ESTRO 2023 - Abstract Book

S270

Sunday 14 May 2023

ESTRO 2023

Teaching Lecture: Bridging the gap between bulky tumours and radiotherapy: Spatially-fractionated radiotherapy

SP-0336 Spatially-fractionated radiotherapy: Tumour-subvolumes, dose-delivery and clinical applications M. Mohiuddin USA

Abstract not available

SP-0337 Partial tumor irradiation: radiobiological rational, indications and treatment outcomes S. Tubin 1 1 Medaustron, Center for Ion Therapy, Radiation Oncology, Wiener Neustadt, Austria

Abstract Text Unresectable recurrent bulky tumors represent a large spectrum of highly complex clinical scenarios that are very challenging to treat. Conventional radiotherapy is ineffective in most of these cases leaving the patients desperate and hopeless. This is due to the large tumor volume and the proximity of the tumor to critical organs and tissues, whose limiting dose constraints make it impossible to apply an ablative dose of radiation, especially if those regions have already been irradiated previously. Additionally, conventional radiotherapy applied to larger treating volumes is associated with lymphopenia, which negatively affects survival. Usually, the only therapeutic option that can be offered to those patients is palliative or best supportive care. That is why improved treatment outcomes for this patient population is needed. Recently, a small group of scientists inspired by the immunomodulatory potential of ionizing radiation moved beyond conventional treatment by giving the radiotherapy quite a different, unconventional form that might overcome the obstacles that make conventional radiotherapy impotent, resulting in an improved therapeutic ratio. This innovative, partial tumor irradiation, adopts different radiobiological mechanisms of action that are based on modulation of anti-tumor immune response. Often, a very dramatic bulky tumor regression, including even complete tumor response, can be observed. The principle behind this innovative approach is to improve the radiotherapy therapeutic ratio by adding an immune-mediated tumor cell killing component to the radiation-mediated tumor cell killing in order to boost the anti- tumor effect. The available literature suggests the safety and effectiveness of this unconventional approach characterized by the high neoadjuvant and immunogenic potential. This lecture will focus on rational, indications and therapeutic potential of novel partial tumor irradiation and its future perspectives.

Teaching Lecture: Outcome measures for trials in radiation oncology

SP-0339 Outcome measures for trials in radiation oncology M. Buyse 1 1 International Drug Development Insitute (IDDI), Biostatistics, Louvain-la-Neuve, Belgium

Abstract Text Generalized pairwise comparisons (GPCs) have been proposed to simultaneously analyze several outcomes of any type (discrete, continuous, possibly censored). GPCs are especially useful when (1) the outcomes of interest can be prioritized (from clinically most important to least important), and (2) clinical thresholds are deemed relevant for some of these outcomes (for instance, survival gains should exceed 6 months to be considered clinically worthwhile). In randomized clinical trials comparing Treatment to Control, GPCs consist of comparing all possible pairs of patients formed by taking one patient from the Treatment group and one patient from the Control group. Each pair is classified as a win, a loss or a tie for the outcome of highest priority. Ties are then classified using the next outcome of lower priority, and the process is repeated until all outcomes have been analyzed. The Net Treatment Benefit (NTB) is defined as the number of wins minus number of losses divided by the number of pairs. NTB is an absolute measure that directly addresses patient-centric questions about the probabilities of benefits and harms from treatment. As such, GPC can potentially be used to individualize treatment choices. This approach may be useful to improve statistical power (because several outcomes are considered in the analysis) as well as to inform decision-making for cancer treatments that may cause serious adverse events.

Teaching Lecture: Challenging scenarios with oligometastatic SABRs - Where do we go now?

SP-0340 Challenging scenarios with oligometastatic SABRs - Where do we go now? S. Harrow United Kingdom

Abstract not available

Teaching Lecture: A leap into clinical practice: Accurate treatment planning in presence of metallic implants

SP-0341 Photons A. Fogliata Italy

Abstract not available