercially available or prototype upright positioning devices or have already commenced treatment with upright patient postures. Yet, there remain many challenges and open questions to embed upright positioning in the modern RT workflow, no international guidelines exist to support clinical practice in upright RT, and there is a lack of professionals trained for upright patient positioning. Much work is still needed to justify the many changes necessary for upright RT. Modern image guidance is paramount to upright RT, and it is yet unclear which imaging modalities are necessary to support upright postures with the same quality as recumbent positioning. In works on prototype upright positioning systems, external alignment similar to recumbent positioning was reported for small patient or volunteer cohorts. Certain clinical advantages, such as reduced breathing motion in upright position, have been reported, but limited cohort sizes do not allow resilient conclusions on the expected treatment quality yes. Redesign of RT equipment for upright positioning, such as immobilization accessories for various body regions, is necessary, where innovations have been presented in recent literature. This review discusses the opportunities of upright RT and puts them in perspective to the current challenges.