ESTRO 2020 Abstract Book

S359 ESTRO 2020

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 A retrospective study on 2526 previously irradiated PCa patients was performed. Patients were treated with 3D- CRT (21.3%), IMRT (68.1%), or VMAT (10.6%). Second tumors incidence was analysed in 3 categories: pelvic, pelvic and abdominal, and “any site”. The correlation with RT technique was analysed using log-rank test and Cox’s proportional hazard method. Results With a median follow-up of 72 months (range: 9-185), 92 (3.6%) cases of second tumors were recorded with 48 months (range: 9-152) median interval from RT. Actuarial 10-year second tumor free survival (STFS) was 87.3%. Ten- year STFS in patients treated with 3D-CRT and IMRT/VMAT was 85.5% and 84.5%, respectively (p: .627). A significantly higher 10-year cumulative incidence of second tumors in the pelvis was registered in patients treated with IMRT/VMAT compared to 3D-CRT (10.7% vs 6.0%; p: .033). This lower incidence of second pelvic cancers in patients treated with 3D-CRT was confirmed at multivariable analysis (HR: 2.42, 95%CI: 1.07-5.47, p: .034). Conclusion The incidence of second pelvic tumors after RT of PCa showed a significant correlation with treatment technique. Further analyses in larger series with prolonged follow-up are needed to confirm these results. cancer (PCa) patients. Material and Methods PH-0649 Can we dose escalate in anal cancer without an increase in dose to OARs? N. Abbott 1 , M. Robinson 2 , J. Copeland 3 , M. Harrison 4 , M. Hawkins 5 , R. Muirhead 2 , R. Adams 6 , D. Sebag-Montefiore 7 1 RTTQA group- Velindre Cancer Centre, Medical Physics, Cardiff, United Kingdom ; 2 Oxford University Hospitals NHS Trust, Oxford, United Kingdom ; 3 Leeds University, Leeds Clinical Trials Research Unit, Leeds, United Kingdom ; 4 Mount Vernon Hospital, Mount Vernon Centre for Cancer, Northwood, United Kingdom ; 5 University College London, UcL, London, United Kingdom ; 6 Cardiff University Department of Cancer & Genetics, and Velindre Cancer Centre, Cardiff, United Kingdom ; 7 St James University Hospital, Leeds Cancer Centre, Leeds, United Kingdom Purpose or Objective PersonaLising Anal cancer radiotherapy dOse (PLATO) is an integrated protocol, including anal cancer trial 5 (ACT5) for high risk patients. ACT5 is a randomised trial comparing UK standard and dose escalated concurrent chemo-radiotherapy. Dose escalation above UK standard dose [1] is to a PTV_Boost encompassing primary disease and positive nodes plus a 5mm margin. A pilot study of 60 patients was carried out across 12 UK sites. This was to allow for planned interim analysis of acute toxicity [2], protocol compliance, and to determine if there is a significant increase to OAR dose metrics associated with dose escalation.

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.

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 Valentini 3 , A.G. Morganti 1 , M. Buwenge 1 1 Radiation Oncology Center, Department of

Dose escalation was as below * Standard arm: PTV_Boost n/a

* Dose escalation arm1: PTV_Boost 58.8 Gy in 28# * Dose escalation arm2: PTV_Boost 61.6 Gy in 28#