ESTRO 36 Abstract Book

S861 ESTRO 36 _______________________________________________________________________________________________

performance status, and total tumor dose. The BN model has an AUC of 0.67 (95% CI: 0.59–0.75) on the external validation set and an AUC of 0.65 on a 5-fold cross- validation on the training data. A model based on TNM stage performed with an AUC of 0.49 (95% CI: 0.39-0.59) on the validation set. Conclusion The distributed learning model outperformed the TNM stage based model for predicting 2-year survival in a cohort of NSCLC patients in an external validation set (AUC 0.67 vs. 0.49). This approach enables learning of prediction models from multiple hospitals while avoiding many boundaries associated with sharing data. We believe that Distributed learning is the future of Big data in health care. References [1] Dehing-Oberije C. et al. Int J Radiat Oncol Biol Phys 2008;70:1039–44. doi:10.1016/j.ijrobp.2007.07.2323. EP-1597 Focal dose escalation in prostate cancer with PSMA-PET/CT and MRI: planning study based on histology C. Zamboglou 1 , I. Sachpazidis 2 , K. Koubar 2 , V. Drendel 3 , M. Werner 3 , H.C. Rischke 1 , M. Langer 4 , F. Schiller 5 , T. Krauss 4 , R. Wiehle 2 , P.T. Meyer 5 , A.L. Grosu 1 , D. Baltas 2 1 Medical Center - University of Freiburg, Department of Radiation Oncology, Freiburg, Germany 2 Medical Center - University of Freiburg, Division of Medical Physics- Department of Radiation Oncology, Freiburg, Germany 3 Medical Center - University of Freiburg, Department of Pathology, Freiburg, Germany 4 Medical Center - University of Freiburg, Department of Radiology, Freiburg, Germany 5 Medical Center - University of Freiburg, Department of Nuclear Medicine, Freiburg, Germany Purpose or Objective First studies could show an increase in sensitivity when primary prostate cancer (PCa) was detected by addition of MRI and PSMA PET/CT information. On the other side the highest specificity was achieved when the intersection volume between MRI and PSMA PET/CT was considered. Aim of this study was to demonstrate the technical feasibility and to evaluate the tumor control probability (TCP) and normal tissue complication probability (NTCP) of IMRT dose painting using combined 68 Ga-HBED-CC PSMA- PET/CT and multiparametric MRI (mpMRI) information in patients with primary PCa. Material and Methods 7 patients (5 intermediate + 2 high risk) with biopsy- proven primary PCa underwent 68 Ga-HBED-CC-PSMA PET/CT and mpMRI followed by prostatectomy. Resected prostates were scanned by ex-vivo CT in a localizer and prepared for histopathology. PCa was delineated on histologic slices and matched to ex-vivo CT to obtain GTV- histo. Ex-vivo CT including GTV-histo and MRI data were matched to in-vivo CT(PET). Contours based on MRI (GTV- MRI, consensus volume by two experienced radiologist), PSMA PET (GTV-PET, semiautomatic using 30% of SUVmax within the prostate) or the combination of both (GTV- union/-intersection) were created. Three IMRT plans were generated for each patient: PLAN77, which consisted of whole-prostate radiation therapy to 77 Gy in 2.2 Gy per fraction; PLAN95, which consisted of whole-prostate RT to 77 Gy in 2.2 Gy per fraction, and a simultaneous integrated boost to the GTV-union (Plan95 union )/- intersection (Plan95 intersection ) to 95 Gy in 2.71 Gy per fraction. The feasibility of these plans was judged by their ability to reach prescription doses while adhering to the FLAME trial protocol. TCPs based on co-registered histology after prostatectomy (TCP-histo), and normal

tissue complication probabilities (NTCP) for rectum and bladder were compared between the plans. Results All plans for all patients reached prescription doses while adhering to dose constraints. The average volumes of GTV- histo, GTV-union and GTV-intersection were 7±8 ml, 9±9 ml and 3±4 ml. In Plan95 union and Plan95 intersection the mean doses on GTV-histo were 95.7±1.5 Gy and 90.7±6.9 Gy, respectively (p=0.016). Average TCP-histo values were 63±29%, 99±1% and 90±11% for Plan77, Plan95 union and Plan95 intersection respectively. PLAN95 union had significantly higher TCP-histo values than Plan77 (p=0.016) and Plan95 intersection (p=0.03). There were no significant differences in rectal and bladder NTCPs between the 3 plans. Conclusion IMRT dose painting for primary PCa using combined 68 Ga- HBED-CC PSMA-PET/CT and mpMRI was technically feasible. A dose escalation to GTV-union resulted in significantly higher TCPs without higher NTCPs. V. Aubert 1,2 , O. Acosta 1,2 , N. Rioux-Leclercq 3 , R. Mathieu 4 , F. Commandeur 1,2 , R. De Crevoisier 1,2,5 1 INSERM, U1099, Rennes, France 2 University Rennes 1, LTSI, Rennes, France 3 Rennes Hospital and University, Department of Pathology, Rennes, France 4 CHU Pontchaillou, Department of Urology, Rennes, France 5 Centre Eugène Marquis, Department of Radiotherapy, Rennes, France Purpose or Objective Using simulation from histopathological cancer prostate specimen, the objectives were to identify the total dose corresponding to various fractionations necessary to destroy the tumor cells (50% to 99.9%) and to assess the impact of the Gleason score on these doses. Material and Methods Histopatological specimen were extracted from 7 patients having radical prostatectomy. A senior uropathologist manually delineated all tumor foci on the hematoxylin and eosin-stained axial slides and assigned Gleason scores (GS) to each individual focus. Antibodies CD31 were used as blood vessel markers. Three slide samples per patient, corresponding to a surface of 2000µm x1200µm, were scanned and used within a simulation model developed in the Netlogo software (Figure 1). The model contained the following cells: tumor cells with a density ranging from 45% to 85%, endothelial cells with a density ranging from 0.3 to 8% and normal cells. The samples were GS:7 (3+4) for 47.6%, GS:7 (4+3) for 28.6% and GS:8 (4+4) for 23.8%. We used the equations of the model simulating the radiation response of hypoxic tumors published by Espinoza et al. (Med Phys 2015) . The model parameters were adjusted to biological values from the literature: diffusion coefficient (2.10 -9 m²/s), Vmax and Km of oxygen consumption (15 and 2.5 mmHg), tumor cells proliferation (1008 hours), half-life of dead cells (168 hours), α (0.15 Gy -1 ) and β (0.048 Gy -2 ) of the linear-quadratic model. Three fractionations were tested, at 2, 2.5 and 3 Gy/fraction at 24h interval. Five simulations were performed by slide sample. The objectives were to identify the total dose, at each fractionation, to kill 50% to 99.9% of the tumor cells. EP-1598 Modelisation of radiation response at various fractionation from histopathological prostate tumors