ESTRO 2022 - Abstract Book

S862

Abstract book

ESTRO 2022

normalization (O. Acosta, France) and 2) statistical analysis (M. Witte, Nederland). Afterwards, the participants were invited to present their research activities and their expectations in attending the WS. As chairs, we were happy to have active participants involved in the discussions from across Europe – including Sweden, Germany, UK and Italy – and Australia. All participants were free to express their comments and proposals, and, based on participant feedback and discussion (Figure), we were able to define potential outputs that will form the follow-on work and that can be summarized as follow: 1) The creation of a Research Consortium in order to perform the first multi-site VBA experiment via a distributed learning approach. We defined the first principal – but not all – characteristics for this proof-of-principle experiment that should define the pathway to larger studies and research questions, such as registration template choice and evaluation of spatial normalization. 2) A workgroup for consensus requirements that VBA should fulfil so as to be implemented into the clinics, taking into account the emerging exemplars on which some groups are currently working.

The brainstorming and planning phase completed during the WS has been then channeled in a rich agenda of follow-up meetings for mapping future work and actionable tasks. In conclusion, we believe that by this WS on mining the RT dose we fulfilled our initial purpose, that is to say to lay the foundation of a VBA community within the ESTRO in order to open new pathways to a common and standardized VBA methodology, thus ensuring its future clinical validation and safe large-scale adoption.

SP-1016 Voxel-based RBE studies in proton therapy

A. Lühr 1

1 TU Dortmund University, Department of Physics, Dortmund, Germany

Abstract Text Protons are considered to be more biologically effective than photons. The proton relative biological effectiveness (RBE) is accounted for by using a fixed value of 1.1 in treatment planning and delivery. However, the RBE of protons is not constant; it varies depending on a combination of dose, endpoint, tissue α / β , and the linear energy transfer (LET) as has been demonstrated in numerous preclinical experiments. Accordingly, the remaining central question is how much the proton RBE variability impacts proton therapy treatment and, in particular, outcome. Therefore, clinical data are urgently needed that help to quantify the variable biological effect and thereby to reduce the uncertainty currently associated with the RBE. In recent years, a couple of retrospective studies considered post treatment image changes as a surrogate for biological effect. These image changes, e.g. contrast enhancements (CE) on post-treatment magnetic resonance (MR) images, were correlated on the voxel level with proton dose as well as LET and used to perform radiation effect modelling. Several studies demonstrated a significant effect of dose and LET, while in some studies the effect was found to be non-significant. In this contribution, first, the motivation why to use voxel-based analysis in proton therapy is discussed. Afterwards, several aspects of voxel-based RBE studies in proton therapy are considered, including the relevance of studied endpoints, requirements for the used imaging and irradiation data, possible analysis strategies and inherent technical and conceptual challenges.

SP-1017 What have we learnt and translation to the clinic?

O. Acosta 1

1 Univ Rennes, CLCC Eugène Marquis, INSERM, LTSI-UMR 1099, IMPACT Team, Radiotherapy Department , Rennes , France

Abstract Text Voxel-based methods have already been applied for unveiling spatially variable dose–effect patterns in radiotherapy, allowing the identification of sub-regions at risk in several anatomical locations such as the lungs, the heart, head and neck (H&N), the rectum or the bladder. Overall, the principles of voxel-based methods rely on the analysis of the local dose–toxicity relationship at fine spatial scales, through (i) non-rigid registration , (ii) dose resampling to a common space, and (iii) voxel-wise comparisons between patients with and without toxicity. The located regions have been shown to be more predictive for toxicity than the whole organs. These steps are well established from the methodological point