ESTRO 2021 Abstract Book

S254

ESTRO 2021

VI, the complete response rate, 5-year overall survival rate, and 5-year disease-free survival rate of the hyperthermia combination group were 88%, 77.8%, and 70.8%, those of the chemoradiation group were 77.6%, 64.8%, and 60.6%. The therapeutic effect of the hyperthermia combination group was good, but there was no significant difference in the survival rate between the two groups. Using this trial data, Dr. Ohguri in Sangyo Medical University reported significant correlations between thermal parameters and complete response rate, local control, and recurrence-free survival rate, suggesting that good tumor temperature elevation improves patient condition. Despite the results of these clinical trials, hyperthermia is not commonly used in Japan. The number of society members is decreasing year by year, and the current number is 401. The reason is that the hospital's income as insurance medical care is very low. The cost of hyperthermia is about $ 900 in a series regardless of the number of times. However, from the evidence in Western countries, hyperthermia is undoubtedly an effective treatment for the specific cases. Under this circumstances, the Japanese Society of Hyperthermia is conducting a systematic review of hyperthermic oncology and is currently preparing clinical practice guidelines for hyperthermia.

SP-0343 Thermoradiotherapy: Clinical evidence and potential indications TBC

Abstract not available

Symposium: Novel model systems for radiobiology research

SP-0345 Normal tissue organoids for radiosensitivity studies R. Coppes 1 1 University Medical Center Groningen, Radiation Oncology & Biomedical Sciences of Cells and Systems, Groningen, The Netherlands Abstract Text Radiotherapy involves unavoidable co-irradiation of the normal tissue, often resulting in side effects that limit the dose to the tumor and/or reduce the quality of life of cancer survivors. The response of normal tissues to irradiation is mainly determined by the survival and regenerative potential of the tissue stem cells and modulated by inflammatory processes, vasculature damage, altered neuronal innervation, and fibrosis. Indeed, transplantation of tissue-specific stem cells has been shown to restore tissue homeostasis and prevent late radiation effects. However, the radiation-induced senescence, fibrosis, and chronic inflammation may chance the stem cell niche to engender an unfavorable environment for the regenerative potential of the tissue’s stem cells. Here changes in the salivary gland stem cell niche will be discussed using irradiated murine submandibular salivary gland tissue and derived organoids. Recently, we have developed methods to culture murine and patient-specific tissue resembling salivary gland-derived organoids (SGO). SGOs contain all the glandular lineages, are able to extensively self-renew, and upon transplantation rescue salivary gland function, allowing the study of radiation responses. The role of stemness factors, senescence, and inflammatory processes in stem cell self-renewal and differentiation and post-irradiation regeneration will be discussed. Using SGO formation efficiency (OFE) as a measure of regenerative potential it is shown that stem cell potency after in vivo irradiation, is time-dependent reduced. Interestingly, the conditioned medium of irradiated SGO reduced the OFE of unirradiated SGO. The potential role of radiation-induced senescence- associated secretory phenotype, hippo-signaling, and autophagy will be addressed. Radiation-induced environmental changes in the stem cell niche have a severe impact on stem cell function. Modulation of these effects may enhance the regenerative potential of surviving stem cells and improve engraftment and regeneration after stem cell transplantation Supported by the Dutch Cancer Society (KWF, grant No. 10650 and 12092) and The Netherlands Organisation for Health Research and Development (ZonMw, Grants nr. 11.600.1023 and 40-43600-98-14003)

SP-0346 Normal tissue organoids in studies of radiosensitivity to protons and carbon ions TBC

Abstract not available

SP-0347 Organoid model system to study response in radiotherapy M. Mahé France

Abstract not available

SP-0348 Patient-derived xenografts as a model system for radiobiology research C. Willey 1 1 The University of Alabama at Birmingham, Radiation Oncology, Birmingham, USA

Abstract Text For many decades, immortalized cell lines have been the mainstay model system for studying cancer biology as well as radiobiology. These cell lines can be cultured indefinitely and easily in a two-dimensional system and are well suited to evaluating radiation responsiveness through clonogenic assays. Moreover, they can be adapted to high throughput methodologies for screening purposes. Unfortunately, these model systems are