ESTRO 2020 Abstract Book

S278 ESTRO 2020

treatments that will improve patient outcomes and spare patients who would not benefit from treatment the toxicity caused by ineffective therapies.

been run to determine safety and indicative efficacy, and results from phase III trials are awaited. In this lecture phase I/II trial results will be reviewed for head-and-neck, lung and prostate treatments. And the headroom for safe focal dose-boosting provided by dose- painting will be compared to estimates of the degree of dose-escalation required to achieve meaningful survival improvements when uniform doses are delivered across tumour volumes. Results will also be reviewed for a preclinical study of rhabdomyosarcoma dose-painting [1]. Unexpectedly, this study found that growth-delays were shorter for tumours treated by boosting regions of high FDG uptake than for tumours treated homogeneously with the same mean radiation doses; and that growth-delays were similar for tumours receiving boost treatments, irrespective of whether the boosts were delivered to regions of high or low FDG uptake. Boost doses are linked to image intensities via prescription functions. Newer ways in which prescription functions are being derived from imaging and recurrence data will be described, emphasizing the need for the functions to reflect mechanistic considerations. A current ambiguity in image interpretation is whether a region of high tracer uptake contains more cells that are radio-resistant or cells that are more radio-resistant – semantics with very large implications for the success of dose-painting. The relative utilities of dynamic and static PET imaging for radiotherapy dose-painting will be characterized using results from a study that determined strengths of correlations between RNA sequencing data and kinetic versus static metrics of FDG uptake by breast tumours. Lastly, the importance of developing motion/mitigation strategies tailored to dose-painted treatments will be considered. [1] Trani D et al 2015 Preclinical assessment of efficacy of radiation dose painting based on intratumoral FDG-PET uptake. Clin. Cancer Res. 215511-5518 SP-0498 Theragnostic approaches for hypoxic tumours J. Adam Academic Medical Center, Amsterdam, The Netherlands

Teaching Lecture: Novel Radiotherapy techniques/treatments (e.g. micro beam, FLASH, etc, possibly immunotherapy)

SP-0495 Novel Radiotherapy techniques/treatments (e.g. micro beam, FLASH, etc, possibly immunotherapy) D. Jaffray (Canada) Princess Margaret Cancer Centre. Toronto, Canada

Abstract not received

Joint Symposium: ESTRO-EANM: Targeting the microenvironment in radiotherapy: where are we now?

SP-0496 Novel approaches to characterise the tumour microenvironment U. Haberkorn 1 1 DKFZ, Nuclear Medicine, Heidelberg, Germany Abstract text Cancer associated fibroblasts (CAFs) constitute a vital subpopulation of the tumor stroma and are present in more than 90% of epithelial carcinomas. These cancer- associated fibroblasts have been shown to play an important role for different aspects of malignant tumors such as migration, metastasis, resistance to chemotherapy and immunosuppression. Therefore, a targeting of these cells may be useful for both imaging and therapy. Since many of these CAFs express the fibroblast activation protein (FAP) which is expressed in activated fibroblasts, but not in quiescent fibroblasts, this membrane-anchored enzyme can be used as a target for radionuclide-based approaches for diagnosis, therapy planning and treatment of tumors, but also for the diagnosis of non-malignant diseases associated with a remodelling of the extracellular matrix. A selective targeting of a variety of tumors can be achieved by inhibitor-based radiopharmaceuticals (FAPIs). Several compounds have been recently introduced as theranostic radiotracer and demonstrated high uptake into different FAP-positive tumors in patients. SP-0497 The BTV turns 21: Current status of clinical trials and future directions J. Fenwick 1,2 1 institute Of Translational Medicine- University Of Liverpool, Molecular And Clinical Cancer Medicine, Liverpool, United Kingdom ; 2 clatterbridge Cancer Centre, Physics, Wirral, United Kingdom Abstract text Dose-painting of biological target volumes identified from functional images was proposed by Ling at the 1998 ESTRO conference. The concept was published in 2000, initiating large-scale endeavors to make radiotherapy dose-painting a reality. Subsequent studies validated tumour functional images against histopathological markers, determined correlations between images and outcomes, characterized image stability during radiotherapy, and showed that boosting of selected tumour subvolumes was dosimetrically feasible. Phase I/II dose-painting trials have

Abstract not received

SP-0499 Biological approaches to hypoxia modification E. Troost 1 1TU Dresden- Med. Faculty Carl Gustav Carus, Radiotherapy and Radiation Oncology, Dresden, Germany

Abstract not available

Symposium: How to combine different treatment modalities in rectal cancer

SP-0500 How to select patients for a multimodal approach G. Beets (The Netherlands)

Abstract not received

SP-0501 When to omit radiotherapy in rectal cancer?

Presentation cancelled

SP-0502 Organ preservation: where are we and where do we go? K. Haustermans University Hospital Gasthuisberg, Leuven, Belgium