ESTRO 36 Abstract Book

S534 ESTRO 36 2017 _______________________________________________________________________________________________

Results Among the 14 cell lines analyzed, strong differences in clonogenic survival were observed. Using the linear- quadratic model, very high goodness-of-fit levels were obtained (R 2 ≥0.98). However, obvious differences in radiosensitivity between several cell lines were not revealed by the respective α/β values which failed to reflect the overall steepness of survival curves. Data reduction by PCA allowed the extraction of radioresistance scores. Notably, more than 70% of the variance in the dataset was covered by the first PC. Correlation of radioresistance scores with mRNA expression levels of DDR regulators identified potential predictors of radioresistance. Target validation using RNA interference and selection of suitable pharmacological inhibitors are ongoing. Conclusion Dimensionality reduction by PCA is a suitable method to extract scores of radioresistance from clonogenic survival datasets which can be correlated with other types of data, such as mRNA expression levels. This approach facilitates the identification of DDR regulators which may be further validated as potential biomarkers of radioresistance and/or targets for radiosensitization. PO-0974 Biomarkers of radiosensitivity for patient stratification and personalized radiotherapy treatment E. Palumbo 1 , C. Piotto 1 , L. Baggio 1 , E. Groff 1 , E. Calura 2 , F. Busato 1 , B. El Khouzai 1 , E. Fasanaro 1 , M. Rigo 1 , L. Loreggian 1 , C. Romualdi 2 , A. Russo 3 , M. Mognato 2 , D. Zafiropoulos 4 , L. Corti 1 1 Istituto Oncologico Veneto IOV-IRCCS, UOC of Radiotherapy, Padua, Italy 2 University of Padua, Department of Biology, Padova, Italy 3 University of Padua, Department of Molecular Medicine, Padova, Italy 4 National Laboratories of Legnaro- Italian Institute of Nuclear Physics, LNL-INFN, Padua, Italy Purpose or Objective The personalization of radiotherapy (RT) represents the goal of future clinical radiation trials. A screening tool able to classify each patient according to his/her own sensitivity to ionizing radiation (IR) before the administration of RT would be essential to set personalized dosing schedules, effective in improving RT outcomes and in reducing side effects. Genetic variation is a likely source for the normal tissue radiosensitivity variation observed among individuals. Mutations in key genes of the DNA-Damage Response (DDR) pathway, or the individual modulation of DDR gene expression after IR- exposure, may underlie these differences. This study aims at defining a genetic signature useful to discriminate patients undergoing RT as radiosensitive, normal and radioresistant and to predict the likelihood of a late IR- toxicity. In this frame, gene expression data concerning DDR pathway, obtained from blood samples of breast and head-neck cancer patients, are overlaid with the individual in vitro radiosensitivity index and the in vivo tissue radiosensitivity detected during the follow-up. We expect to identify a 5-10 gene network determining the individual radiophenotype. Material and Methods 1. Criteria for patient enrolling: breast or head-neck cancer diagnosis; exclusion of congenital syndromes predisposing to radiosensitivity; patients not previously treated with chemo-radiotherapy; age > 18 years; patient agreement to undergo follow-up; informed consent. 2. G2- assay for the prediction of radiosensitivity: an individual radiosensitivity index (IRS) is calculated according to the G2-chromosomal radiosensitivity and the G2 checkpoint efficiency. Details of the protocol are in 1 . 3. Gene expression analysis: Gene expression analysis is performed by quantitative real-time PCR (qRT-PCR) on total RNA

isolated from blood drawns harvested before the administration of the first fractioned dose of RT and 24 h later. 4. Statistical analysis: Anova test is performed to analyse the differential expression across IRS classes and a Spearman analysis is performed to assess correlation between expression and IRS index. Results The expression of DDB2, GADD45A, CDKN1A, and ATM genes following irradiation 2,3 has been correlated with the in vitro IRS evaluated by the G2-chromosomal assay; at present, a positive correlation between ATM expression and IRS could be inferred despite the unavoidable inter- individual variability. The analyses on other DDR genes are The innovation of this study is the use of a molecular biology approach to assess patient radiosensitivity before RT, in the frame of an integrated approach between clinicians and biologists. References 1. Pantelias GE. & Terzoudi G. I. Radiother. Oncol. 101 (2011). 2. Mognato M. & Celotti L. Mutat. Res. Mol. Mech. Mutagen. 578 (2005). 3. Girardi C. et al. PLoS One 7 (2012). in progress. Conclusion PO-0975 Clinical utilization of the radiation-hypoxia- induced abscopal/bystander effect in lung cancer S. Tubin 1,2 , S. Gupta 3 , A.M. Mansoor 4 1 KABEG Klinikum Klagenfurt, Radioonkologie, Klagenfurt, Austria 2 Sylvester Comprehensive Cancer Center- University of Miami Leonard Miller School of Medicine, Department of Radiation Oncology, Miami, USA 3 Georgia Cancer Center- Augusta University- Augusta- GA- USA, Health Sciences, Augusta, USA 4 National Cancer Institute- National Institutes of Health, Radiotherapy Development Branch- Radiation Research Program- Division of Cancer Treatment and Diagnosis, Rockville, USA Purpose or Objective To report on initial results in a small series of consecutive patients treated with high-dose hypofractioneted radiotherapy (1-3 fractions) in the treatment of oligometastatic patients with large tumor masses focusing on application of results previously obtained by in vitro studies on radiation-induced abscopal/bystander effect. Our previous study (unpublished data) focused on targeting tumor hypoxia that induced a strong abscopal/bystander effect. We provide data that support the contention that high-dose radiation to the part of a large gross tumor volume (GTV) has the potency to induce a robust bystander effect, as well as abscopal (distant) effects. Material and Methods In the in vitro studies conditioned medium-transfer experiments with A-549, H-460 lung cancer cells, as well as their hypoxic clones (A-549HR, H-460HR), were performed. All the cells were irradiated in normoxic or hypoxic conditions with 10Gy single dose and cell growth and survival were monitored by real time cell electronic sensing (RTCES) System and colony forming assay, respectively. In the clinical study, 5 consecutive oligometastatic patients with large hypoxic cancers of lung (3), neck (1) and mediastinum (1) were treated with high dose radiotherapy using high-energy photons. All lesions were irradiated partially by targeting the central hypoxic region (Figure 1), which corresponded to 30% of total GTV (Mean GTV volume 181 cc, mean diameter 6, 8 Poster: Radiobiology track: Radiobiology of lung cancer