ESTRO 2020 Abstract book

S392 ESTRO 2020

10^5 times, using the extreme -value as summary statistic).

Conclusion A novel methodology is proposed to analyse the effect of contouring variation on clinical outcome for a large cohort of patients using deviations to a consistent virtual observer. For the studied patient cohort, regions were identified in which contour deviations relate to biochemical recurrence producing some expected and unexpected results: larger contours predicts for better/worse control. This flags the need to include deviation correlations introduced by contouring styles into the analysis. In the future, this methodology could inform contouring protocols based on actual patient outcomes. PH-0648 Radiotherapy of prostate cancer:impact of treatment characteristics on the incidence of second tumor S. Cammelli 1 , M. Ntreta 1 , E. Scirocco 1 , G. Macchia 2 , F. Deodato 2 , S. Bisello 1 , G. Siepe 1 , A.R. Alitto 3 , S. Cilla 4 , V. Experimental- Diagnostic and Specialty Medicine - DIMES- Azienda Ospedaliera-Universitaria S.Orsola-Malpighi, Bologna, Italy ; 2 Fondazione "Giovanni Paolo II", UO di Radioterapia- Università Cattolica del Sacro Cuore, Campobasso, Italy ; 3 Fondazione Policlinico Universitario A. Gemelli- IRCCS, UOC di Radioterapia- Dipartimento di Scienze Radiologiche- Radioterapiche ed Ematologiche, Roma, Italy ; 4 Fondazione "Giovanni Paolo II", UO di Fisica Sanitaria- Università Cattolica del Sacro Cuore, Campobasso, Italy Purpose or Objective It has been hypothesized that radiotherapy (RT) techniques delivering radiations to larger volumes (IMRT, VMAT) are potentially associated with a higher risk of second primary tumors. The aim of this study was to analyse the impact of RT technique (3D-CRT vs IMRT/VMAT) on the incidence of second tumors in prosate Valentini 3 , A.G. Morganti 1 , M. Buwenge 1 1 Radiation Oncology Center, Department of

Results Fig. 2 shows the HR map for contour deviation and high significance regions (p<0.001). There is a reduced risk of biochemical recurrence of 4-8% in the prostate’s left region, bladder and seminal vesicle interfaces per mm increase of the manual contour relative to the reference. Conversely, there is an increased risk of 8-24% in the prostate's right and posterior regions and in the anterior region close to the apex per mm increase of the manual contour relative to the reference. HR maps for Gleason scores 6, 7, and 8 relative to >9 were significant for all pixels (p<0.001), i.e. as expected lower scores have reduced risk of biochemical recurrence independent of contour deviation. The HR maps of patient age and manual CTV volume showed no significant regions.

cancer (PCa) patients. Material and Methods