ESTRO 2021 Abstract Book

S88

ESTRO 2021

M. Høyer 1 1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark

Abstract Text Clinical guidelines ensure sufficient quality in clinical practice and are of special value in areas with variability of clinical practice across or between nations. There is now a growing number of ESTRO-ACROP guidelines covering RT practice in the larger and smaller tumor groups. Breast: Radiotherapy of breast cancer has been an area with broad variability in practice and use of technology and therefore also an area where there is a need for practice guidelines. Breast cancer specialists have succeeded to create a number of high-quality guidelines on eligibility, technologies, target and normal tissue contouring, dose prescription, treatment planning and constraints based on evidence on clinical outcome, pattern of recurrence and anatomy studies. Glioblastoma: Whereas the ASTRO clinical practice guideline gives recommendations on concomitant medication, RT volumes, patient selection, the ACROP guideline gives more specific guidelines on contouring and on techniques in treatment planning. It was one of the first guidelines to be published by the ACROP. Skull base: So far, we have only have had broad guidelines on management of skull base tumors. A newly published ACROP guideline provides specific recommendations on target and OAR contouring and on treatment planning for the radiation oncologist. Abstract not available Symposium: Radiobiology underpinning the interactions between radiotherapy and the anti-tumour immune response SP-0130 Apoptotic caspases - Key regulators of the interaction between radiotherapy and anticancer immunity L. Galluzzi 1 1 Weill Cornell Medical College, Radiation Oncology, New York, USA Abstract Text Caspases have long been subdivided into apoptotic (e.g., CASP8, CASP9, CASP3) and inflammatory (e.g., CASP1, CASP11), a classification that fails to grasp the complexity of caspase signaling in mammalian organisms. Indeed, it is now clear that most (if not all) mammalian caspases regulate inflammatory and immune processes, either directly or as a consequence of their role in cell death signaling. Moreover, pharmacological inhibition or genetic inactivatation of executioner caspases in mammalian cells most often fail to mediate bone fide cytoprotection, but rather changes cell death kinetic and immunological manifestations. Specifically, caspase 3 deletion in mouse TS/A breast cancer cells slowed down cell death induced by hi-dose radiation therapy, but ultimately did not alter the loss of clonogenic survival. Conversely, CASP3 deletion considerably boosted the secretion of type I interferon (IFN) by irradiated TS/A cells, which translated into improved in vivo tumor control, at both irradiated (local) and non-irradiated (abscopal) lesions. In line with this notion, patients with breast cancer exhibiting high levels of CASP3 counterintuitively exhibited a rather poor prognosis as compared to patients with low CASP3 levels. Thus, CASP3 (and potentially other executioner caspases) appears to limit the ability of radiation therapy to drive clinically relevant anticancer immune responses. SP-0129 Look into the future: ESTRO/Guidelines U. Ricardi Italy

SP-0131 Molecular triggers of the abscopal effect by radiotherapy M. Rodrigueq-Ruiz Spain

Abstract not available

SP-0132 Manipulating the immune contexture to improve radiotherapy responses T. Illidge United Kingdom

Abstract not available

SP-0133 Radiation-induced remodelling of the inflammatory microenvironment by tumour cells M. McLaughlin 1 1 The Institute of Cancer Research, London, Radiotherapy and Imaging, London, United Kingdom Abstract Text Immune checkpoint inhibitors are revolutionising the way we think about cancer treatment. Historically, research focused on the direct cytotoxicity of cancer treatments. The success of immunotherapies has pointed to an alternative therapeutic mechanism - the stimulation of an anti-tumour immune response. Studies indicate that the immunogenic properties of radiotherapy, not just its primary function of direct cytotoxicity, are a substantial contributing factor to therapeutic response in patients.