Abstract Book

S34

ESTRO 37

3 Institute Gustave-Roussy, Department of Radiation Oncology, Paris, France 4 Utrecht University Hospital, Department of Radiation Oncology, Utrecht, The Netherlands 5 Institute of Oncology Ljubljana, Department of Oncology, Ljubljana, Slovenia 6 Addenbrooke’s Hospital- Cambridge University Hospitals, Departments of Oncology- Radiology and Gynae-oncology, Cambridge, United Kingdom 7 Mount Vernon Cancer Centre, Department of Radiation Oncology, Northwood, United Kingdom 8 Tata Memorial Hospital, Department of Radiation Oncology, Mumbai, India 9 Oslo University Hospital, Department of Radiation Oncology, Oslo, Norway 10 Regional Cancer Centre Chandigarh, Department of Radiation Oncology, Chandigar, India Purpose or Objective Ureteral stricture is a relatively uncommon complication following pelvic radiotherapy, but can be associated with significant morbidity including loss of renal function and potential life threatening urosepsis. It has been argued that combined intracavitary and interstitial (IC/IS) brachytherapy with application of needles in the parametria, increases the risk for ureteral stricture. This report describes the incidence and risk factors for severe to life threatening ureteral stricture in a large multicentre patient cohort treated with image guided adaptive brachytherapy (IGABT) for locally advanced cervical cancer (LACC). Material and Methods A total of 1772 patients with locally advanced cervical cancer treated within the retrospective RetroEMBRACE (n=610) and the prospective EMBRACE (n=1162) studies were analysed. Treatment included external beam radiotherapy with prescribed dose 45-50 Gy in 25-30 fx with concomitant Cisplatin in 88% of the patients. IGABT was delivered with HDR BT (58%) or PDR BT (42%). Brachytherapy was delivered with combined IC/IS technique in 36% of the patients. Total mean D 2cm3 to the bladder was 78.1 Gy. Severe to life threatening grade 3-4 ureteral strictures were assessed according to CTCAE v.3. Risk factors for were investigated with univariate and multivariable cox regression analysis. Results At a median follow up of 29 (1-163) months, 36 patients were diagnosed with grade 3-4 ureteral stricture. Actuarial 3/5-year risk for ureteral stricture grade 3-4 was 2.0%/3.2%. Patients (n=1370) with TNM stage 1 and 2 tumours had a 0.5%/1.2% and 1.3%/1.3% risk at 3/5 years, respectively. Patients (n=272) with stage 3-4 tumours without hydronephrosis at diagnosis had a risk of 1.8%/4.8% at 3/5 years, compared to 13.6%/23.4% in patients (n=130) with baseline hydronephrosis (figure 1). In univariate analyses, the following risk factors for ureteral stricture were found: Advanced tumour stage III- IV (TNM classification) (p=0.05), hydronephrosis at diagnosis (p≤0.001), tumour volume (CTV HR ) (p≤0.001), and application of needles for brachytherapy (IC/IS versus IC technique) (p=0.02). The following factors were not associated with increased risk in univariate analyses: Age, laparoscopic staging, lymph node boost, CTV HR dose, EBRT dose, bladder D 2cc3 , and brachytherapy dose rate. In the multivariable model only hydronephrosis at diagnosis (p≤0.001) was an independent risk factor for ureteral stricture.

Conclusion In LACC patients treated with IGABT, severe to life threatening ureteral stricture occurred rarely for stage 1- 2 as well as for stage 3-4 without hydronephrosis at diagnosis. The risk for ureteral stricture was considerable in stage 3-4 patients with hydronephrosis at diagnosis. In general, combined IC/IS technique was not a risk factor. However, it cannot be excluded that individual patients with high ureter dose due to needles positioned in close proximity to ureters may be at increased risk of ureteral stricture. OC-0073 Isodose surface volume in cervix brachytherapy: dependence on image guided adaptation and applicator M. Serban 1 , C. Kirisits 2 , K. Nkiwane 2 , I. Dumas 3 , J. Swamidas 4 , A. De Leeuw 5 , R. Hudej 6 , G. Lowe 7 , N. Nesvacil 2 , R. Pötter 2 , J. Lindegaard 1 , K. Tanderup 1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark 2 Medical University of Vienna / General Hospital of Vienna, Department of Radiation Oncology, Vienna, Austria 3 Gustave-Roussy Institute, Department of Radiotherapy, Paris, France 4 Tata Memorial Hospital, Department of Radiation Oncology, Mumbai, India 5 University Medical Centre Utrecht, Department of Radiotherapy, Utrecht, The Netherlands 6 Institute of Oncology Ljubljana, Department of Radiotherapy, Ljubljana, Slovenia 7 Mount Vernon Hospital, Cancer Centre, London, United Kingdom Purpose or Objective To investigate the isodose surface volumes (ISVs) for 85, 75 and 60 Gy EQD2 for locally advanced cervix cancer patients enrolled in the multi-institutional EMBRACE clinical trial. The hypothesis of this analysis was that individualized Image Guided Adaptive Brachytherapy (IGABT) in conjunction with the use of combined intracavitary/interstitial brachytherapy (IC/IS-BT) leads to improved dose conformity and an overall reduction of the ISVs as compared to standard loading, point A based BT. Material and Methods 1201 patients accrued in the EMBRACE study were analysed. EBRT with concomitant chemotherapy was followed by MR based IGABT. Different EBRT/BT fractionation schedules, BT dose rates (HDR/PDR), applicator designs (T&O, T&R, moulds, etc) and implant types (IC or IC/IS) were used. For the ISV calculation of the standard loading systems, 85, 75 and 65Gy EQD2 Point A-prescribed plans were produced in Oncentra treatment planning system for different sized commercial T&R and T&O applicators, including tandem lengths from 4–6 cm, ring diameters of 26, 30 and 34 mm and ovoid inter-channel spacing of 15, 20 and 25 mm. The EMBRACE EQD2 ISVs were calculated for both a/b 10 Gy (tumor)