Abstract Book

S314

ESTRO 37

Conclusion In the setting of isotoxically dose escalated radio- chemotherapy, the outcome after merely FDG-PET based radiotherapy planning was not inferior to that after conventional planning. It enabled higher dose escalation and a clear trend to improved local control. Survival well compared to other recent trials. In contrast to RTOG 0617, we did not observe any adverse effect of higher treatment doses. OC-0599 Ultrahypofractionation for prostate cancer: Outcome from the Scandinavian phase 3 HYPO-RT-PC trial A. Widmark 1 , A. Gunnlaugsson- 2 , L. Beckman 3 , C. Thellenberg-Karlsson 1 , M. Hoyer 4 , M. Lagerlund 5 , P. Fransson 1 , B. Tavelin 1 , D.B. Norman 6 , J. Kindblom 7 , C. Ginman 8 , B. Johansson 9 , M. Seke 10 , K. Björlinger 11 , M. Ågrup 12 , E. Kjellen 13 , L. Franzen 1 , P. Nilsson 14 1 umea University, Radiation Sciences/Onkology, Umeå, Sweden 2 Skåne University Hospital- Lund University, Dept. Of Oncology And Radiation Physics, Lund, Sweden 3 umeå University, Sundsvall Hospital- Sundsvall- And Dept. Radiation Sciences, Sundsvall, Sweden 4 aarhus University Hospital, Danish Centre For Particle Therapy, Aarhus, Denmark 5 kalmar Hospital, Department Of Oncology, Kalmar, Sweden 6 umea University Hospital., Regional Cancer Centre North, Umeå, Sweden 7 university Of Gothenburg-, Department Of Oncology- Institute Of Clinical Sciences- The Sahlgrenska Academy, Gothenburg, Sweden 8 karlstad Central Hospital, Department Of Oncology-, Karlstad, Sweden 9 örebro University Hospital And Örebro University, Department Of Oncology, Örebro, Sweden 10 centrallasarettet Växjö, Department Of Oncology-, Växjö, Sweden 11 önköping Hospital, Department Of Oncology, Växjö, Sweden 12 linköping University Hospital-, Department Of Oncology- , Linköpingt, Sweden 13 Skåne University Hospital- Lund University-, Dept. Of Oncology And Radiation Physics- -, Lund, Sweden 14 Skåne University Hospital- Lund University-, Dept. Of Oncology And Radiation Physics, Lund, Sweden Purpose or Objective Hypofractionated (HF) radiotherapy (RT) for prostate cancer has gained increased attention due to its proposed high radiation-fraction sensitivity. Recent reports from randomised studies comparing moderately hypofractionated (M-HF) and conventionally fractionated (CF) radiotherapy (RT) have supported the value of M-HF. Until now there are no prospective randomised data for ultrahypofractionation (U-HF) regimens. Recently, we presented 2-year toxicity results from the first large randomised trial on U-HF versus CF; the Scandinavian HYPO-RT-PC study 1 . We now report the first results on primary outcome and updated toxicity data from this trial. Material and Methods The Scandinavian HYPO-RT-PC study is a randomised, phase III, non-inferiority trial that recruited patients with intermediate/high-risk prostate cancer (T1c-T3a, PSA ≤20 with one or two of the following risk factors; T3a or Gleason ≥7 or PSA >10). Patients were randomly assigned (1:1) to either CF (n=602), 39 x 2.0 Gy=78.0 Gy over 8 weeks or U-HF (n=598), 7 x 6.1 Gy=42.7 Gy over 2.5 weeks (RT every other weekday). No androgen deprivation therapy was allowed. The treatment schedules were designed to be equieffective for late normal tissue complication probability (α/β=3 Gy). Image

guided RT (3DCRT or VMAT) based on fiducial markers was delivered to the prostate only (CTV) with a 7 mm isotropic CTV-PTV margin. The primary endpoint was time to biochemical or clinical failure and the treatment groups were compared by means of a Cox proportional hazards model. To conclude non-inferiority, a critical hazard ratio (HR) of 1.338 (one-sided α=0.025) was pre- specified, corresponding to a margin of 4% at 5 years. Physician’s evaluation of side-effects was performed according to a modified RTOG scale. The trial number is ISRCTN45905321. Results Between July 2005 to November 2015, 1200 patients from 12 centres were randomised. Analysis was made per protocol and 1180 patients (591 CF and 589 U-HF) with a median follow-up time of 59.7 months [95%CI 57.6−51.8] were eligible for evaluation of primary outcome. The total number of events during the follow-up period was 102 and 100 in the CF and the U-HF group, respectively. The proportion of patients, free of biochemical or clinical failure at 5 years, was 83.8% [95%CI 80.4−87.3] in the CF arm and 83.7% [95%CI 80.3−87.1] in the U-HF arm (Fig. 1). U-HF was found to be non-inferior to CF: HR (95% CI) = 0.992 (0.753, 1.307). There were no significant differences in the prevalence of physician reported late grade 2+ toxicity at four/six years (CF vs. U-HF): urinary 4.1 % vs. 4.1 %, p=0.38 / 3.5 % vs. 2.5%, p=0.75 and bowel: 1.6% vs. 1.6%, p=1.00 / 2.3% vs. 1.2%, p=0.69. Fig. 1. Kaplan-Meier estimated failure-free survival (1=CF, 2=U-HF) F. De Vathaire 1 , C. El - Fayech 2 , N. Haddy 3 , R. Allodji 4 , C. Veres 4 , D. Llanas 4 , N. Journy 4 , V. Souchard 4 , C. Rubino 4 , H. Pacquement 5 , C. Teinturier 4 , B. Fresneau 2 , G. Vu- Bezin 4 , S. Bolle 6 , A. Mazal 7 , P. Poortmans 8 , E. Deutsch 6 , I. Diallo 4 1 institut gustave roussy, academic physics, villejuif, france 2 institut gustave roussy, pediatry, villejuif, france 3 inserm, unit 1018 - cancer and radiation team, villejuif, france 4 inserm, unit 1018 - cancer and radiation team, villejuif, france 5 institut curie, pediatry, paris, france 6 institut gustave roussy, radiotherapy, villejuif, france Purpose or Objective Stroke is one of the major potential long term iatrogenic risk of childhood cancer radiation therapy. Nevertheless, present knowledge is insufficient to predict the long-term risk of stroke following radiation therapy as the dose- response to fractionated high doses of radiatiation to brain is not known Material and Methods We carried out an analysis in a cohort of 7030 5-years survivors of a solid childhood cancer treated in France before 2001, of whom 4150 by radiotherapy, and followed 20 years in average, by self-questionnaire and cross-linkage with French National Hospital and Medical InsDatabase (SNIIR-AM) . During the follow-up, 139 patients developed a permanent stroke, which could be validated. Each of them was matched with 8 controls of the same cohort, on gender, age at childhood cancer and follow-up duration. Radiation dose distribution in cerebral arteries was individually esimated by reconstructing radiotherapy of each case and control treated by radiotherapy, using medical records and anthropometric phantoms. Risk of stroke as modeled as a function of average radiation dose to cerebral arteries, as well as using dose OC-0600 Long term risk of stroke after childhood cancer radiotherapy 7 institut curie, medical physics, paris, france 8 institut curie, radiotherapy, paris, france