ESTRO 2021 Abstract Book

S11

ESTRO 2021

Joint symposium: ESTRO-AAPM: A roadmap for the use of quantitative imaging in radiation oncology

SP-0031 Introduction (O'Connor roadmap) + PET/MRI biomarker discovery and validation for Radiation Oncology K.R. Redalen 1 1 Norwegian University of Science and Technology, Department of Physics, Trondheim, Norway Abstract Text Modern radiotherapy techniques such as intensity modulated radiotherapy (IMRT), volumetric arc therapy (VMAT) and proton therapy are all very flexible treatment techniques where we can obtain high dose coverage in the tumor volume at the same time as we spare organs at risk. This flexibility also gives the opportunity to escalate the radiation dose to more radioresistant areas without increasing the side-effects. In parallel we have also seen technological developments in medical image acquisition and analysis that increasingly provide faster and more detailed imaging for contouring of both targets and organs at risk, treatment planning, response prediction and evaluation, as well as quality assurance. Anatomical imaging has been used for a long time to identify healthy and diseased tissue, tumor size, stage and location of the tumor. On the other hand, functional imaging, in particular magnetic resonance imaging (MRI) and position emission tomography (PET), are imaging methods that allow us to visualise and quantify functional or radiobiological tissue characteristics such as metabolism (FDG-PET), proliferation (FLT-PET), cell density (DW-MRI), perfusion (DCE-MRI) and hypoxia (FMISO-PET). These characteristics are often different for tumors with the same size and stage and are associated with different response to radiotherapy. Therefore, PET and MRI biomarkers are promising to improve individualised radiotherapy. The PET and MRI biomarkers can be used for different purposes; 1) more accurate target and organs at risk delineation, 2) treatment stratification and response monitoring for treatment adaptation, and 3) dose escalation, dose de-escalation or dose-painting of subvolumes. For those imaging biomarkers which demonstrate changes during radiotherapy that is connected to outcomes, there also becomes a possibility to use this information for functional adaptive therapy. Then, both anatomical and functional changes can be re- assessed with imaging during the course of therapy, and response-adaptive radiotherapy may be applied to achieve a better outcome and lower toxicity. Despite the promises, the status is that a very limited number of imaging biomarkers are guiding clinical decisions. Some are not adopted because it has not been possible to show that they measure a relevant biological feature nor enable diagnosis or outcome prediction, while others do not have a real application in clinical use due to lack of efficient strategies for biomarker translation. A paper by O'Connor et al. (1) describes the major translational gaps to close in order to bring a promising imaging biomarker to clinical use. To close the first gap an imaging biomarker must show value in both experimental models and patients. The challenging second translational gap is closed when the imaging biomarker is fully integrated into routine patient care. To achieve this goal the conduct of three parallel pillars of investigations are required; technical validation, biological and clinical validation, and cost effectiveness studies. The presentation will go through these three pillars and explain how PET and MRI biomarker development may be accelerated and translated into clinical use. Imaging biomarker development in radiotherapy applications also require special attention to robust procedures for image acquisition, geometric accuracy and standardisations (2), that also will be discussed. Examples will be provided from recent PET and MRI biomarker development studies in radiation oncology. (1) O'Connor JPB, et al. Imaging biomarker roadmap for cancer studies. Nature Rev Clin Oncol 2017;14:169-186 (2) Gurney-Champion OJ, et al. Quantitative imaging for radiotherapy purposes. Radiother Oncol 2020;146:66- 75

SP-0032 Technical validation of MR imaging biomarkers for interventional trials in radiation oncology TBC

Abstract not available

SP-0033 PET-based radiotherapy adaptation: From biomarker discovery and technical validation to clinical trials S. Graves 1 1 University of Iowa, Radiology, Iowa City, USA Abstract Text Positron emission tomography (PET) has played an increasingly pivotal role in radiotherapy plan development and response assessment. PET imaging has often been utilized for target delineation and detection of metastatic disease, however new radiotracers also show promise for tumor sub-type classification, response prognostication, and early detection of treatment response. This presentation will discuss the roles of new and emerging PET radiopharmaceuticals – particularly those for imaging of prostate cancer, breast cancer, neuroendocrine tumors, primary brain tumors, and fibroblast-promoting tumors – for radiotherapy plan modification and adaptation. Strategies for clinical implementation of novel PET biomarkers, including prospective trial designs, will be discussed in the context of these emerging radiopharmaceuticals.

SP-0034 CT-based quantification of existing biomarkers A. McWilliam 1 1 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom