ESTRO 38 Abstract book

S605 ESTRO 38

stochastic radiation damage, colony growth via proliferation, size-dependent colony scoring. Results We analysed the effects of time-of-scoring and of scoring threshold on cell survival curves and on extracted parameters. These thresholds should have no influence on the outcome within a reasonable range. However, we made contrary observations: cell survival curves undergo an apparent shift when scored at subsequent time points, with (logarithmic) slope decreasing and curvature increasing over time (Fig. 1a). As a result, cell survival parameters and shift considerably when a linear/quadratic formula is fitted to the cell survival curves, the derived /ratio varies over a large range (Fig. 1b). Analysis of colony growth curves suggests that this effect is connected to a dose-dependent proliferation rate.

suggested a strong intratumoral heterogeneity with a slight intertumoral heterogeneity [2]. We studied degree of heterogeneity in γH2AX foci between experimental set- ups ( in vivo and ex vivo ) by subjecting two published in vivo and ex vivo datasets to a statistical model. A lesser degree of heterogeneity was found in the in vivo dataset relative to ex vivo dataset [3]. These results confirmed the necessity of multiple biopsies, regions of interest, and nuclei to obtain an accurate prediction. We currently characterize γH2AX foci in different chromatin distributions to gain deeper insight into the heterogeneity of foci in both set-ups. b) Reflectiveness of ex vivo biopsies to in vivo tumors: We investigated whether ex vivo tumor biopsies can reflect radiation response of the corresponding in vivo tumors. Dose response curves of γH2AX foci showed a comparable radiation response between biopsies and tumors in most of evaluated tumor lines. The slopes of dose response curves could classify tumors according to intrinsic radiosensitivity. Conclusion Overall, our results support the clinical applicability of the ex vivo γH2AX foci assay as a predictive method for radiation sensitivity. To minimize inter-observer variations, a semi-automated foci-counting algorithm is under development. This work was supported by a grant of the Federal Ministry of Education and Research (BMBF 02NUK035C). Reference [1] Menegakis, A. et al., Radiother. Oncol. 116(3), 473– 479 (2015) [2] Rassamegevanon, T. et al., Radiother Oncol. 124(3), 379-385 (2017) [3] Rassamegevanon, T. et al., Int J Mol Sci. 19(9). pii: E2616 (2018) PO-1090 A second (third, fourth...) look at the In Vitro Clonogenic Assay R. KOCH 1 , C. Harmel 2 , I. Dokic 2 , A. Abdollahi 2 , M. Alber 1 , E. Bahn 1,3 1 Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany ; 2 Translational Radiation Oncology, German Cancer Research Center DKFZ, Heidelberg, Germany ; 3 Clinical Cooperation Unit Radiation Oncology, German Cancer Research Center DKFZ, Heidelberg, Germany Purpose or Objective The in vitro clonogenic assay (IVCA) presents the standard in vitro experimental method in radiobiology: the cell survival curve lays the foundation for most biological models in radiotherapy. Since its introduction in 1956, the IVCA has remained basically unchanged: irradiated cells are incubated to form colonies, which are subsequently scored as either doomed or vital, based on their size. Here, we suggest to record the colony growth and show by temporally resolved statistical analysis of colony formation that the underlying basic assumptions of the in IVCA are often not fulfilled, which may lead to systematic errors in cell radiation response parameters α and β. Material and Methods Cells of different strains were seeded onto 96 well plates, irradiated with single doses of 0-7 Gy X-Rays and immediately placed into an incubator with automated acquisition of phase-contrast images in 3 h intervals for up to 9 days (IncuCyte® Live-Cell Analysis System). Image- treatment and automated colony scoring were performed in R/ImageJ with the use of self-developed routines. Colonies were scored and tracked over time based on combined position and shape parameters. Cell survival curves were calculated from the acquired database for different combinations of scoring parameters. A biomathematical colony growth model was developed that numerically simulates the entire experimental procedure:

Conclusion The clonogenic assay rests on the working hypothesis that irradiated cells will either perish after few mitoses, or proliferate constantly to form vital colonies. We observe that, since this condition is not generally fulfilled, systematic errors arise. We propose a temporally and statistically resolved analysis of colony size distributions. This removes the scoring bias by separating cell survival from the effects of colony growth. Additionally, a biomathematical model can be employed for in-depth analysis of the underlying colony formation.

Poster: RTT track: Patient preparation, positioning and immobilisation

PO-1091 Multimedia assisted information to patients with prostate cancer undergoing curative radiotherapy. S. Rahbek 1 , I. Nordentoft 1 1 Herlev Hospital, Radiotherapy, Herlev, Denmark Purpose or Objective To reduce side effects, it is important for patients with prostate cancer, treated with curative radiotherapy, to have an empty rectum and a moderately filled bladder. To ensure that, they need to follow a bladder/bowel protocol. The purpose of this study is:  To use multimedia assisted information in preparing of the patient before radiotherapy treatment to increase the patient awareness of how to follow the instructions of the bladder/bowel protocol. To improve patient understanding of organs anatomical placement in the treatment area. Material and Methods Semi-structured individual interviews of a sample of 10 men undergoing radiotherapy were conducted. Each interview covered 5 topics: Information, understanding, experience, knowledge and improvement. At the end of each interview we showed two images: an animated image, and an x-ray image of the pelvic organs. Additionally, three of the patients were also shown an animated movie. 