ESTRO 2020 Abstract Book

S59 ESTRO 2020

we conclude to the safety of our method at a 95% confidence interval (p<0.05). Conclusion Preliminary results are encouraging. SBRT as a short treatment offers a safe and convenient treatment modality, while reducing costs, and could also challenge watchful waiting policies. Using the binomial law in this trial allows us to demonstrate the safety of prostatic SBRT based on preliminary results. We propose this statistical approach to boost clinical implementation of new technologies in radiation treatments while offering the best safety to patients in the ongoing trials. PH-0117 Radiotherapy of T4M0 prostate cancer : A multicentric retrospective analysis F. Goupy 1 , E. Meyer 2 , P. Pommier 3 , N. Magné 4 , P. Sargos 5 , D. Pasquier 6 , G. Noël 7 , U. Schick 8 , A. Hasbini 9 , S. Supiot 10 , A. Bossi 11 , I. Latorzeff 12 , J. Riverain 2 , L. Duvergé 3 , M. Benna 4 , N. Benziane 5 , T. Le Roy 6 , C. Bigot 7 , M. Rehn 8 , L. Vaugier 10 , B. Le Proust 13 , A. Barateau 14 , B. Campillo- Gimenez 15 , J. Castelli 16 , R. De Crevoisier 16 1 CLCC Eugène Marquis, Radiation Department, Rennes F- 35000, France ; 2 CLCC François Baclesse, Radiation Department, Caen F-14000, France ; 3 CLCC Léon Bérard, Radiation Department, Lyon F-69000, France ; 4 Institut de Cancérologie Lucien-Neuwirth, Radiation department, Saint-Priest-en-Jarez F-42271, France ; 5 CLCC Institut Bergonié, Radiation Department, Bordeaux F-33000, France ; 6 CLCC Oscar Lambret, Radiation Department, Lille F-59000, France ; 7 CLCC Paul Strauss, Radiation department, Strasbourg F-67000, France ; 8 University Hospital Cavale Blanche, Radiation department, Brest F- 29200, France ; 9 Centre Finistérien de Radiothérapie et d'Oncologie, Radiation department, Brest F-29200, France ; 10 CLCC Institut de Cancérologie de l’Ouest, Radiation department, Saint-Herblain F-44800, France ; 11 Institut Gustave Roussy, Radiation department, Villejuif F-94800, France ; 12 Clinique Pasteur, Radiation department, Toulouse F-31076, France ; 13 CLCC Eugène Marquis, Radiation Medical Imaging Department, Rennes F-35000, France ; 14 University Rennes 1- LTSI Laboratoire Traitement du Signal et de l'Image, Inserm U1099, Rennes F-35000, France ; 15 CLCC Eugène Marquis, Clinical Research Direction, Rennes F-35000, France ; 16 CLCC Eugène Marquis, Radiation Department- University Rennes 1- LTSI Laboratoire Traitement du Signal et de l'Image- Inserm U1099, Rennes F-35000, France Purpose or Objective No study has reported dosimetric data and clinical outcome of external-beam radiotherapy (RT) for specifically T4 M0 prostate cancer (PCa). The possibility of escalating the dose to the involved rectum or bladder at a curative intent, while trying to respect the dose constraints in the corresponding organ at risk to limit the toxicity, is not clearly demonstrated. The objective of the study was to analyze the dose distribution and the clinical outcome in a large series of patients having received RT for T4 M0 PCa. Material and Methods This retrospective analysis included all patients who received RT and androgen deprivation therapy (ADT) for T4 M0 PCa, between 1999 and 2019, in thirteen French institutions, with available dosimetric data. Results A total of 101 patients were included. Mean (range) PSA (ng/ml) was 33 (2-356). Gleason score ≥ 8 was reported in 67% of patients. Adjacent involved structures were: bladder (66%), rectum (29%) and other (5%). Lymph nodes were considered as involved on CT-scan/MRI in 37% of patients. The RT technique was 3D-CRT (25%) or IMRT (75%). The median (range) prescribed dose (Gy) to the prostate was 76 (70-80). Dose escalation to the involved adjacent organs was realized for 36% of patients. The mean (range) V95% (in %) for the PTV was 97 (93-100). The

RTOG/QUANTEC dose constraint recommendations (in the OAR excluding the PTV) were exceeded for the rectum in 17% of patients with V70 ≥ 20 %, and for the bladder in 12% of patients with V70 ≥ 35 %. The median follow-up (months) was 35 (quartile: 17-54). The 5-year risks of biochemical and clinical recurrences and cancer-specific death were 47%, 40%, and 30%, respectively (Figure A). The 5-year risks of local, pelvic lymph node, and metastatic recurrences were 14%, 19%, and 41%, respectively (Figure B). Duration of neoadjuvant androgen deprivation therapy (NADT) (months) and prostate dose (Gy) were the most significant prognostics factors of clinical recurrence (HR 1.04 and 0.86 respectively) and death (HR 1.06 and 0.72 respectively). NADT ≥3 months increased the risk of death (RR=2.27 (95%CI: 1.01-5.13); p=0.049). Grade ≥ 2 acute and 5-year late toxicity rates were 11 % and 27% for digestive toxicity, and 29 % and 35% for urinary toxicity, respectively. Risk factors of late urinary toxicity were extra-prostatic urethra/penis bulb involvement (HR=11.5) and PTV volume. Risk factors of late digestive toxicity were history of pelvic surgery (HR=2.6) and prescribed dose to prostate ≥ 76 Gy (HR =4.3).

Conclusion T4 M0 PCa are aggressive tumors with high mortality rate. Patients should receive RT started before 3 months of NADT and delivering a high curative dose (≥ 76 Gy) in the involved rectum or bladder, even if the risk of toxicity is slightly increased. PH-0118 Stereotactic or conventional RT for macroscopic prostate bed recurrence: a propensity score analysis G. Francolini 1 , B.A. Jereczek-Fossa 2 , V. Di Cataldo 3 , G. Simontacchi 4 , G. Marvaso 5 , M.A. Zerella 5 , P. Gentile 6 , F. Bianciardi 6 , S. Allegretta 6 , B. Detti 4 , L. Masi 7 , L.P. Ciccone 4 , A. Bruni 8 , G. Ingrosso 9 , E. Mazzeo 8 , F. Trippa 10 , F. Lohr 8 , L. Livi 11 1 University of Florence- Istituto Fiorentino di Cura ed Assistenza, Radiation Oncology Unit-CyberKnife Center, Florence, Italy ; 2 Department of Oncology and Hemato- oncology-University of Milan, Division of Radiotherapy- IEO European Institute of Oncology- IRCCS, Milan, Italy ; 3 University of Florence - Istituto Fiorentino di Cura ed Assistenza, Radiation Oncology Unit- CyberKnife Center, Florence, Italy ; 4 Azienda Ospedaliero-Universitaria Careggi, Radiation Oncology Unit, Florence, Italy ; 5 IEO European Institute of Oncology- IRCCS, Division of Radiotherapy, Milan, Italy ; 6 UPMC San Pietro FBF, Division Radiotherapy, Rome, Italy ; 7 IFCA, Department of Medical Physics and Radiation Oncology, Florence, Italy ; 8 University Hospital of Modena, Radiotherapy Unit, Modena, Italy ; 9 University of Perugia and Perugia General Hospital, Radiation Oncology Section- Department of Surgical and Biomedical Sciences, Perugia, Italy ; 10 "S. Maria" Hospital, Radiotherapy Oncology, Terni, Italy ; 11 University of Florence, Department of Biomedical- Experimental- and Clinical Sciences “Mario Serio”, Florence, Italy