ESTRO 38 Abstract book

S191 ESTRO 38

OC-0383 Randomised controlled trial for dose- escalated radiotherapy in locally advanced rectal cancer A. Couwenberg 1 , H.M. Verkooijen 2 , M. Berbee 3 , J.P.M. Burbach 4 , S. Hoendervangers 1 , O. Reerink 5 , M.E.P. Philippens 1 , E.C.J. Consten 6 , A.B. Smits 7 , J. Heikens 8 , N. Wijffels 7 , A. Schiphorst 9 , M.M. Lacle 10 , F.J. Wessels 11 , M. Koopman 12 , W.M.U. Van Grevenstein 13 , M.P.W. Intven 1 1 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands ; 2 UMC Utrecht, Imaging Division, Utrecht, The Netherlands; 3 Maastro Clinic, Radiotherapy, Maastricht, The Netherlands; 4 Medisch Centrum Leeuwarden, Surgery, Leeuwarden, The Netherlands ; 5 Isala clinic, Radiotherapy, Zwolle, The Netherlands ; 6 Meander Medical Center, Surgery, Amersfoort, The Netherlands; 7 St. Antonius Hospital, Surgery, Nieuwegein, The Netherlands ; 8 Ziekenhuis Rivierenland, Surgery, Tiel, The Netherlands; 9 Diakonessenhuis, Surgery, Utrecht, The Netherlands; 10 UMC Utrecht, Pathology, Utrecht, The Netherlands; 11 UMC Utrecht, Radiology, Utrecht, The Netherlands; 12 UMC Utrecht, Oncology, Utrecht, The Netherlands; 13 UMC Utrecht, Surgery, Utrecht, The Netherlands Purpose or Objective Patients with locally advanced rectal cancer (LARC) who achieve a good response following neoadjuvant chemoradiation (CRT) are potential candidates for organ- sparing treatment instead of surgery. As the response to radiotherapy is dose dependent, dose-escalated radiotherapy for LARC may render more patients eligible for organ preservation. In this trial, the RECTAL BOOST study, we have investigated the effect of a radiation boost to the primary tumour prior to standard CRT on complete tumour response in LARC patients. Material and Methods This is a multicentre randomised controlled trial (RCT) nested within a cohort according to the cohort multiple RCT design (Figure 1). Patients with LARC participating in a prospective cohort, referred for CRT and with a tumour <10cm from the anorectal angle were randomised. The control arm received standard CRT (25x2Gy with capecitabine 825mg/m 2 bid). The intervention arm was offered a stereotactic, sequential radiation boost of 5x3Gy to the GTV prior to standard CRT. Dose planning for boost treatment involved equal dose constraints for organs at risk as in standard CRT. The primary endpoint was complete tumour response defined as pathological complete response (pCR), or, in patients who opted for a wait-and-see (WS) approach, 2-years local recurrence- free survival (2-yLRFS). We also assessed organ-sparing potential after CRT defined as (near-)pCR, ypT0-1N0, or wait-and-see with the hypothesis that ypT1N0 patients could have received local excision or could have waited longer. Acute toxicity was measured using CTCAE scores v5.0. Patients were included between Sept 2014 and July 2018. Because this abstract includes preliminary results, differences in outcomes were not tested for significance.

Results Of the 64 patients who were offered boost CRT, 52 (81%) accepted and 51 (80%) received boost treatment. At abstract submission, 52 patients in the intervention group and 55 in the control group had complete follow up. In the boost group, 20/52 (38%) patients had a complete response (15 pCR and 5 2-yLRFS after WS) versus 20/55 (36%) patients in the control group (18 pCR and 2 2-yLRFS after WS). Organ-sparing potential was 50% in the boost arm (20 complete responses, 5 ypT1N0 and 1 ypTisN0) versus 36% in the control arm (20 complete responses, no ypT1N0). Grade 3/4 acute toxicity rate was 20/64 (31%) in the boost arm and 10/64 (16%) in the control arm, primarily due to gastrointestinal toxicity (Figure 2). No grade 5 toxicity was observed. Of all patients who underwent surgery, postoperative complications occurred in 21/46 (46%) in the boost arm versus 32/52 (62%) in the control arm.

Conclusion Results suggest that the rate of complete tumour response is comparable between dose-escalated CRT and standard CRT. However, organ-sparing potential after dose- escalated CRT seems higher. Unfortunately, at the expense of an increase in grade 3-4 acute toxicity. Updated results on this RCT will be presented at the meeting. OC-0384 QoL after multimodal treatment of rectal cancer with/without oxaliplatin (phase 3, CAO/ARO/AIO-04) R. Kosmala 1 , E. Fokas 2 , M. Flentje 1 , R. Sauer 3 , T. Liersch 4 , U. Graeven 5 , R. Fietkau 3 , W. Hohenberger 6 , D. Arnold 7 , R. Hofheinz 8 , M. Ghadimi 4 , H. Raab 9 , P. Ströbel 10 , L. Staib 11 , G.G. Grabenbauer 12 , G. Folprecht 13 , W. Uter 14 , C. Gall 14 , C. Rödel 2 , B. Polat 1

1 University Hospital Würzburg, Department of Radiation