Abstract Book

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ESTRO 37

Conclusion Our results suggest, by use of an agnostic machine learning method such as PRFR and biological interpretation, that genome-wide data can be used to predict and explain GU toxicity. The model can be refined upon external validation and incorporation of accurate dose-based predictors. PV-0565 Texture Analysis of 3D dose distributions for predictive modelling of toxicity rates in radiotherapy L. Rossi 1 , R. Bijman 1 , W. Schillemans 1 , S. Aluwini 1 , M. Witte 2 , F. Pos 2 , L. Incrocci 1 , B. Heijmen 1 1 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands 2 Netherlands Cancer Institute Antoni van Leeuwenhoek Hospital, Department of Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective To explore the use of texture analysis (TA) features of patients’ 3D dose distributions to improve prediction modelling of treatment complication rates in prostate cancer radiotherapy, relative to more common DVH parameters. Material and Methods Late toxicity scores, dose distributions, and non- treatment related (NTR) predictors for late toxicity, such as age and baseline symptoms, of 351 patients of the hypofractionation arm of the HYPRO randomized trial (Lancet Oncol 2016;17(4):464-74) were used in this study. Texture analysis was performed for both rectum and bladder 3D dose distributions. 42 TA features were extrapolated from 2 histograms and 5 matrices: grey level frequency histogram, grey level co-occurence matrix (GLCM), grey level run length matrix (GLRLM), grey level size zone matrix (GLSZM) and neighbourhood grey tone difference matrix (NGTDM), see figure 1 for example. TA features and common DVH parameters derived from rectum and bladder dose distributions were used for predictive modelling of gastrointestinal (GI) (rectal bleeding and fecal incontinence) and genitourinary (GU) (nocturia and urinary incontinence) symptoms, respectively. Logistic Normal Tissue Complication Probability (NTCP) models were derived, using only NTR parameters, NTR + DVH, NTR + TA, and NTR + DVH + TA. Results For rectal bleeding, the area under the curve (AUC) for using only NTR parameters was 0.58, which increased to 0.68, and 0.71, when adding DVH or TA parameters respectively. For fecal incontinence, the AUC went up from 0.62 (NTR only), to 0.68 (+DVH) and 0.75 (+TA). For nocturia, adding TA features resulted in an AUC increase from 0.64 to 0.67, while no improvement was seen when including DVH parameters in the modelling. For urinary incontinence, the AUC improved from 0.69 to 0.70 (+DVH) and 0.73 (+TA). Conclusion 3D dosimetric texture analysis features in predictive modelling of GI and GU toxicity rates in prostate cancer radiotherapy improved prediction performance.

Figure 1: A: View on the 3D rectum dose distribution of one of the included patients, B-F: TA histograms and matrices derived from this dose distribution. B: grey level frequency histogram, C: grey level co-occurence matrix (GLCM), D: grey level run length matrix (GLRLM), E: grey level size zone matrix (GLSZM), F: neighbourhood grey tone difference matrix (NGTDM). In C and D, intensities are displayed in logarithmic scale PV-0566 Survival prediction with radiomics of patients with brain metastases of non-small cell lung cancer PV-0567 Minibeam radiation therapy in a commercial irradiator spares normal rat brain Y. Prezado 1 , M. Dos Santos 1 , W. Gonzalez 1 , G. Jouvion 2 , C. Guardiola 1 , S. Heinrich 3 , D. Labiod 3 , M. Juchaux 1 , L. Jourdain 4 , C. Sebrie 4 , F. Pouzoulet 3 1 Centre National de la Recherche Scientifique, Imagerie et Modélisation en Neurobiologie et Cancérologie, Orsay, France 2 Institut Pasteur, Anatomopathology and animal models, paris, France 3 Institut Curie, Experimental Radiotherapy Platform, Orsay, France 4 University Paris Sud, IR4M, Orsay, France Purpose or Objective Minibeam radiation therapy (MBRT) is an innovative synchrotron radiotherapy technique able to shift the normal tissue complication probability curves to very high doses [1]. MBRT seem to involve different biological mechanisms (not well understood yet) different from those in standard RT. However, its exploration was hindered due to the limited and expensive beamtime at synchrotrons. The aim of this work was to evaluate the feasibility of the implementation of MBRT into cost- effective equipment. This would permit the realization of systematic radiobiological studies to evaluate the tumour control effectiveness for various tumour sites as well as to unravel the distinct biological mechanisms involved. Material and Methods A series of modifications of a small animal irradiator (Small Animal Radiation Research Platform-XSTRAHL Ltd.) were performed to make it suitable for MBRT experiments. In particular, an adapted collimator was designed by means of Monte Carlo simulations (Geant4). Peak to valley dose ratio (PVDR) values and full width half at maximum (FWHM) similar to those obtained at the European synchrotron radiation facility (ESRF) [2] were used as figure of merit. As a proof of concept, two groups of animals were irradiated: a first group (series 1) received conventional (broad beam) irradiations, the second series was irradiated with MBRT. The rats brain, excluding the olfactory bulb, were irradiated unilaterally. Thick minibeams (1 mm-wide beams) were employed for this study. The same average dose was deposited in both cases, 20 ± 1 Gy, which corresponds to 58 Gy peak dose in the MBRT case. The animals were followed-up for 6.5 months. At the end of the study a magnetic resonance imaging (MRI) evaluation at a 7T small animal scanner, as well as histological analysis were performed. Results The dosimetric features of our system were shown to be similar to the synchrotron ones [2]. Concerning the in vivo experiment, rats treated with conventional irradiation exhibited very important brain damage, including radionecrosis. In contrast, no substantial brain damage was observed in the animals of the MBRT group. See figure 1. Abstract withdrawn