ESTRO 38 Abstract book

S859 ESTRO 38

have relapsed clinically at the original tumour site.

United Kingdom ; 2 Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Joint Department of Physics, London, United Kingdom ; 3 The Royal Marsden NHS Foundation Trust, Radiotherapy and Imaging, London, United Kingdom ; 4 Guys and St Thomas' Hospital NHS Foundation Trust, Radiotherapy, London, United Kingdom ; 5 Odense University Hospital, Radiotherapy and Medical Physics, Odense, Denmark Purpose or Objective Recurrences after radical bladder radiotherapy occur predominantly within the bladder. Accurate dose mapping is important to determine whether cause of local failure is due to geographical miss, and or insufficient dose. To assess the success of image guided bladder radiotherapy strategies and margin reduction, we aim to determine the dose prescribed and received by the volume that harboured the local failure. Material and Methods Thirty-eight patients with T2 (high risk pathology) or T3- 4N0-3M0 bladder cancer recruited prospectively to an ethics approved phase II radiotherapy protocol treating whole bladder and pelvic lymph nodes with IMRT were retrospectively evaluated. Expansions to create the PTVs are shown Table 1. Soft tissue imaging was acquired prior to treatment with CBCT and registered to bony anatomy followed by soft tissue registration to whole bladder if necessary. Use of neo-adjuvant and concurrent chemotherapy was recommended. Diagnostic imaging (CT/MRI) identifying the site of local recurrence was used to reconstruct the relapse volume (GTV relapse ). This was co-registered with the planning CT. GTV relapse was compared dosimetrically and spatially to the PTV using centroid based approached. Patterns of failure were classified as in Figure 1. Time to local failure was defined from the start of radiotherapy to pathological confirmation of relapse, and was estimated using Kaplan Meier method.

2 patients were excluded from further analysis because no axial imaging identifying relapse was available. Median volume of GTV relapse was 33.9cc (range 7.5- 142.5). Median GTV relapse D 95% was 56.4Gy (range 50.1- 63.8Gy), 88.1% (78.3-99.6) of the prescribed dose (64Gy). Six patients (38%) were classified as experiencing type A failure, 9 patients (56%) as type B failure, and 1 (6%) as type C failure. No other types of local failure were Relapse patterns following bladder radiotherapy suggest local failure occurs at or within close proximity of the original tumour (PTV_ Tumour bed ). Work is on-going to expand the patient numbers and to determine actual radiotherapy dose delivered to GTV relapse from on-line CBCT data using the deformable registration techniques. This will inform whether dose escalation, and or margin modification could improve reported outcomes. EP-1592 Consolidative radiotherapy after loco regional relapse in muscle invasive bladder cancer D. Santamaria Vasquez 1 , X. Maldonado 2 , M. Altabas 2 , D. Moreno 2 , S. Micó 2 , C. Raventós 3 , F. Lozano 3 , R. Morales 4 , J. Giralt 2 1 Vall D´Hebron hospital, Radiation Oncology, Barcelona, Spain ; 2 Hospital Universitario Vall d’Hebron, Radiotherapy, Barcelona, Spain ; 3 Hospital Universitario Vall d’Hebron, Urology, Barcelona, Spain ; 4 Hospital Universitario Vall d’Hebron, Medical Oncology, Barcelona, Spain Purpose or Objective The aim of this study is to report the outcomes of consolidative radiotherapy after cystectomy in locoregional relapse of muscle invasive bladder identified. Conclusion We performed a retrospective analysis of eighty-eight patients with MIBC that had been treated at our institution from January 1999 to August 2018. Forty-nine patients underwent radical cystectomy followed by platinum-based chemotherapy (cisplatin / carboplatin). We identified 31 patients that had loco- regional relapse that received consolidative radiotherapy. These patients are the subject of our study. Overall survival (OS) was calculated using the Kaplan- Meier method. OS was defined as the time from the start of radiotherapy to death. The toxicity was evaluated according to the RTOG toxicity criteria. Results In the select group of 31 patients with loco-regional relapse treated with consolidative radiotherapy, 25 were men, the median age was 65.3 years (range 44-87). Eight patients had local recurrence, 12 patients had regional recurrence, and 11 patients both. All patients completed their radiotherapy course. Treatment volume was local recurrence or positive lymph nodes and regional pelvis. The mean dose of radiotherapy was 54.4 Gy (range 37.5 Gy - 64.8 Gy).No patient received concurrent chemotherapy. Two patients (6%) developed grade 3 gastrointestinal toxicity. No grade 4 toxicity has been reported. No grade ≥2 genitourinary toxicity has been reported. With a median follow-up of 27 months, there was no evidence of disease in 14 patients (45%) after consolidative radiotherapy. Seventeen patients presented metastatic distant progression: 5 hepatic, 4 bone and 4 pleuropulmonary. One patient had local relapse, one patient had nodal relapse and one patient had loco-regional and metastatic relapse. cancer (MIBC) patients. Material and Methods

Results 27/38 (71%) of all patients had disease recurrence. 18/38 (47%) patients experienced first relapse within the bladder following radiotherapy. Median time to local relapse was 9.0 months (95% CI, 6.3-11.7 months). 15/18 (83%) of these patients received neo-adjuvant chemotherapy and 10/18 (57%) had received concurrent chemotherapy. 9/18 (50%) patients relapsed with ≥T2 local disease, and 7/18 (28%) with