ESTRO 2023 - Abstract Book

S91

Saturday 13 May

ESTRO 2023

M. Serban 1,2 , S. Spampinato 2 , A. de Leeuw 3 , I. Fortin 4 , N. Nevascil 5 , C. Kirisits 5 , M. Schmid 5 , U. Mahantshetty 6 , P. Hoskin 7 , B. Segedin 8 , K. Bruheim 9 , F. Huang 10 , B. Pieters 11 , R. Nout 12 , R. Pötter 5 , K. Kirchheiner 5 , I. Jürgenliemk-Schulz 3 , K. Tanderup 2 1 Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada; 2 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 3 University Medical Centre Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands; 4 Maisonneuve-Rosemont Hospital, University of Montreal, Department of Radiation Oncology, Montreal, Canada; 5 Comprehensive Cancer Center, Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria; 6 Tata Memorial Hospital, Department of Radiation Oncology, Mumbai, India; 7 Mount Vernon Hospital, Cancer Centre, London, United Kingdom; 8 Institute of Oncology Ljubljana, Medical Faculty, University of Ljubljana, Department of Radiotherapy, Ljubljana, Slovenia; 9 The Norwegian Radium Hospital, Oslo University Hospital, Department of Oncology, Oslo, Norway; 10 Cross Cancer Institute and University of Alberta, Department of Oncology, Edmonton, Canada; 11 Amsterdam University Medical Centers, University of Amsterdam, Department of Radiation Oncology, Amsterdam, The Netherlands; 12 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, The Netherlands Purpose or Objective To investigate the effect of brachytherapy (BT) applicator and implant type on morbidity and local control in locally advanced cervix cancer treated on the EMBRACE I study. Materials and Methods 1071 patients treated with tandem&ring (T&R) (n=725) and tandem&ovoids (T&O) (n=346) from 19 EMBRACE-I centres were analyzed. After receiving EBRT (45-50Gy in 25-30fx) and MR-guided BT (IGBT) using intracavitary (IC) (n=559) or intracavitary/interstitial (IC/IS) (n=512) implants, patients were prospectively followed (in median 48 months). Local control (LC) and physician-assessed (CTCAE v.3) late morbidity were compared based on (1) applicator type: T&R vs T&O, and (2) implant type: IC vs IC/IS. Moderate-to-severe (G ≥ 2) genito-urinary (GU: cystitis, frequency), gastro-intestinal (GI: proctitis, bleeding, diarrhea) and vaginal (stenosis, mucositis) symptoms were analysed separately. Severe-to-life threatening events (G ≥ 3) were pooled for evaluation of GU, GI and vaginal morbidity. Comparisons between applicator and implant types were evaluated by Cox proportional hazard multiple regression model, adjusting for: patient (baseline morbidity, age, body mass index), disease (local FIGO stage, organ involvement, tumour dimensions, histology, tumour necrosis), and treatment-related confounders (CTV-HR D90%, EBRT dose) (Table 1), which were included in the multivariable analysis (MVA) if significant in the univariate analysis (p ≤ 0.15). Results OAR doses (bladder and rectum D2cm3; ICRU points) for T&O vs T&R were higher by 5-7Gy in IC implants and by 1-5Gy in IC/IS implants, while target dose (CTV-HR D90%) was lower by on average 2.5Gy in T&O compared to T&R applicators. Table 1 shows the hazard-ratios (HR) for individual G ≥ 2 morbidity endpoints and pooled G ≥ 3 GU/GI/vaginal/fistula morbidity in patients treated with T&O IC vs. T&R IC, T&O IC/IS vs. T&R IC/IS and IC vs. IC/IS applicators. In 3/7 and 6/7 evaluated individual symptoms (in IC and IC/IS implants, respectively), the T&O showed a statistically significant (p<0.05) higher risk for G ≥ 2 morbidity compared to T&R. Figure 1 shows examples of adjusted cumulative hazard of individual endpoints (G ≥ 2 cystitis, proctitis and vaginal stenosis). Crude incidence of local failure was 7.3% (25/343) and 6.6% (47/712) in patients treated with T&O and T&R, respectively. In MVA, local control did not statistically differ between the two groups (p>0.1).