ESTRO 2022 - Abstract Book

S461

Abstract book

ESTRO 2022

Tumour growth dynamics – growth rate combined with metastatic seeding efficiency – is the single most important biological feature determining the likelihood of success of local ablative treatment (LAT) in an individual patient. This can be assessed using appropriate clinical imaging. In particular, when it is applied as serial imaging, metastatic lesion doubling times can be calculated, and volume changes of lesions predicted. In the context of selection criteria for LAT, detecting metastases at the edge of image resolution contains essential diagnostic information that might trigger reluctance to use, or postponing LAT. Countability of lesions could thus be a better basic parameter for LAT than number of lesions. The entity of LAT as a treatment option in metastatic disease might best be defined not as a single procedure at one point in time, but as a series of treatments that can be given in a single or multiple sessions to different lesions. Translated into clinical practice, newly appearing lesions that remain amenable to LAT without triggering the start of a new systemic treatment, a change in systemic therapy, or initiation of best supportive care, should thus not constitute failure of LAT from an oncological perspective . In analogy with systemic therapies, failure of LAT would have to be decided when newly appearing lesions could no longer be treated with LAT and are thus progressing beyond LAT . This would have consequences for the definition of endpoints in clinical trials and registries, as a progression-of-disease event entailing failure of LAT would have to be redefined as progression beyond further options of LAT. Progression of an already locally treated metastatic lesion would constitute failure from a technical as opposed to an oncological perspective , needed when comparison of different LAT-modalities is at stake. Abstract Text The oligometastatic scenario is continuously evolving. At the same time survival of metastatic patients is becoming longer. Therefore, although initially we thought to oligometastases as a single “once in a life” moment, new and intriguing data, along with daily clinical experience, are suggesting us that there could be more than one oligometastatic moment in the natural history of a patient. The published experience by Christ et al. shows a continuous increase in the proportion of cancer patients treated with a minimum five courses of radiotherapy from 0.9% in 2011 to 6.5% in 2019 [1]. In our clinical experience [unpublished data], more than half of oligometastatic patients, experiencing a further relapse after a first LAT, progress again in a “oligo” way. Repeating LAT in these patients is becoming routine, but this approach poses new challenges for the radiation oncology community. I would divide these challenges in two main categories: clinical challenges (related to the identification of patients deriving a significant clinical benefit from repeated LAT) and technical challenges (related to cumulative doses, overlapping isodoses or even retreatment for in field recurrence). Another rapidly evolving scenario that questions us as radiation oncologists is represented by “new” systemic therapies. In the last years, traditional chemotherapy has been challenged and in most cases overcome by target therapies and immunotherapy. Lung cancer, renal cancer, melanoma and other solid cancers prognosis was dramatically improved by these new drugs, but this revolution is still ongoing and virtually involving at some point most, if not all, cancer patients. From our point of view, this revolution implies a major effort to establish the role of LAT and SBRT in particular. Indeed, all these drugs, although effective, have an expiration date (i.e. cancer cells become resistant), therefore SBRT can represent a “low cost” approach to destroy resistant clones and prolong “drug life”. Moreover, if patients live longer thanks to more effective systemic therapies, the chances to face an oligometastatic moment increase significantly. This means that many of these patients will require multiple LAT at different time points. Along with the previously cited challenges, the availability of “new” drugs creates other uncertainties concerning unknonwn positive or negative interactions with RT and SBRT. Clinical data about effectiveness and tolerability of such combinations are generally poor, so that clinical experience and practical compromises are often driving our daily clinical practice. We are living a very exciting time for radiation oncologists, with old limitations and borders that are constantly overcome. However, we cannot forget that all these progresses need to be studied, validated and established through a good and trustable clinical and translational research. [1] Christ SM, Ahmadsei M, Wilke L, Kühnis A, Pavic A, Tanadini-Lang S, Guckenberger M. Long-term cancer survivors treated with multiple courses of repeat radiation therapy. Radiat Oncol (2021) 16:208 SP-0518 “It takes more than one course of local ablative radiotherapy in in oligometastatic cancer patients”: challenges and opportunities of repeat LAT and combination with systemic therapy M. Scorsetti 1 1 Humanitas University, Humanitas Research Hospital, Radiotherapy and Radiosurgery department, Milano, Italy

SP-0519 Registry trials for oligometastatic disease: rational and current status of the E2R OligoCare project

P. Ost 1

Belgium Abstract not available

SP-0520 Going beyond clinical trials in the era of real world data

C. Fortpied

Belgium Abstract not available