ESTRO 2024 - Abstract Book

S7 ESTRO 2024 effects in the long term are often under and misdiagnosed. Often these need to be managed by different members of the team. This talk will highlight the possible late effects patients treated for HNC can experience, what survivorship means for this cohort of patients and the challenges in diagnosing late effects. We will explore the use of patient reported outcomes to address what is most important to the patient, not what the clinician thinks is important. Invited Speaker

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Advanced treatment concepts for upright radiotherapy

Thomas Bortfeld

Massachusetts General Hospital, Radiation Oncology, Boston, USA

Abstract:

This talk will shed light on the promise of upright treatment systems to democratize particle therapy by eliminating the need for the large, heavy and costly gantry. Upright treatments are particularly promising in particle therapy because the proton and heavy ion gantries are much bulkier than electron and photon beam gantries. In addition, particle therapy is much less dependent on flexibility of beam placement than standard IMRT/VMAT. It is the combination of this greater advantage of upright treatment in particle therapy, which can potentially facilitate the installation of proton therapy in conventional treatment rooms, and the smaller compromise of not having a gantry that has led to a resurgence of interest in upright fixed-beam treatments. We will first review the potentially reduced flexibility of beam placement in gantry-less upright treatment paradigms and its impact on the ability to shape dose distributions. An analysis of over 4000 patient treatments at our center has shown that the full flexibility of the gantries is not utilized. In fact, there are only a very limited number of gantry angles (primarily the "cardinal" angles), and couch angles at 0, 90, and 270 degrees that have been used far more frequently than others. While the current trend is toward the use of proton arc therapy (PAT), it has earlier been shown that the power of intensity-modulated proton therapy (IMPT) facilitates highly conformal dose delivery from a "small angle" approach. In fact, unlike IMRT/VMAT, which relies on spreading beam angles out over very large angles to achieve the desired level of conformality (which is due to the theory of the Radon transform), IMPT can achieve dose conformality from a single beam. However, for the purpose of skin sparing, spreading out beams is required to some degree. These findings facilitate upright treatment: while arc therapy can be performed on a chair, there is no need for wide arcs, and a single-sided, e.g. anterior, approach is usually sufficient, for example in the case of treatments of the breast. Non-coplanar beams have been shown to be beneficial in some situations. They pose a slightly larger but not unsurmountable challenge for upright treatments: the chair can be tilted backward, forward, or sideways by a limited amount, in addition the beam can be bent out of the horizontal plane. Moving the patient on a chair around a fixed beam requires new strategies in image guidance and real-time adaptation. Other presentations in this session have addressed some of these challenges. New opportunities arise because image guidance systems can be more easily combined with a fixed beam than with gantry-based beam delivery. MRI-guided proton therapy is becoming a possibility. We will report on our very early experience with an ultra-low field MRI system for breast imaging and image guidance. A conceptual design of an image-guided gantry less system integrated into a standard treatment room will be presented.