ESTRO 36 Abstract Book

S726 ESTRO 36 2017 _______________________________________________________________________________________________

EP-1369 Cystectomy with adjuvant radiotherapy for invasive bladder tumors: early results of a phase II study M. Swimberghe 1 , E. Rammant 1 , K. Decaestecker 2 , P. Ost 1 , S. Junius 3 , P. Dirix 4 , G. De Meerleer 5 , V. Fonteyne 1 1 University Hospital Ghent, Radiotherapy, Ghent, Belgium 2 University Hospital Ghent, Urology, Ghent, Belgium 3 Centre Hospitalier de Mouscron, Radiotherapy, Mouscron, Belgium 4 GZA St-Augustinus Hospital, Radiotherapy, Antwerp, Belgium 5 University Hospitals Leuven, Radiotherapy, Leuven, Belgium Purpose or Objective Patients with locally advanced muscle invasive bladder cancer (MIBC) have a high risk of recurrence. Studies have shown a benefit on locoregional control of postoperative radiotherapy (PORT) after radical cystectomy, but its use remains limited due to fear of severe toxicity. With modern radiotherapy (RT) the place of PORT should be reassessed. Material and Methods A phase II study was started to evaluate acute toxicity of PORT with modern RT. All patients underwent radical cystectomy and presented one or more of the following pathological findings: pT3 with lymphovascular invasion, pT4, <10 lymph nodes removed, positive lymph node status or positive surgical margins. A median dose of 50 Gy in 25 fractions is prescribed to the iliac, obturator and presacral lymph nodes. Cystectomy bed is only included in case of positive margins. Treatment is delivered with an arc technique (VMAT). Toxicity is scored at baseline, during, 1 and 3 months after RT using Common Terminology Criteria for Adverse Events version 4.3. Urinary toxicity is scored if a neobladder is present. Local and distal control after treatment were evaluated every 3 months using CT, or earlier on indication. Results Since 2014, 23 patients were enrolled in the study. Due to progressive disease on planning CT 3 patients were excluded. Median follow-up is 4 months (range 1-23). During RT, 4 patients were hospitalized, of which 2 were RT-induced (upper and/or lower gastrointestinal (GI) toxicity). Out of the 5 patients with a neobladder, 4 reported ≤ grade 2 urinary toxicity. One patient developed transient grade 3 nocturia during RT. Three months after RT, 2 patients had surgery for an enterovaginal fistula and obstruction caused by peritoneal metastasis respectively. All other patients had ≤ grade 2 GI and urinary toxicity during follow-up. No isolated local relapse was observed. Seven patients developed distant metastasis of whom 1 patient had simultaneous local and distant relapse and 1 patient had a relapse at the border of the RT-field. Five patients died; 2 were disease-related.

Conclusion Using modern RT techniques, PORT for high risk MIBC is feasible and toxicity is acceptable. Preliminary results on locoregional control are promising but long-term follow- up is warranted. EP-1370 Simultaneous integrated tumour boost planning in bladder cancer: a comparison of strategies S. Hafeez 1 , K. Warren-Oseni 2 , H. McNair 1 , V. Hansen 2 , R. Huddart 1 1 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Radiotherapy and Imaging, Sutton, United Kingdom 2 The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Joint Dept of Physics, Sutton, United Kingdom Purpose or Objective Partial bladder radiotherapy can be utilized with no adverse effect on local control [1, 2]. We sought to compare partial bladder irradiation using a simultaneous integrated boost (SIB) apprach with intensity modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) to inform our current image guided adaptive approach. Material and Methods Seven patients with unifocal T2-T3N0M0 MIBC recruited prospectively to an image guided SIB protocol (NCT01124682) were evaluated. Fixed field IMRT and VMAT plans were created treating whole bladder (PTV Bladder ) to 52Gy and tumour (PTV Boost ) to 70Gy in 32 fractions using Pinnacle v9.6, Philips Medical Systems. The same constraints were applied for both planning approaches. Plan quality was assessed by calculating the conformity index (CI=V 95% /V PTV ), homogeneity index (HI=D 2% - D 98% /D 50% ), dose to target and normal structures. Comparisons were made with Wilcoxon signed rank test. Results The mean PTV Bladder (SD, range) CI for IMRT and VMAT was 1.20 (0.04; 1.14-1.24) and 1.17 (0.06; 1.13-1.30) (p=0.24); mean PTV Boost (SD, range) CI was 1.20 (0.11; 1.06-1.37) and 1.17 (0.13; 1.03-1.31) (p=0.74) respectively. The mean PTV Badder (SD, range) HI for IMRT and VMAT was 0.39 (0.01; 0.37-0.40) and 0.38 (0.02; 0.36-0.40) (p=0.61); and